Table of Content

25 April 2026, Volume 33 Issue 2

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Summary

Research progress and development trends of bridging lost-circulation materials

ZHANG Jinfa, FENG Yongcun, MU Xiaolong, HE Bing, HE Qi, DENG Jin′gen, WANG Weiqi

2026, 33(2):  1-11.  DOI: 10.3969/j.issn.1006-6535.2026.02.001

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Bridging lost-circulation technology is one of the main technologies currently used to control lost circulation;however,under the complex geological conditions of unconventional oil and gas reservoirs,conventional bridging lost-circulation materials show poor adaptability,have a low one-time plugging success rate,and may cause repeated and worsening losses.Therefore,the mechanism of bridging plugging was analyzed,the technical characteristics and development status of various bridging lost-circulation materials were reviewed,and key future research directions were proposed.The results indicate that high-stability composite bridging lost-circulation materials can solve the problem of plugging-layer failure;research should focus on developing high-temperature curable materials and optimizing injection processes.Self-adaptive loss-channel bridging materials can address the mismatch between material size and fracture width;field tests and application promotion should be strengthened.Removable(unplugging)bridging lost-circulation materials can overcome the difficulty of balancing reservoir plugging and reservoir protection;there remains room for improvement in acid-solubility evaluation,acidizing procedure optimization,and regulation of degradability.Biodegradable and environmentally friendly bridging lost-circulation materials have unique environmental advantages,but further research is still needed on optimizing degradation rate and on characterization and control of degradation degree.The results provide technical references for selecting field lost-circulation materials and indicate development directions for bridging lost-circulation materials.

Geologic Exploration

Multi-vintage seismic data fusion processing and implications for high-density acquisition design

HOU Hailong, ZHANG Qing, XIN Tianliang, LI Zhongqian, LI Dongan, WU Liqing, FAN Weihua

2026, 33(2):  12-22.  DOI: 10.3969/j.issn.1006-6535.2026.02.002

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In exploration of ultra-deep small-scale karst fractured-vuggy reservoirs,conventional three-dimensional seismic data often have overly large bin sizes,which makes it difficult to identify effective signals such as diffraction and scattering waves,and cannot meet the requirements for refined characterization of fractured-vuggy bodies.Therefore,seismic data fusion processing technology was applied.Based on two three-dimensional seismic acquisitions in the Aiding 6 Wellblock of the Tahe Oilfield,geophysical attribute differences between datasets acquired in different years were systematically analyzed,including polarity,phase,time shift,frequency,energy,azimuth,and bin grids.Bin-normalization and offset-fusion processing were applied to develop a selective fusion processing technique.The results show that prestack fusion of seismic data can significantly enhance spatial sampling density and improve recognition capabilities for small fractured-vuggy bodies and small faults;after fusion,coverage increases by approximately 20%,signal-to-noise ratio increases by more than 10%,and recognition rate increases by 20%.Through selective fusion processing,near-offset data are applied to characterize small geologic bodies,while mid-and far-offset data support velocity analysis,thereby achieving effects comparable to high-density acquisition and full-offset imaging.This provides a degraded technical basis for secondary seismic acquisition without full-offset acquisition.This study provides a basis for optimizing observation-system design and guides secondary acquisition to obtain appropriate offset data,which can effectively reduce acquisition costs and has important practical significance for promoting efficient seismic exploration.

Fault development characteristics and multi-phase tectonic cycle evolution of Jinghe Oilfield,southern Ordos Basin

QI Xiaolong, TANG Daqing, WANG Weilong, LEI Tao, JIA Huichong, QI Rong, ZHANG Wei, AN Chuan

