Table of Content

25 February 2025, Volume 32 Issue 1

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Summary

Natural hydrogen accumulation patterns and prospects for exploration and development

NI Zhiyong, ZENG Jianhui, LIU Xiaoping, SHI Kai, SHAO Ganggang

2025, 32(1):  1-11.  DOI: 10.3969/j.issn.1006-6535.2025.01.001

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The establishment of China′s "dual carbon" goal has made the search for efficient and environment-friendly energy sources an urgent task. Hydrogen gas, as a clean energy source, is increasingly gaining the attention of researchers. At present, the industrial production of hydrogen is primarily derived from fossil fuels such as petroleum and natural gas, which results in the substantial emission of carbon dioxide during the hydrogen production process. Hydrogen is also industrially produced through the electrolysis of water; however, this method is not yet suitable for mass production due to the associated high costs. Since the 1970 s, numerous instances of natural hydrogen gas accumulation have been discovered worldwide. With its low-carbon and renewable characteristics, natural hydrogen gas is anticipated to become the most promising clean energy source for the future. In China, the study on natural hydrogen gas in China is relatively scarce, and there are no precedents for the exploration and development of natural hydrogen gas. To this end, based on previous study and in conjunction with the global discoveries of natural hydrogen gas, the origins, migration, and accumulation patterns of natural hydrogen gas have been summarized from the perspective of petroleum geology. The study also provides a prospective outlook on the exploration and development of natural hydrogen gas. This study can offer insights for future natural hydrogen gas exploration and development in China.

Development status and prospect of chemical flooding technology for enhanced oil recovery

LI Yanchun, SUI Mingyuan

2025, 32(1):  12-21.  DOI: 10.3969/j.issn.1006-6535.2025.01.002

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In the middle and late stages of water-flooding development in oil reservoirs, the intensification of heterogeneity and the high-temperature, high-salinity environment impose greater demands on the implementation of chemical flooding, presenting new challenges for its application. For this reason, this paper provides a comprehensive summary of the application status and existing issues of polymer flooding, surfactant flooding, alkali flooding, and polycomplex flooding technologies. Additionally, it analyzes the current development status of organic alkaline ternary combination flooding, alkaline-free binary combination flooding, non-continuous chemical flooding, and nanocombination flooding technologies. The study identifies technical bottlenecks and challenges in the performance of oil displacement systems regarding stability, adaptability, evaluation methods, and reservoir damage. It also offers an outlook on low-damage chemical flooding systems and the intelligent development of combination flooding technologies. This study serves as a reference for the research and application of chemical flooding in the oil industry.

Research and progress on factors affecting the flow capacity in unsupported fracture network area of shale reservoir

DUAN Xianggang, HU Zhiming, CHANG Jin, SHI Yuxin, WU Zhenkai, XU Yingying

2025, 32(1):  22-31.  DOI: 10.3969/j.issn.1006-6535.2025.01.003

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To address of issue of the unclear understanding of the gas-liquid flow characteristics and the influence on development patterns within the unsupported fracture network in shale volume fracturing,the research progress on the volume of unsupported fracture networks,water-rock interaction,fracture conductivity,and gas-liquid two-phase flow both domestically and internationally are summarized.Meanwhile,the influencing factors of unsupported fracture conductivity and its impact on the water production and gas production capabilities of the reservoir are analyzed.The study indicates that the unsupported fracture network area (including unsupported artificial fractures,induced fractures, and connected natural fractures) is the major body that connects supported fractures with the matrix and significantly increases the gas leakage area.The conductivity and gas-liquid two-phase flow patterns of unsupported fractures are more complex due to factors such as support conditions,water-rock interaction,and overburden stress,and they are more sensitive to changes in overlying stress.The permeability of water-bearing fractures can decrease by 2 to 4 orders of magnitude with increasing stress.The conductivity and evolution patterns of the unsupported fracture network area during shale gas development are key to the design of the wellbore flowback system and the optimization of production systems,providing a scientific basis for maintaining long-term high and stable production of gas wells.The next key research directions mainly include the mechanism of gas-liquid-solid interaction and micromechanics in unsupported fractures,the main controlling factors of long-term fracture conductivity and gas-liquid two-phase flow models,as well as the evolution patterns of fracture networks throughout the entire life cycle.This research results can provide a scientific basis for the optimal design of wellbore flowback systems and production systems in shale gas development,ensuring long-term high and stable production of gas wells.

