Journal of Southwest Petroleum University(Science & Technology Edition)

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Application and Development of Big Data in Well Engineering

ZHANG Zhi, WANG Xianghui, DING Jian, ZHAO Jie, WU Linfang, HOU Zhenyong

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 1-14. DOI: 10.11885/j.issn.1674-5086.2023.10.29.31

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Industrial 4.0 technological revolution promotes the oil and gas industry to enter a new stage of smart oilfields, which is characterized by digitalization and intelligence. China has made great progress in digital construction and application integration in the oil field, carrying out a number of big data analysis on massive exploration and development data collected, such as drilling, logging, well testing, analysis and testing, oil and gas production, and accelerating automated construction and intelligent decision-making. However, there are some challenges, such as inconsistent standards of well engineering database, difficulties in in-depth data sharing, severe data isolation and so on. In order to accelerate the construction and application of geology–engineering integration and better leverage the big data of well engineering for the construction of smart oilfield, the following work has been carried out: the relationship and difference between big data of well engineering and traditional big data are analyzed; the current situation of oil and gas big data platforms at home and abroad is counted; the characteristics and levels of well data are introduced; the big data algorithm of common well engineering problems is summarized; the scheme of algorithm optimization according to business requirements is proposed. Finally, the development suggestions are put forward for the current problems existing in the application of current big data technology in well engineering.

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Influencing Factors of Gas-bearing Characteristics and Evolution of Occurrence State in Deep Shale in Luzhou Area

JIANG Yuqiang, WU Jianhua, TAO Shiping, ZHOU Anfu, XIE Wei, SUN Yue

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 1-16. DOI: 10.11885/j.issn.1674-5086.2025.03.05.03

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To investigate the characteristics of shale gas occurrence and evolution under stratigraphic conditions of the Longmaxi Formation in the Luzhou Area, volumetric methane isothermal adsorption experiments under different hydration states were conducted. A ternary Langmuir model was employed to fit the shale excess adsorption data, yielding a maximum corrected adsorption capacity of 2.5 cm ³/g. Total organic carbon content and clay minerals were identified as favorable controlling factors for methane adsorption capacity, and increasing water saturation exerts an inhibitory effect on methane adsorption. With increasing burial depth, adsorbed gas content initially increases and then decreases, and free gas content continues to rise. Under hydrated conditions, an equivalent burial depth exists where adsorbed and free gas contents intersect. This critical depth migrates upward with increasing hydration, forming a mixed gas occurrence zone. The evolutionary process of deep shale gas in the Luzhou Area can be divided into four stages. From the early deposition period to the Late Silurian, rapid subsidence of the stratum facilitated the dominance of biogenically derived adsorbed gas. During the Early Devonian to Middle Triassic, continuous subsidence of the strata persisted alongside minor uplift events, yet adsorbed gas remained the predominant occurrence mode. From the Middle Triassic to Late Cretaceous, accelerated burial depth triggered a substantial increase in free gas content. Since the Late Cretaceous to the present, tectonic uplift has halted hydrocarbon generation, but favorable structural preservation conditions in the Luzhou Area have effectively retained free gas.

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Gas Entrapment Characteristics and Its Recovery Mechanisms During Water Invasion Process for Deep Carbonate Gas Reservoirs

ZHANG Ruihan, HU Yuhan, LI Tao, LU Guang, ZHANG Tao, ZHANG Liehui

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 129-140. DOI: 10.11885/j.issn.1674-5086.2023.11.03.34

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Carbonate gas reservoir is usually deposited along with aquifer. Water invasion during the development of these reservoirs results in larger amount of gas trapped within the reservoirs. Therefore, it has great theoretical and practical significance to characterize and understand the pore-scale gas entrapment characteristics and its recovery mechanisms during water invasion process. Based on the CT scanning images for real carbonate reservoir, the characteristics of fractures and pores in fracture-pore type reservoir were extracted. The corresponding etched-glass model was manufactured to conduct gas-water two-phase flow experiments. The invasion dynamics and gas entrapment characteristics were revealed. Furthermore, the effects of pore structure, wettability and pressure gradient on water invasion dynamics were evaluated based on the Lattice Boltzmann Method (LBM). Finally, the mechanism of trapped gas recovery is revealed. The results show that more strongly hydrophobic carbonate reservoirs lead to a larger volume of trapped gas after water invasion. The types of trapped gas include dead-end/corner trapped gas, side-flow trapped gas, snap-off trapped gas, H-shaped trapped gas, and network-shaped trapped gas. When the invasion pressure gradient increases (well production increase), a large volume of gas will be trapped inside the formation in the form of network-shaped trapped gas. In flooded gas reservoirs, intermittent well production(intermittent depressurization and pressurization) can lead to the recovery of the snap-off trapped gas and network-shaped trapped gas.

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Diagenesis of the Low-permeability Reservoir in the Huagang Formation of the Xihu Depression and the Genesis of High-quality Reservoirs

YIN Wenbin, ZHAO Xiaoming, GE Jiawang, LIANG Yueli, WANG Jianwei

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 17-34. DOI: 10.11885/j.issn.1674-5086.2025.01.15.03

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The porosity and permeability of the sand bodies in the Xihu Depression's Huagang Formation are generally poor, while locally developed high-quality reservoirs are often the key to hydrocarbon accumulation. Based on core, thin section data, electron probe, and analytical testing data, the reservoir characteristics and their main controlling factors were analyzed, and a development model for high-quality reservoirs was established. The results show that the H3 Member in the study area mainly develops ultra-low permeability reservoirs, low-permeability reservoirs, and high-permeability reservoirs, with intergranular dissolution pores being the main pore type of the high-quality reservoirs. The sandstone reservoir diagenesis includes compaction, cementation (quartz, carbonate, clay), and dissolution. During the evolution process, the reservoir has experienced acidic modification by meteoric water and hydrocarbon charging. It was found that the source and strong hydrodynamic depositional facies are favorable conditions for the development of high-quality reservoirs. Early carbonate cementation and late hydrocarbon charging modification are the keys to the protection of primary pores and the generation of secondary pores in high-quality reservoirs. The coupling of sedimentary, diagenetic, and tectonic actions in time and space controls the formation of high-quality reservoirs.

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Indicators of Fluid Change in 4D Seismic: An Case Study of 4D Seismic Interpretation in P Oilfield

LI Meng, LI Fayou, ZHANG Wenbiao, LU Wenming, ZHAO Huawei, XU Rui

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 27-36. DOI: 10.11885/j.issn.1674-5086.2024.09.03.01

Abstract （91）

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Fluid dynamic monitoring is a key technology for the efficient development of oil and gas reservoirs. 4D seismic can directly image fluid changes and enable 3D spatial fluid dynamic monitoring, and is therefore widely used in the development of deepwater oil and gas fields, thermal recovery of heavy oil, carbon dioxide sequestration. However, mainstream 4D seismic interpretation methods suffer from high ambiguity and poor reliability when characterizing complex fluid changes. To overcome these technical challenges, this study, based on theoretical models and 4D seismic forward modeling and using phase transformation technology, establishes the relationship between 4D seismic response and different fluid changes, proposes 4D seismic fluid change indicators, and achieves dynamic interpretation of complex fluid change patterns and ranges. The new method proposed in this paper was used to interpret the fluid changes in the 4D seismic data of the deepwater P Oilfield in Angola, West Africa. The interpretation results are consistent with production dynamic information. The fluid change interpretation results show that the differences in seepage characteristics of oil, gas, and water, along with reservoir structural features, control the movement paths of gas and water. Effective monitoring of fluid dynamic changes provides a reliable basis for development plan adjustment.

