Table of Content

25 June 2025, Volume 32 Issue 3

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Summary

Research status and prospects of nano-foam fracturing fluids in unconventional reservoirs

YAO Weida, LI Yu, ZHANG Liang, WANG Peng, HU Jiachen, MA Weiyun, ZHI Guangchao

2025, 32(3):  1-7.  DOI: 10.3969/j.issn.1006-6535.2025.03.001

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Foam fracturing fluids, with benefits like low water content, easy flowback, strong sand-carrying capacity, and less reservoir damage, are a key technology for unconventional oil & gas reservoir development. However, foam decay greatly affects the stimulation by fracturing.With nano-technology progress, adding nanoparticles to boost foam fracturing fluid properties has become a research hotspot. This paper introduces the research progress of nanoparticle impacts on stability, sand-carrying capacity, fluid loss reduction, and damage reduction of foam fracturing fluids. It also points out future research directions, which mainly involve using machine learning algorithms and statistical models to holistically assess factors influencing foam stability, deepening the understanding of nanoparticle-surfactant interactions, developing low-cost and efficient nanoparticles, reducing nanoparticle-induced reservoir damage, and enhancing the stability and dispersion of nano-foam fracturing fluids in complex reservoir environments. The research findings can offer a theoretical reference and technical support for the application and development of nano-foam fracturing fluids in unconventional oil & gas reservoir exploitation.

Geologic Exploration

Development characteristics and genetic mechanism of faults in the Shunnan-Gulong Area, Tarim Basin

HUANG Cheng, LIN Bo, ZHANG Sheng, WANG Yuefeng, YU Fusheng

2025, 32(3):  8-15.  DOI: 10.3969/j.issn.1006-6535.2025.03.002

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To address the issue of differing understandings regarding the nature, evolutionary stages, and genetic mechanisms of the fault system in the Shunnan-Gulong Area, a study was conducted on the fault system in the study area through seismic interpretation, seismic attribute extraction, fault activity intensity statistics, and analysis of the regional tectonic background. The results show that the north-east-east-trending faults are extensional normal faults formed during the early Caledonian passive continental margin stage, driven by north-west to south-east oriented extension from the opening of the Altyn Ocean. These faults were reactivated in the middle Caledonian period to form "P" fractures. The north-east-trending faults are widespread left-lateral strike-slip faults formed during the middle Caledonian compressional-transpressional stage, with stress originating from the north-west to south-east oriented compression generated during the closure of the Altyn Ocean. The north-north-west-trending faults are tensile fractures formed during the late Caledonian to middle Hercynian period due to basement strike-slip, with stress from the nearly south-north compression caused by the closure of the southern Tianshan Ocean. The segmented activity differences in the Cheltenham Fault are the main reason for the segmented activity of the Tazhong No. 1 Fault and the widespread development of north-east-trending compressional-transpressional strike-slip faults. The structural characteristics of strike-slip fault zones are crucial for reservoir size and hydrocarbon migration. This study provides a theoretical basis for analyzing the development process of strike-slip faults and their relationship with hydrocarbon accumulation in the Shunnan-Gulong Area, and laying a foundation for hydrocarbon exploration in the study area and its surroundings.

Accumulation characteristics and exploration directions of coal-measure gas in the marine-continental transitional facies of the Kaiping Syncline

LI Peng, LI Zheng, ZHANG Aiyin, ZHANG Jianya

2025, 32(3):  16-25.  DOI: 10.3969/j.issn.1006-6535.2025.03.003

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The Kaiping Syncline is one of the potential blocks with the most exploration value of coal-measure unconventional natural gas in Hebei Province, but the lack of systematic research on the accumulation geological conditions and the accumulation mode of the Kaiping Syncline restricts the exploration and development process of coal-measure gas in this area. In this regard, through the analysis of test data and the combination of the "three histories (burial history, thermal history, and organic matter maturation history)" simulation and other means, the geological conditions, evolutionary process and mode of accumulation in this area were comprehensively analyzed, and the favorable exploration direction of this area was also analyzed. The results show that The study area has the geological conditions for coal-measure gas accumulation; the Early Triassic and Middle Jurassic-Late Cretaceous are the periods of all-round and efficient accumulation for coal-measure gas; the study area is predominantly characterized by the northwest-wing structural-lithological-hydrological sealing gas accumulation mode, the core lithological sealing gas accumulation mode, and the southeast-wing stratigraphic-lithological sealing gas accumulation mode; and the northwestern wing of Kaiping Syncline is the most favorable area for the next step of exploration and development. The study results are of some significance for the subsequent exploration and development of coal-measure gas in the Kaiping Syncline.

