Table of Content

25 December 2025, Volume 32 Issue 6

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Summary

Research progress on air-space-ground-well integrated monitoring technology for CO₂ leakage in geological sequestration

SUN Yankun, SUN Tianyu, ZHU Tianyuan, LONG Tao, ZHOU Liangchang, PENG Peng

2025, 32(6):  1-13.  DOI: 10.3969/j.issn.1006-6535.2025.06.001

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As a key component of CCUS technology,CO₂ geological sequestration leakage risk isdirectly tied to storage and environmental safety.Systematic research on identifying multi-medium leakage pathways and coordinated monitoring technology is crucial to ensure the long-term reliability of carbon storage projects.Accordingly,based on potential leakage mechanisms in typical storage media(depleted oil/gas reservoirs,deep saline aquifers,deep coal seams) a systematic review was made concerning air-space-ground-well integrated monitoring technologies.On this basis,a multi-scale coordinated monitoring framework and a machine-learning-driven data synchronization analysis system were established,integrating airborne and satellite networking,multi-parameter surface data fusion,and three-dimensional subsurface well monitoring.The results indicated that the integrated air-space-ground-well monitoring system could achieve comprehensive multi-parameter detection and early warning of CO₂ leakage;through multi-source data fusion and intelligent analysis,the accuracy and timeliness of CO₂ leakage detection were greatly improved,providing tailored monitoring solutions for different geological storage conditions.This study presents a smart monitoring theoretical framework and technical approach for carbon sequestration aligned with carbon-neutrality goals,offering important scientific basis and technical support for the safe implementation and standardization of large-scale CCUS projects.

Research progress on hydrogen donors for in-situ heavy oil upgrading

LI Jingjing, WANG Piaoyang, YANG Zhi, TANG Xiaodong, YANG Fuxiang, CAO Chenglong

2025, 32(6):  14-21.  DOI: 10.3969/j.issn.1006-6535.2025.06.002

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In-situ heavy oil upgrading is one of the efficient development techniques for reducing heavy oil viscosity and improving oil quality.In this framework,a key research direction is to develop industrial hydrogen donors with strong hydrogen-supplying capability,abundant availability,reasonable prices and environmental friendliness, in addition to developing efficient catalysts.Investigation was conducted on the mechanisms and application progress of novel hydrogen donors-including inorganic, organic, biomass-based sources-used both at home and abroad,and assessment was made on the applicable conditions of each hydrogen donor in in-situ heavy oil upgrading.The results indicated that in the subcritical water conditions of steam-injected heavy oil recovery,heavy oil molecules containing aliphatic hydrogen or active C-H bonds could release hydrogen through water-gas shift reactions with water;however,due to limited operating temperatures,the hydrogen-supplying capacity remained constrained.Alkanes,alkyl aromatics,and distillates,although effective as organic hydrogen donors, were costly and thus impractical for heavy oil recovery.In contrast,biomass-derived hydrogen donors(e.g.from plants and algae)had more obvious applicable advantages due to their abundant raw materials and carbon-reduction potential.Using the intrinsic hydrogen in renewable biomass as a donor is expected to be an important direction for enhancing future heavy oil upgrading technologies.This study has important implications for promoting green,low-carbon heavy oil development,reducing carbon emissions,and improving oilfield development efficiency.

Geologic Exploration

Dynamic simulation of ultra-deep fault-controlled fracture-vuggy carbonate hydrocarbon accumulation processes in Shunbei Area,Tarim Basin

LIU Yazhou, HUANG Cheng, ZENG Jianhui, HAN Jun, LONG Hui, ZHANG Sheng, LIU Chang, LIAO Wenhao