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Characteristics of Late Miocene Deepwater Sedimentary and the Exploration Prospect in the Shuangfeng Basin

YANG Zhili, WU Jia'nan, FAN Guozhang, LI Li, ZHANG Yuanze

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 15-26. DOI: 10.11885/j.issn.1674-5086.2024.08.30.02

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Shuangfeng Basin is the sediment unloading area of the central canyon of Qiongdongnan Basin, with a huge scale of deep-water sedimentary system. With the acceleration of exploration in the deep water area of the northern South China Sea, the oil and gas exploration prospects in the Shuangfeng Basin are increasingly receiving attention. A systematic study was conducted on the development characteristics and oil and gas geological conditions of the late Miocene deep-water sedimentary bodies in the Shuangfeng Basin through comprehensive analysis of sea level rise and fall, seismic data reflection characteristics, etc. The research results indicate that the deep-water sedimentary bodies in the Shuangfeng Basin were mainly developed in the Late Miocene, with branch channels, channel complexes, channel—levee complexes, lobe etc. The distribution area of deepwater sedimentary bodies reach ten thousands of square kilometers, making it a potential area for ultra large scale reservoirs. Meanwhile, the western and northern depressions of the Shuangfeng Basin have good conditions of source, reservoir, and cap rocks. Due to the Shuangfeng Basin located in the deep-water to ultra deep-water zone, the quality of source rocks, the scale of hydrocarbon generation and expulsion, and the economic viability of exploration targets are uncertain factors in oil and gas exploration in this area. The result has important guiding significance for the analysis of oil and gas exploration prospects, strategic selection of areas and zones in the Shuangfeng Basin.

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Investigation of NGH Secondary Formation in Wellbore During Deep Sea Hydrate Production

JIANG Shuxian, SONG Xuanqi, HE Yufa, LIU Chang, SONG Jinze

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 75-89. DOI: 10.11885/j.issn.1674-5086.2024.04.06.31

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To prevent secondary hydrate formation and enhance wellbore flow, the mathematical model to investigate the temperature and pressure in the development of the argillaceous natural gas hydrate. With the moderate sand control technique, this model predicted the temperature and pressure profiles along the well considering the sand particle size effect and the JouleThompson effect on heat transfer within the hydrate production wellbore. According to the moderate sand control principle, the paper also analyzed how the size of produced formation sand and the wellbore size could affect the secondary formation of natural gas hydrates in the wellbore. The effect is quantitatively described in the sensitivity analysis. Considering the development environment of NGH, several key factors were selected in the sensitivity analysis including produced formation sand size, wellbore diameter and thickness, production rate, thermal conductivity, and NGH formation depth. The analysis recommended the produced formation sand as less than 30 μm and the wellbore thickness as 0.389 m to reduce the risk of NGH secondary formation. The risk secondary NGH formation for shallow reservoir depth was higher than that for deep reservoir. The calculation verified that the installation of local heating electrode could effectively reduce the secondary formation risk of hydrate near the mud line. The research results of this paper provide theoretical support for fine sand control and well structure design of deep sea hydrate reservoir production.

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Research and Application of New Technologies for Expanding Storage and Increasing Production in Carbonate Reservoirs

CHEN Lixin, WANG Xia, ZHAO Bin, YANG Bo, JIANG Yakun

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 98-106. DOI: 10.11885/j.issn.1674-5086.2024.04.18.03

Abstract （81）

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The primary pore and secondary fracture-cave system are the main storage spaces in the fracture-cave carbonate reservoir. The fractures are the infiltration channels for oil and gas. The spatial development of each fracture-cave body is isolated, with poor connectivity, and the scale of single well control fracture-cave is limited. The proportion of oil wells with long shutdowns and low efficiency in Halahatang Oilfield has reached 41% due to small well control reserves. In the early stage, attempts have been made to treat them through repeated acid fracturing and high-pressure expansion water injection, and have achieved some results, but with a short effective period and rapid after treatment decrease for most wells. It is difficult to achieve the recovery of oil wells with small well control reserves relying solely on acid fracturing or expansion water injection. Based on the research of reservoir transformation methods in the early stage, a new method of scale acid fracturing and expansion water injection is proposed to address this issue. First, forms a high-pressure water zone near the well through expansion water injection, opens natural fractures or fractures in the formation. Then, acid pressure is used to achieve simultaneous maximization of acid etched fracture length and acid etched fracture conductivity, communicating with distant well reservoirs. After acid fracturing, large displacement water injection is directly carried out for ultra long distance etching, thereby achieving the goal of“creating fractures and finding holes”. At present, three wells have been implemented, increasing geological reserves by 460 400 tons and cumulative oil production by 47 200 tons. It is expected that the cumulative oil production during the effective period can reach 63 600 tons, providing an economically effective new method for the expansion and production increase of inefficient wells in fractured carbonate reservoirs.

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Simulation Experiment and Hydrocarbon Generation Contribution of Paleogene Source Rocks in the Rich Hydrocarbon Depression of Zhu I Depression

ZHAN Junyan, XU Guosheng, FENG Jin, SHI Yuling, XIONG Wanlin

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 35-48. DOI: 10.11885/j.issn.1674-5086.2025.01.23.02

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The Pearl River Mouth Basin, located in the eastern part of the northern continental margin of the South China Sea, is an important oil and gas bearing basin in China. Among them, many oil and gas fields and oil bearing structures have been found in the Zhu I Depression. The results of the second national resource assessment show that the oil and gas resources in the Zhu I Depression are dominated by oil, supplemented by natural gas, and have great resource potential. In order to systematically evaluate the hydrocarbon generation capacity of source rocks in the hydrocarbon rich sag of Zhu I Depression in the Pearl River Mouth Basin, two sets of four types of source rocks, namely, Wenchang Formation semi deep lake facies, shallow lake semi deep lake facies, Enping Formation shallow lake limnetic facies, and coal measures, were selected to conduct hydrocarbon generation simulation experiments in a semi open and semi closed system to comprehensively obtain the hydrocarbon generation dynamic model of source rocks. Under the guidance of the “genetic method” oil and gas resource evaluation method, combined with the basin simulation software, multiphase source rocks were used for the first time to fully confirm the Zhu I Depression from the thermal evolution degree of the hydrocarbon rich sag, the hydrocarbon generation history of the source rocks, and the intensity of hydrocarbon generation and expulsion. The hydrocarbon rich sag has a large amount of oil and gas resources, and these achievements provide a strong scientific basis for the further exploration and development of Zhu I Depression.

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Experimental Study on Influence Factors and Laws of Borehole Friction Coefficient

JING Jun, FANG Haoyu, SHAN Hongbin, ZHU Xiaohua, NI Zongqing

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 162-171. DOI: 10.11885/j.issn.1674-5086.2023.11.24.32

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Friction coefficient is a key parameter in calculating the drag force when drilling and is obtained by back-calculation based on the data such as weight on bit and hook load, enabling studies on torque and drag. However, few studies have deeply investigated the influencing factors and variation patterns of the friction coefficient between the drillstring and borehole from the perspectives of friction mechanism, microstructure, and the mixed lubricating medium. To address this issue, a friction experimental platform is built and the studies on the influences of drilling technologies (gas drilling and mud drilling), borehole condition (casing and rock borehole) and the diameter, characteristic and distribution pattern of cuttings are made. The research shows that the geometric irregularity of cuttings becomes more pronounced with increasing particle size, serving as the primary factor controlling friction coefficient variations. Compared to the rough surface of borehole rock, the friction coefficient of casing is much lower, suggesting that improving open-hole quality can reduce drag. Additionally, the envelop effect of cuttings bed significantly increases the friction coefficient. The friction coefficient value is within the range of 0.44～0.58 when gas drilling and it is 0.25～0.45 in casing, 0.35～0.55 in borehole rock when mud drilling.

