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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Characterization and Effectiveness Evaluation of Deep Reservoir Fractures Under Oil-based Mud

YANG Fenglai, CHEN Rong, ZHOU Qing, WANG Jun, DAI Li

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 51-64. DOI: 10.11885/j.issn.1674-5086.2024.04.30.01

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The Kuqa Area is a typical fractured tight sandstone reservoir with dense lithology and low porosity. Validity of fractures is a key factor in the formation of a good reservoir. Therefore, how to accurately identify fractures and evaluate their effectiveness is the primary problem in oilfield exploration and development. Due to the needs of drilling engineering, most wells in the Kuqa Area are drilled with oil-based mud. The electrical conductivity of oil-based mud is poor, and it is difficult to effectively identify fractures with early oil-based mud electrical imaging logging tools due their low resolution. Therefore, the combination of oil-based mud electrical imaging logging tools (EI) and ultrasonic imaging tools (UXPL) can be used to extract structures and pick up fractures with different opening degrees, effectively solving the problem of fine identification of bedding and fractures. This article also introduces the method of using non-conductive mud geological imaging (NGI) to identify fractures, and systematically analyzes the relationship between normal stress on the fracture surface, the angle between fracture direction and maximum principal stress, and production capacity. A quantitative standard for evaluating the effectiveness of oil-based mud fractures in the Kuqa Area is established. In practical applications, this set of crack fine identification of fracture and effectiveness evaluation methods effectively guides production operation measures and provides technical means for the evaluation and development of fractured tight oil and gas reservoirs.

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Differential Characteristics and Evolution of Conjugate Strike Slip Faults in the Halahatang Area, Northern Tarim Basin

CHEN Lixin, WANG Shenglei, WAN Xiaoguo, SU Zhou, MA Bingshan

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 19-37. DOI: 10.11885/j.issn.1674-5086.2023.11.17.01

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Non-classical X-type conjugate strike-slip faults are observed in the Halahatang Oilfield, which have obvious differences in zoning, stratification, segmentation and evolution characteristics, constraining oil and gas exploration and exploitation. Based on the 3 400 km$^2$ seismic data, this paper describes the stratification and segmentation characteristics of two strike-slip faults in NE direction and NW direction, and analyzes the differential evolution characteristics and mechanism. The results show that 1) from north to south, fault maturity and extensibility become weaker, and stress perturbation by NE-striking faults increased; from deep to shallow layers, the disturbance effect of NW-trending faults on NE-trending faults became weaker; deformation degree and maturity decreases upward in NW-striking faults, but increases in NE-striking faults. 2) Strike-slip fault underwent multiple evolution stages in Halahatang Area, which can be divided into Middle Ordovician conjugate fault formation stage, Carboniferous-Permian transtensional strike-slip fault reactivation stage, and Meso-Cenozoic transtensional strike-slip fault reactivation stage. The NE- and NW-striking faults had differential fault evolution process. 3) Mechanism of fault formation and reactivation changes during the evolution process. The strike-slip fault system during the Middle Ordovician is controlled by the superimposed deformation of pure shear and simple shear, and were also controlled by stress field, pre-existing structure and regional strata thickness. The reduction of stress from north to south and the change of associated stress field resultes in the difference of fault styles in the south and north.

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Hydrocarbon Accumulation Process and Multiphase Formation in the F$_{\rm{{Ⅱ}}}$21 Strike-slip Fault Zone of Tazhong Uplift

XIONG Chang, ZHAO Xingxing, WU Jiangyong, ZHANG Xinqiao, WANG Peng

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 1-18. DOI: 10.11885/j.issn.1674-5086.2024.02.29.06

