Table of Content

25 December 2024, Volume 31 Issue 6

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Summary

Research Progress on the Mechanism of Oil Displacement by Nanoparticles

Pu Wanfen, Yang Fan, Ren Hao, He Wei, Li Bowen, Zhang Hui, Zhu Jianlin, Cao Xiaodong

2024, 31(6):  1-9.  DOI: 10.3969/j.issn.1006-6535.2024.06.001

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In recent years,nanoparticles have gradually received widespread attention in tertiary oil recovery.At present,the mechanism and development status of nanoparticle are not well understood.For this reason,the paper systematically analyzes research progress of nanoparticle flooding in recent years and summarizes the mechanisms of oil displacement by nanoparticles,including nano-size effects,reduction of interfacial tension,alteration of wettability,disjoining pressure,emulsification,prevention of asphaltene flocculation,and catalytic cracking.It also explores the significant application potential of nanoparticle-driven oil displacement materials in various reservoir types,such as high water cut reservoir,low permeability reservoir,tight oil reservoir,and shale oil reservoir.The paper identifies challenges and development prospects for nanoparticles in oil development and provides references and basis for further research and large-scale application of nanoparticles in enhanced oil recovery.

Research Progress on Magnesium Oxychloride Cement and Its Prospective Application in the Petroleum Industry

Xu Mengran, Bu Yuhuan, Zhao Hengyi, Liu Fang, Pang Xueyu, Zhang Zhen, Xiang Gang

2024, 31(6):  10-23.  DOI: 10.3969/j.issn.1006-6535.2024.06.002

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Conventional cement exhibits issues such as volume shrinkage after curing,high brittleness,and high energy consumption during production.In contrast,magnesium oxychloride cement can effectively mitigate the above weaknesses,and possesses engineering advantages such as high mechanical strength,strong CO₂ adsorption,temperature resistance,and resistance to salt-brine corrosion.Investigating the application of magnesium oxychloride cement in oil and gas well engineering is of significant importance.Therefore,this paper introduces the basic composition,hydration products,and hydration reaction mechanism of magnesium oxychloride cement.It summarizes the current research status of magnesium oxychloride cement in oil and gas well cementing,reservoir sealing,and drilling waste disposal.It identifies existing research issues and research directions,and highlights the potential application prospects of magnesium oxychloride cement in CCUS,salt-gypsum layer cementing,and deepwater shallow formation cementing.The research findings can provide a reference for the application and development of magnesium oxychloride cement in the petroleum industry.

Geologic Exploration

Prediction of Structural Fracture Characteristics of Carbonate Reservoir in Leikoupo Formation of Pengzhou Gas Field

Li Gao, Liang Binbin, Xie Qiang, He Long, Shangguan Ziran, Yang Xu

2024, 31(6):  24-31.  DOI: 10.3969/j.issn.1006-6535.2024.06.003

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To address the issue of the ambiguous understanding of the distribution characteristics and development degree of structural fractures in Leikoupo Formation of Pengzhou Gas Field,taking into account the influence of sedimentary microfacies,layer thickness and bedding plane,a prediction approach of structural fractures in carbonate strata based on engineering geomechanics was established.Taking the fourth member of Leikoupo Formation in PZ-6 well area as an example,the finite element method was employed to assess the trans-scale structural fractures of the well area and individual wells.The results demonstrate that the structural fractures in the well area are mainly oblique fractures,and the fracture linear density in the fault area is approximately 1.3 per metre.The fracture line density of algal dolomite flat and dolomite lime flat is greater than that of other sedimentary microfacies.The relative error between the statistical results and the prediction results of fracture line density in the well area is 6.83%,and the well location can be preferentially deployed in the above two sedimentary microfacies.The prediction results of structural fractures in single wells are in accordance with the logging results by 91.23%,and the formation fracture coefficient at the bedding plane is greater than 1.2,indicating that the structural fractures at the bedding plane are more developed.The thin layer is influenced by the layer,and the principal stress change is more obvious.During the construction,well leakage can be prevented in accordance with the distribution of single well structural fractures.The research results are of great significance to clarify the distribution characteristics of structural fractures,optimal selection of horizons and well location deployment in Leikoupo Formation of Pengzhou Gas Field.