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Intelligent Fault Diagnosis and Disposal of Oil Recovery Wells Based on Large Model

LIU Xin, LU Wenjuan, MIN Chao, SUN Qi, SUN Meng

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 125-136. DOI: 10.11885/j.issn.1674-5086.2024.06.14.02

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In response to the adverse impacts of oil well failures on production efficiency and operational safety in oilfields, this study focuses on rapid and accurate diagnosis and effective mitigation of such failures in complex environments. An intelligent framework for oil well fault diagnosis and disposal based on large models is proposed. First, a multi-modal association rule mining algorithm (M–ARMA) is designed to extract association rules between abnormal data and fault types from multimodal data sources such as pressure, load, and indicator diagrams of oil wells. Second, the XLNet-DC model is proposed to automatically extract fault handling rules from oil well failure reports and maintenance logs. Finally, a knowledge graph for oil well fault diagnosis and handling is constructed, and inference rules for abnormal fault handling are established through entity matching. By integrating real-time faults detected by the oil well monitoring module, the framework enables intelligent fault diagnosis and disposal via knowledge-based reasoning. Experimental validation in an oilfield demonstrates that the proposed method achieves an F ₁ of 93% in knowledge extraction and a fault diagnosis accuracy of 96%. The framework effectively supports the integrated matching of accurate fault identification with appropriate handling strategies, thereby enhancing the safety and stability of oilfield production.

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Physical Model Experiment on Wellbore Deformation and Failure of Coalbed Methane Horizontal Well Considering the Influence of In-situ Stresses

ZHANG Qiangui, DENG Jian, FAN Xiangyu, JIA Lichun, GUO Xiaowei

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 107-118. DOI: 10.11885/j.issn.1674-5086.2024.11.04.02

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Understanding wellbore instability mechanisms in coalbed methane (CBM) horizontal wells under complex stress conditions is crucial for optimizing CBM reservoir drilling. Using a self-developed true triaxial device to simulate surrounding rock deformation, this study examines how differential horizontal stresses and vertical stress variations affect deformation and failure in CBM horizontal wellbores, and obtains the following results: 1) Wellbore deformation can be divided into three stages: slow shrinkage deformation stage, stable shrinkage deformation stage, and accelerated shrinkage until closure stage. 2) In the latter two stages of wellbore deformation, the deformation of the specimen in three directions is mainly controlled by wellbore deformation and failure. 3) As the maximum or minimum horizontal principal stress increases, the slope of the vertical principal stress-deformation curve during the stable shrinkage deformation stage of the wellbore significantly increases, and the strain in all three directions per unit stress increment decreases; simultaneously, the cross-sectional area at wellbore failure increases, with a corresponding increase in critical vertical principal stress and a decrease in vertical strain. 4) When the two horizontal principal stresses increase simultaneously, the aforementioned trends become more pronounced, which is more conducive to maintaining wellbore stability. The findings of this study can provide guidance for the drilling design of CBM horizontal wells.

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Fracture Characteristics and Layer-crossing Propagation Law of CO ₂ Hybrid Fracturing in Laminated Shale

ZHANG Liaoyuan, LU Mingjing, QIU Renyi, ZHANG Zilin, ZHANG Guangqing, ZHOU Dawei

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 64-74. DOI: 10.11885/j.issn.1674-5086.2023.09.14.03

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To investigate the fracture characteristics and layer-crossing propagation law of CO ₂-hybrid fracturing in laminated shale, CO ₂-hybrid fracturing experiments were conducted with the full-diameter Jiyang Sag Shale, and the Cohesive unit model was used to simulate the effect of pre-CO ₂ injection rate on layer-crossing propagation. The results show that: 1) CO ₂ fracturing is easy to activate beddings and natural fractures, which provides conditions for the formation of complex cross fractures in subsequent hydraulic fracturing, and the fracture volume increased by 24.0% with doubled pre-CO ₂ injection rate; 2) The low viscosity and high permeability of CO ₂ easily induce fractures to propagate along weak surfaces (beddings, natural fractures), mineral grain boundaries, and pore directions, resulting in the roughness of CO ₂ fracturing fractures about 50.0% higher than hydraulic fractures; 3) With the increase of CO ₂ injection rate, the ability of fracture to pass through beddings is enhanced. At low CO ₂ injection rate, fracture propagation is dominated by bedding, while fracture propagation is dominated by in-situ stress at high injection rate. The research results provide the mechanism and theoretical understanding of the fracture propagation law of CO ₂-hybrid fracturing of shale oil reservoir in Jiyang Sag. Compared with conventional fracturing in the field, the stimulation volume of CO ₂-hybrid fracturing increased by 12.2%, capacity by 33%, and decline rate of oil production decreased by 6.8%.

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A Review of Researches on Gas Load Forecasting Models Across Different Time Scales

ZHAO Chunlan, ZHENG Wenjuan, CEN Kang, HE Kehan, WANG Hanyao

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 107-124. DOI: 10.11885/j.issn.1674-5086.2024.04.01.04

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Accurate prediction of gas load holds significant practical value for maintaining the dynamic balance between gas supply and demand. With advancements in artificial intelligence technology, gas load forecasting algorithms have undergone substantial development. This study first categorizes forecasting periods into three distinct phases: short-term (ST), medium-toshort-term (MST), and medium-to-long-term (MLT). From an algorithmic perspective, we systematically analyze six representative methods including eXtreme Gradient Boosting (XGBoost) for ST forecasting, two approaches such as Long Short-Term Memory (LSTM) networks for MST forecasting, and two techniques including Prophet for MLT forecasting, and evaluate their advantages, limitations, and application scenarios. Through empirical validation using operational data, we conduct multidimensional comparative analysis of 12 selected models. Our experimental framework encompasses critical aspects including dataset construction, data preprocessing, extrapolative prediction, parameter optimization, and model evaluation across different temporal scales. Finally, we propose forward-looking perspectives on future research directions in gas load forecasting, particularly focusing on practical applications in natural gas dispatch management. This comprehensive investigation provides valuable references for advancing algorithmic research in gas load prediction and its implementation in smart energy management systems.

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A Study on Hole Initiation Pressure and Orientation of Perforated Well in High Stress Reservoir

LIU Hu, LU Qianli, DUAN Hua, XIAO Bin, ZHANG Hang

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 94-106. DOI: 10.11885/j.issn.1674-5086.2024.01.01.01

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It is difficult to accurately predict breakdown pressure of high stress reservoir or reservoirs with complex in-situ stress conditions, which leads to problems such as difficulties in reservoir fracturing, risk of liquid pumping and difficulties in sand pumping. Perforation hole is an important channel connecting wellbore and formation. Studying the initiation pressure and orientation of perforation hole is helpful to the understanding of the breakdown behavior of high stress reservoir or reservoir with complex in-situ stress conditions, and provides a basis for subsequent optimization of sand fracturing process. In this paper, based on the theory of elastic mechanics, the stress field model around the casing perforation well and the perforation hole are established. Based on this model, the initiation pressure and orientation of perforation hole are determined. Compared with the field data of a high stress reservoir, the reliability of the model is proved. Hole initiation pressure and orientation in vertical well under different in-situ stress conditions of high stress reservoir are also analyzed. The results show that for in-situ stress state in both strike-slip fault and reverse fault, when perforating along the direction of the maximum horizontal principal stress, the hole always fracture horizontally, forming a horizontal fracture near the hole, and the initiation pressure is the lowest, and the pattern of near-wellbore fracture on strike-slip fault is more tortuous; when perforating along the direction of the minimum horizontal principal stress, the smaller the horizontal ground stress difference is, the easier the hole is to fracture horizontally, forming a horizontal fracture near the hole, and the initiation pressure is higher, and the pattern of near-wellbore fracture on strike-slip fault is more tortuous; the larger the horizontal stress difference is, the easier the hole is to fracture longitudinally, which tends to form vertical fracture near the hole, and the initiation pressure is lower, and the pattern of near-wellbore fracture on reverse fault is more tortuous. The results of this study are conducive to the efficient development of high stress reservoirs or reservoirs with complex in-situ stress conditions.

