Table of Content

25 February 2026, Volume 33 Issue 1

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Summary

Current state and prospects of fracturing-flowback-based data-driven fracture network diagnostic technology for tight reservoirs

ZHANG Yanjun, XU Hao, CAI Wenbin, ZHOU Desheng, WANG Luyu, LIU Jianbin

2026, 33(1):  1-10.  DOI: 10.3969/j.issn.1006-6535.2026.01.001

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Fracture network diagnosis of tight reservoirs is an important aspect of evaluating fracturing effect.The diagnostic results can not only serve to assess the fracture network transformation,but also provide a theoretical basis for optimizing subsequent fracturing designs.In light of the current insufficient utilization of fracturing-flowback data in tight reservoir fracture network diagnostics,a comprehensive review and analysis of the current situation in fracturing-flowback-based data-driven fracture network diagnostic technology for tight reservoirs was conducted.Key existing issues in tight reservoir fracture network diagnostics were discussed,and the focus areas for future development of data-driven fracture network diagnostic technologies using fracturing and flowback data were identified.The study shows that current tight reservoir fracture network diagnostic techniques exhibit lag effects,non-uniform fracture closure effects,and inter-well interference effects in closely spaced volume-fractured wells.It is necessary to establish a full-cycle(fracturing-shut-in-flowback)fracture network diagnostic method,develop diagnostic techniques based on pressure decline curves during shut-in,and advance fracture network diagnostic techniques under inter-well interference conditions.The results of this study provide new ideas and technical support for the development of fracturing-flowback-based data-driven fracture network diagnostic technology in tight reservoirs.

Geologic Exploration

Characteristics and diagenesis of lacustrine mixed sedimentary rocks of the Neogene Lower Youshashan Formation in Dafengshan structural belt, Qaidam Basin

HE Hui, XIE Lin, LI Xianming, HE Jianhong, LI Shiyuan, HOU Mingqiu, MA Pengshan

2026, 33(1):  11-21.  DOI: 10.3969/j.issn.1006-6535.2026.01.002

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To clarify the lithological classification,diagenetic types,and genetic mechanism of the tight mixed sedimentary rocks of the Neogene Lower Youshashan Formation in Fengxi Area of the Dafengshan structural belt,northwestern Qaidam Basin,an integrated analysis was made using core observation,thin-section identification,X-ray diffraction,and other techniques.A new classification scheme for fine-grained mixed sedimentary rocks was proposed,which specified the rock types of the Lower Youshashan Formation mixed rocks in Fengxi Area and further guided the division of mixed-rock facies and analysis of the main development controlling factors.The results show that algal dolomite and micritic dolomite are the most favorable rock types in the study area,followed by algal limestone and micritic limestone.Diagenetic processes include dolomitization,dissolution,authigenic mineral filling,and fracturing.Based on the diagenetic analysis,the Lower Youshashan Formation reservoir is subdivided into five diagenetic facies.The genesis of the lacustrine mixed sedimentary rock reservoir in the Dafengshan area is controlled by multiple factors;with increasing burial depth,various diagenetic processes lead to further reservoir densification,but constructive diagenesis still enables the formation of high-quality reservoirs.This study provides valuable guidance for the identification of mixed sedimentary rocks and for research on favorable“sweet-spot”diagenetic facies in the Dafengshan structural belt of northwestern Qaidam Basin.

Occurrence characteristics of deep coal-measure gas in Junggar Basin and a quantitative characterization method for free gas saturation