2026, 33(2):  23-33.  DOI: 10.3969/j.issn.1006-6535.2026.02.003

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Jinghe Oilfield is located at the junction of three major structural units of the Ordos Basin.It has undergone multiple phases of tectonic activity,resulting in extremely complex fault development.To better understand the fault structural characteristics and evolutionary processes in Jinghe Oilfield and their impact on hydrocarbon exploration,a systematic study was carried out based on detailed structural interpretation of 3D seismic data,integrated with the basin tectonic evolution characteristics and regional geodynamic setting.The fault types,geometric characteristics,differential activity patterns,and genetic evolution of faults in Jinghe Oilfield were comprehensively analyzed.The results show that the study area is mainly characterized by strike-slip faults and normal faults,with clear stratified and segmented differences in fault activity.From bottom to top,an oblique extensional and right-lateral strike-slip fault system has developed in the Lower Paleozoic;a fault system with weakly inherited activity along the main faults in the Upper Paleozoic;and a left-lateral strike-slip inversion fault system in the Mesozoic.The faults in Jinghe Oilfield have undergone five major phases of activity,with the primary active periods being the Caledonian and Yanshan-Himalayan orogenies.The main hydrocarbon accumulation period is the middle-late Early Cretaceous,which aligns well with these fault activities.The Yanshanian orogeny reactivated strike-slip faults in the study area,connecting the Chang 7 source rock interval with the underlying Chang 8 reservoir,which is of great significance for hydrocarbon migration,accumulation,and differential enrichment.This study provides theoretical reference for research on the fault system of Jinghe Oilfield and for guiding exploration practice.

Characteristics and main controlling factors of a pore-type limestone reservoir of the Changxing Formation on the Mianyang-Guang′an shallow-water shelf in central Sichuan

LIN Yi, HE Kailai, CHEN Xiao, LI Yang, LI Yiwen, XU Shiyu, ZHAO Chunni, SHAN Shujiao

2026, 33(2):  34-43.  DOI: 10.3969/j.issn.1006-6535.2026.02.004

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The Changxing Formation on the Mianyang-Guang′an shallow-water shelf in central Sichuan is rich in oil and gas resources and can serve as an important successor exploration area.The Changxing Formation primarily develops pore-type limestone reef-shoal reservoirs,which is a new type of deep carbonate reservoir.In view of the insufficient understanding of the reservoir characteristics, the lower limits of physical property,and main controlling factors of the Changxing Formation limestone reservoir,a study was carried out based on drilling data and a variety of analytical methods including core and thin-section observation,capillary pressure analysis,gas-water infiltration tests,and production capacity simulation.The basic reservoir characteristics,the lower limits of physical properties,the pore preservation mechanism of the limestone reservoir,and the main factors controlling reservoir development were investigated.The results show that reservoir rocks in the study area are mainly sponge-framework reef limestone and bioclastic limestone,with pore space do minated by organism cavity pores,intergranular dissolution pores,and intragranular dissolution pores.Overall,the reservoir exhibits moderate porosity and low permeability,with localized zones of high porosity and permeability.Multiple experimental methods cross-validated that the effective porosity lower cutoff for the Changxing Formation limestone reservoir in central Sichuan is 2.10%,the water saturation upper limit is 48.9%,and the permeability lower cutoff is 0.010 mD.The reef-shoal body provides the material basis for reservoir development,and a relatively closed overpressure diagenetic system is key to preserving pores in the deep Changxing Formation reef-shoal complex limestones.Furthermore,during early hydrocarbon charging,the emplacement of hydrocarbons reduces the nucleation sites for cement growth,which is one of the important conditions for pore preservation.This study provides a theoretical basis for the development of deep pore-type limestone reservoirs in the Sichuan Basin.It also offers reference for the identification of effective reservoirs and the estimation of natural gas geological reserves in the deep Changxing Formation reef-shoal gas reservoirs of central Sichuan.