Abstract （158）

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Aiming at the complicated phase distribution of Ordovician reservoirs in Fault F$_{\rm{{Ⅱ}}}$21 of Tazhong Uplift, we make a comprehensive analysis of tectonic analytical geochemistry, and find out that the plane distribution of oil and gas physical properties such as oil density, gas drying coefficient, gas oil ratio, etc. is closely related to strike-slip fault segment structure, that condensate gas reservoir develops in the north of the wing tail structure zone, and that volatile oil reservoir and crude oil reservoir develop successively in the south area. The crude oil in the F$_{\rm{{Ⅱ}}}$21 fault is the same as that of the northern depression Fuman and Shunbei areas, mainly from Lower Cambrian source rocks. The maturity of crude oil decreases from north to south along the fault zone. Natural gas in the north of the fault zone is mainly crude oil cracking gas, and in the central and southern parts mainly kerogen cracking gas. The Ordovician reservoir in the F$_{\rm{{Ⅱ}}}$21 fault zone underwent multi-stage oil and gas injection, and the wing tail graben site was a favorable filling point for oil and gas, and the strong charging and transformation of pre-salt crude oil cracking gas in the Himalayan period was an important reason for the formation of condensate gas reservoir in the northern part of the fault zone. Affected by the paleostructural, the oil resources generated in the Late Caledonian and Late Hercynian periods were mainly accumulated in the southern nose uplift area of the wing tail graben structure.

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Numerical Calculation of Multi-field Damage Coupling Fracture Initiation Pressure for Ultra-deep and Extra-deep Carbonate Reservoirs

GUO Jianchun, GUAN Chencheng, REN Jichuan, GOU Bo, ZENG Ji

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 85-96. DOI: 10.11885/j.issn.1674-5086.2024.06.06.01

Abstract （142）

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Ultra-deep carbonate reservoirs are characterized with high initiation pressure, leading to difficulties in fractures initiating. Acid can react with the reservoir matrix, enhancing porosity, increasing permeability, and deteriorating the mechanical properties of the rock, thereby reducing the initiation pressure. However, there lacks accurate calculation methods of fracture initiation pressure for acid-damaged carbonate reservoirs, making it challenging to design initiation pressure reduction measures. This study tested the dynamic Young$'$s modulus of cores after drilling fluid immersion and acid displacement, establishing a damage evolution equation for carbonate rocks under different fluid disturbance states. In addition, a numerical calculation model was established to couple flow, chemical, and stress-damage fields during acid fracturing to estimate the fracture initiation pressure. The results indicate that when both drilling fluid and acid fluid are affected, for reservoirs with a porosity below 4.32% and an acidizing time less than 4.08 minutes, the damage factor is below 0, which means that it is unable to mitigate the increase in Young's modulus caused by drilling fluid. During the operation of ``acid displacement of wellbore + acid immersion damage+ acid fracturing", the 8 833 m section of Well P1 reached the fracture initiation condition at the 73rd minute with the damage factor of 0.301 and fracture initiation pressure decrease of 29 MPa; as a result, this well was opened successfully. The calculation deviation of the model ranged from 1% to 5%, resulting in an improved accuracy of 3 to 10 percentage points when compared to traditional analytical models, this indicates that the model is particularly valuable for the calculation of fracture initiation pressure and designing acid damage measures in the Dengying Formation, as well as in similar carbonate reservoirs.

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A Study on Cement Slurry Circulation Fluid Mixing for Deep Well Casing Cementing in the Sichuan-Chongqing Area

YANG Fujie, SUN Jinfei, XU Kewei, LUO Hanlin, LI Zaoyuan

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 178-188. DOI: 10.11885/j.issn.1674-5086.2024.03.01.03

Abstract （131）

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During the process of cement injection in deep wells, due to the influence of complex wellbore conditions such as long sealing sections, narrow gaps, and high eccentricity, the annulus fluid is prone to mixing, and the mixing may increase the friction of the mixed section, causing cementing leakage. In order to solve the problem of inaccurate ECD prediction of high eccentricity annulus in the casing cementing operation of the oil layer in the Gaomo in eastern Sichuan, a cementing fluid mixing simulation and an experimental study on the rheology of the slurry were carried out. The study calculated the slurry in real time based on CFD. According to the changes in the fluid proportion of each section, the wellbore ECD was calculated by fitting the rheological equation through rheological experiments. The results proved that the eccentricity is the main factor affecting the change of the mixing ratio. When the eccentricity is low, the proportion of drilling fluid, spacer fluid and cement slurry is 5：1：4, and when the eccentricity is high, the ratio is mainly 7：1：2; the ECD of the mixed grout is 0.2$\sim$0.8 g/cm$^3$ higher than the conventional ECD in the upper grouting section, and is 0.2$\sim$0.5 g/cm$^3$ higher in the lower pure cement section. This study reveals the impact of complex well conditions in deep wells on the mixing ratio between fluids and the equivalent density of the wellbore. It is of great significance to ensure the safe cementing operation of deep wells in Sichuan and Chongqing and improve the quality of cementing.