Geological characteristics and resource potential of coal-derived oil in the third member of Shahejie Formation in the eastern sag of Liaohe Depression, Bohai Bay Basin

YU Xuefeng, YU Fusheng, GUO Qiang, HUANG Shuangquan

2025, 32(3):  26-34.  DOI: 10.3969/j.issn.1006-6535.2025.03.004

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The cause and source of high-wax crude oil in the third member of Shahejie Formation in the eastern sag of Liaohe Depression, as well as its exploration potential, remain unclear. Through comprehensive analysis of the coal-forming environment, coal-measure hydrocarbon source rock indices, and crude oil geochemical features of the upper sub-member of the third member of Shahejie Formation in the eastern sag, the source-reservoir configuration and hydrocarbon-generating potential were assessed, which clarified the main controlling factors for coal-derived oil accumulation. The study shows that the upper sub-member of the third member of Shahejie Formation in the eastern sag is a period of fault-depression transition, in which the lake basin gradually silts and fills up under the background of stable tectonics, forming a large area of floodplain deposits; the coal-measure stratum is stably developed, and the coal-measure hydrocarbon source rocks are rich in chitin groups and desmocollinite, which have strong oil-generating capacity. The main controlling factors for coal-derived oil accumulation are the large thickness of coal-measure hydrocarbon source rocks in coal accumulation centers, thedevelopment of fracture transport systems in tectonically deformed zones, and the close and direct configuration of coal and sand. The coal-measure strata of the upper sub-member of the third member of Shahejie Formation in the eastern sag can generate oil, with a total coal-derived oil resource of 0.8×10⁸ t. This finding has led to exploration discoveries, expanded new source rock series, and offers significant reference for exploring coal-measure strata in the Liaohe Depression and the entire Bohai Bay Basin.

Influence of differential thermal evolution and hydrocarbon characteristics of Permian hydrocarbon source rocks on hydrocarbon enrichment pattern in the central depression of Junggar Basin

HAN Yang, YANG Haibo, JIANG Wenlong, YANG Huang, XIANG Wei, GUO Wenjian, WANG Tao

2025, 32(3):  35-46.  DOI: 10.3969/j.issn.1006-6535.2025.03.005

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The Permian hydrocarbon source rocks in the central depression of the Junggar Basin are the most important source of oil and gas in the basin. To sort out the hydrocarbon-generation evolution and enrichment patterns of multi-phase oil and gas under the "source control" background, basin simulation and experimental analysis techniques were employed to reconstruct the thermal evolution history, hydrocarbon generation history, and accumulation process of the Permian hydrocarbon source rocks in different hydrocarbon-rich depressions of the central depression. The study shows that the Permian hydrocarbon source rocks began to mature in the Late Triassic and are currently mainly in the high-maturity condensate gas generation stage, mostly reaching the over-mature stage in the depression centers. The hydrocarbon generation process of the Permian hydrocarbon source rocks can be divided into three enrichment patterns: continuous injection of mature oil-rich and gas-poor type, multi-stage adjustment of deeply buried high-maturity gas-rich type, and early loss of early-mature oil and gas-rich type, with the peak hydrocarbon generation rate reaching up to 450 mg/g. The Mahu Sag tight oil and shale oil, the conventional oil of the Triassic system in the western annular zone of the Shawan Sag (west of Well Pen 1), the tight gas of the Permian system in the eastern annular zone, and the shale gas within Permian source in the Dongdaohai Sag are the four oil and gas enrichment areas in the study area. The research results can provide important support for the next step of oil and gas exploration in this area.