Analysis of Coal Rock Characteristics and Coal-forming Environment of the No.8 Coal Seam in the Benxi Formation in Yichuan Area,Ordos Basin

Shen Baiping, Li Rongxiang, Bai Hongtao, Zhu Lianfeng, Lei Hu, Lu Jichao

2024, 31(6):  32-38.  DOI: 10.3969/j.issn.1006-6535.2024.06.004

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To clarify the vertical dominant reservoir and favorable exploration zone of No.8 coal seam in the Benxi Formation of the Yichuan-Shangzhenzi Block in the Yishan Slope of the Ordos Basin,the cores of No.8 coal seam in the Benxi Formation of the Yichuan Area were selected,and the sedimentary environment and coal-forming evolution characteristics of No.8 coal rock were comprehensively analyzed through experiments such as macro coal rock classification,microscopic component identification,major and trace element analysis.The results indicate that the No.8 coal rock of the Benxi Formation is the mixed accumulation product of bright coal,semi-bright coal,and dull coal.The organic components of the coal rock are mainly vitrinite,followed by inertinite.The inorganic components mainly consist of clay minerals such as kaolinite and illite-montmorillonite mixed layer,containing a small amount of quartz and feldspar.The middle and lower parts of the coal are rich in organic components,and the bright coal is well-developed,which constitutes a high-quality coal seam.The evolution degree of coal facies and coal rock is the main controlling factor of hydrocarbon accumulation,and the low water-covered forest swamp is the favorable exploration zone.This understanding is highly significant for the analysis of the enrichment law of No.8 coal seam in the Benxi Formation in the Yichuan area and has an excellent guiding significance for the exploration and development of coalbed methane.

Fractal Characteristics of Shale Pore Throats at Various Scales and Their Dominant Controlling Factors in the First Member of the Shahejie Formation in the Linque Sub-sag of the Nanpu Depression

Gao Yongliang, Li Guoyong, Liu Xiaoping, Ma Qian, Meng Lingjian, Wang Jianwei, Wei Yaqiong, Zhuang Dongzhi

2024, 31(6):  39-48.  DOI: 10.3969/j.issn.1006-6535.2024.06.005

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This study aims to address the insufficient analysis and evaluation of the pore-throat structure in the shale reservoir of the first member of the Paleogene Shahejie Formation in Nanpu Depression.To achieve this,we utilized scanning electron microscopy(SEM),constant-rate mercury injection experiments,and fractal theory to evaluate the fractal dimension of pore-throats at different scales.The findings indicate that the pore throats in shale can be classified into two distinct types:large-scale and small-scale.Furthermore,the fractal dimensions of the pore throats vary significantly across different scales.The small-scale pore throats exhibit strong compaction and cementation,primarily consisting of intercrystalline pores,intragranular pores,and tubular throats.The degree of heterogeneity is low,and the deformation of pore throat space is minimal,resulting in a smaller fractal dimension.The predominant types of large-scale pore throats in shale reservoirs are intergranular pores,pore-shrinking throats,and curved throats.These pore throats exhibit significant reservoir space and deformation phenomena.The pore structure in shale reservoirs is highly heterogeneous,with a large fractal dimension.The presence of various types and sizes of pore throats in shale reservoirs results in distinct heterogeneity characteristics in the pore structure.The fractal dimension is an effective measure of the complexity of the reservoir pore structure.The research findings offer a crucial scientific foundation for the exploration and development of shale oil reservoirs,which is beneficial in enhancing the efficiency of shale oil development and holds significant importance for the later development of oil fields.