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Reflections on Completion Engineering and Recovery of Ultra-deep Oil and Gas Wells

REN Jinming, PAN Zhaocai, HUANG Kun, FENG Shaobo, ZHANG Bao

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 169-177. DOI: 10.11885/j.issn.1674-5086.2024.06.19.02

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The continuous development of ultra-deep oil and gas reservoirs is closely related to the completion design of oil and gas wells. However, due to limitations in drilling equipment, the presence of high-pressure saline layers, geological characteristics such as prone-to-collapse and prone-to-leakage formations, as well as economic evaluation considerations, the completion methods for ultra-deep oil and gas wells exhibit significant diversity (open-hole completions, completions using small-sized reservoir casings not exceeding $\phi$127 mm, and so on). Designs featuring production strings traversing the perforation top boundary and even the perforation bottom boundary are also common, and permanent packers are often preferred. These factors can potentially increase operational difficulties, prolong operation times, elevate costs, and impact well productivity and ultimate recovery rates. By analyzing two already developed ultra-deep oil and gas reservoir blocks as case studies, it was discovered that the accumulation of sand or silt is a crucial factor contributing to low well productivity, subsequently adversely affecting recovery rates. In response, the study proposes that the research and design of ultra-deep well completions should anticipate scenarios of sand or silt accumulation. The objective is to prolong the duration of sand or silt accumulation, thereby creating favorable conditions for subsequent operations and ultimately enhancing recovery rates. To achieve this, the study conducted thorough scientific research and optimization on five key aspects: completion methods, reservoir casing sizes, completion string configurations, packer type selection, and sand pocket designs. Building upon these optimizations, comprehensive calculations were further performed for drilling and completion investments, drilling and completion cycles, and economic evaluation indicators. In cases where economic evaluation indicators fail to meet expectations, increasing single-well production is suggested as a means to resolve potential conflicts between enhancing well construction quality and meeting economic evaluations.

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Construction of Injection and Production Well Pattern for Fault-controlled Fractured-vuggy Carbonate Vertical Plate-shaped Reservoirs

DENG Xingliang, ZHANG Shifan, WANG Peng, WANG Peng, ZHANG Jie

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 74-84. DOI: 10.11885/j.issn.1674-5086.2024.01.29.02

Abstract （133）

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The fracture-vuggy structure and connection relationship of fault-controlled fracture-vuggy carbonate reservoirs are complex, and traditional well pattern deployment is prone to produce low-productivity wells. A three-dimensional injection and production well pattern needs to be constructed to increase productivity. The influence of different factors on the sweep coefficient of the three-dimensional injection and production well pattern in the Manshen 3 and Manshen 4 well areas of the Tarim Fuman Oilfield was studied through reservoir numerical simulation, and a pilot test plan was designed to predict productivity. The results show that the sweep coefficient is the largest when the gas injection wells and production wells are arranged in a single staggered manner in the Manshen 3 well area; the greater the depth of the production wells, the greater the sweep coefficient; the sweep coefficient is stable within the range of 500$\sim$1 000 m between injection and production wells, and decreases significantly when the distance increases to 1 500 m. The sweep coefficient is the largest when gas injection wells, water injection wells and production wells are arranged in a single staggered manner in the Manshen 4 well area. In the pilot test, the plans of ``N$_2$ injection in the shallow part and production in the deep part" and ``N$_2$ injection in the top part, water injection in the bottom part, and production in the middle part" are adopted in the Manshen 3 and Manshen 4 well areas respectively. The recovery rates at the end of the stage reach 21.3% and 22.4% respectively, which is a significant improvement compared to the basic depletion development and water injection development plans.

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Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 1-.