2025, 32(6):  22-32.  DOI: 10.3969/j.issn.1006-6535.2025.06.003

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The Shunbei Area of the Tarim Basin is abundant in ultra-deep hydrocarbon resources,however,the spatiotemporal correlation of the geological conditions for hydrocarbon accumulation is complex and not well understood.Therefore,by analyzing testing data and using basin modeling techniques,the processes of hydrocarbon generation,migration and accumulation in the Shunbei Area were reproduced;the causes for variability in hydrocarbon property were investigated;the mechanisms of ultra-deep hydrocarbon migration-accumulation and the reservoir-formation models were revealed.The results indicated that the Middle-Late Caledonian and Late Hercynian were the critical periods for hydrocarbon migration and accumulation,whereas during the Himalayan period,hydrocarbon reservoirs were reworked and redistributed.Three hydrocarbon-generation patterns developed in the source rocks of the Shunbei Area,namely,an oil-rich/gas-poor double-peaked pattern,a balanced oil-gas double-peaked pattern,and a gas-rich/oil-poor double-peaked pattern.Strike-slip faults served as the primary migration pathways.The hydrocarbon volumes in sub-salt,inter-salt,and supra-salt layers exhibited theinversely-proportioned relationship of"one wanes,the other waxes":the Xiaoerbulake Formation and Sayarik Formation,being closer to source rocks,preferentially experienced migration and accumulation,while low-upwelling zones acted as transfer stations for hydrocarbon re-migration.Laterally,the oil and gas fields in the Shunbei Area were controlled by the main fault belts and exhibited a belt-like distribution.Vertically,the main fault zones connected to source rocks and branched upward;the greater the fault activity was, the more developed was the fracture-vuggy system.Within the same fault zone,multi-stage mixed hydrocarbon charging was the dominant factor causing variations in hydrocarbon properties at different locations.Overall, the reservoirs in the Shunbei Area were characterized by "multi-source relay hydrocarbon supply,dominant fault-controlled migration and multi-phase mixed charging accumulation".This study provides a methodological reference for future hydrocarbon exploration in the Shunbei Area.

Aptian unconformity characteristics and their controlling role on petroleum reservoirs in the South Gabon Basin

LI Haibin, HUANG Jianliang, REN Yan

2025, 32(6):  33-39.  DOI: 10.3969/j.issn.1006-6535.2025.06.004

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During the Early Cretaceous Aptian,widespread regional unconformities formed along the mid-South Atlantic rift basins, acting as major hydrocarbon migration pathways.With the South Gabon Basin in West Africa as an example, using seismic, drilling, reservoir data analysis was made on the types, structures and spatial distribution of Aptian unconformities to study their control on petroleum accumulation.Results showed that above and below the unconformity,overlaying anticlines(thrust-related folds)and relict erosional structures developed,respectively.Vertically,a dual-layer structure existed:the upper layer consisted of widely distributed water-conducting sandstones with good properties,high sand fractions and effective sealing by overlying salt, serving as long-distance hydrocarbon migration pathways;the lower layer of semi-weathered sandstones and rapidly varying shales lacked thick weathered clay caps and could not act as effective lateral conduits.These characteristics led to formation of structural-stratigraphic composite petroleum traps in the interior sag,overthrust anticline traps in the central uplift,and faulted traps in the outer sag.This study provides valuable insight for exploration in South Atlantic rift basins.

Multi-stage fracture characteristics and determination of stages in Ordovician carbonate reservoirs of the Tarim Basin