Geologic Exploration

Seismic identification of the western boundary of the northern section of the Deyang-Anyue rift trough and its geological significance

ZHANG Benjian, PENG Siqiao, CHEN Xiao, ZHANG Xihua, LIU Ran, CHEN Yangui, YANG Hanxuan, YANG Tao

2025, 32(1):  32-39.  DOI: 10.3969/j.issn.1006-6535.2025.01.004

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Due to data constraints,the western boundary of the northern section of the Deyang-Anyue rift trough has not been clearly defined,which greatly hinders the research on the sedimentary patterns of the Dengying Formation in the region and the exploration of the overlying Permian gas reservoirs.To address this issue,geological features on the eastern side of the Deyang-Anyue rift trough were correlated with 2D and 3D seismic data so as to recharacterize the western boundary of the northern segment of the rift trough.Furthermore,the significance of this western boundary for the exploration of medium-deep carbonate oil and gas resources in southwestern Sichuan is discussed from the perspectives of reserves control,hydrocarbon control and reservoir control.The study shows that the overall trend of the Sinian Dengying Formation in southwestern Sichuan is thick to the southwest and thin to the northeast. The Dengying Formation in the Danleng Area is thick and stable and has no characteristics of rift trough deposition.The western boundary of the northern section of the Deyang-Anyue rift trough runs approximately north-south,roughly distributing along the line of Jingyan-Renshou-Pengshanbei-Xinjin-Wenjiang.The Deyang-Anyue rift trough overall presents a half graben that is steep to the east and gentle to the west. The slope of the platform margin in southwestern Sichuan Basin is relatively slow with no obvious uplift of the platform margin mound and beach body.The study of the distribution characteristics of the Deyang-Anyue rift trough has important implications for the sedimentary patterns,reservoir distribution,source rock distribution and hydrocarbon accumulation of medium-deep marine carbonate rocks in southwestern Sichuan.

Characteristics of abnormal high pressure and its controlling role on hydrocarbon accumulation in Xiagou Formation of the Ying′er Sag

XIAO Wenhua, GAO Jihong, WEI Haoyuan, WEI Jun, ZHOU Zaihua, WU Haihong, GAO Xujia, ZHAO Xu

2025, 32(1):  40-50.  DOI: 10.3969/j.issn.1006-6535.2025.01.005

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To addressthe issues of unclear development characteristics of abnormal high pressure and unclear control of reservoir in Xiagou Formation of Ying′er Sag,based on the measured formation pressure data,the distribution characteristics,evolution law and genetic mechanism of abnormal high pressure were analyzed by using basin simulation technology,combined with logging,geochemistry and reservoir physical properties,and its influence on reservoir physical properties,oil and gas migration and accumulation,and organic matter evolution was clarified.The results show that the abnormal high pressure of Xiagou Formation in Ying′er Sag is generally developed,and the characteristics of vertical zoning are obvious.The top interface of abnormal high pressure gradually deepens from west to east,and the development horizon and amplitude of abnormal high pressure in different structural belts are obviously different.The pressure evolution and tectonic movement are synchronous.It has experienced five evolution stages:before the deposition of Zhonggou Formation,at the end of Zhonggou Formation,before the deposition of Paleogene,before the deposition of Neogene,and from Quaternary to present,and finally formed the characteristics of anomalous high pressure in the north and strong in the south.The formation mechanism of abnormal high pressure in the study area includes four kinds of effects:unbalanced undercompaction,hydrocarbon generation,clay mineral dehydration and overpressure transmission.Abnormal high pressure can slow down the damage of compaction to reservoir physical properties and play a positive role in improving reservoir physical properties.Abnormal high pressure provides the driving force for oil and gas migration,controls the direction and distribution range of oil and gas migration,and also inhibits the formation of organic matter and the evolution of hydrocarbon substances,and broadens the oil generation window.The research results indicate that the Changshaling tectonic belt is a favorable area for oil and gas migration and accumulation,which has a certain guiding role in the oil and gas exploration of Xiagou Formation in Ying′er Sag.