Abstract （103）

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Water Injection and Gas Injection to Enhance Oil Recovery in Yingmai 2 Fracture-vuggy Reservoir

CHEN Fangfang, PENG Debing, WANG Na, WANG Zhangheng, ZENG Qixin

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 149-158. DOI: 10.11885/j.issn.1674-5086.2024.02.22.03

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In order to solve the problem that a large amount of remaining oil has not been produced in Yingmai 2 ultra-deep fractured cavernous reservoir, a visual physical model is prepared based on the characteristics of typical reservoir structures, and physical simulation experiments of EOR with different development methods such as water injection and gas injection are carried out. By comparing the water cut and recovery efficiency at different stages, the effects of different development methods on residual oil production in Yingmai 2 fracture-vuggy reservoir are quantitatively analyzed. The feasibility of alternate development modes of water injection, gas injection and gas water after bottom water flooding is studied by using the prepared fissure-hole model and fault solution model, and the reasonable injection and production modes to further improve the recovery efficiency of Yingmai 2 fractured-vuggy reservoir are as follows: low injection and high production water injection, high injection and low production gas injection and alternate gas injection. Among them, gas-water alternation can greatly improve oil recovery. The research results can provide support for further enhancing oil recovery in Yingmai 2 fracture-vuggy reservoir.

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Leakage Prevention and Plugging Technology of Shale Gas Well of Lower Cambrian Qiongzhusi Formation, Southern Sichuan

YAN Yancheng, TANG Tao, ZHANG Shengjun, WANG Zhiguo, HE Miao, HE Xinxing

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (6): 177-186. DOI: 10.11885/j.issn.1674-5086.2024.12.19.01

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The Cambrian Qiongzhusi Formation shale gas resources in southern Sichuan are 2 206$\times$10$^8$ m$^3$, which is an important area for increasing natural gas reserves and production in the Sichuan Basin. The geological structure of the block is complex, with karst caves and large fractures developing in the upper strata, dissolution fractures and caves developing in the middle marine strata, and faults, folds and dissolution fractures developing in the lower strata, resulting in different types of leaks from the surface of shale gas wells in southern Sichuan to the target layer. Well leakage occurs rapidly, with large leakage volume and long processing time. In response to the above problems, an analysis of well leakage characteristics was carried out. With the geological engineering integrated leakage prevention and plugging that combines avoidance, prevention and plugging as the guiding idea, the leakage characteristics of each formation were carefully analyzed. Through technical idea adjustment, key material research and selection, indoor system optimization experiments and field application iterative upgrades, we have formed a geological engineering integrated track design based on seam and hole prediction and leakage prevention technology by improving formation pressure bearing capacity while drilling, non-return lost circulation broad-spectrum bridge slurry plugging technology, loss-returning lost circulation composite plugging technology and reservoir temperature control solidification. Using knotted leakage plugging technology, an integrated leakage prevention and plugging technology system for hierarchical classification prevention and control of shale gas wells in the Qiongzhusi Formation has been constructed. The application results show that the lost circulation control time is reduced by 65%, providing technical support for the efficient development of shale gas in the Qiongzhusi Formation.

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Hydrocarbon Expulsion Efficiency of Shale in the Da$'$anzhai Member of Central Sichuan Basin and Its Exploration Enlightenment

ZHANG Benjian, LU Jungang, ZHANG Rui, JIANG Qijun, XIAO Zhenglu

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (2): 15-25. DOI: 10.11885/j.issn.1674-5086.2022.06.08.03