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An Experimental Study on Mixed Gas of Depleted Gas Reservoir Type Gas Storage with CO ₂ as Cushion Gas

HU Shuyong, YANG Xiaochen, DENG Yi, ZHENG Xingming

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 90-97. DOI: 10.11885/j.issn.1674-5086.2024.05.24.01

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When used as the cushion gas of underground gas storage, CO ₂ can maintain the stability of pressure inside the gas storage, prevent working gas from escaping from the bottom edge, prevent edge and bottom water from invading, and provide power for gas production. However, the injected CO ₂ will mix with natural gas, and the strong injection and production in the gas reservoir may cause the fluctuation of CO ₂ and CH ₄ mixing zone, thus affecting the purity of produced gas. In this paper, mixed gas experiment of sand filling vessel and multiple injection and production experiment of CH ₄ and CO ₂ were carried out to study the mixed gas characteristics of CO ₂ and natural gas as well as the influence of different working cycle and working system on the mixed zone. The numerical simulation results were tested with laboratory experiment results. The experimental results show that under the same production system, with the increase of injection-production cycle, the mole fraction of CO ₂ in the sampling gas also increases gradually at very small scale and the mixing zone moves up slowly. The mole fraction of CO ₂ in the sample gas decreases with the increase of the gas production rate. The gas production rate will have an impact on the development of the mixing zone, but the impact is not significant.

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A New Method for Sand Production Prediction of Gas Storage Wells Based on Fuzzy Comprehensive Evaluation

LIAO Wei, HUANG Haibing, HU Shuyong, ZHANG Shijie, LI Xinlu

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 141-150. DOI: 10.11885/j.issn.1674-5086.2024.11.11.32

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Affected by the operation mode of gas storage with strong injection and production, the risk of sand production is prone to occur in the reservoir during peak shaving and gas production. Once sand is produced, it will seriously affect the life and peak shaving capacity of the gas storage. The commonly used qualitative empirical sand prediction methods lack intuitive and comprehensive results, and a single prediction index has great limitations. In response to this problem, qualitative experience sand prediction methods such as porosity method, acoustic time difference method, combined modulus method, sand production index method and Schlumberger ratio method are considered comprehensively, and analytic hierarchy process and fuzzy comprehensive evaluation decision-making are adopted to establish qualitative experience. The fuzzy comprehensive evaluation model for sand production prediction can predict and analyze the sand production results of different perforation sections. Application examples show that this method has realized the prediction of formation sand production results in different perforation sections, improved the accuracy and comprehensiveness of formation sand production prediction, which is of great significance to the long-term safe operation of gas storage.

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A New Method for Grading and Evaluating the Development Effectiveness of Fault Controlled Fracture-cavity Reservoir

YUAN Xiaoman, LU Zhongyuan, GUO Qiang, WANG Huailong, ZHAO Xinyue

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 137-148. DOI: 10.11885/j.issn.1674-5086.2024.09.15.31

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The ultra deep fault controlled fracture vuggy carbonate reservoir has strong heterogeneity and obvious spatial dispersion distribution characteristics. Different from clastic rock reservoirs, the geological characteristics of reservoirs between wells and the development effects in different development stages are different. There is no standardized method to scientifically evaluate the development effects of this type of reservoir in different development stages. Aiming at the typical fault zone of Fuman Oilfield, an overall technical approach to grading and evaluating the development effectiveness of single well (well group units) in the natural energy development stage and water injection development stage has been proposed. Five key principles for determining the development effectiveness evaluation index system have been clarified, and four key indicators for the natural energy development stage and nine key indicators for the water injection development stage of this type of reservoir have been selected. A comprehensive evaluation index system for different development stages was established using analysis hierarchy process. This research method and technical process can provide standardized and scientific research ideas in the process of building development effectiveness grading evaluation index systems for different development stages in other types of oil reservoirs. It can provide technical support for searching for potential zones in developed areas and optimizing development methods, and has good prospects for promotion and application.

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An Experimental Study on Start-up Mechanism of Micro-residual Oil by New Chemical System

WEI Hongtao, ZHANG Xiaoqin, GUAN Wenting, YANG Fengrui, ZHOU Yu

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 178-186. DOI: 10.11885/j.issn.1674-5086.2023.12.11.01

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Based on the microfluidic glass model of three typical oil layers in Daqing Oilfield, the start-up mechanism of the new alkali-free medium phase system on the micro residual oil was studied by means of microscopic oil displacement visualization, contact angle wettability measurement and interfacial tension measurement instruments. The new system has smaller particle size and stronger solubilization effect of emulsified oil droplets, and significantly improves the swept volume and oil washing efficiency. Compared with other composite systems, the new system has stronger wettability and can achieve rapid wettability reversal in a very short time to change the wettability. In this paper, the rapid deformation ability of the new system is studied by means of visual experiment. Compared with other chemical systems, this property is more conducive to the start-up and migration of micro-residual oil, increases the injection performance of the system, and provides help for the expansion of the sweep volume of the system. Another existing form of corner micro-residual oil in the reservoir is proposed, and the mechanism that the new system starts this kind of residual oil by breaking the regional pressure field balance is given. Through the research, the micro-residual oil start-up and migration mechanism of the new alkali-free system is defined, which provides technical means and support for further research on the oil displacement mechanism of the new alkali-free system.

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The Influence of Supercritical Retrograde Condensate on Gas Well Productivity in BZ19-6 Condensate Gas Reservoir

JIANG Weijun, YANG Zhicheng, MA Yue, ZHANG Caiqi, YU Xiyan, SUN Lei, LIU Yang

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 72-82. DOI: 10.11885/j.issn.1674-5086.2023.07.27.01

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During the two-year production test of the four well sections in the ultra-large BZ19-6 condensate gas reservoir, near-wellbore reservoir damage and productivity decline occurred due to the supercritical reverse strong retrograde condensation behavior of the formation fluid. To clarify the impact mechanism of supercritical retrograde condensation on gas well productivity, this study integrates experimental methods including phase behavior evolution analysis of formation fluids, core damage tests, and numerical simulation of gas-oil two-phase seepage dynamics, combined with supercritical fluid extraction technology and near-critical non-equilibrium thermodynamics theory. The results reveal the saturation distribution of retrograde condensate in the near-well zone and its constraining effect on gas-phase seepage capacity, quantifying the specific impact of condensation damage on well inflow performance. The findings provide technical support for dynamic analysis, rational production allocation, and development adjustment in the early production test stage of the BZ19-6 condensate gas reservoir and similar reservoirs.

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Accumulation Conditions and Exploration Direction in Deepwater Gulf of Mexico Basin

TIAN Bing, TANG Jun, QIU Shangkun, ZHAO Wenrong, CHEN Tingyu

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 49-63. DOI: 10.11885/j.issn.1674-5086.2024.08.31.01

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To further understand the hydrocarbon accumulation rules of the deepwater Gulf of Mexico Basin, using the seismic, drilling and geochemical test data of the study area, the tectonic-sedimentary evolution characteristics and the accumulation conditions are systematically analyzed, and the hydrocarbon accumulation model and exploration direction are discussed. The oil and gas exploration are mainly concentrated in four major geological regions, namely, basin, sub-salt, folded belt and abyssal plain, which is the result of the complex interaction between sedimentation and tectonics in Mesozoic and Cenozoic. The marine marlstones of the Upper Jurassic Tithonian and Oxford Stages are the main hydrocarbon source rocks in the deep-water area, showing the characteristics of “deep burial”, “old age” and “late hydrocarbon generation”. The reservoirs are of various types, and generally show the characteristics of “multi-layer system”, “new age”, “fast burial” and “high pore permeability”. The penetrating transportation channels associated with salt rock movement and accompanying fault activity are crucial for oil and gas transportation. There are three types of deep-water tectonic circles: structural traps with four-way closures, combined structural/stratigraphic traps with three-way closures, and stratigraphic traps. To sum up, three reservoir-forming combination models were formed, which are “early source fault communication—late fault or salt-body flanking closure—high level accumulation”, “subsalt overpressure and low temperature—fault communication—salt-body/salt-welding occlusion accumulation” and “near-source vertical migration—lateral transport adjustment—dominant structure accumulation”. The Wilcox sandstones in sub-salt and folded belt, Jurassic aeolian sandstones in the eastern basin and abyssal plain are favorable exploration targets in the deepwater Gulf of Mexico Basin.