Fine charcterization of lobate shallow-water delta sandbodies and remaining oil potential tapping in Bohai Block BZ19-X

ZHOU Junliang, ZHAO Junshou, BAI Qingyun, WANG Quanlin, WANG Yue

2025, 32(1):  51-60.  DOI: 10.3969/j.issn.1006-6535.2025.01.006

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Bohai Block BZ19-X is characterized by the development of multi-stage superimposed lobate shallow-water delta sandbodies. However, the unclear understanding of the internal depositional sequences and superimposition patterns of these composite lobate bodies has constrained the potential for remaining oil recovery in the block. To address this issue, core samples, analytical tests, well logging, and seismic data have been utilized to determine the depositional characteristics of lobate shallow-water delta deposits and to establish well-to-seismic response models. By using the sandbody boundaries delineated by planar seismic attributes as a control and integrating well-to-seismic fusion with bed flattening and isochronous stratigraphic slicing, the fine characterization of different superimposed types of composite lobate shallow-water delta sandbodies has been achieved, thus providing a foundation for the potential of remaining oil recovery. The results show that: within the study area, the fluvial control over lobate shallow-water delta deposits is evident, and the plane can be divided into channel areas, bar complex areas, and shallow lake areas. Affected by the lateral migration and vertical cutting of channels, multiple lobate bodies develop both laterally and vertically. The main lateral contact styles are separated, side-lapping, side-cutting, and inter-connected, while the vertical superimposition patterns are primarily divergent, weakly-cutting, shallow-cutting, and deep-cutting. Lateral contact and vertical superimposition lead to the continuous development of sandbodies. Affected by the contact and superimposition styles of sandbodies, as well as the degree of well network control, single-stage sandbodies without well control and those with an incomplete well network, as well as composite sandbodies with a high degree of well control, tend to have concentrated remaining oil in the interwell and marginal areas. The results of this study provide effective guidance for the recovery of remaining oil in high water-cut oil reservoirs in the block and have reference significance for the development adjustment of similar blocks at home and abroad.

Research and application of shale oil fracture prediction method based on dynamic time warping algorithm

WANG Jing, SHU Qinglin, DU Yushan, ZHANG Qiang, ZHANG Yuliang, ZHU Huiyong

2025, 32(1):  61-70.  DOI: 10.3969/j.issn.1006-6535.2025.01.007

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The continental faulted lake basin in Jiyang Depression is rich in shale oil and gas resources,with great potential for exploration and development and developed fractures.However,due to the development of fractures,frequent well kicks and lost circulation during drilling seriously affect the drilling efficiency,and it is urgent to improve the prediction accuracy of fractures.To address of this issue,the dynamic time warping algorithm is used to calculate the integer time shift,correct the residual anisotropic time difference in the prestack gather,and improve the resolution of the seismic data.Based on the time difference caused by the propagation of the seismic longitudinal wave in the anisotropic medium,the azimuthal anisotropy direction and relative intensity are determined,and finally the development direction and development density of the fracture are determined.This method does not rely on ellipse fitting, and directly regards the anisotropic time difference as the data matching problem of integer time shift.Compared with the pre-stack anisotropic inversion module in commercial software,it effectively solves the problem of multiple solutions of fracture prediction.The prediction results are compared with the imaging logging interpretation results of real drilling and the abnormal drilling speed and the location of gushing and leaking in the drilling process.The prediction rate reaches 85%,which proves that the method has high reliability in predicting fractures.This prediction method can provide strong technical support for the efficient development of shale oil in the future.

Classification and evaluation methods for the production capacity of deep low-medium rank coalbed methane

CHEN Guojun, PAN Tuo, ZHANG Fan, GAO Ming, MAO Chenfei, ZHANG Xiao, ZHANG Wenqian, FAN Xiaoqin