DU He, FENG Jianwei, WAN Dongping, XU Shouyu, XING Huilin

2025, 32(6):  40-49.  DOI: 10.3969/j.issn.1006-6535.2025.06.005

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Aiming at the challenges of deep burial, complex stages and difficulty in quantitative characterization of fractures in Ordovician carbonate reservoirs in the Tarim Basin, taking typical outcrops in northwestern Tarim as research objects, digital outcrop characterization technology was used to systematically identify and describe fractures. Based on fracture occurrence statistics and structural trace analysis, the superposition relationships of multiple fracture sets were analyzed. Through carbon-oxygen isotope analysis, acoustic emission experiments,other testing methods, the main fracture-forming stages and stress field evolution characteristics of outcrop fractures were determined. The study shows that fractures in the northwestern Tarim outcrop area can be divided into multiple sets based on strike: 330°fracture set, 270°fracture set, 250°and 210° fracture sets, 300°and 0° fracture sets, etc. Their formation corresponds to Middle Caledonian, Late Caledonian-Early Hercynian, Late Hercynian-Indosinian, and Himalayan,four main tectonic stages.After comparing the fracture development characteristics of the Halahatang Oilfield, it was clarified that the reservoir mainly develops three stages of tectonic fractures and the quantitative distribution law of multi-stage fractures was revealed. Compared with the fracture parameters interpreted by imaging logging, the average compliance rate reached 80%. The research conclusions confirm the effectiveness of outcrop studies in determining the stages of subsurface reservoir fractures and can provide reliable geological basis for the exploration and development of karst fracture-cavity reservoirs in the Tarim Basin.

Morphology and indicative significance of ternary structural inversion structures in the Doseo Basin

ZHANG Yi, ZHENG Qifang, KONG Lingwu

2025, 32(6):  50-57.  DOI: 10.3969/j.issn.1006-6535.2025.06.006

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Ternary structural inversion structures are one of the most typical structural styles in the Doseo Basin, but research on their geometric characteristics, genetic mechanisms and geological significance remains entirely unexplored. Based on theories of plate tectonics, structural geology, petroleum geology and sedimentology, this study applies techniques such as seismic fine interpretation and structural analysis to investigate the geometric characteristics and geological significance of the ternary structural inversion structures in the Doseo Basin. The results indicate that ternary structural inversion structures can be divided into three types based on boundary convergence degree: bilateral strong convergence type, bilateral weak convergence type, and unilateral convergence type; based on mirror plane morphology, they can be divided into recumbent S-type, sickle-shaped, and approximately straight-line types; tectonic inversion during the Late Cretaceous Santonian and Maastrichtian periods controls the formation of ternary structural inversion structures; the widely developed ternary structural inversion structures throughout the basin clearly indicate that the basin inversion intensity is moderate; on the plane, ternary structural inversion structures are distributed near the Borogop Fault, some are located between the Borogop Fault and the eastern inverted anticline zone I, and on the eastern inverted anticline zone I. These areas all represent significant future exploration targets. The research results have guiding significance for deepening and enriching inversion structural styles and inversion structural theory and provide certain technical support for oil and gas exploration deployment.

Sequence stratigraphic division and reservoir control of the middle-lower Ordovician Yingshan Formation in Shunbei Area,Tarim Basin

TANG Xiaofei, BAO Dian, HAN Changcheng, DAI Jincheng, LIU Lipeng, ZHANG Bowen

2025, 32(6):  58-68.  DOI: 10.3969/j.issn.1006-6535.2025.06.007

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To establish a sequence stratigraphic framework for the middle-lower Ordovician Yingshan Formation on an open-to-restricted carbonate platform in the Shunbei Area of the Tarim Basin,and to investigate how sequence stratigraphy controls favorable reservoirs and to build reservoir models,outcrop,core,well-logging and seismic data were used, third-order sequence boundaries were identified.Upon this,INPEFA(Integrated Prediction Error Filter Analysis)well logging cycle and Dmey wavelet transform were applied to Th/U ratio log curves.Combined with Fischer diagram methods,fourth-order sequences were produced,which enabled classification of reservoir types and characteristics,analysis of their reservoir-control effects,and determination of reservoir development patterns under multiple factors.In the study area,two third-order sequences(SQ1-SQ2)and four fourth-order sequences(YSQ1-YSQ4)were identified.Based on fracture characteristics and depositional context, sequence SQ1 contained more thin interbedded tuffaceous limestone layers and higher dolomite content than SQ2,making it more prone to bed fracturing and reservoir development.Within the fourth-order sequences(YSQ1-YSQ4),four bottom-top reservoir types were identified:fracture reservoirs associated with the main fault,dolomite reservoirs formed by burial or hydrothermal processes,limestone fracture reservoirs controlled by secondary faults,and karst(dissolution-cavity)reservoirs closely linked to penecontemporaneous processes.This study provides a theoretical basis for high-frequency sequence stratigraphy controls reservoirs and clarifies directions for predicting favorable reservoirs.