Microscopic pore structure characteristics and genesis of coal-measure tight sandstone reservoirs in Longtan Formation of Qianxi Area

HUANG Zhengxin, ZHANG Xiaoli, YANG Zhaobiao, HE Jinxian, WU Meng, CAO Wenjie, LI Juhao

2026, 33(2):  44-53.  DOI: 10.3969/j.issn.1006-6535.2026.02.005

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Tight sandstone gas exploration in the Qianxi Area is still at the preliminary stage,and no large scale tight gas reservoir has been found so far.Given the insufficient understanding of the pore structure and genesis of the coal-measure tight sandstone reservoirs of Longtan Formation in this area,thin section analysis,X-ray diffraction,scanning electron microscopy(SEM),high pressure mercury intrusion,and negative pressure porosity-permeability experiments were conducted to systematically investigate the pore structure,porosity-permeability relationships,brittleness characteristics,and the effects of diagenesis and tectonism on reservoir development.The results show that Longtan Formation sandstones in Qianxi Area are typical tight sandstone,with an average porosity of 4.14% and an average permeability of 0.032 8 mD,corresponding to ultra-low porosity and ultra-low permeability reservoirs.Pore types are mainly primary pores,secondary pores,organic-matter pores, and microfractures.Secondary pores consist predominantly of intragranular dissolution pores and intergranular dissolution pores,and microfractures account for up to 35%,greatly influencing reservoir storage and permeability.Reservoir development is controlled by both diagenetic and tectonic processes:compaction is intense and cementation is significant,whereas microfractures formed by tectonic activity play a decisive role in reservoir performance.The upper member sandstones of Longtan Formation exhibit better reservoir properties than the lower member,and tight sandstones from deltaic deposits exhibit better reservoir properties than those from lagoon-tidal flat deposits.This study provides important guidance for the exploration and development of coal-measure tight gas in this area.

Seismic fracture prediction technology based on multi-pixel attribute fusion for deep coal-measure gas reservoirs

ZHANG Guowei, XIE Huiwen, LI Ling, ZHAO Tiantian, HOU Xinyu, SHEN Lin

2026, 33(2):  54-63.  DOI: 10.3969/j.issn.1006-6535.2026.02.006

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Fractures are the main flow conduits in coal reservoirs,and the accuracy of their prediction directly affects development outcomes.Targeting the issues of low signal-to-noise ratio of seismic data,great difficulty and low accuracy in post-stack fracture identification for the Kizilnur Formation coal reservoirs in Dibei Area of Tarim Basin,a multi-attribute pixel-level fusion technique was applied to comprehensively identify coal reservoir fractures.Considering the fracture-controlling effect of structural deformation intensity,a nonlinear relationship model was established among fault zones under structural control,structural curvature,and fracture density.The research shows that the multi-attribute fusion volume is more sensitive to subtle deformation and small faults,predicting fracture spatial distribution with little noise influence and yielding clear sheet-like features.Fractures in Dibei Area exhibit significant structural zonation:fracture density grows exponentially with structural curvature;high-angle tensile fractures predo minantly develop in the core of structural uplifts,with apertures of 20-35 μm;the deviation between dominant fracture orientations and the direction of maximum curvature is less than 10°.This fracture prediction method has guided subsequent well deployment in Dibei Area;the correspondence between predicted fractures and image log results reaches about 80%,fully demonstrating the method feasibility in guiding fracture prediction and optimizing drilling deployment,providing critical support for efficient development of deep coal-rock gas.

Reservoir Engineering

Feasibility and key technologies for synergistic development of steam huff-and-puff and steam flooding in shallow-layer high pour-point oil reservoirs