2025, 32(1):  71-78.  DOI: 10.3969/j.issn.1006-6535.2025.01.008

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A variable skeleton porosity calculation method based on coal-rock components is proposed in this study to address the issues such as low accuracy in calculating the porosity of deep coal rock reservoirs and the difficulty in applying critical factors methods to evaluate production capacity in deep coal rocks whereas it is applicable in shallow coal reservoirs.Furthermore,two models,namely matrix quality (Q_m) and structural quality (Q_s),are established based on gas saturation calculation models that are developed on the basis of ratios of measured acoustic travel time to reconstructed acoustic travel time.Based on these models and according to production capacity levels,the coal rock reservoirs are classified into three categories.The results show that compared to shallow coal reservoirs,the matrix porosity,cleat porosity,gas saturation,and coal mass structure of deep coal reservoirs are the primary factors affecting production capacity.The accuracy of porosity calculation with key parameters has improved by employing methods such as variable skeleton porosity,dual-lateral cleat porosity,and acoustic travel time method and gas saturation.Theprecision of porosity calculation has increased from 68.1% to 90.5%.The production capacity classification and evaluation method established on these key parameters has significant predictive effectiveness in deep low-medium rank coal reservoirs,achieving a prediction coincidence rate of 91.0%.This classification and evaluation method can provide technical support for the next coalbed methane exploration.

Fault-caprock configuration and relationship with longitudinal distribution of hydrocarbons in the south-central section of the Eastern Sag in the Liaohe Basin

LI Hongyan, HAN Hongwei, JIANG Youlu, SHEN Che, GUO Qiang

2025, 32(1):  79-87.  DOI: 10.3969/j.issn.1006-6535.2025.01.009

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In response to the unclear impact of fault-caprock configuration sealing capacity on the longitudinal distribution of hydrocarbons in the central-southern segment of the Eastern Sag of Liaohe Basin, this study investigated the characteristics of the longitudinal distribution of hydrocarbons by utilizing the well-to-seismic and geological data, and evaluated the sealing capacity of fault-caprock configuration by employing the entropy weight method combined with TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) to reduce subjectivity in weight determination. The study shows that: the types of hydrocarbon enrichment in the study area can be divided into three categories: deep enrichment type, shallow enrichment type, and multi-layer enrichment type. Fault-caprock configurations can be divided into type I with good sealing capacity and type II with poor sealing capacity.Type I fault-caprock configuration in Member 3, Shahejie Formation is distributed in the central segment for controlling the deep enrichment of hydrocarbons. The combination of type I and type II fault-caprock configurations between the Member 3, Shahejie Formation and the Dongying Formation controls the multi-layer enrichment and shallow enrichment of hydrocarbons. The results of this study provide reference significance for the next steps in oil and gas exploration.

Main control factors of gas-water distribution in the Upper Paleozoic gas reservoirs of the Qingyang Gasfield in the Ordos Basin

XIA Hui, WANG Long, LI Ya, ZHANG Daofeng, ZHANG Yuanyuan, ZHU Wangming, ZHANG Wei, LIU Ping

2025, 32(1):  88-97.  DOI: 10.3969/j.issn.1006-6535.2025.01.010

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The complex distribution of gas and water in the Upper Paleozoic gas reservoirs of Qingyang Gasfield restricts the efficient development of the gas field. To solve this problem, we comprehensively utilized data from drilling and logging wells, 3D seismic, gas testing and production to systematically carry out study on the classification of formation water types, the distribution pattern of gas and water and the controlling factors, so as to clarify the main control factors for the distribution of gas and water. The results show that:the formation water in the study area is primarily distributed in the Shan 1 Member, with the water-producing layers in the He 8 Member being relatively limited.On a plane, a high water-bearing area in the center and medium water-bearing areas in the west and east can be delineated. The formation water can be categorized into structural low-lying trapped water,interlayer fracture water, and isolated lens-body water. Structural low-lying trapped water is distributed in the western part of the study area,influenced by regional tectonic characteristics and the intensity of hydrocarbon generation; interlayer fracture water is primarily found in the central part of the study area, controlled by the fault system;isolated lens body water is distributed in the eastern part of the study area, mainly controlled by the heterogeneity of the reservoir and the migration distance.This achievement provides theoretical reference for the study of gas-water distribution in tight sandstone gas reservoirs under complex structural backgrounds, as well as for the study of natural gas accumulation. It also offers geological basis for the subsequent efficient development of gas fields.