Abstract （180）

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The hydrocarbon expulsion efficiency of source rock is an important parameter in petroleum resources assessment. The study of hydrocarbon expulsion efficiency can not only guide the resource evaluation, but also be an important scientific means to verify the reliability of the resource evaluation results. To remedy the defects of current hydrocarbon generation potential method, an improved hydrocarbon generation potential method is proposed, and the hydrocarbon expulsion efficiency of shale in the Jurassic Da$'$anzhai Member of central Sichuan Basin was obtained by using this method. The results show that under the current geological conditions, the hydrocarbon expulsion efficiency of the shale in the Da$'$anzhai Member is distributed between 0${\sim}$62.6{\percent}. With the increase of organic matter maturity, the hydrocarbon expulsion efficiency gradually increases, and the oil saturation index increases first and then decreases. When $R_{\rm o}$ is in the range of 0.95%${\sim}$1.72%, oil saturation index is greater than 100 mg/g, and the movable hydrocarbon content of shale strata is higher. The lithofacies combination has a significant effect on the hydrocarbon expulsion efficiency. In the longitudinal direction, there is a tendency for shale to expel hydrocarbon from shell limestone, the development of interlayer fractures in interbedded combinations is conducive to shale oil flow and production. It is concluded that the interbedded assemblage in the lower part of the first submember in the area with $R_{\rm o}$>1.25% is the key exploration target for shale oil in the Da$'$anzhai Member. The results can provide theoretical guidance for the exploration and development of shale oil in the Jurassic Da$'$anzhai Member of central Sichuan Basin.

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A Radial Unsteady Water Invasion Model for Ultra-deep Multi-porosity Reservoirs

XIAN Bo, ZHU Songbai, ZHOU Jie, FAN Qiuhai, NIE Yanbo

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 97-106. DOI: 10.11885/j.issn.1674-5086.2024.02.01.02

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In order to further understand the water invasion law of ultra-deep multi-porosity reservoir, the radial unsteady water invasion model for ultra-deep multi-porosity reservoirs was established in dual-porosity reservoirs and tri-porosity reservoirs by assuming that the aquifer was infinite or closed. Mathematical methods such as Laplace transform were used to solve the model, and the cumulative water invasion solution in Laplace space was obtained. Then the cumulative water invasion solution in real space was obtained through numerical inversion. The water invasion curves of infinite aquifer and closed aquifer in multi-porosity reservoirs were programmed and their differences were compared. Then the parameter sensitivity of the water invasion curves in multi-porosity reservoir was analyzed. Finally, the model was verified and analyzed by using the field data of ultra-deep fractured-vuggy reservoir in Tarim Basin combined with the principle of material balance. The results show that the water invasion curve of the infinite aquifer keeps rising, and the water invasion curve of the closed aquifer keeps stable in the later stage and there is a“water invasion step”. Water radius and storativity ratio mainly affect the position of water invasion curve. The inter-porosity flow coefficient mainly affects the time of“water invasion step”. The water invasion model can accurately calculate the amount of cumulative water invasion. The water invasion model established and the water invasion curves drawn can provide theoretical reference for the study of water invasion mechanism in ultra-deep multi-porosity reservoirs.

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Nitrogen Injection Technology for Improved Oil Recovery in Fractured-vuggy Carbonate Reservoirs

SHE Zhicheng, CHEN Lixin, XU Sanfeng, XIAO Yun, ZHANG Jian

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 138-148. DOI: 10.11885/j.issn.1674-5086.2024.04.14.01

Abstract （183）

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The Ordovician reservoir in Halahatang is a typical fractured-vuggy carbonate reservoir. The karst reservoir is well developed, and the reservoir permeability space is mainly composed of karst caves, dissolution holes and fractures of different sizes, which are discrete in general, locally continuous, multi-scaled in reservoir collective space, and complex in morphology and distribution. Water injection and displacement are the most important development methods for this type of reservoir. After 15 years of development, the number of single wells and units with water injection failure is increasing year by year. After water flooding failure, gas injection becomes the most important means of fractured-vuggy carbonate reservoir extraction. The gas injection extraction technology has been tested and applied in Halahatang. And the six-factor gas injection well selection standard has been established. The wells are selected from six aspects, including karst background, well-reservoir relationship, drilling depth, reserve scale, production dynamics, and remaining oil type. The gas injection parameters are designed according to five aspects, including gas injection timing, gas injection method, gas injection volume, stewing time, and indicator curve. Some preliminary understandings of gas injection well selection principles and gas injection parameters design have been obtained, which is hoped to provide reference for gas injection development of fractured-vuggy carbonate reservoir.