YANG Xiao, HU Zhengzhou, PAN Tuo, YAO Weijiang, CHEN Guohui, XIE Fei, FU Jiyou

2026, 33(1):  22-32.  DOI: 10.3969/j.issn.1006-6535.2026.01.003

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In view of the inadequate understanding of the pore structure refined characterization and gas occurrence mechanism in deep coal-measure gas reservoirs of the Junggar Basin,a quantitative characterization method for free gas saturation was proposed based on pore types and gas occurrence space.A correspondence was established between different pore types in coal rock(micropores,mesopores and macropores)and different gas occurrence states(adsorbed gas,free gas).The adsorption space do minated by micropores and the free gas space composed of mesopores-macropores are quantitatively delineated,overco ming the limitation of traditional methods lacking targeted linkage between pore types and gas occurrence states.By integrating measured gas content,isothermal adsorption,overburden porosity-permeability and other experimental data,targeted corrections were made for the bias in free gas content caused by dynamic adsorption-desorption-diffusion changes in measured total gas,as well as for the compression effect on free space under reservoir conditions.This achieved accurate quantification of in-situ free gas space and the space occupied by in-situ free gas,and ultimately established a calculation model for free gas saturation.This method,for the first time,systematically couples pore types with gas occurrence states and introduces free gas saturation as a key evaluation parameter.Application results show that in Dimei Well and Caimei Well areas,free gas saturation is below 35%,belonging to the model of moderate gas generation capacity-relatively strong storage space-relatively low free gas saturation;in Qixin Well area,despite lower pore development,free gas saturation is mostly above 75%,belonging to the model of strong gas generation capacity-moderate storage space-high free gas saturation.This method effectively reveals the controlling mechanism of different pore types on gas occurrence,deepens the understanding of gas occurrence and production mechanisms.The combined evaluation model of gas generation capacity-gas storage capacity-free gas saturation can provide a basis for optimizing future development plans and improve the production efficiency of coal-measure gas.

Effect of the Chepaizi-Mosuowan Paleo-Uplift on the depositional system of the Xishanyao Formation in Shixi Area based on depositional forward modeling

FU Lei, XIE Lei, LI Junfei, ZHANG Chunguang, HAN Zijian, WANG Xuehua, ZHANG Jianguo, WANG Runchao

2026, 33(1):  33-42.  DOI: 10.3969/j.issn.1006-6535.2026.01.004

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In the southern part of the Luliang Uplift Shixi Area of the Junggar Basin,the Xishanyao Formation(J₂x)offers favorable oil and gas prospects,but studies on its tectono-sedimentary system have been relatively limited.Thus, based on well logs,seismic data,core samples,employing Dionisos forward modeling and the sediment distribution related to the Chepaizi-Mosuowan Paleo-Uplift and its margins were characterized.The results showed that during J₂x deposition,the Chepaizi-Mosuowan Paleo-Uplift was a low-amplitude NE-SW trending anticline that underwent rapid uplift during the J₂x₂,J₂x₃ and J₂x₄ stages,producing stratigraphic overlap and deposition missing.A dual provenance sedimentary system from the north and northeast gradually interfingered and merged into a single deltaic deposition system in the J₂x₃ and J₂x₄,developing various sub-facies such as underwater distributary channels,inter-distributary bays and mouth bars.Variations in the uplift rate of the Chepaizi-Mosuowan Paleo-Uplift controlled the coupling between accommodation space and sediment supply,thereby influencing sediment distribution;the coarse-grained fan deposits derived from this source constituted favorable reservoir sand body.This study provides valuable guidance for research on the J₂x sedimentary system in the Shixi Area.

Factors influencing tight sandstone oil bearing property in Chang 8 of Qingcheng Area