Sedimentary Characteristics and Favorable Reservoir Prediction of the Second Member of the Triassic Baijiantan Formation in Mahu1 Well Area

Cheng Guangyi, Zhou Donghua, Li Guohao, Wang Yang, Peng Licai

2024, 31(6):  49-56.  DOI: 10.3969/j.issn.1006-6535.2024.06.006

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This study addresses the unclear understanding of the sedimentary characteristics and favorable reservoir distribution of the Second Member of the Triassic Baijiantan Formation in the Mahu1 Well Area,as well as the difficulties in reservoir evaluation and reserve calculation.A fine division and prediction of sedimentary facies and favorable reservoir distribution in the Second Member of the Baijiantan Formation were conducted by using integrated data such as logging,well testing,oil testing,and seismic data,and techniques such as sedimentary facies division,correlation of sand body connected well,seismic attribute analysis,seismic acoustic impedance inversion,and stratal slicing.The results indicate that the Second Member of the Baijiantan Formation witnesses the main development of delta front subfacies that can be further divided into sedimentary microfacies such as underwater distributary channels,inter-distributary channels,and sheet sands.Its main body consists of underwater distributary channels that exhibit a tongue-like distribution from north to south.The underwater distributary channels at the delta front serve as favorable reservoir facies,primarily distributed in the central and northern parts of the Mahu1 Well Area.This research provides new insights into the distribution range of favorable reservoirs in the Second Member of the Baijiantan Formation,which is of significant importance for further reservoir evaluation,reserve confirmation,and development in the study area.

Paleogeomorphology Control of J₂s¹₂ in the Central Sichuan Basin on the Development of Channel Sand Bodies

Wu Xintao, Liu Li, Ge Jiawang, Feng Xiaofei, Hu Chengjun, Xiao Yao, Song Linke

2024, 31(6):  57-66.  DOI: 10.3969/j.issn.1006-6535.2024.06.007

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The Shaximiao Formation is currently a key target for exploration and development of continental tight oil and gas in the Sichuan Basin,and the main gas-bearing series is the channel sand bodies of J₂s¹₂.However,the research on the coupling relationship between the channel sand bodies and palaeogeomorphology is scarce,which restricts further fine exploration and development of tight gas.To address this issue,based on the establishment of an isochronous framework in the central Sichuan Area and employing the principle of sedimentary compensation,the paleogeomorphology of the J₂s¹₂ was semi-quantitatively restored using the impression method while fully considering the differential compaction of strata.An integrated analysis of core,well logging,and seismic data was conducted on the J₂s¹₂ section of the sedimentary system,which then serves as the basis for analyzing the coupling relationships between various ancient landform units and sedimentary microfacies.The seismic multi-attribute integration method was utilized to predict the thickness of the sand bodies,proposing that palaeogeomorphology controls the distribution of channel sand bodies and the preferential pathways for sediment transport,namely "the valley transporting sand,interfluvial hill separating sand,and gentle slope stopping the sand".Research results indicate that J₂s¹₂ in the central Sichuan Area features ancient landform pattern of alternating valleys and hills,with higher elevations in the westsouth and lower elevations in the eastnorth,and an overall gentle slope.The area primarily consists of major river valleys,tributary valleys, interfluves,and gentle slopes.The main morphological units developed include primary valleys,tributary valleys,interfluvial hills,and gentle slopes.The J₂s¹₂ section in the study area features a continental river sedimentary system,with channel sand bodies distributed in a banded pattern.The ancient landform units of the J₂s¹₂ section control the distribution of sedimentary microfacies,with channel deposits concentrated in the valleys and floodplain deposits more frequently occurring on the gentle slopes. This research provides valuable insights for the subsequent exploration of tight gas.

Sedimentary Characteristics and Models of Shallow-Water River-Dominated Delta in Qigu Formation,Junggar Basin