WANG Guodong, YANG Xingchao, FENG Tian, LI Xin, JIA Dalei

2026, 33(2):  64-71.  DOI: 10.3969/j.issn.1006-6535.2026.02.007

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In response to the increased difficulty in development and production stabilization caused by low formation temperature and low formation pressure in shallow-layer high pour-point oil reservoirs,a comparative study was conducted using one-dimensional and two-dimensional scaled physical simulation apparatuses to evaluate three development methods:water flooding,cyclic steam stimulation,and steam flooding assisted by cyclic steam stimulation.The feasibility of cyclic steam stimulation and steam flooding assisted by cyclic steam stimulation was verified,and the optimal development mode was determined.The results show that water flooding exhibits critical deficiencies,including low recovery efficiency,pronounced risk of water channeling,and deterioration of crude oil properties.Cyclic steam stimulation effectively enlarges the reservoir heating radius,achieving a stage oil displacement efficiency exceeding 40% and a recovery factor greater than 25%.Under the steam flooding plus cyclic steam stimulation assisted development mode,the ultimate recovery factor can exceed 50%,while the produced crude oil properties remain stable.During the development process,it is necessary to simultaneously ensure adequate heat supply and energy replenishment to maintain the formation temperature consistently above the wax appearance temperature of the crude oil.This study not only fills a gap in dedicated research on the development of shallow-layer high pour-point oil reservoirs,but also provides reliable experimental evidence and key technical support for the efficient development of similar reservoirs.

Effect of CO₂ pre-fracturing on fracture networks in shale oil reservoirs

CUI Chuanzhi, QIAN Yin, WU Zhongwei, WANG Junkang, ZHANG Shiming, LYU Qi, CHENG Ziyan

2026, 33(2):  72-78.  DOI: 10.3969/j.issn.1006-6535.2026.02.008

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To investigate the influence of CO₂ pre-fracturing on the scale and morphology of fracture networks in shale oil reservoirs,a three-dimensional geological model that includes natural fractures was constructed using Petrel software,based on the reservoir characteristics of a shale oil formation in the Dongying Sag.By using the fracture network volume and network complexity as evaluation indices of fracturing effectiveness,analysis was made on the impact of CO₂ pre-injection volumes on these indices under different natural fracture densities and horizontal stress differences.The results showed that natural fracture density had little effect on fracture network volume;increasing CO₂ injection volume first reduced and then increased the network volume,with a sharp increase occurring once the CO₂ injected per stage exceeded about 120 t which point the low viscosity and high diffusivity of CO₂ dominated.Higher natural fracture density led to higher network complexity;in reservoirs with well-developed natural fractures,increasing CO₂ injection caused network complexity to rise and then level off.Horizontal stress difference significantly affected network complexity:branching fractures formed more readily under low stress-difference conditions.This study provides theoretical guidance for designing horizontal-well CO₂ pre-fracturing in shale oil reservoirs.

Mesoscopic seepage characteristics of high-temperature tight sandstone based on GBM-FEM

LI Gao, SU Tengyue, YANG Xu, ZHANG Yi, LI Hongtao, WANG Yanmin

2026, 33(2):  79-88.  DOI: 10.3969/j.issn.1006-6535.2026.02.009

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To reveal the mesoscopic seepage behavior of tight sandstone after thermal treatment,laboratory electric heating experiments on tight sandstone were combined with a heterogeneous grain-flow model and finite element method(GBM-FEM)to investigate the generation of thermally induced microcracks,changes in seepage pathways,and permeability variations in tight sandstone after heat treatments at 300-900 ℃,clarifying the evolution of thermally induced microcracks and seepage behavior at the mesoscopic level.Results show that after lower-temperature treatment,uneven thermal expansion between minerals causes the development of microcracks,providing a small number of high-permeability points;the pressure drop tends toward linear,and flow paths are mainly through pore throats.As temperature increases,intragranular cracking turns significant,high-permeability points are widely distributed,and pressure presents sudden-drop phenomena,and microcrack pore-throat seepage becomes pro minent.Thermally induced microcracks exhibit stage-wise nonlinear growth with increasing temperature,developing first as intergranular microcracks followed by intragranular microcracks;their heterogeneous propagation leads to transformations in mesoscopic seepage pathways.700 ℃ is the threshold at which intragranular microcracking and permeability sharply increase.These findings provide a theoretical basis for optimizing parameters in tight sandstone reservoir wellbore thermal stimulation techniques.