Reservoir Engineering

Mechanism of CO₂ gravity miscible displacement and oil displacement experiment in buried hill reservoirs

GUO Fajun, LIANG Fei, CHEN Hong, QI Huan, ZENG Qingqiao, WANG Ruisi, LI Yiqiang, WU Yongen

2025, 32(1):  98-105.  DOI: 10.3969/j.issn.1006-6535.2025.01.011

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To address the unclear mechanism of CO₂ gravity flooding implemented in Balixi fracture-type buried hill reservoir,this paper,considering the reservoir characteristics and development status,explored the interaction mechanisms between reservoir fluids and CO₂ through the gas injection expansion,core displacement,and NMR scanning experiments,and studied the effect of CO₂ gravity flooding after water injection at the bottom of the reservoir,clarifying the production patterns of crude oil within the pore and fracture reservoir spaces.The study shows that:after the injection of CO₂,the viscosity of crude oil is reduced by 57%,and its volume is expanded by a factor of 1.83,indicating that CO₂ has a significant effect on reducing the viscosity and expanding the volume of crude oil.The results of PVT (Pressure-Volume-Temperature) experiments indicate that the presence of a water phase has almost no effect on the interaction between crude oil and CO₂.During the oil-gas mass transfer process,CO₂ can extract and strip the C₂-C₁₂ components from the oil,which is conducive to the recovery of lighter fractions,while heavier fractions (C₁₀-C₃₆₊) remain in place.Implementing CO₂ gravity miscible displacement after water injection at the bottom of the reservoir can further enhance the recovery of crude oil.Both the degree of oil-gas mass transfer and the gas injection rate affect the oil displacement efficiency.The stronger the degree of oil-gas mass transfer and the lower the injection rate,the more effectively CO₂ can extract,strip,and dissolve,thereby fully producing the contiguous remaining oil and the remaining oil that has not been in direct contact with CO₂.Based on NMR experiment results,the reservoir space can be divided into pore space and fracture space.Compared with CO₂ non-miscible flooding,CO₂ gravity miscible flooding after water flooding can improve the recovery from both matrix and fractures.After miscible flooding of twice the pore volume,the recovery from the matrix is 49.3%,and that from the fractures is 99.3%.Field practice has demonstrated that top-injected CO₂ gravity miscible displacement is an effective means of succession development for enhancing oil recovery in the Balixi buried hill reservoir.

Molecular simulation of electric double layers at tight reservoir surface under external electric field

YANG Shanshan, NING Zhengfu, LYU Fangtao

2025, 32(1):  106-112.  DOI: 10.3969/j.issn.1006-6535.2025.01.012

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To address the lack of understanding of the electrokinetic phenomenon of the electric double layers at the surface of tight reservoirs under an external electric field and the difficulty in accurately characterizing the micro-characteristics of the interfacial electric double layers through macroscopic experiments,this study investigated the impact of the electrokinetic phenomenon of electric double layers on wettability and crude oil seepage under an external electric field from a microscopic perspective, established a model of the electric double layers on the surface of tight reservoirs under an external electric field by employing the molecular dynamics simulation to explore the influence mechanism of the electric double layers on the surface of tight reservoirs at 313 K and 20 MPa.The analysis results indicate that:after the application of an electric field, the diffusion of solution ions is reduced,the electric double layers undergo expansion,and the electrostatic interactions on the charged surfaces lead to a thicker and more stable water film, which is beneficial for the water wettability of rock surfaces.The greater the electric field intensity, the higher the ion density in the electric double layers,and the more pronounced the electroviscous effect.The oil-phase seepage velocity increases due to the interfacial viscous resistance,but the increase is limited.The formation water solution internally produces a stronger ion hydration effect under the electric field,and changes in ion hydration occur with different ions when the electric field intensity is altered.The research findings are of significant importance for the development of micro-theories of tight reservoirs under external electric fields.