Zhang Mei, Ren Xincheng, Shang Fengkai, Xu Youde, Qu Yansheng

2024, 31(6):  67-76.  DOI: 10.3969/j.issn.1006-6535.2024.06.008

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The Upper Jurassic Qigu Formation in Area-A within the hinterland of Junggar Basin is a hotspot for oil and gas exploration in recent years.Numerous wells have achieved high-yield oil and gas flows,demonstrating significant potential for oil and gas resources.In light of the sedimentary system of the shallow water delta front in the Qigu Formation,the controlling factors and patterns of favorable sand body distribution remain unclear.Based on the data of core,logging,seismic,heavy minerals and trace elements,the sedimentary characteristics of the shallow water river-controlled delta in the Qigu Formation within the study area are investigated.The study reveals that the river-controlled shallow-water delta is formed in a sedimentary environment characterized by multi-source supply,a shallow water body,frequent oscillations,and a medium hydrodynamic force.The predominant sand body type is mainly the river-bar complex,and the rock is generally oxidized.Based on the thickness,particle size and bedding scale of gravel,the river dam complex is categorized into three types:main channel+residual mouth bar,branch channel+residual mouth bar and residual mouth bar.Among them,the branch channel+residual mouth bar and the river dam complex dominated by residual mouth bar constitute favorable sand bodies.Their distribution is mainly governed by the variation of base level,the influence of river channel supply,ancient landform,river and wave.Favorable sand bodies are vertically distributed in the middle section of the base level rise;on the plane,they are distributed in the slope area and platform area at a moderate distance from the main channel.The research outcomes have deepened the investigation of the sedimentary characteristics of river-controlled shallow-water delta,offering a foundation for the subsequent optimization of the zone and also furnishing a reference for similar blocks.

Reservoir Engineering

Optimization Design and Field Test of SAGD Electric Heating Preheating Start-up Parameters for Double Horizontal Wells in Shallow Super-Heavy Oil Reservoirs

He Wanjun, Sun Xin'ge, Wu Yongbin, Luo Chihui, Guo Hao, Zhang Jipeng, Li Shuxian

2024, 31(6):  77-83.  DOI: 10.3969/j.issn.1006-6535.2024.06.009

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Due to the large fluctuation of pressure difference between injection and production wells during the preheating and start-up process of SAGD steam injection cycle in continental heterogeneous ultra-heavy oil reservoirs in Xinjiang Oilfield,it is difficult to control on site.Steam is easy to enter the oil layer of high permeability horizontal section,which is easy to cause local preferential connection or steam channeling in horizontal section.The development of steam chamber is not balanced, which leads to the low utilization degree of horizontal section,thus affecting the production effect of SAGD.Therefore,the development method of putting electric heaters into the horizontal section of SAGD in double horizontal wells is proposed.The oil layer between injection and production wells is uniformly heated by the principle of heat conduction,and the key operation parameters of SAGD electric heating preheating start-up are optimized,including SAGD electric heating start-up wellbore pretreatment,fluid replacement cycle operation parameters and SAGD production time.The SAGD electric heating preheating start-up operation process is formed.SAGD electric heating preheating start-up field test was carried out in the shallow ultra-heavy oil double horizontal well of FHW01TW Well Group in Chong A Well Area of Xinjiang Oilfield.The preheating startup time was reduced from 320 days to 163 days,3.79×10⁴ t steam was saved and 4 846.6 t CO₂ emission was reduced.This technology will become one of the important means to reduce CO₂ emission in SAGD development of shallow double horizontal wells.

Extension of Characterization Method of Concave-S Shape Water Cut Rising Law in Water Flooding Oilfield

Yuan Yingzhong, Tang Ziqi, Ling Xiao, Huang Dongmei, Yu Chengchao, Qi Zhilin, Yan Wende

2024, 31(6):  84-90.  DOI: 10.3969/j.issn.1006-6535.2024.06.010

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Aimed at the issue that the concave-S-shaped water cut rising law of water flooding oilfield is difficult to diagnose and the fitting effect is unsatisfactory,considering the circumstance that the S-shaped water cut rising curve deviates from the straight line in the high water cut stage,and the concave water cut rising curve strengthens or weakens the S-shaped water cut rising curve,the quadratic term,the logarithmic term related to water saturation and the morphological index n related to water cut are introduced,and the extended water flooding curve equation characterizing the "concave S-shaped" water cut rising law is established.The new equation integrates the characteristics and advantages of concave and S-shaped water cut rising curves,broadens the application scope of conventional water cut rising curves,and enhances the accuracy of the description of the water cut rising law.The research results are applied to WZ Oilfield.The outcomes reveal that the relevant parameters of the equation are acquired by employing the multiple regression analysis method,and the "concave-S shaped" water cut rising law is comprehensively characterized.The fitting effect is significantly enhanced,and the fitted R² reaches 0.977 8.In the actual application process,the coefficient of the extended waterflooding curve equation can be acquired through regression based on the existing production data,and the cumulative oil production at different water cuts can be predicted correspondingly,or the water cut at different cumulative oil production can be predicted.The research outcomes play a crucial role in accurately analyzing or predicting the law of water cut rise in oilfields.