Molecular dynamics simulation of microemulsion phase behavior

ZHOU Zhijun, ZHANG Qi, YI Xi, LI Juntao, WANG Shuyang, WANG Chenzhu

2026, 33(2):  89-99.  DOI: 10.3969/j.issn.1006-6535.2026.02.010

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In response to the insufficient understanding of phase behavior regulation-control mechanisms of microemulsions in oil displacement processes,a molecular structure model of an C₈H₁₈-SDBS/C₄H₁₀O-NaCl solution was constructed using Materials Studio based on molecular dynamics principles.Systematic simulations were conducted to investigate the wetting mechanism and interfacial behavior of microemulsions.Through molecular dynamics,iso-butanol(C₄H₁₀O)and sodium dodecylbenzenesulfonate (SDBS) ratios were screened to find the optimal compatibility and lowest total energy of the system.The adsorption configuration,spatial distribution,interaction energy,and radial distribution function were then analyzed.The results show that the minimum binding energy of the system C₈H₁₈-SDBS/C₄H₁₀O-NaCl is -68.21 kcal/mol,corresponding to a composition of 8.0%C₄H₁₀O+0.5%NaCl+4.0%SDBS,at which the system is the most stable;NaCl has an insignificant effect on system stability.In terms of wetting behavior,changes in iso-butanol(C₄H₁₀O)concentration induce phase transitions.At 6.0%~7.5% iso-butanol(C₄H₁₀O),oxygen atoms primarily interact with the hydrophilic head of SDBS,rendering the system water-wet;at 8.0%,oxygen interacts equally with hydrophilic and hydrophobic groups,making the system neutral;at 8.5%,oxygen preferentially associates with hydrophobic groups,rendering the system oil-wet.The microemulsion formed with 8.0% iso-butanol(C₄H₁₀O)yields the best results in reducing interfacial tension and modulating wettability:it can improve microscopic oil displacement efficiency,expand macroscopic sweep volume,increase the recovery efficiency by 31.3 percentage points,and reduce water cut by 20.2 percentage points.This study provides important guidance for optimizing microemulsion formulations for oil displacement and enhancing oil recovery.

Capacity expansion experiment of reconstructing gas storage in gas reservoirs with edge and bottom water

ZHANG Guangdong, JIA Jiqiang, ZENG Daqian, MO Chaoping, ZHANG Guangquan

2026, 33(2):  100-108.  DOI: 10.3969/j.issn.1006-6535.2026.02.011

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In response to the problem that the drainage and capacity expansion mechanism of converting gas reservoirs with edge and bottom water into gas storage and its main influencing factors are unclear,taking the Wen 24 Gas Reservoir as an example,an experimental evaluation method for multi-cycle injection-production drainage and capacity expansion in gas reservoirs with edge and bottom water converted into gas storage was constructed.Experiments on the effects of gas injection rate,formation dip angle and reservoir physical properties on multi-cycle injection-production drainage and capacity expansion in gas reservoirs with edge and bottom water were carried out,revealing the mechanism of injection-production drainage and capacity expansion in gas reservoirs with edge and bottom water.The results show that the capacity expansion rate decreases by 2.550 percentage points as the gas injection rate increases from 0.3 mL/min to 0.9 mL/min;when the formation dip angle increases from 0°to 60°,the capacity expansion ability increases by 7.110 percentage points;when the reservoir permeability increases from 25 mD to 107 mD,the capacity expansion rate increases by 7.229 percentage points;in the repeated injection-production stage,the increment in capacity expansion rate in the first two cycles accounts for 85% of the entire stage.Compared with the huff-and-puff method,the injection-production method increases the capacity expansion rate by 2.787-3.978 percentage points.The gas-drive drainage stage has the most significant capacity expansion effect,but as the gas injection rate increases,the capacity expansion efficiency gradually decreases;the injection-production method is more suitable for the conversion of gas reservoirs with edge and bottom water into gas storage.These results have important guiding significance for understanding the capacity expansion mechanism and parameter optimization of converting gas reservoirs with edge and bottom water into gas storage.

