Table of Content

25 June 2023, Volume 30 Issue 3

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Summary

Application and Prospect of Acid Fracturing Technology with Microencapsulated Solid Acid

Yang Zhaozhong, Peng Qingdong, Wang Zhenpu, Li Xiaogang, Zhu Jingyi, Qin Yang

2023, 30(3):  1-8.  DOI: 10.3969/j.issn.1006-6535.2023.03.001

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The conventional acid fracturing working fluid system has problems such as too fast acid-rock reaction and short effective distance, the microencapsulated solid acid is one of the effective means to solve this problem, and it is commonly used for deep acid fracturing of unconventional oil and gas reservoirs. This study describes the mechanism of action, structure and performance characteristics of microencapsulated solid acids, summarizes the research progress of acid fracturing technology with microencapsulated solid acid, and indicates the main research directions of acid fracturing technology with microencapsulated solid acid in the future. This study can provide technical support for the stimulation of ultra-high temperature carbonate reservoirs, and provide theoretical guidance for the research and application promotion of acid fracturing technology with microencapsulated solid acid.

Geologic Exploration

Sedimentary Pattern of the Shaofanggou Formation in the North Santai High Area of the Eastern Junggar Basin and its Control on Reservoir Development

Luo Liang, Hu Chenlin, Tang Ya'ni, Dan Shunhua, Han Changcheng, Liu Ziming

2023, 30(3):  9-18.  DOI: 10.3969/j.issn.1006-6535.2023.03.002

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To understand the sedimentary characteristics and sedimentary patterns of the Triassic Shaofanggou Formation in the North Santai High area of the eastern Junggar Basin and clarify the constraints on reservoir development, a study on the sedimentary patterns of the Shaofanggou Formation and its control on reservoir development was carried out on the basis of sedimentology and in combination with the data such as core, thin section, grain size and conventional physical properties. The study shows that there are nine typical petrographic types developed in the Shaofanggou Formation, namely channeled interlaminated conglomerate phase, platy interlaminated conglomerate phase, massive laminated conglomerate phase, channeled interlaminated sandstone phase, platy interlaminated sandstone phase, massive laminated sandstone phase, wave-formed sand laminated sandstone phase, parallel laminated siltstone phase and massive laminated mudstone phase; the Shaofanggou Formation is mainly dominated by braided river delta phase, and the sedimentary microphases include 10 types such as floodplain, abovewater braided river channel, channel bar, natural dike, underwater braided river channel, interdistributary area, underwater natural dike, estuary bar, prodelta mud and beach bar, among which, underwater braided river channel, estuary bar and beach bar reservoirs have the best physical properties, with average porosity of 17.31%, 20.66% and 21.81%, and average permeability of 6.89, 7.05 and 12.98 mD, respectively. The reservoir properties in this area are mainly controlled by sedimentation, and the high-quality reservoirs are mainly developed in underwater braided channels, estuary bar and beach bar microphase. The study can provide a theoretical basis for further fine exploration and development of oil and gas within the study area.

Reservoir Characteristics and High-quality Reservoir Control Factors of He8 Member in Daning-Jixian Area of Ordos Basin

Guo Qiqi, Er Chuang, Zhao Jingzhou, Teng Yunxi, Tan Shijin, Shen Congmin

2023, 30(3):  19-28.  DOI: 10.3969/j.issn.1006-6535.2023.03.003

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To address the problem of unclear distribution of high-quality reservoirs in He8 Member in Daning-Jixian Area, the reservoir development characteristics and influencing factors were analyzed from petrology and mineralogy, diagenesis and other aspects by using cast thin section, X-ray diffraction, cathodoluminescence and scanning electron microscope. The results show that the rock type of the He8 member reservoir is mainly lithic quartz sandstone, and the lithology is mainly of medium and coarse sandstone; the type of reservoir space includes intergranular dissolution pore, feldspar dissolution pore, lithic dissolution pore and clay mineral intercrystalline pore, etc. The reservoir has low-porosity and low-permeability physical properties, but it is a dense reservoir with good porosity-permeability correlation; the compaction is the main factor for the dense reservoir in the study area, the average compaction reduction rate is 80.16%, the average cementation reduction rate is 17.00%, the dissolution can improve the reservoir properties, the average dissolution increase pore rate is 7.34%; the high-quality reservoir does not exist in the middle or at the top or bottom of the sand body, its development in the sand unit follows the distribution pattern “Upper and lower sides of the sand body center”; under the influence of factors such as compaction resistance, dissolution conditions and various types of cementation properties, the high-quality reservoirs are mostly developed in quartz sandstone and medium and coarse sandstone. The research results can provide reference for the accurate prediction of high-quality reservoirs in the study area.