Identification of Horizontal Fracture Morphology and Flow Characteristics in Shallow Oil Reservoirs

Shi Tiaotiao, Shi Lihua, Wu Xiaoting, Tong Changbing, Shen Zhenzhen, Cai Jianchao

2024, 31(6):  91-99.  DOI: 10.3969/j.issn.1006-6535.2024.06.011

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Aiming at the problem of unclear understanding of fracture morphology and water flooding seepage law after fracturing in shallow reservoirs,the Chang 6 Reservoir in the eastern area of Yanchang of Ordos Basin was taken as the research object.The fracture morphology was identified by laboratory experiments of fracture pressure gradient and instantaneous pump-off pressure.The three-dimensional flow pressure and streamline distribution characteristics of a single horizontal fracture under real formation conditions were simulated by large-scale true triaxial laboratory experiments.Based on the Newman product method and Green's function concepts,a numerical model of elliptical horizontal fracture considering fracture skin effect and wellbore storage effect was established.This model reveals the impact of fracture morphology,fracture distribution location,and permeability anisotropy on horizontal fracture flow characteristics.The research indicates that the pressure drop across horizontal fractures shows an asymmetric distribution along the horizontal direction,with longer propagation distances along the major axis and shorter distances along the minor axis.Fracture morphology,permeability anisotropy and fracture distribution position have great influence on bottom hole pressure and fracture flow at the initial stage,but have little influence on horizontal fracture flow at the later stage.Building on these findings,a development mode of staggered bottom water injection is put forward.Field application demonstrates significant enhancement in oil recovery and terrific effects on water production control.This research can provide technical references for water injection development in shallow oil reservoirs.

Production Splitting Method of Early Gas Well Development Based on Productivity Difference

Gan Wenjie, Ji Lidong, Yuan Quan, Liu Ronghe, Wang Yongqiang, Zhang Qian, Wang Yukun

2024, 31(6):  100-105.  DOI: 10.3969/j.issn.1006-6535.2024.06.012

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Gas production serves as the fundamental parameter for assessing the output of each production layer in multi-layer commingled gas wells.To address the issue of inaccurate production splitting in multi-layer commingled gas wells,based on the gas layer productivity difference and material balance principle,according to reservoir geological parameters and production dynamic data,the production splitting of gas wells during the unstable flow stage is carried out,and an early production splitting method of multi-layer commingled gas wells based on productivity difference is formed.Taking two-layer commingled wells as an example,a numerical model is established to verify the accuracy of the method.The results indicate that the relative error of the calculation results of the production splitting method based on the productivity difference is less than 5% in comparison with the numerical simulation method for the gas wells that have been in production for 5 years,and the accuracy is higher.Compared with the KH method which merely considers the static parameters,the calculation accuracy of this method has been significantly improved.Due to the error accumulation effect,this method is not applicable for long-term prediction.The early production splitting method of gas well development based on productivity difference can promptly obtain the production of each layer of early development,which provides a novel calculation concept for the accurate splitting of gas well production.