Fault-stability laws of underground gas storage facilities based on fluid-solid coupling

XU Haitao, LIU Kang, YU Xuefeng, CHEN Guoming, SU Yunhe, WANG Chengxin, MA Zhe

2026, 33(2):  109-116.  DOI: 10.3969/j.issn.1006-6535.2026.02.012

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During injection-production operations of underground gas storage facilities,frequent pressure fluctuations disturb the in-situ stress field and may induce fault reactivation,seriously threatening sealing integrity.To solve this problem,a simulation model of underground gas storage in a depleted gas reservoir was established based on fluid-solid coupling mechanisms;the dynamic evolution of formation parameters under cyclic injection-production was analyzed;and the impacts of injection-production rate and injection-production location on fault stability were investigated.Results show that during injection-production of underground gas storage,pore pressure and effective stress at the fault location corresponding to the injection-production well change significantly under cyclic injection-production.The reservoir top and the fault-projection position corresponding to the injection-production well constitute high-risk areas prone to fault slip.Higher injection-production rates and smaller distances between injection-production locations and the fault lead to greater pore-pressure increase in the reservoir,more likely disturbing the stress field near the adjacent fault and increasing the risk of fault slip.This study provides a theoretical basis for fault-stability evaluation and optimization of injection-production processes for underground gas storage facilities.

A new method for calculating temperature distribution at the steam-chamber front in SAGD considering a mobile oil drainage surface

HE Xujiao, PANG Zhanxi, XUE Duan, ZHANG Chengguang, HAN Ruijing

2026, 33(2):  117-125.  DOI: 10.3969/j.issn.1006-6535.2026.02.013

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To overcome the difficulty in quantifying heat-transfer laws and temperature distribution at the steam-chamber front during SAGD in heavy-oil reservoirs with top water,based on a SAGD heat-transfer model and according to the change in crude-oil flowability before and after the heavy-oil temperature inflection point,the oil zone outside the steam-chamber front was divided into two regions:mobile oil and immobile oil.Based on the one-dimensional transient heat-conduction equation and moving boundary conditions,a new model was established for calculating temperature distribution at the steam-chamber front during SAGD,and a calculation method was further developed for the critical oil-zone thickness between the steam chamber and the top-water layer as well as the nitrogen insulation-layer thickness.Results show that when Du 84 Block in the Liaohe Oilfield has been producing with SAGD(steam assisted gravity drainage)for 15 years,the critical thickness between the top of the steam chamber and the bottom boundary of the top-water layer is 17.60 m;when the nitrogen-layer thickness reaches 3.29 m,the nitrogen insulation measure can maintain the temperature at the top of the oil zone such that it remains lower than the temperature inflection point.This method can provide theoretical guidance for long-term effective development of heavy-oil reservoirs with top water and for applying SAGD-assisted fluid stimulation technologies.

Drilling & Production Engineering

Fracture propagation patterns during hydraulic fracturing under different helical perforation parameters in shale oil reservoirs

ZOU Linhao, SHANG Litao, LI Bingjun, SU Yi′nao, JIANG Tianxiang, LI Wei, ZHAO Huan, WANG Jianbo

2026, 33(2):  126-134.  DOI: 10.3969/j.issn.1006-6535.2026.02.014

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Hydraulic fracturing plays a critical role in oil and gas reservoir development,and perforation parameters significantly affect the morphology and propagation of fractures in shale oil reservoirs.To optimize perforation parameters and improve stimulation effectiveness,laboratory true triaxial hydraulic fracturing experiments were conducted to investigate the effects of perforation parameters on fracture morphology,propagation patterns,and breakdown pressure.The results show that perforation phasing has a significant effect on fracture initiation and propagation.When the perforation phasing is 90°,the hydraulic fracture area is the largest,and a complex“丰(feng)”-shaped fracture surface is prone to form;when the perforation phasing is 60°,the fracture area is the smallest,and effective interlayer-crossing fractures are difficult to form.Increasing the number of perforations helps improve fracture complexity and the capability of interlayer propagation.With increasing perforation phasing,the stress superposition and interference effects between perforation tunnels weaken,and the breakdown pressure increases gradually;with increasing number of perforations,the breakdown pressure shows an overall decreasing trend.For hydraulic fracturing of shale oil reservoirs,it is recommended to adopt a perforation scheme with 90° perforation phasing and a high number of perforations under the premise of ensuring wellbore integrity.This study provides a theoretical basis for optimizing fracture propagation and morphology in shale oil production.