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Prediction of the Effect of Pressure-bearing Plugging of Fractured Formation Under Non-uniform In-situ Stress

LIU Yang, ZHANG Pei, MA Qi, WANG Junli, MA Tianshou

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 119-128. DOI: 10.11885/j.issn.1674-5086.2023.09.04.01

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Pressure-bearing plugging is an important method to solve the problem of lost circulation in fractured formation. Accurate prediction of pressure-bearing capacity of leakage formation is the core basis of scientific application of pressure-bearing plugging technology. For this purpose, on the basis of analyzing the variation of fracture width under non-uniform in-situ stress, the crack tip stress intensity factor when considering in-fracture plugging is derived based on superposition principle, and an analytical model for predicting the pressure-bearing capacity of plugged fractured formation is established. Compared with the traditional model, the prediction results of this model have higher accuracy and reliability. Finally, the influence of different engineering and geological parameters on the pressure-bearing capacity of plugged fracture is analyzed. The results show that increasing the fracture tip length and reducing the fluid pressure at the fracture tip during plugging treatment are beneficial to improving pressure-bearing capacity of fractured formation. When a low-permeable plugging zone is formed in the vicinity of borehole wall, it is necessary to optimize the length of the plugging zone to maximize the pressure-bearing capacity of plugged fracture. When the formation permeability is determined, pressure-bearing capacity of plugged fracture decreases with the increase of the ratio of in-situ stresses, and increases with the increase of elastic modulus, Poisson's ratio and fracture toughness.

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The Research of Fracture and Pore Dual-media Reservoir Gas Well Production Capacity Formula

PENG Peng, WANG Xiaopei, ZHANG Yongling, ZHAO Boyong, LIU Zhaolong

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 83-93. DOI: 10.11885/j.issn.1674-5086.2023.12.18.03

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Reasonable evaluation of production capacity is very important for gas well production. It is the foundation for the long-term development of gas field. The ultra-deep and ultra-high-pressure fractured tight sandstone gas reservoirs in front of Kuche mountain of Tarim Oilfield is characteristic of tight matrix and developed fractures. The seepage characteristics often manifest as the dual-media reservoir features of fractures and matrix. The entire flow process is divided into three stages: fracture flow, transitional flow and overall system flow. In response to the lack of targeted production capacity evaluation methods, the research has been conducted on the early production capacity evaluation formula corresponding to the fracture flow stage, transitional stage and on the long-term stable production capacity corresponding to the fracture porosity flow stage. The production capacity evaluation formula for dual-media reservoir gas wells considering the skin factor and the high speed non-Darcy coefficient has been theoretically established. The examples of calculation show that the result of production capacity formula is closer to the testing production than the conventional point method empirical formula, demonstrating good applicability in ultra-deep and ultra-high-pressure fractured tight sandstone gas reservoirs.

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Diagenesis and Pore Evolution in Low-permeability Reservoirs of the Baodao A Deepwater Gas Field

YANG Li, LI Hua, WANG Panrong, PENG Zhichun, PAN Yan

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 37-46. DOI: 10.11885/j.issn.1674-5086.2024.09.12.01

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Baodao A Gas Field is the first deep water and deep gas field discovered in Baodao Depression. The main gas group of the Baodao A Gas Field is the third member of the Lingshui Formation. The water depth of the gas field varies greatly, the fault system is well developed, the reservoir highly heterogeneous, and the diagenetic phenomena abundant. Affected by the diagenetic transformation, the physical properties of the gas field are poor and the distribution law is complex. Therefore, based on the experimental data of thin section of rock, X-ray diffraction of clay minerals, and oxygen isotope analysis, the reservoir physical property, diagenetic characteristics and quantitative evolution of pores of the low permeability reservoir in the third member of Lingshui Formation in the study area are systematically described. The results show that: mechanical compaction reduces the porosity of the reservoir by 22.0%, which is the main factor of reservoir compaction in the third member of Lingshui Formation in the study area. The porosity of the reservoir is increased by 11.9% by solution and decreased by 13.7% by cementation. The process of pore evolution reveals that compaction is the primary factor contributing to early changes in reservoir physical properties, while mineral dissolution during the middle and late stages of oil and gas charging enhances reservoir space. Subsequently, late-stage carbonate cementation further densifies the reservoir. This research achievement effectively guides the prediction research of favorable reservoirs, provides geological basis for the efficient development of gas fields, and lays a foundation for ensuring the country’s accelerated advancement into the deep sea.

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The Influence of Transportation Environment on the Quantization Accuracy of Ultrasonic Internal Detection

CAI Liangxue, ZHENG Yuejun, LU Yifeng, XU Guangli

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 168-177. DOI: 10.11885/j.issn.1674-5086.2024.01.15.02

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Ultrasonic internal detection has been widely used in the field of pipeline detection and monitoring due to its advantages of easy operation and accurate detection. The echo signal contains a lot of information, but the change of working conditions will affect the echo signal. In order to explore the influence of pipe pressure or flow rate on the measurement accuracy of wall thickness, an ultrasonic internal detection simulation experiment system was used to carry out experiments. Under different pipeline transport conditions, ultrasonic internal detection signals are collected and characteristic parameters are extracted to analyze the fluctuation of echo signals. The wall thickness of the pipeline is calculated by using the transit-time method, and the influence of different pipeline transport environments on the calculation accuracy of wall thickness is analyzed. The results show that with the change of pressure and flow rate, the moment of receiving the echo signal is advanced or delayed, and its amplitude fluctuates. The fluctuation range of the wall thickness accuracy error is between -0.71% and 0.96%. This indicates that the pipe flow state (0.3~1.2 MPa, 8.129~15.023 m ³/h) has no significant influence on the measurement accuracy of wall thickness, and the influence of pipeline transportation environment on the accuracy of ultrasonic internal detection of pipe wall thickness can be ignored, which provides theoretical support for accurate analysis of ultrasonic internal detection data.

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Compatibility of Viscoelastic Gel for Synergistic Water Plugging in High Temperature and High Salinity Reservoirs in Tahe Oilfield

HE Shiwei, WU Weipeng, YANG Min, HOU Jirui, ZHANG Wei, MA Dongchen

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 172-182. DOI: 10.11885/j.issn.1674-5086.2024.05.11.04

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Gel water plugging is the main technical method for recovery in the middle and late development of Tahe Oilfield. As the reservoir temperature and salinity continue to increase, the water plugging effectiveness of a single gel system is low, and its system development and use of water plugging materials urgently need to be optimized and improved. In this regard, this paper is based on the research of two independently developed sets of high temperature resistance, high salinity and dilution resistance water plugging systems. Through infrared, thermos-gravimeter, rheology and other analyses, the dilution resistance and compatibility of gel materials are systematically evaluated. At the same time, based on core experimental simulation, a dynamic plugging model for the collaborative application of the two gel systems is proposed to compound water plugging to further improve the dynamic plugging rate and plugging effect. Results show that the two gel systems can be applied to high temperature conditions of 140 ℃ and have good dilution resistance in water with a salinity of 24×10 ⁴ mg/L. While ensuring good compatibility of the two gels, they are used synergistically. Their excellent erosion resistance makes the collaborative water plugging rate greater than 99%. Studies have shown that different gel systems with good compatibility can combine to block water and have good application potential in high temperature and high salinity environments.