Dissolution characteristics and impact on properties of the He 8 Reservoirs in the Yanchuan Area

HUANG Xingyu, DU Guichao, HE Yawen, GUO Ruiliang, ZHU Lin, JIA Wenhao, WANG Hao, WANG Fengqin

2025, 32(3):  47-56.  DOI: 10.3969/j.issn.1006-6535.2025.03.006

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To address the unclear impact of dissolution on the properties of the He 8 Reservoir in the Yanchuan Area of the Ordos Basin, this study used mercury injection, porosity and permeability tests, core observation, thin-section identification, and scanning electron microscopy to analyze the development characteristics of He 8 sandstone reservoir dissolution and its impact on reservoir properties. The results show that the He 8 Member is a typical ultra-low-porosity, tight reservoir divided into three types: quartz sandstone, lithic quartz sandstone, and lithic sandstone. The reservoir has undergone intense diagenesis, with dissolution being the main factor for secondary pore formation and property enhancement. All three reservoir types experienced acidic dissolution during the late early diagenetic stage B to the middle diagenetic stage A. Quartz sandstone reservoirs, with low soluble components and weak dissolution, mainly have intergranular pores. Lithic quartz sandstone, strongly dissolved, forms high-quality reservoirs with abundant secondary pores. Lithic sandstone, subjected to strong compaction rock chip deformation resulting in densification of the sandstone, is a tight reservoir. A dissolution development model was established based on sandstone type. The study results offer a significant reference for "sweet spot" differentiation and favorable area prediction in the He 8 tight sandstone reservoir.

Key technologies to improve post-stack seismic inversion accuracy

ZHANG Xichen, ZHANG Jianwei, LUO Ya′neng, LI Jingye, GU Xiaodong, FU Hui, WANG Zixin, DING Yan

2025, 32(3):  57-65.  DOI: 10.3969/j.issn.1006-6535.2025.03.007

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To address the issues of low resolution, suboptimal continuity and limited reliability in conventional post-stack seismic inversion processes,this study systematically analyzes the importance of each inversion step from the perspective of the inversion workflow. By employing various methods and techniques, the resolution, continuity, and authenticity of the inversion results are improved, and a new high-accuracy post-stack seismic inversion workflow is established. The study shows that improving the vertical resolution of inversion results can be achieved through four methods: high-resolution inversion techniques, resolution-enhancing preprocessing of seismic data, wavelet adjustment, and high-frequency merging of inversion results with models. Improving the lateral continuity of the inversion results can be achieved through two methods: inversion stability adjustment and low-frequency merging of inversion results with models. The enhancement of inversion effectiveness must adhere to the authentic characteristics of reservoirs and should be achieved under the constraints of well-cross-section validation, planar validation, inversion residual validation, and well-point validation. Additionally, four key applicability considerations for the new inversion workflow are proposed: improvement methods should be selected based on the geological context and specific prediction objectives; it is challenging for inversion results to simultaneously meet the requirements of vertical resolution and lateral continuity, necessitating a trade-off between the two; excessive enhancement of inversion effectiveness may compromise the reliability of the results; and the time-depth relationship of wells must be ensured to be accurate. Future reservoir predictions will become more refined and complex, and the aforementioned methods and techniques may have promising applications, potentially serving as a reference for detailed inversions in other regions.

Development characteristics and evolution of strike-slip fractures in the Fuxian Area of the southern Ordos Basin

ZHANG Cheng, TANG Daqing, QI Rong, ZHANG Wei, FENG Quan

2025, 32(3):  66-75.  DOI: 10.3969/j.issn.1006-6535.2025.03.008

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The Fuxian Area of the southern Ordos Basin is rich in oil and gas resources. This area is characterized by the development of small-displacement strike-slip faults, which play an important controlling role in the migration and accumulation of oil and gas. Through detailed interpretation of 3D seismic data in the Fuxian Area, combined with previous research results and oil and gas exploration practices, the development characteristics and evolutionary causes of strike-slip faults in the Fuxian Area were explored. The study shows that small-scale and small-displacement strike-slip faults are mainly developed in the Fuxian Area of southern Ordos Basin, with a low degree of development. Both horizontal and vertical displacements of the faults are not significant. On the profile, the faults are mainly characterized by steep upright, flower-like, and "y"-shaped features, while on the plane, the faults exhibit multiple orientations and a chaotic distribution pattern. The fault activity can be divided into four stages, namely right-lateral tensional activity during the Caledonian period, right-lateral strike-slip activity during the late Hercynian period, inherited strike-slip activity during the Indosinian period, and left-lateral strike-slip activity during the Yanshanian period to the early Himalayan period. The evolution of the faults is mainly influenced by the basement faults and the multi-stage tectonic activities in the southern part of the basin. The activation of the basement faults and the attenuation of the tectonic stress transmitted from the basin margin to the interior of the basin result in the fault activity in the study area being characterized mainly by small-displacement weak strike-slip motion. This study provides a theoretical reference for the study of oil source faults and exploration practices in the Fuxian Area.

