Journal of Southwest Petroleum University(Science & Technology Edition)

Ground Stress Field Inversion and Fracture Prediction Based on MLR-ANN Algorithm

ZHANG Bohu, HU Yao, WANG Yan, CHEN Wei, LUO Chao

2024, 46(3): 1-12. DOI: 10.11885/j.issn.1674-5086.2022.08.20.01

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Shale gas reservoirs are deeply buried in China, and the distribution law of ground stress is complex due to tectonic movement. It is difficult for traditional methods to reflect the magnitude and direction distribution of regional in-situ stress accurately. A coupling algorithm of multiple linear regression and artificial neural network is proposed to invert the shale gas reservoir and surrounding ground stress in Changning-Jianwu Block, southern Sichuan. Using the comprehensive fracture coefficient method, the reservoir fractures are predicted and the fracture development areas are divided. The in-situ stress in the study area is mainly compressive stress, and the direction is about NE115°. The stress around the fault caused by tectonic movement is relatively concentrated, and shear cracks are easy to develop. The cracks are mainly developed and medium developed. The study area has a high degree of fracture development in the upper part of the Wufeng Formation and the structural fault near the bottom of the Longmaxi Formation. The research results have important reference value for well pattern arrangement, fracturing optimization design and casing damage prevention of shale gas extraction.

Prestack Inversion Method with ATpV Regularization Based on Reweighted L1

PAN Shulin, CHEN Yaojie, YIN Cheng, GOU Qiyong, ZHANG Dongjun

2024, 46(3): 13-26. DOI: 10.11885/j.issn.1674-5086.2022.08.20.02

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Seismic prestack inversion can accurately obtain various parameters of underground reservoir media, and is one of the important technologies in oil and gas exploration and development. Due to unknown natural fators, seismic inversion is a typical ill-conditioned problem, and a regularization constraint objective function is usually used to alleviate the ill-conditioned inversion problem. However, the regularization constraint ignores the amplitude information of the stratigraphic boundary, and the reweighting method can overcome this problem well and restore the sparsity better. A pre-stack three-parameter inversion method for ATpV regularization based on reweighted L1 (ATpV-L1 method) is proposed. The reweighted L1 method is combined with ATpV regularization for the first time and introduced into the pre-stack inversion. The Alternating direction multiplier algorithm (ADMM) is used to establish the inversion framework, and the objective function is optimized in blocks, which effectively improves the convergence speed. The manuscript first introduces the ATpV-L1 method, and establishes the pre-stack inversion objective function based on ATpV-L1. Then the theoretical model data is used to compare the inversion results of the new method and the ATpV regularization method, and the effect of this method is verified. Finally, the actual data is used for experimental analysis, which further verifies the inversion accuracy of the new method and verifies the feasibility of the method. The experimental results show that the proposed method can effectively recover the sparsity of the inversion results and improve the inversion accuracy.

Rock Physics Characteristics of Shale Gas Reservoir in Southeast Sichuan

LIU Wenge, YIN Cheng, CHEN Kang, TIAN Fafa, PENG Da

2024, 46(3): 27-36. DOI: 10.11885/j.issn.1674-5086.2022.09.10.03

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The shale of Longmaxi Formation in Sichuan Basin has become one of main layers of gas exploration in China, because it is rich in organic matter and has a moderate burial depth. Shale reservoirs are characterized by strong non-homogeneity, and the anisotropy of physical parameters and brittleness are affected by various factors, which is not conducive to the logging interpretation and the prediction of seismic “sweet spot”. Based on the above reasons, shale samples are collected in the field geological outcrop section in Shuanghe, Changning, Sichuan, and Sanbaiti of Huaying Mountain, Chongqing. Rock physics test and parameter analysis are conducted in the laboratory. Related research contents include: using X-ray diffraction to analyze the mineral composition and content of rock samples, studying the influence of ambient pressure and temperature change on seismic velocity under test conditions, determining the relationship between seismic velocity and mineral composition, and the change of shale anisotropy parameters. To some extent, the results of research reveal the control effect of clay content in gas reservoir on shale anisotropy and britleness in southeast Sichuan, and summarize the empirical formulas between anisotropic parameters, so as to provide geological basis for rock physical modeling, anisotropic parameter inversion and brittleness evaluation.