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Intelligent Classification of Deep-water Submarine Fan Lithofacies Based on Small Sample

ZHEN Yan, LIU Xiaowei, ZHANG Yihao, ZHAO Zhen, XIAO Yifei, ZHAO Xiaoming

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 60-71. DOI: 10.11885/j.issn.1674-5086.2024.09.15.02

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Aiming at the problems of high cost, difficulty in operation, high technical requirements, limited number of rock core-taking and small number of lithofacies samples obtained in the exploration and development of deep-water submarine fan reservoir, an intelligent classification method of deep-water submarine fan lithofacies based on small samples was proposed. First, the Empirical Mode Decomposition (EMD) and sliding window are used to construct multi-layer image styles input for each well point as inputs. Secondly, the lithofacies recognition model is constructed by using Long Short-Term Memory (LSTM) and Convolutional Neural Networks (CNN) algorithms. The Generative Adversarial Networks (GAN) model was used to expand a few class samples. Finally, a Genetic Algorithm (GA) was introduced to optimize the model parameters. Taking Akpo Oilfield in the Niger Delta Basin of West Africa as the research area, this method is used to carry out the intelligent identification of lithofacies. Research shows that the lithofacies classification accuracy of the GAN-GA-CNN model proposed in this paper can reach 94.22%, which greatly improves the prediction accuracy compared with the original CNN model, proving the feasibility of the proposed method.

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Research and Improvement of Interface Mechanical Behavior of Screw Motor Based on Cohesive Zone Model

REN Meipeng, XIE Renjun, ZHU Xiaohua, SHI Changshuai, ZHANG Xingquan

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 151-167. DOI: 10.11885/j.issn.1674-5086.2023.10.16.02

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Aiming at the problem of debonding failure of the stator rubber bushing of the screw motor, the failure mechanism of the stator bushing of the 7/8 head conventional and equal wall thickness screw motor was studied. The principle of rubber-metal interface cohesion was adopted in the study. Through rubber-metal bonding mechanics test and rubber uniaxial tensile test, and finite element and numerical analysis, the interface shear stress was found to be the main factor causing the bushing bonding failure, and the minimum arc radius $R$ of the bushing profile was the main reason for the change of the maximum interface shear stress. The drilling fluid and interference have a significant effect on the shear stress at the interface of the equal wall thickness bushing. When the drilling fluid pressure increases from 15 MPa to 60 MPa, the maximum shear stress at the interface of the equal wall thickness bushing increases by 146%, and the equal wall thickness screw motor is more prone to bonding failure. Finally, the different wall thickness bushing structure is proposed. The interface shear stress of the different wall thickness bushing is less than that of the equal wall thickness bushing, and decreases with the increase of the minimum arc radius $R$, which has good heat dissipation. The service life of the bushing with different wall thickness is proportional to the minimum arc radius when fatigue failure occurs. The maxi-mum service life is predicted to be 240.99 h when fatigue failure occurs. The first fatigue failure area is the inner cavity arc top of the bushing, which is consistent with the actual failure phenomenon. This paper provides a theoretical basis for the design optimization of screw motor, and makes an important contribution to improve the working life of screw motor.

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Distribution Patterns and Controlling Factors of Axial Submarine Fan Sandbodies in the X Oilfield, North Sea, UK

CAO Shuchun, YU Jitao, QI Mingming, BU Fanqing, WU Shenghe, SHEN Mo

Journal of Southwest Petroleum University(Science & Technology Edition) 2025, 47 (6): 47-59. DOI: 10.11885/j.issn.1674-5086.2025.02.21.03

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Submarine fan reservoirs are a hotspot for oil and gas exploration and development in the world. The distribution pattern and genesis of sand bodies are complex. At present, there is a lack of research on the axial submarine fan sand bodies in deepwater grabens. Taking the B Formation of Upper Jurassic of the X Oilfield in the North Sea, UK as an example, this paper attempts to investigate the distribution patterns and controlling factors of axial submarine fan in the deep-water graben environment, by well and seismic data mining. The results show that submarine fan sand bodies are mainly of proximal bypass type, presenting banded, lobate or tongue shapes. Lobate sandbodies are thick and wide with a low length-width ratio of 5, which were formed by lateral migration or retrogradation superposition, commonly seen in B4 Oil Group. In contrast, banded sandbodies are relatively thin and narrow with a high length-width ratio of 10, which were formed by vertical superposition. This type of sandbodies is developed in the B2 Oil Group. The distribution of submarine fan sand bodies is mainly controlled by paleogeomorphology. The longitudinal steep slope (greater than 6°) driven by the differential subsidence of the graben, causes the submarine fan sand bodies to present proximal bypass type. The limitation of the internal graben affects the morphology and superposition style of the submarine fan. Compared with the thin mud-rich submarine fan sand bodies, the thick sand-rich submarine fan sand bodies are relatively less restricted, which are mostly lobate and tongue-shaped, and are lateral superposed. The lateral symmetry of the graben landform affects the lateral development position and migration direction of the submarine fan.

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Negative-positive Coupling Risk Assessment Method for Oil and Gas Pipelines

PU Hongyu, LI Yi, SHANG Yaoping, RUAN Chao, REN Yunbo

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (2): 149-161. DOI: 10.11885/j.issn.1674-5086.2025.10.21.02

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Oil and gas pipeline risk assessment is a complex systems engineering project. To address the limitations of traditional risk assessment methods when applied to China's oil and gas pipelines, this paper proposes a new method called“negativepositive coupling risk assessment ” . Based on the actual operating conditions of China's pipelines, this method innovatively integrates positive factors that enhance pipeline safety and negative factors that pose threats into the same assessment framework. It focuses on analyzing the coupling mechanism between these factors, establishes a framework system for failure probability indicators and a framework system for failure consequence indicators in the research, provides a specific score calculation method, and adds correction index values for coupling effects. Through the application of an example of a natural gas pipeline in southwest China, the feasibility and effectiveness of this method are verified. The correction range of the coupling effect on the risk value is between 6% and 14%. Applying this method can accurately identify key risk control points and provide a clear direction for risk mitigation decisions, thereby effectively preventing intermediate events and major accidents. It holds important practical guiding significance for reducing the accident probability of China's oil and gas pipelines and ensuring the safety of energy arteries.

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Technological Advancements and Research Directions for Oil Reservoir Type Underground Gas Storage

YU Chenglin, LIU Wei, SHANG Lin, ZHENG Jiapeng, GAO Guangliang, HE Haiyan, LI Chun

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 1-10. DOI: 10.11885/j.issn.1674-5086.2025.12.14.02

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Undersaturated oil reservoirs utilized for underground gas storage are devoid of primary gas caps and are characterized by multiphase fluid coexistence and compositional exchange. Currently, they encounter critical challenges, including an inadequate understanding of gas-liquid interactive displacement mechanisms and suboptimal precision in performance indicator design. By analyzing the special characteristics of gas-liquid interaction flooding and fluid properties periodic changes in oil reservoir type UGS, key theoretical and technical challenges have been proposed. Recent key developments have been summarized, and future research directions have been proposed. Research has shown that oil reservoir type UGS faces key scientific issues, such as the expansion mechanism of under gas-liquid interactive displacement and the interphase mass transfer mechanism, as well as technical issues such as secondary gas cap formation and control, index design, and efficient liquid discharge expansion. Special site selection indicators such as water drive efficiency and sweep efficiency have been proposed in oil reservoir type UGS. Simulation experiments reveal that the interactive displacement efficiency of fluid and oil has increased by 10.3 and 12.5 percentage points respectively compared to single gas displacement. Considering the factor of phase mass transfer, the effective storage capacity increases by 17.8%. In the future, oil reservoir type UGS will deepen theoretical and technological research on mechanism of space utilization and phase interaction, UGS construction parameter design, and secondary gas cap formation and control. The research results provide important basis for scientifically guiding the UGS design, achieving peak shaving capacity, and improving the oil recovery.