WANG Guoxi, ZHONG Hongli, CAI Yongji, LI Hailong, LIU Meirong

2026, 33(1):  43-51.  DOI: 10.3969/j.issn.1006-6535.2026.01.005

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To address the big difference in sandstone oil-bearing property in Chang 8 of Qingcheng Area and the unclear controls on oil layer distribution,drilling,logging and experimental data were integrated by using porosity inversion,pore-throat restoration,overlays of geological factors,investigations were conducted on the relationships with oil bearing property concerning sedimentary microfacies,pore throat characteristics,structure and caprock conditions.The results show that the Chang 8 sandstones in the study area were deposited in delta-front environments,including three microfacies:underwater distributary channels, mouth bars and lateral splays of underwater distributary channels.Among them,the single sand bodies in the underwater channel facies ranged between 2~15 m in thickness,with well-developed coarse pore throats that were tightly clustered-these facies were most favorable for hydrocarbon accumulation.The mouth bar facies had single sand bodies between 2~8 m in thickness with relatively concentrated pore throat sizes.The channel-splay facies had thinner(2~3 m)sand bodies with finer pore throats;their reservoir quality and oil-bearing property were poorer than the other two facies.The late Early Cretaceous experienced large-scale hydrocarbon migration and accumulation, and the movable-fluid saturation of the Chang 8 reservoir was generally high(mostly above 70%),which is favorable for hydrocarbon charging.In late diagenesis,the channel splay sand bodies were further compacted and strongly cemented,which resulted in finer pore throats and reduced movable-fluid saturation.After the reservoir formation,there were possible redistribution of hydrocarbons for the oil layer distribution was not closely controlled by anticlines but was strongly associated with fault zones.Hydrocarbon accumulation tended to be enhanced where the overlying mudstone seal exceeded 10 m in thickness.This study provides a theoretical basis for identifying geological "sweet spots" in Qingcheng Area and offers insights for understanding hydrocarbon accumulation in analogous areas.

Controlling factors and quantitative evaluation of stratigraphic-trap accumulation in the Baikouquan Formation, Mahu Sag,Junggar Basin

LI Yipu, WAN Zexin, ZHENG Menglin, WANG Xiaolong, BAO Yiyao, AN Zhiyuan, CHEN Hong, XIAO Qilin

2026, 33(1):  52-59.  DOI: 10.3969/j.issn.1006-6535.2026.01.006

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To clarify the main controlling factors for formation of stratigraphic-unconformity hydrocarbon traps in the Baikouquan Formation of the Mahu Sag in the Junggar Basin,petroleum geology theory and probabilistic methods were applied to systematically analyze the reservoir architecture,identify and quantify the primary geological influencing factors,and a set of comprehensive quantitative evaluation methods were formulated.The results showed that,under the Mahu Sag's paleo-geomorphology and characteristic sedimentary system,the hydrocarbon generation areas were alkaline with abundant algal organisms; the source rocks were rich in organic matter with high conversion rates and great hydrocarbon-generation potential;and these were accompanied by extensively distributed heterogeneous tight sandstones.This combination provided the Mahu Sag with stable source conditions and favorable reservoir settings.Moreover,the combined unconformity-fault system allowed hydrocarbons to escape from source layers and migrate along faults into reservoirs with integrity and effective retention.Thestudy offers a critical basis for quantitative evaluation of reservoirs in the Mahu Sag,significantly improving accuracy and providing valuable guidance for further exploration.

Reservoir Engineering

Pyrolysis reaction characteristics and influencing factors of deep coal

WANG Xiyou, WANG Guodong, WU Fangjie, WANG Zhongyuan, ZHAO Shuang, SHI Li

2026, 33(1):  60-65.  DOI: 10.3969/j.issn.1006-6535.2026.01.007

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Underground coal gasification(UCG)is an efficient method to directly convert deep coal into coalbed methane(CBM),meeting energy needs while reducing environmental impact.In order to effectively utilize deep coal resources,this study used deep coal from the Liaohe Basin as an example to clarify pyrolysis reaction characteristics and influencing factors in the deep coal gasification process.Experiments were conducted to investigate the effects of heating rate and pressure on the pyrolysis behavior and product characteristics of coal samples,and to explore the patterns of gas release during pyrolysis and the variations in product composition.The results show that for Liaohe deep coal,the optimal heating rate is 10 ℃/min,at which the semi-coke yield increases significantly with increasing pressure.Pressure has a notable influence on the composition of gaseous products:at 0.1 MPa,the pyrolysis gas consists mainly of H₂ and CO,whereas at 4.0 MPa the CH₄ content is highest at 47.2%.This study provides theoretical support and technical reference for the underground coal gasification of deep coal in the Liaohe Basin.