Optimization of Double-layer Targets and Benefit Evaluation for Deep Shale Gas Horizontal Wells

LUO Jingchao, YAN Jianping, SHI Xuewen, ZHONG Guanghai, ZHENG Majia

2024, 46(3): 37-49. DOI: 10.11885/j.issn.1674-5086.2022.08.17.01

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The deep (>3500m) shale gas is enriched in Wufeng Formation--Longmaxi Formation in Luzhou Area, southern Sichuan. In order to ensure the goal of increasing and stable production of shale gas, it is necessary to realize the three-dimensional production of L$_1$ submember shale gas. The data of core, logging and production are used to study the reservoir characteristics, quantitative evaluation of reservoir quality and simulation of fracturing height of deep shale gas formations in the study area. Combining with quantitative evaluation of reservoir quality and simulation of fracturing height, an intelligent optimization and benefit evaluation method of double-layer targets for deep shale gas horizontal wells is established. The results show that: 1)the overall physical properties of Long-1 subsection become worse from deep to shallow, L$_1^1$—L$_1^3$ layer is dominated by first-class desserts, and L$_1^4$ layer is dominated by second-class sweet spot, with a thickness of more than 40 meters; 2)the intelligent optimization method of horizontal well target in deep shale gas reservoir can quickly obtain two sets of information such as optimal depth, sweet spot quality, fracturing height and target benefit evaluation ($Q$) of horizontal well; 3)the plane dominant area of the first set of target benefit evaluation is consistent with the current high production well area, considering the target benefit evaluation $Q$ value of L$_1^4$ small layer and the actual production of the second set of target horizontal wells that have been established, we predicted that the second set of targets in the deep shale gas reservoir in southern Sichuan has a certain development value and potential, and defined the dominant areas on the two sets of target planes. The study provides a basis for large-scale realization and production prediction of double-layer targets in deep shale gas reservoirs.

Reservoir Characters and Controlling Factors of Upper Urhe Formation in Shawan Sag

HU Tingting, YU Haitao, WU Chenxiao, GUAN Jian, YU Jingwei

2024, 46(3): 50-65. DOI: 10.11885/j.issn.1674-5086.2022.03.14.01

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Upper Urhe Formation in Shawan Sag has the similar reservoir conditions with that in Mahu Sag, but basic characters and controlling factors of objective reservoirs in Shawan Sag have not been clarified clearly, which hinders further exploration. On the basis of observation of drilling cores, analysis of thin sections, SEM, pressure mercury and physical property, we analyze the petrological, reservoir characteristics and their controlling factors of the study area. The results show main rock type in the first member of Upper Urhe Formation is sandy conglomerates, and reservoir spaces are mainly primary inter-granular pore and flake curved throat type, which suggests extra-low porosity and extra-low permeability reservoir. Main rock type in second member of Upper Urhe Formation is conglomeratic sandstone, and reservoir spaces are mainly primary inter-granular and intergranular dissolved pores, with flake throat, which suggests reservoir belong to low porosity and low permeability reservoir. Controlling factors of reservoir quality are mainly sedimentary factor and diagenesis factor. Sedimentary environment and tuffaceous content decide distribution of reservoirs of high quality and reservoir property, and compaction has the greatest effects on physical property of reservoirs, with cementation and dissolution causing further difference to physical property. Abnormal pressure improves reservoir quality in a certain degree. All controlling factors make pore structures more complex in second member of Upper Urhe Formation, and reservoir property better.

Application and Prospect of Choline-based Deep Eutectic Solvent in EOR and CCUS

BAI Jiajia, CHEN Zhangxing, KANG Yili, CHEN Mingjun, TAO Lei

2024, 46(3): 66-76. DOI: 10.11885/j.issn.1674-5086.2022.11.24.01

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Deep Eutectic Solvent (DES) has the advantages of low saturated vapor pressure, non-flammability, non-explosion, non-toxicity, easy degradation, good electrochemical and thermal stability, etc. DES has a good surface activity, and the hydrogen bond network in DES has a good synergistic oil displacement effect with anionic/cationic surfactants. The researches on synergistic effect of DES and common surfactants is still in the initial stage, and the mechanism of Enhanced Oil Recovery (EOR) of their compound system is still unclear. On the basis of comprehensive analysis and summary of the physical and chemical properties of choline-based DES, this paper explores the EOR mechanism of DES and its mixed system with anionic/cationic surfactants, reveals the mechanism of carbon dioxide absorption by DES, and puts forward some suggestions on the application of DES in EOR and carbon capture, utilisation and storage (CCUS) of heavy oil reservoirs, low permeability reservoirs. The research results are of significance in guiding the popularization and application of DES in EOR and CCUS.