Evaluation method and influencing factors of brittleness characteristics in low-permeability sandstone reservoirs

FAN Tingen, FU Xiaofei, YANG Renfeng, YANG Erlong, WANG Sheng, PANG Shuyi

2025, 32(6):  69-77.  DOI: 10.3969/j.issn.1006-6535.2025.06.008

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To address the problem that the unclear brittleness characteristics and influencing factors of low-permeability sandstone reservoirs restrict fracturing optimization design, the study takes cores from the Wenchang Formation in the Pearl River Mouth Basin and the third member of the Shahejie Formation in the Bohai Bay Basin as research objects. Using the principle of post-peak energy conservation, the brittleness characteristics and main controlling factors of reservoir rocks were analyzed, and a comprehensive evaluation method was constructed. The study shows that the brittleness of rocks varies significantly across different layers; quartz and calcite promote brittleness, while clay minerals and porosity reduce brittleness; when porosity is greater than 10%, porosity is the main controlling factor (brittleness is generally low) and mineral composition is a secondary factor; when porosity is not greater than 10%, mineral composition is the main controlling factor and porosity has little influence. This study can provide an important basis for fracturing optimization design in low-permeability reservoirs.

Prediction of shale content in tight sandstone reservoirs of the Lower He 8 Member in Jingbian Gasfield

LUO Guanghui, DAI Heng, YU Jie, ZHANG Xiaoli, YANG Yi, LI Yajun, YAN Yuanzi, ZHOU Zhijie

2025, 32(6):  78-85.  DOI: 10.3969/j.issn.1006-6535.2025.06.009

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To address challenges such as complex and variable sandstone types, unclear identification of lithology and effective reservoirs and low accuracy in porosity log interpretation in the tight sandstone reservoir of the Lower He 8 Member of the Upper Paleozoic Shihezi Formation in the Ordos Basin, a prediction model for shale content of these three types of sandstone was established through analysis of the logging response characteristics of quartz sandstone, lithic quartz sandstone and lithic sandstone. The results indicate that the distribution ranges of natural gamma logging values for quartz sandstone, lithic quartz sandstone and lithic sandstone are large, with minimum values of 20.0, 30.0 and 40.0 API respectively;The absolute error of the shale content prediction model is less than 5.0%, indicating reliable prediction accuracy of the model. This achievement can provide technical support for lithology identification and effective reservoir prediction in the study area and also provide reference for calculating shale content and porosity in other complex tight sandstone reservoirs.

Reservoir Engineering

Evaluation of stratigraphic movable water in fluvial channel sandstone gas reservoirs and its impact on recovery

LI Mingqiu, ZHANG Guangdong, YU Peng, WANG Huiqiang, XU Weichong, SHI Erhan, FENG Yan