Online NMR displacement experiment on gas-water mutual displacement during multi-cycle injection-production in a water-invaded gas reservoir

YANG Xiaosong, ZENG Daqian, PANG Jin, ZHANG Guangquan, ZHOU Chunxi, ZHU Sinan, WU Tongtong, ZHANG Ming

2026, 33(1):  66-74.  DOI: 10.3969/j.issn.1006-6535.2026.01.008

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Due to the complex gas-water mutual displacement flow mechanisms and insufficient understanding of the evolution of effective storage space during multi-cycle injection-production in water-invaded gas reservoirs,this study selected the core from Well 5 of Wen 96 Gas Storage as research object and carried out online nuclear magnetic resonance(NMR)displacement experiments under multi-cycle gas-water mutual displacement.By real-time monitoring of T₂ spectra and signal distribution characteristics,the effects of reservoir physical properties,displacement pressure,and injection-production rates on gas-water mutual displacement efficiency were systematically analyzed.The results indicate that reservoir properties have a significant impact:in low-permeability reservoirs with permeability below 5.00 mD,the recoverable gas pore volume decreases by about 15% after multi-cycle injection-production,whereas in high-permeability reservoirs with permeability above 80.00 mD,it decreases by only about 2%,with most of the pore volume reduction occurring in the first three cycles.Displacement pressure correlates logarithmically with recoverable space,and a critical pressure of around 17 MPa is identified.Below this threshold,displacement efficiency declines significantly,while above it,fluid distribution tends to become homogeneous.When the injection-production rate is increased to 2.0 mL/min,the movable space increases by about 7%,indicating that high-rate injection-production can reduce fluid entrapment by enhancing drive forces.The cumulative seepage hysteresis effect induced by multi-cycle injection-production continues to reduce effective storage space,a phenomenon calling for special attention in long-term operation.This study provides theoretical guidance and technical support for site selection optimization,injection-production parameter optimization,and operational efficiency improvement in water-invaded gas storage reservoirs.

Molecular dynamics study of CO₂ pressure effects on dynamic wettability of hydroxylated and methylated quartz

YAN Zhiming, WANG Fengjiao, LIU Yikun, CHU Mingxuan, REN Mengyao

2026, 33(1):  75-83.  DOI: 10.3969/j.issn.1006-6535.2026.01.009

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To clarify the dynamic wettability changes during CO₂ injection in unconventional reservoirs,molecular dynamics simulations were performed of water droplets wetting hydroxylated quartz and methylated quartz surfaces at various CO₂ pressures.The study shows that hydroxylated quartz is initially strongly hydrophilic,while methylated quartz is initially weakly CO₂-affine;as CO₂ pressure increased,the water wettability of both decreased,with smaller changes for hydroxylated quartz and larger changes for methylated quartz.With higher CO₂ pressure,CO₂ and water molecules co-adsorbed on the methylated quartz surface,forming a discontinuous CO₂ adsorption film that reduced non-bonded interactions and led to lower hydrophilicity until at 44.96 MPa the water contact angle reaches to 180.00°.As CO₂ pressure increases,the number of water molecules in the contact line region decreased and their motion space is compressed,reducing water molecular jump frequency and increasing jump distance.Compared with methylated quartz,hydroxylated quartz remains more hydrophilic with higher water molecule jump frequency and shorter jump distance.This study revealed the dynamic mechanisms of contact angle change for hydroxylated vs. methylated quartz under varying CO₂ pressures,established relationships between contact angle,relative permeability and CO₂ pressure and then a more accurate description of capillary pressure is proposed.These results provide new theoretical support for nanoscale fluid flow and a more reliable basis for reservoir evaluation,productivity prediction, and development strategy.