Establishment and Application of Relationship Charts between Water Content in Class Ⅱ Oil Reservoirs and the Timing of Polymer Flooding

Wei Changqing, Zhou Congcong

2024, 31(6):  106-113.  DOI: 10.3969/j.issn.1006-6535.2024.06.013

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To address the issue of poor geological conditions of the Class Ⅱ reservoirs in Daqing Oilfield,the complex development law of polymer flooding and the difficulty in determining the timing of polymer flooding,a typical geological model of the second-class reservoirs was established by numerical simulation method.Taking the water content index commonly used in oilfield development as the control parameter,the relationship between water content and polymer flooding timing and its influence on the development effect of polymer flooding were studied,and then the relationship between water content and polymer flooding timing was established.The method of determining the reasonable timing of polymer flooding in the Class Ⅱ reservoirs blocks is given.The research shows that the earlier the polymer injection timing is,the better it is for the Class Ⅱ reservoir blocks,but the timing of stopping polymer injection should generally be selected when the water content of the block reaches 96.00% to 97.00%.The application results show that the established chart is practical and effective for the actual block,and can clearly show the development law of polymer flooding.This chart has important predictive guiding significance for determining a reasonable polymer flooding timing for polymer flooding or the blocks that are about to be polymer flooding.

Optimization of injection-production parameters of CO₂ huff and puff in tight reservoirs considering variable cycle gas injection and economic benefits

Niu Zijing, Zhao Zhongjun, Zhang Yuan, Hu Jinghong

2024, 31(6):  114-119.  DOI: 10.3969/j.issn.1006-6535.2024.06.014

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The oil exchange rate of CO₂ huff and puff decreases with the increase of CO₂ huff and puff cycle.In order to improve the rate,the numerical simulation method is used to optimize the injection-production parameters of CO₂ huff and puff with variable injection time,and the economic evaluation is carried out.The results show that the cumulative oil production of the cyclic gas injection scheme is 32 983.4 m³,and the oil change rate reach to 1.11,which is higher than the optimal scheme of orthogonal experiment.The economic evaluation results show that the CO₂ huff and puff scheme with variable cycle gas injection has the best economic benefits,with a net present value of 345.07×10⁴ yuan and an internal rate of return of 18.06%.The research results can provide theoretical guidance for the efficient development of CO₂ huff and puff in tight reservoirs.

Optimization of Amphipathic MoS₂ Nanofluids for Enhanced Oil Recovery in Low-Permeability Reservoirs by Response Surface Methodology

Liang Tuo, Yin Chengfeng, Qu Ming, Yang Erlong, Hou Jirui, Yang Changhua

2024, 31(6):  120-129.  DOI: 10.3969/j.issn.1006-6535.2024.06.015

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By exploring the influence of multi-factor interaction on enhanced oil recovery of nanofluids,a response surface experimental is designed by using Box-Behnken method in Design Expert.Taking the recovery rate as the objective function,a quadratic polynomial regression equation is established among the injection pore volume multiple,the injection rate and the permeability.The significance analysis shows that the factors affecting the enhanced oil recovery by nanofluids are:permeability,injection pore volume multiple,injection rate;The response surface analysis indicated that the interaction between injection rate and permeability has the greatest impact on the enhanced oil recovery of nanofluids.In addition,the effects of permeability,shut-in time and injection mode on the enhanced oil recovery of nanofluids were studied by using the control variable method.The research indicates that when the nanofluid injection rate is 0.2 mL/min,the injected pore volume multiple is 0.5,the permeability is 1.00 mD,the shut-in time is 6 hours,and the injection mode is multi-cycle pill injecting,the recovery rate can be further increased by 18.63 percent points after a single water flooding.The research results have reference significance for the technical optimization of amphipathic MoS₂ nanofluids for enhanced oil recovery in low-permeability reservoirs.

Drilling & Production Engineering

Research and Application of Expansion Lotion Profile Control and Flooding Technology for Ultra-deep High-temperature High-salinity Reservoirs