2025, 32(6):  86-91.  DOI: 10.3969/j.issn.1006-6535.2025.06.010

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During test production in the Sha-1 section of the Tianfu gas field,some wells encountered water,but it remains unclear whether movable formation water is present and how it affects recovery.To address this,study was made on the fluvial channel sandstone gas reservoir of the Tianfu Sha-1 section using laboratory gas-drive-water experiments,analysis of sealed core data and CT scanning to assess reservoir water mobility and movable intervals,clarifying the occurrence state of formation water in the porous medium.We also established a high-temperature high-pressure experimental simulation of movable water′s effect on gas-water two-phase deliverability was to evaluate how movable water influenced recovery.The study showes that the water saturations of three sealed cores(X211, X206, X212)all exceeded the irreducible water saturation of the experimental cores,indicating a coexistence of gas and water in the reservoir;average movable water saturations were 21.31%,18.41% and 7.93% respectively.After gas-drive tests,gas preferentially swept large pores,while formation water mainly occupies small pores-tighter reservoirs retained more water with higher bound-water saturation.At the same decline rate,as water saturation increased,gas recovery decreased,and movable water has a greater impact on low-permeability reservoirs.These results are significant for evaluating movable water and calibrating recovery in similar gas reservoirs.

Low-temperature oxidation patterns and thermodynamics in light oil reservoirs under air injection

LIU Penggang

2025, 32(6):  92-99.  DOI: 10.3969/j.issn.1006-6535.2025.06.011

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Addressing the unclear patterns of low-temperature oxidation(LTO)and high safety risks of conventional air flooding in light oil reservoirs during high-pressure air injection,this study took the Xinjiang X reservoir as an example.Using static isothermal oxidation tube experiments and non-isothermal thermogravimetric analysis(TG/DTG-DTA),combined with chromatography,infrared spectroscopy,physical property measurements,and the classical Arrhenius kinetic model,analysis was done from a microscopic perspective about the changes in crude oil hydrocarbon molecular structure and oxidation characteristics during oxidation.Results showed that the main LTO reactions of the crude oil were oxygen-addition,polycondensation,and C-C bond scission.Increasing oxygen concentration and the heterogeneous catalytic effect of reservoir rock facilitated LTO,deepening oxidation and generating more fuel-grade residue precursors.Crude oil in 13% O₂ depleted air still exhibited high oxidation reactivity and strong fuel-residue generation capacity,and the presence of clay minerals and active metal elements in the reservoir rock indicated great potential for implementing oxygen-depleted air injection in the Xinjiang X reservoir.This study provides positive guidance and theoretical support for implementing oxygen-depleted air flooding in high-clay-content light oil reservoirs.

Prediction of gas hydrate formation conditions based on an improved PR-Henry model

ZHANG Qian, JIANG Liangwei, LIU Fang, PENG Xiaodong, YAN Ping

2025, 32(6):  100-106.  DOI: 10.3969/j.issn.1006-6535.2025.06.012

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Predicting hydrate formation conditions is of great significance for the efficient development of natural gas and safe, efficient pipeline transport.To analyze the effects of ion type and salinity in formation water on hydrate formation conditions,scaled particle theory (SPT)-adjusted PR-Henry model was used to calculate the fugacity of each component in the gas-water phases.Based on this and thermodynamic theory,a calculation method was proposed to identify hydrate formation type and predict hydrate formation conditions under different temperature conditions.The study showed that for a hydrocarbon-CO₂-water mixed system,compared with traditional models,the improved model reduces the relative error between calculated hydrate equilibrium conditions and experimental data from 0.255 to 0.073,achieving good accuracy.At low salt concentrations,NaCl and CaCl₂ had similar inhibiting effects on hydrate formation,but as salinity increased,CaCl₂ inhibition was significantly greater than that of NaCl.These findings offer useful reference for gas hydrate development and safe natural gas pipeline transportation.

Comprehensive evaluation method for preferential seepage channels in massive unconsolidated sandstone reservoirs