Application of a temperature-resistant gel plugging system in steam flooding heavy oil reseruoir

YAN Ruisheng

2026, 33(2):  135-142.  DOI: 10.3969/j.issn.1006-6535.2026.02.015

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To tackle the problems of frequent steam channeling,shrinkage of steam swept volume,and low thermal-energy utilization caused by formation heterogeneity during heavy-oil steam flooding,a synergistic plugging technology combining temperature-resistant gel particles and nano-micron temperature-resistant gel was applied,and a functional plugging system with temperature resistance up to 260 ℃ was developed.Results show that the temperature-resistant gel particles have excellent thermal stability,strong deformability,and thermal coalescence behavior,allowing targeted plugging of large pore channels and high-permeability channels.The nano-micron temperature-resistant gel has low initial viscosity,strong mobility,and high plugging strength;it gels rapidly at high temperature and can effectively fill small channeling pathways.By injecting gel particles first to establish a plugging framework and then injecting nano-micron gel to fill gaps,a combined process achieves synergistic and efficient plugging of high-permeability and steam-channeling pathways.This technology was applied to a steamflood pilot well group in the Qi 40 Block of the Liaohe Oilfield.After plugging,no steam channeling occurred between steam-injection wells and surrounding production wells,and the staged cumulative incremental oil was 1 085 t,significantly improving steam utilization and thermal-recovery performance.This technology can provide effective technical support for managing steam channeling in similar heavy-oil reservoirs.

Study on the deterioration behavior of shale mechanical strength under hydration

SHAO Xianyu, WANG Ke, WANG Zhiqiang, ZHAO Lingyun, LI Zhixuan, TAN Yongsheng, GAO Wei

2026, 33(2):  143-150.  DOI: 10.3969/j.issn.1006-6535.2026.02.016

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In response to the insufficient understanding of rock mass hydration on mechanical strength in underground engineering,a combined approach of rock mechanics experiments and numerical simulation was used,with Longmaxi Formation shale as the study object.Uniaxial compression tests and Abaqus finite element simulations were conducted on rock samples after different soaking times to investigate the impact of hydration on shale mechanical properties and its failure mechanism.The results show that hydration weakens the shale cohesion,thereby significantly reducing its peak stress and elastic modulus.Moreover,as hydration time increases,the failure mode of the rock transitions from brittle to plastic.Meanwhile,there exists a critical point in the deterioration of shale mechanical strength under hydration:the post-deterioration mechanical strength is about 69.19% of that in dry conditions.The findings are of great significance for understanding the hydration-induced mechanical deterioration behavior of underground engineering rock masses and guiding stability evaluations for engineering projects.

Optimization and application of high-flow-rate heavy-oil electric submersible pumps in the Tahe Oilfield

SONG Zhengcong, HAN Guoqing, XIE Xiang

2026, 33(2):  151-158.  DOI: 10.3969/j.issn.1006-6535.2026.02.017

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With the promotion and application of flow potential regulation technology in the Tahe Oilfield,high-flow-rate heavy-oil electric submersible pumps have exhibited high failure rates such as motor lead cable burnout and protector failure.To address these issues,a three-dimensional temperature-field finite element simulation method was applied.By optimizing the topology of permanent magnet motors and the heat-dissipation structure of motor heads,heat accumulation was reduced and temperature resistance of motor lead cables was improved.Through physical isolation design and labyrinth flow-path design,and leveraging the high density and strong stability of heavy-oil isolation fluids,a heavy-oil protector with a dynamic“liquid piston”was designed to achieve physical isolation between heavy oil and the capsule chamber,thus avoiding protector capsule failure caused by direct contact with heavy oil.Through optimization of the motor and protector designs,the adaptability of high-flow-rate heavy-oil electric submersible pumps to flow potential regulation technology was improved,providing technical support for promoting this technology in the Tahe Oilfield.