Wang Lei, Ye Rongjun, Chen Derui, Xu Wenjun, Zhang Jianpeng

2024, 31(6):  130-136.  DOI: 10.3969/j.issn.1006-6535.2024.06.016

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The channel sand reservoirs in the Tarim Basin are categorized as ultra-deep,high-temperature,and high-salt reservoirs,characterized by strong reservoir heterogeneity.Injected water tends to channel along the central part of the channel with better physical properties.To address this issue,physical simulation studies on swelling emulsion flooding were conducted using visualized micro-models and heterogeneous long-core models.The study analyzed the characteristics and mechanisms of flooding,optimized the flooding parameters and slug combination methods,and implemented in-situ applications.The results indicate that the remaining oil distribution types after water flooding in channel sand reservoirs mainly include multi-branch cluster,parallel throat,corner concave,dispersed isolated droplet,and contiguous blocky types.The flooding mechanism of the swelling emulsion involves deep migration+viscosity increase and pressure enhancement,swelling plugging+deformation migration and stripping oil film+push-pull dragging.The optimized flooding parameters are as follows:injection volume is 0.30 times the pore volume,mass fraction is 8%,emulsion particle size is in the micrometer range,injection rate is 0.52 mL/min,and the injection slug combination is 0.15 times the pore volume of small-particle-size lotion particles+0.15 times the pore volume of large-particle-size emulsion particles.In-situ applications demonstrate significant flooding effects,with the daily oil production of the flooding well group increasing to a maximum of 26.4 t and the water content decreasing to a minimum of 32.1%.The research achievement is of great significance for tapping the remaining oil potential in ultra-deep,high-temperature,high-salt channel sand reservoirs with strong heterogeneity.

Crack Propagation Characteristics of Hard Shale Based on Acoustic Emission

Zhang Zhen, Cui Shuai, Liu Huize, Liu Houbin, Wu Pengcheng, Gou Qiyong

2024, 31(6):  137-144.  DOI: 10.3969/j.issn.1006-6535.2024.06.017

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To address the issue of wellbore instability and collapse in shale gas development,with Longmaxi shale as the research subject,based on uniaxial compression experiments and acoustic emission technology,the influences of bedding dip angles on shale failure,crack types,and the variation process of characteristic parameters of acoustic emission during the compression process were investigated.The results indicate that the main crack of the rock sample inclined at an angle of 30° traverses the bedding plane.The failure of the rock is predominantly governed by the rock matrix,and a certain bedding weak plane exists,resulting in the inclined macrocrack not fully propagating along the bedding plane.The coupling failure of rock samples with dip angles of 45° and 60° occurs.The rock failure is mainly controlled by the bedding plane,resulting in conspicuous slip failure.The failure plane along the bedding weak plane penetrates the entire rock sample.The rock sample with a dip angle of 90° is dominated by splitting failure.The crack propagation is influenced by the bedding plane,and the rock failure is governed by the weak bedding plane and the rock matrix.The count of acoustic emission ringing exhibits a fluctuating pattern and a disparity exists.Prior to the peak stress and when the rock sample is on the verge of being destroyed,the count of ringing increases rapidly to the maximum value.For the majority of the time,the acoustic emission energy is relatively low,and the acoustic emission energy rises as the crack propagates.When the rock sample fractures,the release of acoustic emission energy attains the maximum value.The positioning point display model processed by the clustering algorithm is superior to the Geiger algorithm positioning model in the expression of single concentrated rock macro-surface cracks and shedding areas.This study can provide a theoretical reference for wellbore stability analysis in shale gas development.

Study on the Influencing Factors of Diversion Agent Performance Suitable for New Volume Fracturing Technology

Liu Shun, Liu Jianbin, Chen Xin, Zhou Zhixiang, Huang Kai, Du Hengyi, Zhang Yalong, Wang Zongzhen