WU Lijuan, ZHU Qixing, WU Wenjie, LOU Yishan, YANG Xiao

2025, 32(6):  107-115.  DOI: 10.3969/j.issn.1006-6535.2025.06.013

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To address the adverse impact of preferential seepage channels formed during long term water flooding in unconsolidated sandstone reservoirs on development performance,this study takes Z Oilfield as a case study to propose a refined identification method for preferential seepage channels in massive unconsolidated sandstone reservoirs by integrating geological data with production dynamics and employing comprehensive evaluation algorithms,numerical simulation and reservoir engineering methods.The study shows that preferential seepage channels in Area Y can be classified into three intensity grades (strong, moderate and weak) based on their developmental characteristics, reservoir damage degree and waterflooding-induced impacts on remaining oil distribution.Key evaluation indicators include geological factors such as reservoir rhythm,cementation index, porosity, permeability and dynamic production parameters.Through cluster analysis of 589 well datasets using an improved K-means algorithm, a graded evaluation criterion was established.The plane distribution of preferential seepage channels is identified using an entropy-weighted TOPSIS algorithm, their development depth via time-variant numerical simulation and their development direction through reservoir multi-information inversion.Applying these findings to Oilfield Z and implementing channel governance shows significant results with the recovery rate projected to reach 61.54% in 5 years and a cumulative oil increase of 158.5×10⁴ t, greatly improving water-flooding efficiency.This research offers crucial scientific insights for long-term water-flooding reservoir development and enhancing water-flooding efficiency.

Characteristics of fluid distribution and synergistic enhancement mechanisms during CO₂+viscosity-reducing agent injection in heavy oil reservoirs

ZHANG Yang, WANG Xiaoyan, WANG Haifeng, ZHANG Zufeng, ZHANG Nan, BAO Lei, PANG Zhanxi

2025, 32(6):  116-123.  DOI: 10.3969/j.issn.1006-6535.2025.06.014

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Faced with the difficulties of thermal development and low recovery in mid-deep heavy oil reservoirs,and based on the CO₂ solubility in heavy oil and the operational principle of viscosity-reducing agents,micro-scale flow simulations were conducted involving synergistic viscosity reduction and enhanced production experiments.The study examined the mechanism by which CO₂ and CO₂+viscosity-reducing agent jointly improved heavy oil recovery.Experimental results showed that under reservoir conditions,CO₂ dissolved in heavy oil to form minute CO₂-in-oil bubbles(0.016-0.051 mm in diameter),significantly improving crude oil mobility;after displacement,the swept coefficient reached 56.4% and oil recovery degree 37.3%.The viscosity-reducing agent caused crude oil to form fine emulsion droplets,expanding the CO₂ sweep area;the viscosity reduction rate exceeded 99.0%,and the swept coefficient reached 65.3%,with recovery up to 46.2%.This indicated that CO₂ improved oil flowability via solution-induced expansion and viscosity reduction,and its synergistic action with the viscosity-reducing agent could substantially enhance displacement efficiency and sweep extent.The formation of foam oil and blockages by emulsified droplets were the key mechanisms improving sweep efficiency.This study provides practical guidance for enhancing recovery in mid-deep heavy oil reservoirs and for realizing CO₂ geological styorage.

Visualization experiment of water invasion development in thick-layer marine sandstone reservoir with bottom water

DAI Ling, LIU Chenglin, ZHAO Yulong, SUN Changwei, GU Yue, TANG Xiaolong, ZHOU Xiang, XIE Longgan

2025, 32(6):  124-132.  DOI: 10.3969/j.issn.1006-6535.2025.06.015

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Aiming at the problem of unclear understanding of water invasion streamlines and remaining oil distribution patterns caused by interlayers during the water invasion development of thick layer marine sandstone reservoirs with bottom water,two dimensional visual reservoir waterflooding experiments were conducted to explore the effects of interlayers and well patterns on the water invasion development of reservoirs with bottom water from the aspects of microscopic streamline evolution,macroscopic development performance and spatial distribution of remaining oil.The results indicate that interlayers in bottom water invasion development reservoirs can delay water coning to some extent and extend the water-free oil production period,with the recovery degree during the water-free oil production period reaching over 30.00%;"secondary edge water" and gravitational differentiation are the main mechanisms for oil production in the upper part of interlayers,while "erosion" is the main mechanism for oil production in the lower part of interlayers;under the composite interlayer distribution mode,reasonable well placement can increase the oil displacement efficiency from 65.51% to 71.42% and the sweep efficiency from 80.10% to 95.23%,effectively improving development performance.The research findings contribute to clarifying the water invasion development characteristics and the spatial distribution patterns of remaining oil in thick layer marine sandstone reservoirs with bottom water,providing guidance for the efficient development of such reservoirs in the eastern South China Sea.