Reservoir Engineering

Experimental study on enhancing tight oil recovery by CO₂-alternating-alkane huff-n-puff

LI Zhihao, PI Yanfu, LIU Li, YANG Jiawen, CAI Dongrui

2025, 32(3):  76-85.  DOI: 10.3969/j.issn.1006-6535.2025.03.009

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To address the decline in single-cycle recovery and the slowdown in cumulative recovery increase during the later stage of gas huff-n-puff,CO₂,methane,ethane,and propane were selected to carry out extraction experiments using a high-temperature and high-pressure reactor,and gas chromatography was employed to determine the oil components extracted with different gases.Combined with the viscosity changes of the remaining oil after extraction,the molecular mass selectivity of different gases was compared.Moreover, CO₂ huff-n-puff and CO₂-alternating-alkane huff-n-puff experiments were conducted to evaluate the recovery enhancement effects of different injection methods.The experiments revealed that propane has the highest extraction rate,reaching 62.60% at 30 MPa,ethane andCO₂ achieve 53.07% and 49.25% respectively at 30 MPa,and methane has the poorest extraction ability,only 20.47% at 30 MPa.Propane shows the most uniform molecular mass selectivity,extracting all oil components,and ethane preferentially extracts light and medium components,mainly those within C₂₅,while CO₂ and methane mainly extract light components within C₁₅.The huff-n-puff experimental results showed that CO₂-alternating-alkane huff-n-puff enhances recovery by over 10% compared to CO₂-only huff-n-puff,with significant improvements in later-stage recovery per cycle.This research offers valuable insights for enhancing tight oil recovery.

Prediction method for water invasion in carbonate gas reservoir with bottom water before water breakthrough

PANG Jin, HUO Yuchen, XU Shenhao, CHEN Lin, OU Jiaqiang, YANG Yang, KONG Xiangling

2025, 32(3):  86-93.  DOI: 10.3969/j.issn.1006-6535.2025.03.010

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To address the poor applicability of existing methods for predicting water invasion and evaluating aquifer activity in carbonate gas reservoirs with bottom water before water breakthrough,the reservoir characteristics and water invasion behaviors of such reservoirs were systematically analyzed.A mathematical model for bottom-water coning in carbonate gas reservoirs with bottom water was developed,incorporating derived formulas for calculating breakthrough time and water cone height.The morphological evolution of water cones at different production stages was characterized,enabling prediction of water invasion volume and water drive index before gas well breakthrough.The research results are applied to the Well PT102 in the Deng-2 gas reservoir of the Penglai Gasfield in central Sichuan, indicating that this method combines theoretical derivation with practical application,achieving dynamic description and quantitative prediction of water invasion before gas well water breakthrough,and solves the problem of early water invasion prediction in gas wells,addressing the insufficient accuracy and applicability of traditional methods.The predicted water breakthrough time is 169 days,with an absolute error of only 8 days (relative error 4.5%) compared to the measured value of 177 days.The water invasion volume before water breakthrough reaches 2.52×10⁴ m³,and the water drive index stabilizes at 0.30,verifying the model′s reliability.Reasonably reducing gas well production can effectively delay the water breakthrough time and significantly suppress the degree of water invasion.When the gas well production is reduced by 25%,the water breakthrough time can be delayed by about 24%,the cumulative water invasion volume is reduced by 18.4%,and the water drive index decreases from 0.30 to 0.27,indicating a significant suppression of water body activity.The research results fill the gap in early water invasion prediction methods for carbonate gas reservoirs with bottom water before water breakthrough and provide a reference for optimizing production allocation in similar gas reservoirs.