2024, 31(6):  145-150.  DOI: 10.3969/j.issn.1006-6535.2024.06.018

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The technology of volume fracturing by diversion agent requires that the deblocking time is within a few hours,whereas it usuallysustain several days,which cannot meet the requirements.To address the issue,an aqueous solution polymerization method was employed,utilizing cellulose as the main component,acrylamide as the graft monomer,and N,N-methylene bisacrylamide as the crosslinking agent,to synthesize a diversion agent.The study investigated the effects of temperature,salinity,oxalic acid content,and particle size of the crosslinking agent on its performance under reservoir conditions.The results indicate that the temporary storage agent exhibits good temperature resistance,with a residual rate remaining stable;at a temperature of 60 ℃,the flowable time of theagent is 2.60 hours,the dissolution time is 7.43 hours,and the residual rate is 7.25%.The dissolution rate slightly slows down with increasing salinity,and its dissolution rate in CaCl₂ solution is slower than in NaCl solution,which demonstrates good salt tolerance.The diversion agent exhibits good compatibility with fracturing fluids,with slightly extended flowable time and dissolution time in the fracturing fluid.The oxalic acid content has a minimal impact on the residual rate of theagent.As the particle size of the agent decreases,its flowable time and dissolution time exhibit a trend of slow decrease followed by an increase,and the flowable time and dissolution time with combined particle sizes are longer than those with a single particle size.The research results provide a theoretical basis for optimizing the performance of diversion agent and studying their migration patterns.

Molecular Dynamics Simulation of Wax Deposition in Shale Oil Wells:Variation of Mechanical Properties and Characteristics

Zhang Wei, Xu Yuzhu, Wen Yimin, Liu Jianyi, Lang Dongge

2024, 31(6):  151-158.  DOI: 10.3969/j.issn.1006-6535.2024.06.019

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In view of the unclear understanding of the variation law of mechanical properties of wax blocks during the wax deposition process in terrestrial facies shale oil and gas fields,taking nC₅H₁₂-nC₂₄H₅₀ as an example,the diffusion and aggregation behavior of wax molecules in waxy shale oil were studied by molecular dynamics simulation,the mechanical parameters of wax blocks and their variation with temperature were analyzed.The findings reveal that when the temperature exceeds 50 ℃,the wax molecules are loosely distributed,and the elastic modulus and Poisson's ratio of waxy shale oil are 0.With the decrease of temperature,the distance between wax molecules decreases,and the viscosity,elastic modulus and Poisson's ratio of waxy shale oil increase,and ultimately evolving into wax crystals.At the same temperature,the shear modulus of the wax block is lower than its bulk modulus,making the wax block more susceptible to detachment from the pipe wall due to shear forces.When the temperature falls below 50 ℃,the shear modulus of wax becomes positive,indicating the onset of wax deposition in the wellbore,and the wax removal operation needs to be carried out.As the shear modulus of wax increases,the sequence of wax removal methods is hot washing,chemical wax removers,and wellbore scraping.This study quantitatively obtained the variation law of mechanical parameters of wax deposition in shale oil and gas wells with temperature, which is helpful to guide the formulation of wax removal and prevention measures.

Integrated Geological Engineering Design for Complex Lithology Low-Permeability Condensate Gas Reservoirs

Ran Lingbo, Wang Jia, Lu Wenting, Nan Rongli, Zhang Renping

2024, 31(6):  159-164.  DOI: 10.3969/j.issn.1006-6535.2024.06.020

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The Xinjiang Oilfield saw retrograde condensation in the production of the complex lithology and low-permeability condensate gas reservoir of the Jurassic San'gonghe Formation in the Qianshao 2 Well Area,and significant variability in oil test results between vertical and horizontal wells,which indicates the rational construction parameters for staged fracturing in horizontal wells need further optimization.In order to address these issues,a three-dimensional geological and three-dimensional in-situ stress model of the target area was established through integrated geological engineering research methods.Based on the actual reservoir characteristics and stress characteristics,the influence of fracturing scale on formation pressure and temperature is studied,and the presence of condensation during fracturing is also assessed through actual phase diagrams.In this way,the horizontal well fracturing plan was eventually improved.The study indicates that horizontal well fracturing has a positive effect on the development of this kind of condensate gas reservoir,for a large amount of fracturing fluid injection increases the formation pressure,offseting the influence of temperature field reduction on the condensate oil precipitation.The average permeability of the target layer is 1.86 mD,indicating good reservoir properties.Optimal fracturing results are obtained when the cluster spacing in horizontal wells is 25 m,and the sand addition per cluster is approximately 20.0~25.0 m³.This research provides important references for the rapid development and production building of condensate gas reservoirs with similar geological characteristics.