Numerical simulation of lost-circulation fracture initiation in collapsed wellbores

LI Shuai, XU Jiangwen, WANG Mingxing, GONG Jie, CHEN Xi, FU Haifeng, YAN Xingming, QIAN Fengxue

2026, 33(2):  159-165.  DOI: 10.3969/j.issn.1006-6535.2026.02.018

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The collapse pressure of an open-hole wellbore and the initiation pressure of lost-circulation fractures directly determine the safe mud weight window during drilling.In light of the limitations of traditional lost-circulation pressure calculation methods under collapsed non-circular borehole conditions,as well as the neglect of borehole size effects,the displacement discontinuity method and a dual criterion(tensile strength and fracture toughness)were used to establish a numerical model,clarifying the characteristics of lost-circulation pressure variation for both circular and non-circular“cat ear”collapsed boreholes.The multiple initiation positions and deviation characteristics of lost-circulation fractures in elongated collapsed boreholes and their effects on lost-circulation pressure were also investigated.Numerical simulation results indicate that the lost-circulation pressure for both circular and non-circular“cat ear”collapsed boreholes exhibits a size effect.However,the lost-circulation pressure of a purely“cat ear”-shaped borehole does not differ significantly from that of a purely circular borehole.For small-sized boreholes,the lost-circulation pressure is governed by fracture toughness and is markedly influenced by size,whereas for large boreholes,fracture initiation is governed by tensile strength and the size effect is weaker.As the “cat ear” borehole elongates and the local radius at the initiation point increases,the mud weight window gradually widens.Axial elongation of the “cat ear” borehole causes lost-circulation fractures to deviate from the maximum principal stress direction,leading to four fracture initiation points around the borehole and the formation of an X-shaped lost-circulation fracture pattern.This study provides reference for addressing lost-circulation issues in collapsed open-hole wellbores during drilling.

Intelligent dewatering and gas production technology for medium-shallow coalbed methane wells and its application

LI Jinping, ZHAO Hengping, WANG Ruiqi, MENG Yanjun, HE Risheng, PAN Jun, WEN Lianhui, GOU Ziqi

2026, 33(2):  166-174.  DOI: 10.3969/j.issn.1006-6535.2026.02.019

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Coalbed methane is complex in terms of geological conditions,and the on-site manual management mode largely constrains the effective realization of gas production potential in coalbed methane wells,making economic development difficult.Intelligent dewatering and gas production technology is one of the important approaches to reduce cost and improve efficiency,and to enhance large-scale development benefits for coalbed methane wells.During dewatering and gas production of medium-shallow coalbed methane wells,there are challenges such as the lack of quantitative algorithms for production regimes,difficulty in coordinating production regimes with reservoir energy and gas-water production and supply,and difficulty in continuous dewatering due to coal fines-induced pump sticking.Therefore,full life-cycle intelligent dewatering and gas production technology and intelligent coal fines control technology were developed,and field application effects were introduced using the Yunlian Muai coalbed methane field as an example.The results show that the intelligent dewatering and gas production technology for medium-shallow coalbed methane wells embeds quantitative algorithms for production regimes,and divides the dewatering and production process into six stages:equipment break-in stage,single-phase water stage,casing pressure buildup stage,pressure-controlled production enhancement stage,stable production stage,and decline stage.Corresponding system functions are invoked stage-by-stage for intelligent control,enabling quantitative,intelligent,and refined management throughout the full life cycle.For the problem of coal fines-induced pump sticking,real-time monitoring and early warning of parameters such as bottomhole flowing pressure and torque are used to intelligently identify coal fines in the wellbore;combined with an intelligent well-washing technology without moving the tubing string,refined management of flowing pressure during well washing is achieved,effectively solving production challenges caused by coal fines-induced pump sticking.This intelligent technology yields significant cost reduction and efficiency improvement,and achieves coordinated unity of low cost,high efficiency,high quality,and refined and intelligent management,providing technical references for efficient coalbed methane development.