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Optimization of Pseudo Elastic Wave Reverse Time Migration with Logging Correction in TTI Media

ZENG Qingcai, WANG Qinghua, ZENG Tongsheng, CHEN Sheng, ZHANG Kai

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 38-50. DOI: 10.11885/j.issn.1674-5086.2024.04.17.03

Abstract （126）

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In anisotropic media, seismic waves have different velocities in different propagation directions. The use of isotropic wave equations cannot accurately describe the propagation of seismic waves, which can lead to inaccurate positioning of deep events during imaging. On the basis of the TTI medium elastic wave equation, this paper sets the shear wave velocity to a smaller value and introduces a source loop to eliminate pseudo shear wave artifacts. On the other hand, logging data is used to constrain and correct the parameters field, in order to improve the imaging accuracy of deep and complex structures. The reverse time migration(RTM) method can have an impact on imaging due to low-frequency noise. Therefore, based on the Laplacian filtering operator for denoising, the paper extracts the angle domain common imaging point gathers(ADCIGs) and uses angle-selected stacking imaging to suppress strong amplitude low-frequency noise caused by inaccurate migration parameters. The real data requires a large amount of computation during imaging. In this article, the CPU/GPU cooperative operations are used to accelerate migration and improve computational efficiency. The model and real data results show that the TTI-RTM method based on logging data constraints can accurately image deep and complex structural target areas, which also proves the feasibility of the method.

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Technology for Precise Positioning of Ultra-deep Fracture-porous Carbonate Reservoirs

LI Guohui, GUO Yue, SUN Jiaqing, DING Yao

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 65-73. DOI: 10.11885/j.issn.1674-5086.2024.04.16.02

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The fracture-porous carbonate reservoirs in the Tarim Basin is deeply buried, and have small storage spaces and strong heterogeneity, bringing difficulties to accurate location of reservoirs and precise positioning of reservoir spaces. This poses great challenges for well-targeting and optimizing drilling trajectories, and limits well deployment and rapid production. To address these challenges, a study on precise reservoir positioning driven by VSP (Vertical Seismic Profile) was conducted using pre-stacked seismic data such as gathers and velocity fields, as well as VSP data collected during drilling operations. By optimizing the processing work-flow, the timeliness of delivering results within 72 hours was ensured, and precise positioning of the reservoir was achieved without affecting the drilling speed. This method has been successfully applied in the real-time tracking of more than 120 wells, resulting in an improvement in the direct drilling encounter rate of the reservoirs from 60$\%$ to 80$\%$, and increasing in the success rate of drilling to over 90$\%$. It provides valuable insights for reservoir prediction and precise positioning in similar fracture-porous reservoirs.

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Typical Characteristics and Types of Well-test Curves of Ultra-deep and Fault-controlled Formation in Shunbei Region

ZHANG Ning, LI Zongyu, ZHANG Yun, NIE Renshi, LI Jingshun

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 115-122. DOI: 10.11885/j.issn.1674-5086.2024.02.21.01

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Fractures and sheet cave mainly develop in the ultra-deep and fault-controlled formation in Shunbei region. Horizontal well is adopted in this region to exploit the oil and gas because horizontal well can transversely pass through the fractured-caved formation. The well-test curves are complex and various. According to the middle curve characteristics after the wellbore storage and skin effects, the real well-test curves of Shunbei Region can be divided into 3 categories. The curve characteristics of the 3 categories can directly reflect the different contact relationship of horizontal well with fractures and caves. In addition, according to the late curve characteristics, the 3 categories can be further divided into 9 subcategories. The curve characteristics of the 9 subcategories differ each other and reflect different development status of fractures and caves in the periphery of horizontal well. At the end, the physical models of 3 categories and 9 subcategories, which are corresponding to the real well-test curves of 3 categories and 9 subcategories, are presented for well-test interpretations and evaluations. The research results in this article can be used to guide the work of well-test analysis and study for Shunbei region, and can also be used to guide the work of well-test study for other deep and fault-controlled formations

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A Study on the Characteristics and Mechanism of Air Displacement of Deoxygenated Air in Tazhong Deep Heavy Oil

WU Zangyuan, ZHANG Xun, LI Yang, YAO Jie, FENG Qihong

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 131-137. DOI: 10.11885/j.issn.1674-5086.2024.02.29.03