Drilling & Production Engineering

Integrated geo-engineering numerical simulation methods and applications for buried-hill oil and gas reservoirs

WANG Tao, XIAO Yang, FAN Aibin, BAO Xiaolong, XIA Hantao, WANG Jiahao, DING Lingling, TANG Yi

2025, 32(6):  133-140.  DOI: 10.3969/j.issn.1006-6535.2025.06.016

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A block in the South China Sea is a major development area for the eastern South China Sea Oilfield.Its principal reservoir-a Pre Paleogene buried-hill formation-presents complex geology,challenging stimulation,and limited research data.To improve development efficiency,an integrated geo-engineering research approach was adopted,combined with deep diagenesis theory on the existing geological model of the buried-hill reservoir.And an analysis was made on the deep diagenetic environment,stress-strain response characteristics,and geological-mechanical modeling research was conducted.A multi field coupled artificial fracture network model and an unstructured grid reservoir productivity simulation model were developed to simulate and analyze how engineering parameters affected the geometry of hydraulic fractures and production performance,allowing optimization of these parameters.The results showed that the geological mechanical modeling method based on deep diagenesis theory could effectively restore the reservoir′s true diagenetic environment and clearly quantify the relationships between injection parameters (injection volume,fluid volume, proppant concentration)and post-fracture well productivity.The optimal values were found to be a rate of 5-6 m³/min,a fluid volume of 600-650 m³,and a proppant concentration of 11%-15%.The integrated geo-engineering approach could fully and accurately recover the actual reservoir characteristics of this complex block,which has significant implications for stimulation and development of unconventional reservoirs.

Plugging mechanism and technical countermeasures for weak gel flooding in unconsolidated sandstone reservoirs

GAO Jianchong, LIU Yigang, LU Xiangguo, LIU Jinxiang, HE Xin, MENG Xinzhi, WANG Yuqing, HUANG Wenjing

2025, 32(6):  141-149.  DOI: 10.3969/j.issn.1006-6535.2025.06.017

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Aiming at the problem of successive plugging in oil wells during the late stage of weak gel flooding in the unconsolidated sandstone reservoir of Bohai L Oilfield, research on the plugging mechanism and plug removal technical countermeasures for weak gel flooding oil wells in this reservoir was carried out. The results indicate that the plugging material in oil wells consists of water, heavy components of crude oil, polymer and inorganic matter with contents of 63.99%, 14.82%, 14.48% and 6.71% respectively. Among the inorganic matter, the contents of CaCO₃, MgCO₃ and SiO₂ are 60.00%, 20.50% and 13.00% respectively.Among the heavy components of crude oil, the contents of alkanes, aromatic hydrocarbons, resins and asphaltenes are 13.78%, 9.97%, 32.84%, and 43.40% respectively. The limited space on offshore platforms causes a large amount of insufficiently matured polymer gel particles to accumulate on the screen during weak gel injection. These particles subsequently mature slowly to form flexible gel bodies, which entrain mud and sand during migration to form multi-component encapsulated plugging material. During production, they cause plugging again due to the constraints of the screen and pump inlets. To remove on-site plugging, the best depolymerizer combination "0.05% potassium persulfate + 0.05% ferrous sulfate + 0.10% citric acid", organic solvent combination "30.00% diesel oil + 20.00% dimethyl sulfoxide + 2.00% sodium dodecyl sulfate + 0.50% penetrant" and scale dissolver combination "10% hydrochloric acid + 4% hydrofluoric acid + 1% corrosion inhibitor Lan826" were preferentially selected. On site, by alternately injecting slugs of depolymerizer, organic solvent, and scale dissolver, the composite plugging material near the oil well was effectively removed, with significant liquid and oil increase performance. The daily liquid production increased by 166.4%, and the daily oil production increased by 185.3%. This research can provide reference for oil well plug removal in offshore oilfields.