Numerical simulation of carbonated water flooding and CO₂ sequestration rule

LI Shaopeng, SU Lina, HAN Rui, DANG Faqiang, MA Rui, XU Xinping, LI Songyan

2026, 33(1):  84-93.  DOI: 10.3969/j.issn.1006-6535.2026.01.010

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The method of dissolving CO₂ in water to form carbonated(CO₂-saturated)water and then injecting it into the reservoir can overcome CO₂ high mobility and gravitational segregation,improving crude oil properties and increasing recovery.However,the effects of different operational parameters on carbonated water flooding and CO₂ storage remain unclear.Therefore,numerical simulation was performed to study how different development schemes,CO₂ molar concentrations in carbonated water,and reservoir permeabilities affects carbonated water flooding performance and CO₂ sequestration.Results show that after reservoir depletion,switching to water flooding and alternating water-gas flooding yielded oil recoveries of 45.3% and 53.5% respectively.Switching to CO₂ flooding increases recovery to 63.7%,but CO₂ storage is only 31.9% due to gas channeling.In contrast,switching to carbonated water flooding achieved 58.2% recovery oil factor(between that of water and CO₂ floodings)with CO₂ storage of 44.0%.Higher CO₂ concentration in carbonated water significantly improved recovery:high CO₂ concentrations improved oil-water flow properties and accelerated CO₂ diffusion into the oil phase,markedly enhancing oil rheology and oil recovery.Furthermore,carbonated water flooding effectively increases recovery in reservoirs of different permeabilities,while reducing CO₂ channeling and enhancing CO₂ sequestration.Carbonated water flooding is therefore an effective technique for improving oil recovery and achieving CO₂ storage,with important implications for future oil-gas development and carbon sequestration.

Micro-scale percolation experiments of CO₂ injection in mid-deep low-permeability heavy oil reservoirs

WU Yang, ZHOU Xiang, SUN Xin'ge, DONG Hong, ZHAO Yulong, ZHANG Liehui, JIANG Qi

2026, 33(1):  94-102.  DOI: 10.3969/j.issn.1006-6535.2026.01.011

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In response to the poor thermal recovery efficiency and the insufficient understanding of the mechanisms of production enhancement by CO₂-prefixed energy-storage fracturing in mid-deep low permeability heavy oil reservoirs,a microscopic visualization model and nuclear magnetic resonance(NMR)instrumentation were employed to conduct micro-scale CO₂ injection experiments.Investigations were made concerning the effect of the injected gas phase and energy-storage fracturing on recovery enhancement by CO₂ injection from the perspectives of micro-scale percolation mechanisms,production enhancement mechanisms,and the spatial distribution patterns of remaining oil.Experimental results indicated that the oil recovery factor increased with CO₂ injection pressure:higher pressure resulted in a larger swept volume and stronger stripping of remaining oil.As the gas injection cycle increased,the contribution of oil recovery from large pores in the core exceeded 95%,while the end-pore residual oil in small pores was gradually mobilized;higher pressure led to greater mobilization of remaining oil in small pores.After energy-storage fracturing,at an injection pressure of 14.20 MPa,the cumulative oil displacement efficiency reached 70.20%,yielding the highest development efficiency.Prior to CO₂-prefixed energy-storage fracturing,the single-cycle oil-exchange efficiency increased with the number of injection-production cycles,and the cumulative exchange efficiency was negatively correlated with injection pressure;after fracturing,heavy oil recovery clearly improved,with cumulative exchange efficiency rising from 0.50 to 0.66.These findings help clarify the flow characteristics,recovery enhancement mechanisms,and remaining oil distribution patterns in CO₂-injected mid-deep low-permeability heavy oil reservoirs,and offer guidance for efficient development in CO₂-prefixed energy-storage fracturing.

Flow diversion characteristics of viscoelastic emulsion droplets in heterogeneous pores