Sedimentary Characteristics and Favorable Reservoir Evaluation of Braided Fluvial Alluvial Fan Controlled by Paleo Gully Geomorphology

Sun Yili, Fan Xiaoyi

2023, 30(3):  29-37.  DOI: 10.3969/j.issn.1006-6535.2023.03.004

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The stratigraphic space stacking pattern and sedimentary characteristics of alluvial fan controlled by paleo gully geomorphology are more complicated, making it difficult to conduct the study of sedimentary characteristics with existing model. Guided by the research results of the modern Baiyanghe alluvial fan and combined with seismic, core, well logging, physical properties, oil-bearing characteristics and other data, the fluvial alluvial fan controlled by paleo gully geomorphology in Shawan Formation, Chunguang Oilfield was systematically studied in terms of palaeogeomorphology, lithofacies characteristics, microfacies distribution and other sedimentary characteristics, and a dynamic sedimentary evolution model was established. The results of the study show that this area was featured by two-channel paleo gully geomorphology, and the formation went through the filling process of gully-filling-progradation-retrogradation, with unbalanced deposition. Limited by the regional location, sedimentary subfacies were developed only at the middle and rear of the fan. The early stage was a flood period, and the fan was dominated by sedimentation. Controlled by the paleo gully geomorphology, the restricted channelized fan deposits were also developed. From the middle to the end of the fan, gravity current deposition was converted to traction current deposition. The late stage was a flood regression period, and with the filling and consolidation of the strata, the unrestricted fan deposits were developed and dominated by sheet flow deposit. On the basis of fine identification of sedimentary microfacies, the classification and evaluation criteria for reservoirs were established, the study results were applied to the northwest of Chunguang Oilfield, and three favorable areas were selected, and new wells were deployed to achieve breakthrough in the paleo-gully alluvial fan reservoirs. The study results have deepened the understanding of sedimentary evolution characteristics of alluvial fans controlled by different landforms and have important significance for the study of sedimentary characteristics of paleo-gully alluvial fan reservoirs.

Influence of Alkaline Environment Diagenetic Evolution on Reservoir Performance in the Second Member of Shahejie Formation of Qibei Slope

Liu Jinku, Deng Mingjie, Zhang Ze, Li Guoliang, Fang Jinwei, Wang Chunpu, Wang Feiyang, Tan Quan

2023, 30(3):  38-46.  DOI: 10.3969/j.issn.1006-6535.2023.03.005

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In order to deepen the understanding of the diagenetic environment, evolution mode and pore development mechanism of the reservoir in the Second Member of Shahejie Formation of Qibei Slope, the characteristics of alkaline environmental diagenesis, diagenetic evolution mode, alkaline environmental genesis mechanism and its influence on pore development of the dense sandstone reservoir in the Second Member of Shahejie Formation were studied by means of rock (cast) thin section, scanning electron microscopy and X-ray diffraction analysis. The results show that there are various alkaline environment diagenesis phenomena in the reservoir, such as quartz dissolution, multi-phase carbonate mineral cementation and metasomatism, anhydrite metasomatism and alkaline clay mineral assemblage; the current reservoir diagenctic stage is in the mesogenetic A₂ sub-stage, and the diagenetic environment has experienced alkaline-acidic-alkaline changes during the whole diagenetic evolution; in the early diagenetic stage, the formation of the alkaline diagenetic environment was closely related to the saltwater lake basin environment in the same sedimentary stage. In the mesogenetic A₂ sub-stage, due to the enrichment of metal cations, the acidic water source was reduced and heavily depleted, resulting in the increase of the pH value of the pore water medium and a return to the alkaline diagenetic environment; the multi-phase carbonate cement formed in the alkaline environment filled the pores in large quantities, which significantly reduces the reservoir space, and at the same time, the early alkaline fluid medium in the reservoir also suppressed the dissolution modification intensity of the acidic fluid to the reservoir, but the quartz dissolution in the alkaline environment formed a large number of secondary pores, which is the main mechanism of pore development in the reservoir within the study area. The research results are of guiding significance for predicting the distribution of high-quality reservoirs in the study area.