Impact of pore structure on imbibition characteristics in Qingshankou Formation shale oil reservoirs,Songliao Basin

CHEN Hongan, FU Lanqing

2025, 32(3):  94-103.  DOI: 10.3969/j.issn.1006-6535.2025.03.011

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To analyze the relationship between pore structure and imbibition characteristics in favorable lithofacies of the Qingshankou Formation shale oil reservoirs in the Gulong Sag,Songliao Basin,a comprehensive experimental study was conducted.Based on systematic analysis of lithological and physical properties of three typical lithofacies,integrated experimental methods including high-pressure mercury intrusion,low-pressure nitrogen adsorption,pressurized imbibition and huff-n-puff testing,and nuclear magnetic resonance scanning were employed to investigate how pore structure characteristics affect imbibition behavior across different lithofacies.The results show that the pore structure parameters of the feldspathic laminated shale,organic-rich clayey laminated shale,and clayey laminated shale in the Qingshankou Formation of the Songliao Basin exhibit a consistent trend:decreased submicron-level pore volume,reduced sorting coefficient,and increased displacement pressure and median pressure.The feldspathic laminated shale has pore structure advantages closely related to imbibition recovery,with the highest first-cycle and overall recovery rates.The organic-rich clayey laminated shale and clayey laminated shale have large nano-pore volumes.Increasing the imbibition-huff-n-puff pressure difference and the number of imbibition-huff-n-puff cycles can boost recovery.The research findings can offer a technical basis for shale oil imbibition development.

Experimental study on huff-n-puff of CO₂-hydrocarbon gas mixtures in shale oil

PAN Xianggang, WANG Qijun, CHEN Hua, CHENG Yunlong, YU Qiangang, HUO Jiahua, LI Xin

2025, 32(3):  104-110.  DOI: 10.3969/j.issn.1006-6535.2025.03.012

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To study the injection process of CO₂-hydrocarbon gas mixtures in shale oil and understand the impact of various parameters and the fluid production degree in nano-micron-sized pore throats, nuclear magnetic resonance (NMR) experiments were conducted to reveal the huff-n-puff characteristics such as changes in final recovery, T₂ distribution curves, and the mobilization of crude oil in different pore sizes during injection, and explain the effects of gas mixture type, injection method, and total organic carbon (TOC) on the huff-n-puff efficiency. The results show that CO₂ + C₃H₈, compared with CO₂ + CH₄, has stronger miscibility with crude oil. Under the same gas injection pressure conditions, the final recovery of CO₂ + C₃H₈ huff-and-puff can be increased by 3.21 percentage points, with C₃H₈ contributing more to shale oil recovery. Combining the strong compressibility of CO₂ + CH₄ and the strong miscibility of CO₂ + C₃H₈, injecting CO₂ + CH₄/CO₂ + C₃H₈ can effectively produce crude oil in large, medium, and small pores of the shale, with the final recovery reaching 28.97 percentage points. As TOC of the shale increases, more crude oil is adsorbed and dissolved during saturation, reducing recovery but increasing gas mixtures diffused into kerogen. This study provides a theoretical basis for the field implementation of huff-n-puff injection of CO₂-hydrocarbon gas mixtures in shale oil.

Optimized design of reservoir engineering for gas injection development in deeply buried hill reservoirs with strong volatility