XIE Wenchao, ZHOU Yazhou, YANG Wenbin, YIN Daiyin

2026, 33(1):  103-111.  DOI: 10.3969/j.issn.1006-6535.2026.01.012

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Aiming at the insufficient understanding of the multiphase fluid microscopic seepage laws after crude oil emulsification in chemical flooding, the lattice Boltzmann method was used to describe the seepage behavior of the continuous phase fluid, combined with the immersed boundary method to describe the migration behavior of emulsion droplets. The mechanical equation for elastic deformation of emulsion droplets was introduced to establish a mathematical model for emulsion droplet seepage at the micro-pore scale. Through numerical simulation of heterogeneous pores, the transport and deformation characteristics of emulsion droplets with different particle sizes, viscosities and elasticities in pores were studied. The fluid diversion behavior after emulsion droplets form retention plugging in large pores was quantitatively analyzed and the influence of the interfacial rheological properties of emulsion droplets on fluid seepage in heterogeneous pores was clarified. The results indicate that the fluid diversion effect after plugging is obvious when the emulsion droplet size is close to or larger than the pore size; high viscosity and high elasticity droplets increase the fluctuation amplitude of the surrounding fluid seepage velocity, and significantly reduce the fluid seepage velocity and flow rate in the pore; the contribution rate of the emulsion droplet size factor (particle sizes of 3 and 8 μm) to expanding the sweep volume is 6.99%, the contribution rate of the emulsion droplet viscosity factor (viscosity ratio of droplet to external continuous phase of 1 and 5) is 3.46%, and the contribution rate of the emulsion droplet elasticity factor (elastic parameters of 200 and 70) is 6.75%. The research results are of great significance for clarifying the mechanism of emulsion profile control and flooding.

Drilling & Production Engineering

Shale physico-mechanical properties under ultrasonic excitation

XIONG Jian, TAO Shiwei, LIU Xiangjun, LIANG Lixi, DING Yi

2026, 33(1):  112-120.  DOI: 10.3969/j.issn.1006-6535.2026.01.013

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To further investigate the factors influencing the physico-mechanical properties of organic-rich shale,experiments were conducted on Lower Silurian Longmaxi Formation shale from Changning Area of Sichuan Basin using an ultrasonic excitation system,a multi-frequency acoustic testing system,and a high-temperature high-pressure triaxial rheometer.The effects of ultrasonic excitation duration,power and frequency on the shale petrophysical and mechanical characteristics were analyzed,focusing on changes in shale porosity-permeability,P-wave velocity,attenuation coefficient,compressive strength,elastic modulus and Poisson's ratio.The experimental results show that shale porosity,permeability and P-wave attenuation coefficient increase with longer excitation time or higher ultrasonic excitation power;whereas shale P-wave velocity,compressive strength,and elastic modulus decrease with increasing ultrasonic excitation time and power,and Poisson's ratio increases slightly.With other factors constant,different ultrasonic excitation frequencies influence shale physico-mechanical properties,but the degree of influence is relatively insignificant.This study provides reference for validating the feasibility of ultrasonic stimulation for shale gas exploitation and for shale gas engineering applications.

Wellbore temperature field numerical simulation and influencing factors analysis considering drill tool heat generation

YU Yang, SU Yi'nao, HE Jun, SUN Weixu, GENG Jingzhou, ZHANG Yuhao

2026, 33(1):  121-129.  DOI: 10.3969/j.issn.1006-6535.2026.01.014

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To prevent drill tool failure caused by local heat generation during drilling operations,a numerical simulation model of the wellbore temperature field incorporating local heat sources was established to accurately calculate the wellbore temperature during drilling fluid circulation.In addition,the influencing factors of the heat source item was analyzed.The results show that compared with a model without a heat source item,the model including a local heat source predicts a bottom-hole temperature about 8.0^oC higher,and the model accuracy is improved to 98.42%. Under the influence of the local heat source,the bottom-hole drilling fluid temperature can exceed the formation temperature,at which point the drill bit is prone to high-temperature damage.The friction coefficient,drill pipe diameter and bit diameter,weight on bit,and rotary speed all have significant effects on the local heat generation and should not go neglected in wellbore temperature field prediction.This study provides an important theoretical basis for optimizing drilling parameters and designing safety drill-tool in deep high-temperature wells,and offers guidance for ensuring drilling safety and preventing downhole failures.

Safety analysis and application of special connection threads for ultra-high-torque screw drilling tools

XIONG Jianhua, YI Xianzhong, QIN Saibo, CHEN Zhixiang, YI Jun, XIONG Yuancai, YIN Zuopeng, XU Yonghe