Phase Development Pattern of Weathered Volcanic Reservoirs in Shixi High, Junggar Basin

Zhang Xiao, Chen Guojun, Li Junfei, Zhang Fan

2023, 30(3):  47-55.  DOI: 10.3969/j.issn.1006-6535.2023.03.006

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To address the problem of poorly understood structural characteristics of weathered volcanic reservoirs and lack of effective delineation methods, the four phase patterns of weathered volcanic rocks are established and classified from top to bottom, namely, strongly weathered clay phase, weathered hydrolysis phase, weakly weathered leaching and disintegration phase and unweathered parent rock phase, by taking weathered volcanic rocks in Shixi High, Junggar Basin as a study object and combining petrophysical experiments, FMI imaging data and comprehensive well logging and mud logging data. The weathered volcanic reservoir composite index and weathering composite index were constructed by using well logging data to finely classify the phases of weathered volcanic rocks, and the weakly weathered leaching and disintegration phase was clearly defined as the dominant phase of weathered volcanic rocks. The application in Shixi High, Junggar Basin is remarkable and provides a reference for the study of phases of the same type of volcanic reservoirs.

A New Technique for the Evaluation of Complex Reservoir Fluids While Drilling on Light Hydrocarbon Analysis

Li Hongru, Tan Zhongjian, Fu Qiang, Guo Mingyu, Tian Qingqing, Han Minggang, Li Yanxia

2023, 30(3):  56-62.  DOI: 10.3969/j.issn.1006-6535.2023.03.007

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To address the problems of difficult fluid evaluation while drilling for Palaeocene reservoirs in the Southwest Zone of Bozhong Sag, strong multi-solution, and contradictory response characteristics of mud logging and well logging data, a water content analysis based on light hydrocarbon sensitive parameters, well field light hydrocarbon carbon ring dominance analysis, biodegradation analysis based on alkane series comparison, and a method for evaluating well field light hydrocarbon fluids based on mathematical algorithms such as principal component analysis and support vector machine were established, and the example applications were performed. The evaluation results show that the reservoir water content plate based on light hydrocarbon sensitive parameters and the biodegradation degree interpretation plate based on alkane series comparison are effective in identifying fluid properties in the study area; the well field light hydrocarbon carbon ring dominance analysis method can be used for comparative analysis of reservoir genesis and origin, and has obvious advantages over conventional mud logging methods in evaluating fluids in complex reservoirs with multi-stage charging; the light hydrocarbon analysis method based on mathematical algorithms such as principal component analysis and support vector machine has a high compliance rate of about 85% in evaluating the fluid properties of complex reservoirs. This technical method has been applied in the study area with good results, which provides a new idea for the evaluation of complex reservoir fluids while drilling and has a good application prospect.

A Numerical Simulation Method for Shale Acoustic Wave Based on Equivalent Medium Theory

Li Xiansheng, QiuXiaoxue, Chen Mingjiang, Li Wei, Liu Xiangjun, Yang Bei

2023, 30(3):  63-72.  DOI: 10.3969/j.issn.1006-6535.2023.03.008

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Numerical simulation of acoustic wave is very important for the study of anisotropy characteristics of shale and the study of shale acoustic wave correction in highly inclined well. In order to study the anisotropic characteristics of shale acoustic wave, an equivalent shale model composed of argillaceous and sand layers was established on the basis of equivalent medium theory, the calculation methods of the stiffness coefficient and acoustic wave velocity of the equivalent shale model were derived from the elasticity theory, and the influences of the elastic parameter, thickness, angle and density of the lamina on the stiffness coefficient and the elastic wave velocity of the equivalent shale model were analyzed. The study shows that the thickness ratio of argillaceous layer to sandy layer affected the stiffness coefficient of equivalent medium. The stiffness coefficient of equivalent shale model increased with the increase of parameter ratio. Lamet coefficient of argillaceous layer affected the relationship between P-wave velocity and lamina angle and the extreme value of S-wave velocity, but had no effect on SH wave. The acoustic wave velocity was increased with the increase of shear modulus or parameter ratio of the argillaceous layer, and the shear modulus had a great effect on the relationship between the three wave velocities and the lamina angle. When the lamina density was constant, the P-wave velocity was decreased gradually and stabilized with the increase of lamina angle, the S-wave velocity increased first and then decreased, and the SH wave velocity decreased gradually. When the lamina angle was constant, the three wave velocities were decreased gradually with the increase of lamina density. This study plays a guiding role in the shale acoustic numerical simulation and acoustic logging correction.