Study of the CO₂-C₂H₆ enhanced crude oil extraction and miscibility

WANG Chengwei, SU Yuliang, WANG Wendong, LI Lei, HAO Yongmao

2025, 32(1):  113-119.  DOI: 10.3969/j.issn.1006-6535.2025.01.013

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In response to the unclear understanding of the synergistic mechanism of CO₂-C₂H₆ and the variation in miscibility during the tight reservoir development,high-temperature and high-pressure PVT device was utilized to conduct oil and gas phase behavior and extraction experiments.The study investigated the phase behavior and extraction characteristics between CO₂-C₂H₆ mixture and crude oil,and simulated the occurrence status and the mixed-phase pressure change characteristics by molecular dynamics.The study shows that:compared with the injection of CO₂ only,the addition of ethane results in a decrease of about 0.1% in the high carbon molecular weight percentage of crude oil.Ethane can effectively enhance the extraction capability of the injected gas on crude oil,transforming high carbon hydrocarbons into lower carbon hydrocarbons such as C₅.Both CO₂ and CO₂-C₂H₆ mixture are capable of extracting C₂,C₄,and C₆ from multi-component oil molecules into the gas phase,lowering the intermolecular forces in the oil phase and enhancing the mobility of crude oil.The diffusion and miscibility capabilities of the gas mixture in crude oil are stronger than those of pure CO₂.The gas mixture is more likely to form miscibility with crude oil,thereby increasing the degree of oil production.This study provides theoretical guidance for the synergistic enhanced recovery technology of CO₂-C₂H₆ gas mixture injection in tight oil reservoirs.

Study on the hierarchical characterization method of breakthrough flow channels in offshore unconsolidated sandstone heavy oil reservoirs driven by polymer flooding

ZHANG Peng, WEI Zhijie, LIU Yuyang, CUI Yongzheng, YONG Wei, ZHANG Jian, ZHOU Wensheng

2025, 32(1):  120-126.  DOI: 10.3969/j.issn.1006-6535.2025.01.014

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The reservoir of offshore unconsolidated sandstone reservoir is loose and possesses strong heterogeneity.Breakthrough flow occurs during the development of polymer flooding,resulting in ineffective water circulation and seriously affecting the development effect.In view of the above problems,considering the mechanism of polymer flooding,an interwell dynamic calculation model of polymer flooding based on interwell connectivity unit is constructed.On this basis, the characteristic parameters of breakthrough flow channel intensity are determined,and the comprehensive evaluation factor of breakthrough flow channel intensity is formed.A breakthrough channel hierarchical characterization method suitable for polymer flooding in offshore heavy oil reservoirs is established.The research outcomes are applied to the breakthrough flow channel identification of polymer flooding in offshore S Oilfield.The results indicate that compared with the Eclipse model,the historical fit speed of the proposed method can be increased by 154 times,and the fitting error is within 10%.In S1 Area, large channels are identified in A02,A19 and K29 wells,and preferential flowing channels are identified in A13 and A21 wells.The results are in good accordance with the tracer monitoring results,which proves that the new method is reliable.At the same time, two sections of large channels and six sections of preferential flowing channels are identified in S2 Area,which provides support for tapping the potential of remaining oil in this area.The research findings can provide guidance for targeted management and sustainable high efficienct development of inefficient channels in oilfield driven by polymer flooding.

Experiment on effective capacity of gas storage reconstructed from Baogu-2 Reservoir

HE Haiyan, XIN Chunyan, SHANG Lin, ZHU Shijie, XIANG Zuping, GAO Guangliang, SUN Yanchun, WANG Yi

2025, 32(1):  127-134.  DOI: 10.3969/j.issn.1006-6535.2025.01.015

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The capacity constitutes one of the most crucial indicators for the reconstruction of gas storage.The greater the capacity of the gas storage,the stronger the capabilities of carrying,gas storage and peak shaving,and the greater the ability to guarantee the demand for gas.Therefore,forecasting the capacity holds significant importance for the construction of gas storage.In order to clarify the effective capacity of the gas storage reconstructed from the Baogu-2 Reservoir,a multi-period interactive displacement relative permeability experiment and a long core injection-production experiment were conducted.The experimental results indicate that after 5 cycles of oil-water mutual displacement,the capacity decreases by 7.71 percentage points.After gas-water mutual displacement and gas-oil mutual displacement,the capacity increases by 1.50 and 3.14 percentage points respectively.After 5 cycles of injection-production experiments,the reservoir capacity space increased by 32.38 percentage points.Multi-cycle injection and production can continuously mobilize the internal fluid of the core to enhance the capacity.Effective measures ought to be adopted to prevent edge and bottom water from intruding oil areas,minimize oil-water mutual drive,and improve the effective displacement of injected gas to pure oil areas and water-flooded areas,so as to realize efficient storage construction in mutual drive areas.Reasonable design of injection-production plan can further improve the effective capacity of gas storage.This study can offer technical support for the reconstruction of gas storage in edge and bottom water reservoirs.