JIANG Yong, ZHANG Lei, ZHENG Hua, YANG Chenxu, HUANG Lei

2025, 32(3):  111-118.  DOI: 10.3969/j.issn.1006-6535.2025.03.013

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The BZ-A oil reservoir in the Bohai Sea is a rare highly volatile metamorphic rock buried hill reservoir.The reservoir is characterized by thick layers,low porosity and permeability,strong heterogeneity,randomly distributed fractures, and large fracture dip angles.The deployment of injection and production well networks is an important issue that needs to be urgently addressed for the efficient development of the oil field.To this end,a dual-medium reservoir compositional model was established based on the fluid and reservoir development characteristics of the BZ-A oil reservoir.A study on the deployment strategy of three-dimensional well networks for gas injection development was conducted,and a quantitative analysis of the key influencing factors of gas injection development well networks and their coupling relationship with fracture development was performed.The results show that the BZ-A oil reservoir is suitable for development with associated gas reinjection to supplement energy,making full use of the structural position and gravity-assisted oil displacement mechanism for the deployment of injection and production well networks.Gas is injected at the top of the high structural positions, while oil is produced from the middle and lower parts of the low structural positions,forming a spatial three-dimensional well network.The development method using highly-deviated wells with a 45° angle to the fracture direction is adopted, which increases the oil drainage area and enhances the single-well production capacity.The optimal injection-production well spacing along the fracture direction is approximately 1 000 m,and the reasonable well spacing perpendicular to the fracture direction is approximately 800 m.The oil production rate during the peak period is 3%, and the recovery rate for gas injection development is 28.4%.The research findings have been applied to the development practice of the BZ-A buried hill oilfield,where the initial production capacity of oil wells ranges from 132 to 340 m³/d,achieving good development results.The research results are of reference significance for the preparation of development plans and efficient gas injection development of buried hill oil and gas fields.

Study on engineering design and pilot test of reservoir fireflood after waterflood in conglomerate ordinary heavy oil reservoirs

LI Yuying, CHEN Hong, ZENG Qingqiao, ZHOU Xian, ZHANG Minglong, DU Jiande

2025, 32(3):  119-125.  DOI: 10.3969/j.issn.1006-6535.2025.03.014

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In response to the unclear adaptability of fireflood technology in the late stage of waterflood development of ordinary heavy oil reservoirs,the feasibility of fireflood technology in the late stage of waterflood development of ordinary heavy oil was studied by using a one-dimensional physical simulation device in combination with reservoir geological development parameters.The study shows that low-viscosity ordinary heavy oil has good crude oil properties and can be ignited at 280 ℃ under the condition of 75% water saturation.The oil bank advance is sustained,indicating the feasibility of implementing fire flooding technology.Numerical simulation methods were used to determine that the pilot test used an inverted seven-spot areal pattern with a well spacing of 150 m,and the optimal gas injection intensity was 2 000 m³/(d·m).The research results were applied to the fireflood field test of the Menggulin conglomerate oil reservoir.After ignition,the effect was obvious.The daily oil production increased from 16.7 t before implementation to 62.2 t,an increase of 272.5%,and the comprehensive water cut decreased from 90.3% to 59.7%.It fully indicates that fireflood technology can be used as a major technology to improve the recovery rate of ordinary heavy oil reservoirs in the late stage of waterflood development.This study result can provide a reference for the transformation of development methods for double-high ordinary heavy oil reservoirs.

Drilling & Production Engineering

Effect of electrode structure on high-voltage electric pulse rock fragmentation mechanism

ZHU Xiaohua, LIU Weiji, ZHANG Youjian

2025, 32(3):  126-132.  DOI: 10.3969/j.issn.1006-6535.2025.03.015

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In oil drilling operations, the challenges of cost, environmental protection, and efficiency in hard rock fragmentation urgently need to be addressed. High-voltage electric pulse drilling, with its high efficiency, eco-friendliness, low tool wear, and time-cost advantages in rock fragmentation, has become a research hotspot. To advance the understanding of the mechanism of high-voltage electric pulse fragmentation of heterogeneous hard rock, models of hard rock with different heterogeneity indices were developed using Particle Flow Code (PFC) software and Voronoi diagram. Additionally, a 2D electro-breakdown numerical model for single-pair electrodes fragmenting heterogeneous hard rock was established. The study focused on the effects of electrode structure, pulse discharge voltage, and rock heterogeneity on the high-voltage electric pulse heterogeneous rock fragmentation mechanism. The study shows that the plasma channel tends to initiate at local dielectric weak points, guiding its discharge path, closely related to the rock′s heterogeneity. The electrode tip′s discharge enhances the local electric field, improving rock fragmentation effect but minimally affecting plasma channel growth. Greater heterogeneity indices make hard rock more prone to electro-breakdown, significantly increasing fragmentation and penetration depth. Higher pulse discharge voltages promote deeper electric damage accumulation, favoring hard rock fragmentation. The study offers theoretical and technical support for applying electric pulse rock fragmentation in complex deep-formation well conditions.