Pressure drop evaluation and parameter optimization in near-well sand-control zones of loose sandstone reservoirs

YIN Bin, DONG Changyin, LI Gaofeng, REN Shijun, LI Chong, LIU Youchuang, LI Zhendong, LI Na

2025, 32(6):  150-157.  DOI: 10.3969/j.issn.1006-6535.2025.06.018

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Addressing the issue of sand-induced wellbore plugging leading to elevated pressure drop in loose sandstone reservoirs,53 near-well sand-control zone pressure drop tests were conducted to evaluate the evolution of pressure drop in three sand-control zones:the wire-wrapped screen section,the gravel-pack annular section, and the fracture section.Results indicated significant differences among these zones:in the screen section, initial pressure drop was small(0.002-0.016 MPa)but rose rapidly to 0.200-3.000 MPa as particles gradually clogged the screen and outer annulus;in the gravel-pack section,initial pressure drop was only 0.002-0.030 MPa but could increase up to 50-fold under sustained sand intrusion;in the fracture section,wider fracture widths yielded lower pressure drops,and for a conventional ceramic proppant pack the pressure drop was lowest-only 60% and 96% of that in the hydrophobic ceramic and quartz sand packs,respectively.Combining these results,it is recommend that in the screen zone fine sand be released early in production to allow coarse sand to accumulate first and establish stable channels,and that 0.200 mm precision screens be used.In the gravel-pack zone,the gravel size should be reasonably matched,and coated sand should be preferred to enhance blockage resistance.In the fracture zone,propped fractures wider than 20 mm with large-particle conventional ceramic proppant are recommended to effectively reduce near-well pressure differentials.These findings provide technical support for optimizing sand-control processes and low-pressure development.

Pre-injected CO₂ foam fracturing technology for deep coalbed methane in the Daji Block of the Ordos Basin

WANG Zilin, ZHU Weiping, XU Dong, WANG Yubin, CHEN Mengqi, JIAO Han, LIU Chunaqing, HE Pengbo

2025, 32(6):  158-164.  DOI: 10.3969/j.issn.1006-6535.2025.06.019

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To address the issues of excessive water consumption,high production decline and insufficient fracture extension during deep coalbed methane(CBM)development in the Daji Block of the Ordos Basin,a pre-CO₂ foam fracturing process for CBM was developed.Through rheological analysis,foam stability evaluation fracturing fluid formulation tests,a guar-gum/polymer gel CO₂ foam fracturing fluid system was established.Experiments showed that under simulated reservoir temperature and pressure,foam quality between 82% and 85% and half-life greater than 250 min achieved,which providing high foam stability,low formation damage,and strong sand-carrying capacity.Based on CO₂ abilities to enhance energy and promote fracturing and to displace and desorb methane,a combined process of pre-CO₂ foam energy enhancement plus high-proppant fracturing with a high sand volume guar gum/polymer system was innovatively proposed.Using a co-injected diverting sand and staged sand ramping mode,the first deep CBM pre-CO₂ foam fracturing was implemented in the Jishen X-7 well in the Daji Block,which achieved a maximum sand ratio of 38%(average 28%)-a record.The results showed that this process increased daily production by 75% compared to guar-gum fracturing wells,reduced fracturing water use by 34% versus conventional wells,increased fracture network complexity by 8%,and which resulted in a stabilized post-fracturing production period with daily gas output of 7×10⁴ m³ and stabilized casing pressure rising to over 1.2 times initial.The successes in increasing production and reducing water indicate that the pre-CO₂ foam fracturing technology is a new approach for green,efficient development of deep CBM.