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A Study on the Formation Conditions and Influencing Factors of Secondary Gas Cap in Oil Reservoirs Conversion into Gas Storage

MA Xiaoli, LI Cong, JIANG Mingjie, GU Xiao, XIN Chunyan, TIAN Zhongjing

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 11-22. DOI: 10.11885/j.issn.1674-5086.2025.12.15.01

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With the transformation of China's energy structure and the growth of natural gas consumption demand, the coordinated development of oil and gas has become an important development direction. It is of great significance to reconstruct gas storage in old reservoirs to revitalize oilfield assets and improve regional peak shaving and gas storage capacity. In the process of reservoir construction, the formation and migration of secondary gas cap is the key to the synergistic extraction, drainage and expansion of gas storage and the formation of high-speed injection and production capacity in the later stage, which is the core problem affecting the efficient capacity of gas storage. This paper explores the formation conditions and migration rules of secondary gas cap, and provides theoretical support for gas drive expansion scheme. Based on physical simulation, numerical simulation and reservoir engineering methods, the changes of gas saturation and formation pressure are analyzed to determine the critical conditions for the formation of secondary gas cap, and to reveal the influence mechanism of well pattern, formation dip angle, reservoir heterogeneity and other factors on the development and migration of gas cap. The results show that the well pattern and formation dip angle are the main controlling factors for the stability of secondary gas cap, and the strong heterogeneity of reservoir will inhibit the uniform expansion of gas cap. The study clarifies the key control parameters of gas cap evolution, provides a basis for optimizing the injection-production system, and has theoretical and engineering guiding significance for the coordinated development of oil and gas and the efficient construction of gas storage.

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A Study on Phase State Characteristics During Multi-cycle Injection in the Collaborative Construction of Underground Gas Storage with Nanpu 1-5 Weak Volatile Reservoir

GAO Guangliang, MA Xiaoli, GU Xiao, JIANG Mingjie, LI Dan, LI Chun

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 71-80. DOI: 10.11885/j.issn.1674-5086.2025.12.23.01

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Compared with conventional underground gas storage construction in depleted gas reservoirs, fluid compositional migration and phase behavior changes are more complex during multi-cycle injection-production in weakly volatile oil reservoirs. To reveal the phase-equilibrium evolution during cyclic injection-production, this study takes the Nanpu 1-5 weakly volatile oil reservoir as the target and establishes a phase-equilibrium experimental procedure and theoretical simulation model for multi-cycle injection-production. The variations in the composition, phase behavior, saturation, and recovery degree of produced and residual fluids were investigated. The results show that after five injection-production cycles, the oil saturation decreased by 2.4%, which is conducive to increasing gas storage space. The methane content of the produced gas increased from 93.8% to 95.3%, while CO ₂ and C ₂₊ components gradually decreased, indicating a weakening extraction effect of the injected gas. The C ₇₊ mole fraction of the residual oil increased by 9.2%; under the upper and lower pressure limits, the solution gas-oil ratio decreased from 185 and 88 m ³/m ³ to 78 and 35 m ³/m ³, respectively, and the oil formation volume factor decreased from 1.57 and 1.32 to 1.24 and 1.16, respectively, indicating gradual heavy-end enrichment of the residual oil. This study clarifies the relationships among compositional migration, phase behavior evolution, and gas storage space expansion, providing a basis for optimizing cyclic injection-production strategies in similar oil-reservoir-based underground gas storage projects.

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A Study on the Geological and Gas Reservoir Engineering Plan for PG2 Underground Gas Storage

SHANG Lin, HE Haiyan, GAO Guangliang, SUN Yanchun, WANG Miao, LI Cong

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 81-93. DOI: 10.11885/j.issn.1674-5086.2026.02.09.01

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The integrated construction of oil reservoir-type gas storage coupled with natural gas flooding for enhanced oil recovery has emerged as a significant direction in recent years. Through mechanisms such as gravity segregation, miscible displacement, and extraction, this approach can effectively improve crude oil recovery while establishing large-scale seasonal peak-shaving capacity. Taking the PG2 Underground Gas Storage of Jidong Oilfield as an example, this paper systematically conducts geological condition evaluation for gas storage construction, sealing analysis of cap rocks and faults, design of injection-production capacity, and optimization of storage capacity parameters, thereby demonstrating the feasibility of converting such oil reservoirs into gas storage facilities. The results indicate that the target block features thick reservoirs, favorable physical properties, excellent fluid characteristics, and regionally stable cap rocks with strong sealing capability. The comprehensive evaluation shows that the dynamic sealing pressure limit of the geological body reaches 44.9 MPa, providing a solid geological foundation for gas storage construction. The proposed scheme achieves a working gas volume of over 9.0×10 ⁸ m ³, a daily peak-shaving capacity of nearly 0.1×10 ⁸ m ³, and an expected increase in crude oil recovery of approximately 20 percentage points compared to water flooding. These results confirm that converting blocky volatile oil reservoirs into gas storage is technically feasible, economically effective, and the associated methodologies can serve as an important reference for similar reservoirs aiming to simultaneously enhance oil recovery and provide gas storage peak-shaving services.

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Fault Pressure-bearing Capacity Assessment for Gas Storage Conversion in Nanpu 1-5 Reservoir

WU Haitao, MA Xiaoli, LIU Mancang, XU Shujuan, LI Yehui, QIU Xiaosong

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 35-44. DOI: 10.11885/j.issn.1674-5086.2025.12.15.03

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The primary risk associated with repurposing complex fault-block oil reservoirs into gas storage facilities lies in the potential loss of fault seal integrity under alternating high and low pressure conditions during cyclic injection and production. Therefore, a quantitative assessment of the pressure-bearing capacity of faults is critical to ensuring the safe operation of such gas storage sites. This study, based on seismic data, drilling records, and production dynamics from the Nanpu 1-5 Reservoir, conducts a graded and staged evaluation of faults. Through four-dimensional geomechanical simulations covering the entire lifecycle of reservoir development and gas storage injection-production operations, the safe pressure-bearing capacity of faults is quantitatively evaluated. The results indicate that faults F1 to F6 generally exhibit large throws, characterized by sealing interfaces between gas-bearing layers and tight formations, demonstrating excellent sealing performance. The Nanpu 1-5 Reservoir is divided into four fault blocks: NP1-7, NP105X1, NP1-5X1090, and NP105X5. Critical weak points in these fault blocks are identified as boundary faults F2(NP1-7), F2(NP105X1), F5, and F6, with safe pressure-bearing capacities of 27.4, 28.9, 28.9, and 27.5 MPa, respectively. These findings provide a scientific basis for optimizing the maximum operating pressure of the NP1-5 gas storage facility. The methodology can be extended to enhance the operational efficiency of existing gas storage facilities through pressure optimization.

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Study on Rock Mechanical Characteristics of Reservoir and Caprock in Medium-deep Gas Storage with Different Lithologies

DUAN Bin, WU Haitao, HAN Dongliang, ZHAO Yao, WANG Miao, ZHANG Ziyu

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 45-58. DOI: 10.11885/j.issn.1674-5086.2025.12.02.04

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In order to address the differences in mechanical properties of reservoir and cap rocks in middle and deep UGS, this paper selects mudstone, shale, sandstone, and dolomite cores from four UGS (P, M, X, S) and systematically compares their mechanical properties through uniaxial, triaxial, and fatigue compression experiments. The results are as follows: 1) The mechanical strength and deformation resistance of shale in UGS X are weaker than those of cap mudstone of UGS P. The compressive strength and elastic modulus of dolomite in UGS X are much higher than those of sandstone, and its compressive strength can reach more than twice that of sandstone. 2) For UGS with the same sandstone, the deeper the burial depth, the stronger the compressive strength and deformation resistance, and the strength increase of dolomite due to confining pressure is the greatest. Comparison of mechanical parameters of sandstone and mud stone in P UGS, mudstone has slightly higher strength and deformation resistance than sandstone. 3) An increase in burial depth and a decrease in porosity and permeability can significantly enhance rock strength, with a positive correlation between elastic modulus and compressive strength. Fatigue experiments show that the strength of mudstone in deep UGS only decreases by 10% after 1 000 injections, while the strength fluctuation of mud stone in middle UGS reaches 20%. The deep cap rock is more suitable for high-pressure alternating loads. 4) Microstructure analysis reveals that dolomite has high strength due to dense intergranular cementation, while sandstone's porous structure and weak cementation result in weaker mechanical properties. The research results provide experimental support for long-term safe operation of UGS.