A new method for characterizing the pore-throat structure of tight sandstone based on nuclear magnetic resonance and constant-rate mercury intrusion

LIU Ke

2025, 32(1):  135-143.  DOI: 10.3969/j.issn.1006-6535.2025.01.016

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Tight sandstone features small pore throats,a complex pore structure and severe heterogeneity.To accurately characterize the pore throat structure characteristics of tight sandstone reservoirs,taking the tight sandstone of the third member of Yingcheng Formation in Changling Fault Depression,Songliao Basin as an example,the pore structure of tight sandstone was investigated by means of field emission scanning,casting thin section,constant-rate mercury injection and nuclear magnetic resonance method.Through the combination of NMR with CMP experiment,the distribution of pore and throat radius was effectively identified,and the lower limit of pore throat radius of movable fluid was defined.The experimental results indicate that the average throat radius of the target reservoir ranges from 0.331 to 0.824 μm,the average pore radius ranges from 17.600 to 24.290 μm,and the average pore-throat connectivity ratio ranges from 27.62 to 53.17.The lower limit of the pore throat radius of movable fluid is within a range.The lower limit r₁ and the upper limit r₂ can divide the fluid into the bound zone,the transition zone and the movable zone.As the permeability decreases,r₁ gradually increases,r₂ gradually decreases,the range of the bound zone becomes larger,and the range of the transition zone and the movable zone becomes smaller.The increase of r₁ will lead to the increase of adsorption pore porosity,the decrease of seepage pore porosity and the deterioration of reservoir quality.r₁ can be used as an index to evaluate the boundary of reservoir flow capacity.The research results can provide a basis for optimizing high-quality tight sandstone reservoirs.

Drilling & Production Engineering

Optimization of process parameters for microwave-enhanced coalbed methane mining technology at mine scale

WANG Xiyou, QIN Yang, LIU Ziwei, ZHU Jingyi, XIE Shiyi, JIN Xinxiu, DU Bodi, YU Jialu

2025, 32(1):  144-152.  DOI: 10.3969/j.issn.1006-6535.2025.01.017

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Enhancing the recovery rate of coalbed methane is an essential requirement for achieving large-scale and effective development of coalbed methane. Existing studies have shown that microwaves have the feasibility of improving coalbed methane recovery rate at the core scale, but relevant studies at the mine scale are relatively scarce. For this reason, a microwave heating well model at the mine scale is established to couple the electromagnetic field, temperature field and mechanical field within the coalbed, to explore the influencing factors of microwave heating parameters, and to optimize the process parameters, thereby ensuring the effectiveness and stability of microwave heating wells. The study shows that: Microwave heating wells are mainly vertical or horizontal wells, which are made of copper waveguides (BJ 22 or BJ 26 type) and ceramic casing materials, the temperature and thermal stress in the coalbed and wellbore are positively correlated with microwave power and heating time. The coalbed in the vicinity of the well generates heat by its own dielectric loss, while the coalbed in the area far from the well mainly relies on contact heat transfer to increase temperature. A microwave operating mode of 500 W to 100 W over 33 days has improved the effectiveness and operational stability of the coalbed. Optimizing process parameters alone cannot meet practical application requirements; therefore, a combination of intermittent cyclic variable power microwave heating patterns, microwave-absorbing medium enhanced coalbed thermal conduction technology, and hydraulic fracturing techniques should be employed to enhance the practical effects of microwave heating of the reservoir. The study results can provide technical support for the promotion and application of microwave-enhanced coalbed methane mining technology.