Rapid Hydrarate Generation Technology and Devices

GE Kun, WEI Haoqi, WANG Jiaqi, ZHANG Xinyu

2024, 46(3): 77-93. DOI: 10.11885/j.issn.1674-5086.2022.06.28.02

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Gas hydrate technology has broad application prospects in the fields of natural gas solid state storage and transportation, seawater desalination, carbon dioxide storage, etc. The rapid formation of hydrate is considered to be one of the key problems restricting the application of hydrate technology. But the hydrate reactors have not been developed completely, and the formation rate cannot meet the industrial requirements due to the late start of researches on rapid hydrate formation. Therefore, realization of the rapid formation of hydrate is one of the urgent problems to be solved in the application of gas hydrate technology. The influence factors restricting the rapid formation of hydrate are analyzed with consideration of hydrate formation mechanism. Then the structures and principles of rapid hydrate generation devices of various types are reviewed, and the advantages and disadvantages of the reactors are analyzed from the perspective of mass transfer and heat transfer. Finally, suggestions for future research directions are provided: the device with good application prospects should be strengthened and improved gradually to expand the scale; and new types of reactors are constructed using high-tech equipment; standard reactor evaluation system should be established.

Prediction of Critical Pressure Difference for Sand Production of Deep HTHP Wells in Southern Margin

MA Dudu, JIANG Beibei, LIU Tao, WU Yue, HE Yuan

2024, 46(3): 94-101. DOI: 10.11885/j.issn.1674-5086.2022.11.24.26

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Sand production prediction of deep ultra-high pressure horizontal wells is difficult and there are few targeted studies, so it is difficult to formulate reasonable and effective sand control measures, which has a great impact on oilfield production and economic benefits. With comprehensive consideration of the fluid flow in the wellbore, the stress change of wellbore rock under high temperature difference, fluid seepage effect, the complex distribution of in-situ stress on the wellbore, the formation pressure failure and the influence of water invasion on sand production, this paper establishes a sand production prediction model suitable for the critical pressure difference of sand production in deep high temperature and high pressure wells in the southern margin. The analysis shows that high drawdown is the dominant factor; the temperature difference between the wellbore and the formation caused by high production will produce stress in the wellbore and affect the stability of the wellbore; in the later stage of production, the decrease of formation pore pressure will increase the circumferential stress of wellbore, and the invasion of formation water will reduce the rock strength, both of which will increase the risk of sand production. The results of sand production differential pressure verification by using the example well in the southern margin are consistent, which can provide guidance and reference for the prediction of sand production critical differential pressure of similar deep high temperature and high pressure wells and the formulation of reasonable production differential pressure.

Analysis of Vortex-induced Vibration and Fatigue Characteristics of High-pressure Riser in Shallow Sea

JIANG Yufeng, XU Wanhai

2024, 46(3): 102-108. DOI: 10.11885/j.issn.1674-5086.2022.06.20.01

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With the continuous development of oil and gas resources in the East China Sea, jack-up platforms with lower development costs will be widely used. The marine environment where the riser is located is complex and changeable. Due to the large ratio of structural length to diameter, vortex-induced vibrations will occur under the action of ocean currents. In this paper, the wake oscillator model is used to predict the vortex-induced vibration of the high-pressure riser. Based on the content of the DNV specification, the S-N curve method is used to calculate the structural fatigue. The model is discretely solved by the finite difference method. The research focuses on the influence of the top tension with the vortex-induced vibration and fatigue characteristics of the riser. It is found that the top tension will affect the vortex-induced vibration response of the riser, and further change the fatigue life of the structure, and head affect the safety of the structure.

Research on non Plug-in Hydraulic Intelligent Control Technology and Its Application

GE Song, YUAN Hui, YU Zhigang, LI Xinyan

2024, 46(3): 109-116. DOI: 10.11885/j.issn.1674-5086.2022.04.12.01

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Water injection allocation is an important means for oil fields to achieve effective water injection into wells. At present, open hole perforation completion is commonly used in the Weizhou sea area, and the water injection string is a bridge type eccentric or concentric integrated string, with an average water injection of 4～6 layers. The wellbore trajectory is complex and the dog legs are large, requiring the use of steel wire operations to complete the deployment of the fishing nozzle. The operation is difficult, time-consuming, and the success rate is low, and the occupation of the wellhead affects the high-yield well operation. In order to improve intelligent and refined operations, a non plug-in hydraulic sub control water injection column and supporting hydraulic control intelligent water injection tools have been designed, which can rely on the ground control system to complete intelligent online ground testing and adjustment. A water distributor nozzle model is established and the friction coefficient is determined through experiments, the flow pressure relationship is accurately described and the injection accuracy is improved. The application has been completed in Well A6 of Weizhou 6-13 Oilfield, achieving hydraulic fine separation and control, breaking through the application challenges of high temperature, complex wellbore trajectory, and large well depth. The testing and adjustment efficiency has been improved by 90%, and the injection accuracy has reached 95% of the reservoir index.