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Research on the Hydrolytic Degradation of Brittle Shale and Wellbore Stability in the Pugu 2 Gas Storage Reservoir

ZHOU Yan, SONG Wei, WU Yan, WANG Jinzhong, HU Yongke, YANG Yan, PAN Junying

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 145-156. DOI: 10.11885/j.issn.1674-5086.2026.03.12.02

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Frequent wellbore instability poses a significant challenge during the drilling of large-diameter wellbores in the hard and brittle mudstone of the Dong 3 Member in the Pugu 2 Gas Storage Reservoir. Based on the scale effect theory in rock mechanics, this study conducted comparative mechanical degradation experiments on intact and crushed mudstone samples immersed in drilling fluid. A wellbore collapse prediction model considering the time-dependent seepage damage was subsequently established to reveal the fracture-fluid coupling damage mechanism. The results are as follows: 1) The well-developed micro-fracture network in the mudstone transforms singular hydration diffusion into a severe hydration-seepage coupling damage. 2) The rock degradation exhibits a significant scale effect and nonlinear time-dependent characteristics. During the initial immersion phase (0~4 d), the strength decay rate of the crushed samples is 1.54 times that of the intact ones. 3) A wellbore collapse pressure prediction model considering the time effect of fracture seepage damage was established. The calculation results show that, the critical collapse density of the 9.5 in. well position exceeded the safety warning line on the second day, and compared with the 12-day stable period of the 8.5 in. conventional section, the safe operation window was shortened by more than 80%. Based on this, a collaborative anti-collapse strategy of micron-scale rigid plugging and film-forming agents and a 48 h rapid drilling and completion operation suggestion were proposed, providing a theoretical basis for safe drilling in complex sections of gas storage reservoirs.

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Multiscale Geomechanical Research on Dynamic Sealing Properties of Gas Storage Reservoirs

WANG Miao, SHANG Lin, WANG Jiuli, WANG Lina, LI Chaofeng, DUAN Bin

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 23-34. DOI: 10.11885/j.issn.1674-5086.2025.12.02.03

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To effectively guide the design of the upper limit pressure for the operation of gas storage reservoirs in complex fault-block oilfields and ensure their safe and efficient operation, it is imperative to conduct a comprehensive evaluation of the sealing performance of the geological body. By introducing a multi-scale geomechanical model for simulation, we took the Nanpu 1 Gas Storage Reservoir as an example, on the basis of the single-reservoir geomechanical model, and establish a large-scale multi-reservoir interaction in-situ stress model for the first time. The four-dimensional stress field distribution under different pore pressures was simulated, and the stress changes and stability of faults and cap rocks were analyzed. On the basis of the traditional geomechanical model, a quantitative characterization method for the stress interference effect of multi-reservoir interaction was constructed, to reveal the superimposed influence mechanism of multi-gas storage reservoirs' coordinated injection and production on the regional stress field. A multi-dimensional and multi-index evaluation method for the integrity of geological bodies was proposed, achieving quantitative evaluation of cap rock tensile failure, shear failure and fault slip, and then a full-system monitoring system was deployed. The research results show that the deformation of the Guantao Cap Rock during the operation of the gas storage reservoir is small; there is no risk of fault activation in the early operation of the gas storage reservoir for hydrocarbon-controlling fault F2; the critical pressure for simulating fault slip activation is 34.5 MPa, and there is a risk of instability in the integrity of the gas storage reservoir geological body. The upper limit pressure for operation was determined to be 27.2 MPa based on the combined critical pressures for cap rock tensile failure, cap rock shear failure, and fault slip activation obtained from models of different scales. The research results provide a fine and quantitative assessment of the operational safety of gas storage reservoirs under the influence of dynamic stress fields and scientifically guide the optimization design of the upper limit pressure and monitoring system.

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Selection Analysis of Centrifugal Compressors for Gas Storage Facilities

ZOU Xuejing, ZHANG Xu, WANG Xufeng, LI Mengxia, MENG Hong

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 188-196. DOI: 10.11885/j.issn.1674-5086.2025.12.24.03

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Gas injection compressors serve as the core power equipment for pressurized gas injection in gas storage, and the unit configuration scheme directly determines the peak-shaving capacity, operational stability and energy consumption level of gas storage. To clarify the adaptation law of centrifugal compressors with different structures in gas storage engineering, optimize the type selection and configuration of compressors, and reduce the project operation cost, a study on the type selection and application of centrifugal compressors for gas storage is carried out. Adopting the methods of literature investigation, structural comparative analysis and engineering economic comparison, this paper systematically summarizes the application status and technical development trend of compressors in domestic gas storage facilities. The structural characteristics, technical bottlenecks and applicable working conditions of three mainstream centrifugal compressor units, namely single-cylinder single-stage, single-cylinder two-stage and high-low pressure cylinder types, are compared and analyzed. Combined with actual gas storage engineering projects, quantitative economic comparison of different compressor configuration schemes (single-cylinder single-stage and single-cylinder two-stage) is conducted from the dimensions of equipment cost, operating energy consumption and maintenance cost. The research results show that the single-cylinder single-stage unit features a simple structure and is suitable for low-pressure conventional gas injection scenarios, while the single-cylinder two-stage centrifugal compressor matches the injection operating conditions of medium-to-high-pressure gas storage and delivers optimal overall performance. The research conclusions define the adaptation boundaries of different types of centrifugal compressors as well as the bottlenecks and improvement directions of domestic centrifugal compressors, which can provide theoretical reference and technical guidance for the type selection, structural optimization and engineering configuration of compressors in gas storage facilities.

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Research on Key Technologies for Pullback in Land-to-sea Directional Drilling of Submarine Pipelines for Gas Storage

HAO Dayong, ZHANG Lingxuan, ZHANG Tao, MAO Qingzhe, ZHANG Guoxing, FAN Jiaxi

Journal of Southwest Petroleum University(Science & Technology Edition) 2026, 48 (4): 181-187. DOI: 10.11885/j.issn.1674-5086.2026.05.11.01

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To address the constraints of limited water depth and poor riser safety during the landfall of subsea pipelines for injection, production and transmission of offshore gas storage reservoirs in shallow coastal waters, key control technologies for pipeline pullback in land-to-sea directional drilling are investigated. Three pullback operation modes are classified according to the layout of pipeline prefabrication and traction equipment, and the optimal construction scheme is selected based on site conditions. A novel four-section model for calculating the total length of pullback pipelines is established, with calculation criteria defined for each section. Referencing GB/T 50423 and NEN 3650 standards, a three-stage formula for pullback force is derived by taking full account of resistances on land, inside boreholes and on seabed. The combined prefabrication on land and traction via drilling rig on anchored barge is verified as the optimal solution. Calculations with a safety factor of 3.0 yield a maximum design pullback force of 4 160.92 kN, matching a 500 t offshore drilling rig. Comparison of the applicability of fixed platforms, jack-up platforms and anchored barges confirms the 8-point mooring barge as the preferred operating platform. A calculation method for anchor cable touch-down points is developed based on the catenary equation, alongside comprehensive protection measures for existing subsea facilities. The proposed technologies provide technical support for similar landfall projects of subsea pipelines for offshore gas storage reservoirs via directional drilling in shallow coastal waters.

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