Fatigue life prediction of sheave wheels for ultra-deep well drilling rigs

YI Xianzhong, QIN Saibo, LIU Hangming, YUE Rongchang, XU Zhixin, PI Yunsong, CAI Xingxing, JI Yusong

2025, 32(3):  133-141.  DOI: 10.3969/j.issn.1006-6535.2025.03.016

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To address the issue of unclear understanding of the fatigue life of critical components in the drilling rig hoisting system, specifically the deadline anchor, the fatigue life analysis was conducted using the finite element method, taking the JZG97 type deadline anchor used in the ZJ150 drilling rig as an example. Through orthogonal experiments, the structural parameters of the weak link (sheave wheel) of the deadline anchor were optimized. Furthermore, a BP neural network fatigue life prediction model was established to predict the fatigue life of the vulnerable parts. The results show that the optimal parameters are a rib width of 90 mm, a sensor arm fillet radius of 270 mm, and a rib thickness of 230 mm. This increases the sheave wheel′s fatigue safety factor to 1.78, a 19.46% improvement over the initial design. The BP neural network model has a fitting accuracy of 97.84% and a maximum error of less than 4.870% between the predicted value and the simulated value. It proves to be accurate, fast-converging, and generalizable, enabling reliable fatigue life prediction of the deadline anchor without constructing complex functional regression relationships. This research offers guidance for structural optimization and life prediction of deadline anchors in ultra-deep well drilling equipment.

Design method for well-killing parameters in ultra-deep fractured formations using direct-push method

ZHAO Haijian, LI Dawei, WEI Sizhuang, WANG Xuesong, WU Guang, LI Qingfeng

2025, 32(3):  142-149.  DOI: 10.3969/j.issn.1006-6535.2025.03.017

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To address the issue of unreasonable well-killing parameter calculations for the direct-push method in ultra-deep fractured formations, which leads to significant construction safety risks, research, based on seepage theory, wellbore afterflow theory, and gas-liquid two-phase flow theory, has been conducted to investigate the initial distribution state of fluids in the wellbore before well-killing, the pressure variation patterns in the wellbore and formation during well-killing, and the design methods for well-killing fluid density and displacement. Additionally, a dual-gradient well-killing fluid density calculation method and a minimum well-killing fluid displacement calculation method have been established. The study shows that considering overflow circulation, shut-in afterflow, and shut-in slippage before well-killing, and using a drift flow model, it more accurately calculates the height and gas holdup of gas-liquid two-phase flow. The dual-gradient killing fluid density design method proposed with the goal of reservoir protection can reduce the amount of drilling fluid pushed into the formation and significantly lower the risk of reservoir contamination. By integrating the characteristics of bubble slippage under high wellhead backpressure and counter-current gas-liquid flow conditions, the minimum killing fluid displacement for the direct-push method is calculated based on the slippage velocity of small bubbles, which is more practical. The dual-gradient killing fluid density design method and the minimum killing fluid displacement calculation method have been compared and verified with actual well-killing cases and full-scale experiments, with errors all within 20%, indicating that the well-killing parameter design method is scientific and rational. This research method and its results can provide technical references for field engineers when using the direct-push method for well killing.

Simulation of high extension of fractures in Changning bedded shale reservoirs

ZHENG Jian, LIU Hong, Xiao Yongjun, LIU Bingxiao, XIAO Hui, LUO Xin, XIE Jiajun, LIU Lei