Intelligent Security Assessment of Gathering and Transportation SCADA System in High Sulfur Gas Field

YANG Li, QIN Hongmei, XIE Tianyi, GENG Xinyu

2024, 46(3): 117-129. DOI: 10.11885/j.issn.1674-5086.2023.11.07.01

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In order to reveal the impact of randomness and incompleteness on the security status evaluation results of SCADA system in the high sulfur gas field, a grey cloud security evaluation method based on the improvement whitening weight function with cloud model is proposed. Firstly, the evaluation results were graded and a combination weight optimization model was designed. Then, a sample matrix was determined according to the expert scoring rules. The cloud model was used to improve the whitening weight function and calculate the grey evaluation weight matrix. Finally, the final risk value was obtained by the step-by-step evaluation formula and the system risk assessment status was determined. The effectiveness of the proposed method was verified in 3 accutal application scenarios. The results indicate that, compared with method of AHP, CV, LW and MWM, the discretization of the proposed combination optimization weighting method is 0.456, the discretization of MWM, CV, AHP and CV are 0.514, 0.860, 1.294, and 1.225 respectively. The proposed combination optimization weighting method has the smallest discretization, indicating that it is more effective than other methods. This model combines the incompleteness of risk indicator information in SCADA security assessment with the incompleteness and randomness of expert knowledge, which can not only qualitatively evaluate and predict the overall security status of the SCADA system, but also achieve the quantification of secondary indicator risk. This method can reveal the vulnerability level of various risk indicators and provide direction for the next step of safety reinforcement. The proposed method is not only conducive to identifying the security status of SCADA systems in high sulfur gas fields, but also provides a reference for security assessment in other industries.

A Study on Operation Optimization of Multi-gas Source Pipeline Network in Energy Measurement System

LIU Shitao, ZHOU Jun, LIU Cui, QIN Yixiong, LIANG Guangchuan

2024, 46(3): 130-146. DOI: 10.11885/j.issn.1674-5086.2022.03.22.01

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In view of the current situation of the multi-source natural gas supply pattern of“one network” in China, the traditional volume measurement and trading system is no longer suitable for the operation and development of China′s natural gas pipeline. The use of energy measurement can better reflect the energy characteristics of natural gas itself and promote the integration and upgrading of the natural gas market. On the basis of considering the implementation scheme of natural gas energy metering system and the demand of non-resident users for natural gas quality, this paper creatively puts forward the operation optimization model of multi-gas source pipe network under the energy measurement system. The model takes the maximization of pipeline operation profit as the goal and the gas supply volume and pressurization mode of the whole line as the decision variables. The model is applied to a long-distance pipeline in China, and the optimal solution of the model is obtained by using GAMS/ANTIGONE solver. The optimization results show that the optimization results under different energy measurement system implementation schemes are better than the actual operation schemes on site, and the maximum operating profit is increased by 32.05%. Among them, the gas purchase cost accounts for the highest proportion in the pipeline operation cost, which is comprehensively affected by the gas price, gas supply volume and calorific value of each gas source; the pipeline transportation cost and compressor station operation cost are indirectly affected by the gas supply volume of each gas source; the higher the calorific value content of natural gas at the demand node is, the higher the gas sales revenue.

Optimizing the Operation of Data Center Energy Supply Systems Considering the Utilization of Pressure Energy