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Static oxidation experiments were carried out for the Tazhong deep heavy oil reservoir, the composition of oil and gas produced with different oxygen content and different oxidation times was analyzed, and the oxidation characteristics, oxidation pathways and oxidation mechanisms of crude oil and deoxygenated air in the process of deoxygenated air injection in the reservoir were studied. The experimental results showed that the oxygen consumption rate of crude oil was positively correlated with the oxygen content of oxygen-reduced air and negatively correlated with the oxidation time. The amount of generated carbon dioxide also increased with the increase of oxidation time and oxygen content of oxygen-reduced air. The reaction between crude oil and oxygen-reduced air can increase the viscosity of crude oil to a certain extent. The increase amplitude of viscosity was greater with higher oxygen content of oxygen-reduced air and longer oxidation time. After oxidation, the content of saturated hydrocarbons and aromatic hydrocarbons in crude oil decreased, while the content of resin and asphaltene increased, especially asphaltene. The C==O stretching vibration peak appeared in the crude oil after oxidation, and the vibration peak became stronger with the increase of oxygen content in oxygen-reduced air, indicating that the oxidation process of crude oil involved oxygenation reactions to generate substances such as aldehydes. With the increase of oxygen content, the oxidation reaction deepened continuously.

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Heat Transfer Model of Deep Reservoir and Calculation of Oil Column Height

LIU Yong, YUAN Xiaoman, LU Zhongyuan, YE Sijie, LI Xiaolong

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 107-114. DOI: 10.11885/j.issn.1674-5086.2024.02.21.03

Abstract （143）

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Deep oil reservoir is characteristic of deep buried depth and large thickness, and is hard to drill through the oil formation. To address the issue of oil column height calculation for deep oil reservoirs, we established a heat transfer model of deep reservoir by considering the vertical heat transfer process from the oil-water interface to the wellbore after well production. We solved the model using variable substitution, variable separation and Fourier transform, and then derived the calculation formula of oil column height. By only using the temperature data at the bottom hole before and after well production, we can calculate oil column height. A pilot test was carried out at an oil well of a deep reservoir located at Tarim Basin to demonstrate the calculation process of oil column height. At the same time, by substituting the testing well data into the heat transfer model, we simulated the values of formation temperature and temperature gradient at different location of the oil formation at different production time. Then, we plotted the temperature distribution curve for different production time and the dynamic temperature curve for different formation location. The simulation results showed that formation temperature distribution took on nonlinear dynamic variation characteristics. The established heat transfer model is a good tool to calculate oil column height for deep oil reservoirs.

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A Study on the Kinetic Characteristics of Tazhong Deep Heavy Oil with Different Oxygen Contents

ZHOU Daiyu, DU Xuan, DU Hongbao, YAN Gengping, LUO Hao

Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (4): 123-130. DOI: 10.11885/j.issn.1674-5086.2024.02.29.04

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The oxidation process of crude oil in oxygen-reduced air is complex. In order to accurately analyze the oxidation reaction of crude oil under reservoir conditions, it is necessary to carry out comprehensive qualitative and quantitative studies. In order to further explore the oxidation mechanism of crude oil in the process of deoxygenated air flooding, and to clarify its oxidation heat release, weight loss and kinetic characteristics, the thermal analysis experiment of Tazhong deep heavy oil reservoir in Tarim Oilfield is carried out. DSC results show that the increase of oxygen content significantly promotes the oxidation heat effect of crude oil, and the overall oxidation heat release and peak heat flow of crude oil increase greatly with the increase of oxygen content. TG experiments show that with the increase of oxygen content, the low temperature oxidation interval of crude oil keeps shortening, and the mass consumption in the low temperature oxidation stage is reduced. The temperature range of the low-temperature oxidation interval gradually narrows with the increase of oxygen content in the oxygen reduction air (the deepening of oxidation degree) during static oxidation. Based on the TG experiment data, the activation energy of crude oil in the low-temperature oxidation stage obtained with Friedman and OFW methods is close, and the activation energy increases with the increase of conversion rate. The average activation energy of crude oil used in the experiment in the low-temperature oxidation stage in oxygen reduced air with oxygen content of 5% is 81.04 kJ/mol.

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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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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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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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Journal of Southwest Petroleum University(Science & Technology Edition) 2024, 46 (6): 187-192.

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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

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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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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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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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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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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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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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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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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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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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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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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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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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