2025, 32(3):  150-159.  DOI: 10.3969/j.issn.1006-6535.2025.03.018

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The bedding of the Longmaxi Formation shale in Changning is developed,and the fracture height is limited during hydraulic fracturing,which is not conducive to connecting with high-quality “sweet spots” and reduces the effective seepage range,thereby affecting the hydraulic fracturing effect.In response to the above issues,based on the discrete element method of particle flow and considering the fluid-solid coupling effect,a simulation model for the coupling of horizontal section clustered perforating,bedding fractures, and fracture propagation in bedded shale was established.The model was used to simulate and analyze the fracture height propagation law.The field application results are consistent with the model simulation results.The study shows that bedding has a strong inhibitory effect on the fracture height propagation of shale fracturing,and the presence of bedding fractures causes the fracture height to deviate from the vertical extension.When the tensile strength of the bedding fractures is low,the fractures are more likely to activate and propagate along the bedding fractures,resulting in a relatively smaller fracture height.The difference between the vertical stress and the minimum horizontal principal stress has a much greater impact on fracture height propagation than the Young′s modulus and Poisson′s ratio.Under low stress difference, the fractures almost propagate along the bedding direction,and the fracture height is greatly restricted.The clustered perforating parameters and the amount of fracturing fluid have a relatively greater impact on fracture height.It is recommended to use a low viscosity (50 mPa·s),high flow rate (18 m³/min),and large volume (2 000 m³) method for volumetric fracturing.The recommended number of perforation clusters is 6,with a cluster spacing of 12 m.After fracturing,the test well has good vertical extension and a large fracture volume,with a tested daily gas production of 21.5×10⁴ m³.The research results can provide a reference for the stimulation of similar shale reservoirs.

Mechanism of screen blockage by collapse products in the deep carbonate reservoir and preference of well completion methods in Shunbei Oilfield

SU Peng, HUANG Youyi, LI Weiliang, LI Lintao, DONG Changyin, ZHANG Jinyi

2025, 32(3):  160-167.  DOI: 10.3969/j.issn.1006-6535.2025.03.019

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The deep carbonate reservoirs in the Shunbei Oilfield face serious wellbore collapse and control issues during development. To explore the blockage mechanism of the collapse products in this reservoir and design a reasonable completion method, anti-collapse completion simulation experiments were conducted under different collapse product combination modes, studying the adaptability of perforated screen and slotted screen completion methods. The study shows that the blockage mechanism of collapse products includes stepwise progressive bridging of particles, large particle bridging-small particle free passage, and large particle bridging-small particle interstice accumulation. When the median particle size of the collapse products is 3.83, 3.35, 2.00, 1.65 and 1.54 mm respectively, slotted screen completion is generally feasible, while perforated screen is not suitable for the pure sand particle mode with a median particle size of 1.54 mm. Under the condition of relatively continuous particle size distribution of collapse products, it is recommended to use perforated screen and appropriately increase the hole density. Under the condition of relatively discontinuous particle size distribution of collapse products and a small proportion of sand particles, it is recommended to use perforated screen and appropriately increase the hole density; if the proportion of sand particles is large, it is recommended to use slotted screen and appropriately reduce the slot width. This study can provide a reference for the anti-collapse completion design of carbonate reservoirs.

Crack propagation pattern of the petal teeth of the cardan universal joint for screw drilling tools

LIU Shujie, MA Chuanhua, YE Daohui, XIAO Ping, GUAN Qinqin, ZHANG Ruiyao

2025, 32(3):  168-174.  DOI: 10.3969/j.issn.1006-6535.2025.03.020

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To address the issue of easy petal tooth fracture and short service life of the cardan universal joint for screw drilling tools under complex downhole load conditions, optimization schemes for petal tooth cross-sectional structures in the form of trapezoidal, rectangular, or fan-shaped were proposed. Based on fracture theory and numerical simulation methods for crack propagation, a virtual crack propagation simulation physical model was established. The distribution patterns of equivalent stress and crack stress intensity factors in the crack area were studied for the original and optimized structures when cracks were located on the left (zone Ⅰ), middle (zone Ⅱ), and right (zone Ⅲ) of the petal tooth root. Furthermore, field tests were conducted to verify the effectiveness of the optimized structure. The study shows that when cracks were distributed in zones Ⅰ,Ⅱ, or Ⅲ, the optimized structure could reduce the equivalent stress and stress intensity factor at the crack tip, with the average crack propagation capability decreasing by 18.6%, 16.2%, and 12.1% respectively. Among them, the rectangular cross-section reinforcement structure was the optimal solution. When cracks were located in thezone Ⅱpetal tooth root, the stress at the crack tip was the highest, and the propagation capability was the strongest; when cracks were located in the zone Ⅰ petal tooth root, the stress at the crack tip was the lowest, and the crack propagation capability was the weakest; when cracks were located in the zone Ⅱ petal tooth root, the propagation capability was between the two. Field test results verified the reliability of the optimized structure, with an average service life increase of 18.77%. This study can provide a reference for the life prediction and structural optimization of cardan universal joint petal teeth.