2026, 33(1):  130-139.  DOI: 10.3969/j.issn.1006-6535.2026.01.015

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The threaded connection is the weak link in the housing of a screw drilling tool.To reduce the occurrence of thread fracture failures during downhole operations and improve the mechanical performance of connection threads,finite element simulation was used to analyze the load-bearing characteristics,mechanical performance,fatigue resistance,and vibration resistance of four new special connection thread structures under complex loads.A field application of the optimized new special connection thread was carried out in the LU208H2 Block.The results indicate that the new special connection thread structure Ⅲ exhibits better load-bearing performance.Under complex loads and alternating bending moments,its structural strength meets material strength safety requirements,and the failure risk is low.Under vibrational excitation loads,the contact pressure distribution of the special connection thread structure Ⅲ is relatively uniform and meets strength safety requirements,demonstrating good vibration resistance.In field trials,the new special connection thread structure Ⅲ not only enhanced the mechanical performance of the drilling assembly and the rock-breaking effectiveness of the bit,but also allowed a single connection thread to operate continuously for over 1500 hours without any failures,showing excellent performance.These results provide reference for the structural design of connection threads in ultra-high-torque screw drilling tools.

Convective heat transfer of CO₂ fracturing fluid in shale reservoir fractures considering filtration loss

SUN Shihui, ZHANG Wan, YI Tinglong, GAO Yanwen, TENG Shifu

2026, 33(1):  140-146.  DOI: 10.3969/j.issn.1006-6535.2026.01.016

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To clarify the effects of key operational parameters on fracturing performance during convective heat transfer of CO₂ fracturing fluid in fractures(taking into account of filtration loss),numerical simulations were made on the heat and mass transfer of liquid CO₂ fracturing fluid in shale reservoir fractures.Focusing on fracture temperature,pressure and density fields,analysis centered on the influencing factors of CO₂ convection.The results show that after CO₂ injection,along the fracture length,the CO₂ fracturing fluid temperature gradually rose to a peak,then slightly decreased before stabilizing;the CO₂ pressure decreased gradually with a slow decline initially and a rapid decline later,eventually stabilizing; the CO₂ density decreased to a minimum then slightly rises before stabilizing.As the injection rate increases, the maximum temperature of the CO₂ fracturing fluid decreases and the total filtration loss increases.Raising the injection temperature increased CO₂ temperatures deeper in the fracture(farther from the inlet)and also raised total loss.Increasing the injection pressure raised the CO₂ temperature nearer the fracture inlet and reduced total loss.These findings can provide a theoretical reference for designing CO₂ fracturing operations in shale reservoirs.

Flow field simulation of an electroflotation tank using Fluent software

ZHAO Wensen, JING Bo, HUANG Junsong, LIU Changlong, LAN Xitang, LI Geng, YIN Xianqing, GAO Jianchong

2026, 33(1):  147-153.  DOI: 10.3969/j.issn.1006-6535.2026.01.017

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In offshore platform produced-water treatment systems,gas flotation tanks are difficult to maintain,leading to reduced oil removal efficiency as service time increases,which significantly increases the cost of produced water treatment.To improve the treatment effeciency,it is proposed to retrofit the unit into an electroflotation tank that can provide certain oxidation and sterilization effects on the produced water while maintaining oil removal performance,thereby reducing the burden on subsequent processes.However,at present there is no industrial implementation of electroflotation tanks,and related research is scarce.To investigate the feasibility of the electroflotation tank retrofit,steady-state simulations of the oil removal process in an electroflotation tank were carried out using Fluent software to exa mine the effects of current density,residence time,and other parameters on the oil content of the treated water.The simulation results show that the oil content at the water outlet decreases with increasing residence time and with increasing current density,and the latter effect is more obvious.The electroflotation tank can achieve optimal performance at a current density of 150 A/m² and a residence time of 20 minutes,under which the oil content is reduced from 1 000.00 mg/L to 62.54 mg/L,meeting the discharge standard.This result demonstrates the feasibility of retrofitting an electroflotation tank and can provide technical reference for upgrading aging flotation units on offshore platforms.