Transport and placement patterns and application of micronized proppant

LI Ting, WU Qingmiao, YANG Dan, ZENG Sijia, ZHAO Jiale, HE Meiqi, ZHOU Zhuo, YANG Jiahao

2025, 32(1):  153-160.  DOI: 10.3969/j.issn.1006-6535.2025.01.018

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To address the issue of inadequate support for numerous micro-fractures during reservoir volumetric fracturing, this study has identified micronized proppant with smaller particle sizes and superior suspension performance as the preferred choice. The transport and placement patterns of this proppant within complex fractures were investigated using Fluent software, and the fracturing effects were compared between 70/140-mesh ceramic proppant and micronized proppant using FracMan software. The study shows that: micronized proppant is predominantly placed within secondary fractures, exhibiting a distribution pattern characterized by a "high in the front and low in the back" morphology. In primary branch fractures, a significant amount of micronized proppant remains in suspension, with only the 200-mesh micronized proppant undergoing sedimentation. The equilibrium height and area of the sandbanks formed are relatively small, failing to create effective sandbanks. The placement pattern of micronized proppant is significantly influenced by particle size. As the mesh size of the proppant increases from 200 to 600 meshes, the equilibrium height and area of sandbanks in secondary and tertiary branch fractures gradually increase. When the mesh size reaches 800 mesh, the particle size is so small that a large number of proppant particles remain in suspension and do not settle to form effective sandbanks, leading to potential under-support in the near-well micro-fractures. Compared to 70/140 mesh ceramic proppant, micronized proppant travels a greater distance and more readily penetrates into secondary and micro-fractures. The use of micronized proppant can increase the complexity of the fracture network, enhancing the shale reservoir stimulation volume by 17.71%, resulting in a significant improvement in reservoir stimulation effectiveness. This study can provide valuable insights for the application of micronized proppant.

Effect model of deep-penetration composite chemical deplugging in sandstone reservoirs

SUN Yide

2025, 32(1):  161-166.  DOI: 10.3969/j.issn.1006-6535.2025.01.019

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To address the issue of low recovery rates due to long-term polymer plugging in sandstone reservoirs,this study proposes a method of deep-penetration composite chemical deplugging for sandstone reservoirs.By leveraging sand-free deep-penetration fracturing,the deplugging fluid was delivered deep into the reservoir to enhance the deplugging effectiveness. The numerical reservoir simulation is employed to investigate the seepage patterns of the deplugging fluid along deep-penetration fractures,and a production prediction model for deep-penetration deplugging is constructed to evaluate the impact of factors such as the length of deep-penetration fractures and the amount of deplugging fluid on the deplugging effect. The study shows that:after the injection of the deplugging agent into the formation,the agent forms a dumbbell-shaped distribution in the affected area,improving the permeability of the reservoir.As the length of the fracture increases,the effective deplugging area gradually enlarges.With the increase in construction flow rate,the effective deplugging area first increases and then decreases.Both the fracture half-length and the amount of deplugging fluid have a certain impact on the deplugging effect,with the optimal deplugging effect achieved when the deep penetration fracture half-length is approximately 1.4 times the radius of the contamination zone.The findings of this study can provide a reference for the design of deplugging and production increase processes in sandstone reservoirs.

Impact of fracture propagation direction on proppant transport patterns within the main hydraulic fractures of horizontal wells

QI Shengjin

2025, 32(1):  167-174.  DOI: 10.3969/j.issn.1006-6535.2025.01.020

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In the process of hydraulic fracturing horizontal wells in the Dongsheng Gasfield, there is a lack of research on the proppant transport patterns within the main hydraulic fractures, leading to suboptimal reservoir stimulation effect. To address this issue, a visual parallel plate fracture simulation system was employed to conduct proppant placement experiments under different fracture extension directions within the main hydraulic fractures. The influence of displacement, sand ratio, fracturing fluid viscosity, and proppant particle size on sand dune morphology was simulated using Fluent software. The study shows that: The orientation of fracture propagation and the proppant placement are the primary factors affecting the growth pattern of sand dunes and the frontal placement efficiency. Compared to horizontal and upward fracture extensions, the height of the sand dune at the entrance is 1.79 times and 12.17 times when the fracture extends downward, with the frontal placement rates being 1.21 times and 6.09 times, respectively. The contribution of single fracture production is increased by 2% and 24%, respectively.Construction parameters do not influence the growth pattern of sand dunes; however, the pumping method of large-displacement and high-viscosity fracturing fluids can effectively reduce the time required for sand dunes to reach equilibrium height, thereby enhancing the migration capacity of proppant. The pumping method with high sand ratios and large particle sizes can achieve a more desirable main hydraulic fracture placement effect in a relatively short period. The research results can provide reference for the optimization of gas field fracturing process.