YANG Wei, CHEN Nengcong, ZHANG An'an, LI Fanmao, MO Ziyan

2024, 46(3): 147-158. DOI: 10.11885/j.issn.1674-5086.2022.09.10.01

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Aiming at the problems that the pressure energy of natural gas pipeline network is not fully utilized and the adaptability of application scenarios is insufficient, a data center energy supply optimization method with comprehensive utilization of natural gas pressure energy is proposed under the background of the increasingly prominent problems of high energy consumption and carbon pollution in the data center. Firstly, the data center energy supply system architecture considering the comprehensive utilization of natural gas pressure energy for power generation and refrigeration is designed. Then, based on the exergy analysis theory, the power generation and refrigeration output characteristic models of natural gas pressure energy are established. Considering the energy consumption and heat dissipation characteristics of IT equipment in the data center, the power demand model and cold power demand model of the data center are established. Secondly, considering the energy supply constraints of distribution network, the power constraints of gas turbines, absorption chillers and battery charging and discharging power constraints, the optimal scheduling model is constructed with the minimum daily operating cost as the objective function. Finally, the simulation is carried out according to the energy consumption demand data setting example of a natural gas pressure regulating station and a class A data center in Southwest China, which verifies the feasibility and economy of the proposed system scheme and optimization method.

Structural Design and Evaluation of High Strength Thread of Mandrel Hanger

LIU Yang, SHE Yangzhou, LIAN Zhanghua, YI Xianzhong

2024, 46(3): 159-169. DOI: 10.11885/j.issn.1674-5086.2022.01.18.01

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In order to prevent failure accident caused by the insufficient strength of the connecting thread at the lower end of the mandrel, the mechanical property experiment of the mandrel material is carried out by using the design and calculation method of high temperature and high pressure of casing string, finite element numerical simulation and experimental means, and a high-strength thread structure for the mandrel hanger is developed, and the finite element calculation of three-dimensional of the thread is carried out under the ultimate composite load. The compression load has a great influence on the stress of the first tooth of the internal shoulder of the internal thread, and the rest of the internal and external thread is relatively safe. The tensile load alleviates the influence of makeup torque on the shoulder of internal and external threads to a certain extent. From the calculation results, it is concluded that the overall stress of the internal and external threads is less than the allowable yield limit of the material, and the contact pressure of the threaded joint is greater than the external fluid pressure, which can form an effective seal. The research results provide a theoretical basis for the selection and use of the threaded structure of the mandrel hanger.

A Study on Sealing Performance of UGS Well Casing Thread Under High-speed Injection-production

SONG Wei, ZHOU Yan, WU Yan, YANG Yan, YE Shengjun

2024, 46(3): 170-178. DOI: 10.11885/j.issn.1674-5086.2022.02.20.01

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The sealing of casing thread is a key factor affecting the safety of UGS (Under Gas Storage) well for periodic highspeed injection and production operation, so the integrity of sealing of gas storage well is extremely important. It is necessary to focus on the influence of gas storage well injection and production process on the sealing property of the string, especially the variation law of the special thread joint sealing structure performance of the UGS string caused by the alternating load in the process of circulating injection and production. Based on the theory of finite element method, combined with the actual working condition of the UGS well and field data of a special thread joint used in a UGS well in northern China, a special thread joint finite element calculation model is established and the cycle injection-production condition, temperature, injection-production pressure, axial load and pitting of the effects of the casing thread seal UGS is studied. The results show that the temperature has little effect on the structural integrity and sealing integrity of the casing thread joint, but the injection-production pressure, axial load, and pitting have a great effect on it, which should be controlled at a low value. This study can provide a reference for sealing failure determination and pipe string design of gas storage wells.

Research and Application of WC-Co Cemented Carbide Erosion Model

AI Guosheng, ZHANG Bo, FENG Chunyu, ZHANG Xinqing, JIANG Jiwei

2024, 46(3): 179-188. DOI: 10.11885/j.issn.1674-5086.2022.07.12.01

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WC-Co cemented carbide is the main material for manufacturing fixed throttle valve spool. The high-pressure natural gas carries the impurity particles at the bottom of the well during the throttling and depressurization process, which causes erosion damage to the core part of the throttle valve spool. To this end, a WC-Co cemented carbide grade YG15 was used of the target material in the study, and an indoor erosion test platform was constructed to determine the erosion model of YG15 cemented carbide and to verify it with simulation. The erosion model was further applied to the fixed throttle valve erosion simulation to predict the service life of the fixed throttle valve spool. The results show that the impact angle function of YG15 cemented carbide and the velocity index at 90°impact angle is 2.48; the erosion wear of YG15 cemented carbide increases from 847.1 mg to 1 235.6 mg when the erosion angle increases from 30°to 90°. The most serious throttle erosion is located at the throttle hole, and the erosion wear rate increases with the increase of particle mass flow rate; the life prediction of fixed throttle valve is that the throttle valve fixed nozzle should be replaced once half a year when the particle mass flow rate is small, and once a year when the particle mass flow rate is large.

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