Exploration and application of real-time diagnostic technology for shale gas wellbore integrity based on artificial intelligence algorithms

CHEN Xuezhong, LI Shuang, CHEN Man, ZHU Kun, CHEN Chao, GAO Shangjun, PENG Yuanjin, LIU Zhiheng

2026, 33(1):  154-159.  DOI: 10.3969/j.issn.1006-6535.2026.01.018

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As the development period of shale gas reservoirs extends,factors such as string corrosion and erosion have led to increasingly serious wellbore integrity problems in shale gas wells,which seriously affects the liquid unloading process and suppresses gas well productivity.To address this issue,a real-time wellbore integrity diagnostic model was established using a logistic regression algorithm and field monitoring data.On this basis,a long short-term memory(LSTM)neural network algorithm was applied to improve diagnostic accuracy,ultimately achieving real-time,precise diagnosis of wellbore integrity.Applying this method enabled automatic and effective online diagnosis of tubing perforation and break-off in 23 shale gas wells in the test area,with an accuracy of 100%.The diagnostic efficiency for wellbore integrity issues was improved by 96.7%,the frequency of anomalies was significantly reduced,and production declines caused by wellbore integrity issues were effectively controlled,with the production loss attributable to wellbore integrity problems reduced by 78%.This study provides reference for the efficient and rapid identification of wellbore integrity issues in shale gas wells and for the intelligent application of gas well production monitoring,diagnosis,and analysis.

Preparation and detection methods of a carbon quantum dot-embedded tracer-functional microsphere flooding agent

KUAI Jingwen, JU Ye, LIU Changlong, LIU Fenggang, XU Guorui, ZHANG Wenxi

2026, 33(1):  160-166.  DOI: 10.3969/j.issn.1006-6535.2026.01.019

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To improve the detection sensitivity of polymer microspheres in produced fluids,a tracer-functional microsphere flooding agent embedded with carbon quantum dots,combining profile control and tracer functions,was developed using seed embedding and ionic bond fixation techniques.Its performance was evaluated,and a detection method with high accuracy and short duration was established.The results show that the tracer microsphere flooding agent has excellent transport capability and can form deep plugging in the core;under a permeability of 300.0 mD,the plugging efficiency of the tracer-functional microsphere flooding agent is 88.9%.The developed detection method for the tracer-functional microsphere flooding agent,involving oil-water settling separation,n-hexane washing and separation,and 90 minutes of UV irradiation,achieves a detection time of less than 2 hours.Compared with traditional methods,this approach effectively removes interference from impurities in the produced fluid through the oil-water settling and n-hexane washing separation steps,thereby improving the accuracy of tracer microsphere detection results.These findings enable rapid and efficient monitoring and adjustment of the flooding process,allow evaluation of oil stabilization and water control effects,and provide technical support for efficient oilfield development.

Optimization of formulation and performance of an annular chemical packer material for high-temperature horizontal wells

SU Zhihao, FU Meilong, LIU Yiwen, LI Xudong

2026, 33(1):  167-174.  DOI: 10.3969/j.issn.1006-6535.2026.01.020

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In view of issues such as casing deformation and frequent failure of packers in high-temperature reservoir water injection wells,a chemical packer material suitable for horizontal well annuli in high-temperature reservoirs was developed.Its thixotropic properties,annular filling performance,and strength were tested,and the system sealing efficiency was evaluated.The results indicate that the optimal formulation of the high-temperature ACP(annular chemical packer)material is 4.000% acrylamide monomer+2.500% LAP thixotropic agent+0.007% ammonium persulfate initiator+(0.005% to 0.007%)MBAm crosslinker.The system structural recovery rate is 0.726,meeting industry standards.After intense shearing for 60 seconds and then standing for 60 seconds,the network structure of the system recovers and its cohesive strength increases,indicating good thixotropic performance.At 90 ℃,the system can achieve instantaneous annular filling with no gravitational collapse,and it migrates axially in a piston-like manner to both sides,maintaining the integrity of annular filling.The sealing efficiency is 99.68%,and the breakthrough pressure gradient is 7.5 MPa/m,indicating excellent sealing capacity.After 60 days,the system axial slip pressure and radial breakdown pressure remain above 0.5 MPa,indicating that excessive pressure does not cause the gel to slide in the annulus between the screen and the wellbore or cause the gel damage.Thus,this material can be directly used for water shutoff in high-temperature horizontal wells.This study provides theoretical guidance for horizontal well water injection development.