Reservoir Engineering

Study on the Generation and Decomposition Characteristics of Methane Hydrate in Fully Visible Dual Reactor

Mao Gangtao, Li Zhiping, Wang Kai, Ding Yao

2023, 30(3):  73-80.  DOI: 10.3969/j.issn.1006-6535.2023.03.009

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In order to clarify the generation and decomposition characteristics of methane hydrate and its influencing factors, a high-pressure fully transparent double-reactor test platform was designed and built to conduct initial and secondary generation and decomposition tests of methane hydrate with high-purity methane and deionized water as the study objects. During the tests, the samples were stirred or not stirred to make a comparison. The experimental results showed that the hydrate generation included four stages: induction, rapid generation, slow generation and stabilization. Stirring could promote the hydrate generation. At the speed of 400 r/min, the lower reactor consumed 93.6% more methane than the upper reactor. Meanwhile, the memory effect was more obvious, and the induction time in the secondary generation was shortened by 62.5 %, and the methane consumption was increased by 254.0% compared with the primary generation. There is much for reference of the study for the development of hydrate.

Study on Damage Mechanism and Conductivity of Unpropped Fractures in Tight Sandstone Gas Reservoirs

Sun Yongpeng, Wang Chuanxi, Dai Caili, Wei Linan, Chen Chao, Xie Mengke

2023, 30(3):  81-87.  DOI: 10.3969/j.issn.1006-6535.2023.03.010

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For the change in unpropped fracture conductivity after fracturing in tight sandstone gas reservoirs, an experimental method for unpropped fracture conductivity evaluation with fracture wall simulation was established to investigate the damage mechanism of conductivity in terms of the microscopic morphology, roughness, strength and other aspects of the fracture wall, and to clarify the variation law of fracture conductivity. The study shows that after the fracture was exposed to water, the wall clay was hydrated and compacted under stress, and the average height of the wall was decreased by 8.5%; meanwhile, the fracture wall was softened and the average hardness decreased by 34.3%. The more frequent the change in production nozzle size, the higher the conductivity of the unpropped fracture under high stress; the fracture conductivity of the third well opening was 91.7%-98.5% lower than that of the first well opening; the conductivity of misaligned fractures was 18.1-140.4 times that of non-misaligned fractures. With the formation water displacing fracturing fluid after fracturing, the conductivity of the final fracture was 3.45 times that of the original fracture. In this paper, the conductivity damage mechanism in the production of tight gas reservoirs was defined, and the variation law of unpropped fracture conductivity under the action of different factors was clarified, which provides a basic theoretical basis for the protection of unpropped fractures in tight sandstone gas reservoirs.

Experimental Study on Direct Current Enhanced Oil Recovery Technology for Tight Reservoirs

Jia Zejiang, Ning Zhengfu, Zhang Wentong, Mao Zhu, Wang Zhipeng, Cheng Zhilin

2023, 30(3):  88-96.  DOI: 10.3969/j.issn.1006-6535.2023.03.011

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To address the problem of poor development due to difficult water injection in tight oil, the application of DC electric field is proposed to enhance the recovery of tight oil. Taking the tight sandstone core of the Upper Triassic Yanchang Formation in the Ordos Basin as the research object, the DC electric field displacement effect and the mechanism of action were investigated through DC electric field constant velocity displacement experiments, wetting angle measurements and XRD test experiments. The study shows that the DC electric field enhanced recovery rate of tight oil is positively correlated with the electric field intensity; the development effect when the DC electric field is applied at the beginning of water flooding is better than that when the DC electric field is applied after the end of water flooding, both of which can increase the average recovery rate through water flooding by 29.06 and 14.68 percentage points respectively at 10 V; the recovery rate is accelerated after the DC electric field is applied; the DC electric field can not only reduce the flow resistance through electroosmotic flow to decrease the difficulty of water injection, but also enhance the hydrophilicity of the rock through electrochemical reaction to improve the oil displacement efficiency. The study provides a new idea for the efficient development of tight oil.

Experiment of DME Water Flooding Enhanced Recovery of Heavy Oil Reservoirs

Zhang Liang, Wei Huchao, Zhang Xiangfeng, Shi Zhenpeng, Zhao Zezong, Wang Xiaoyan, Zhang Yang, Yang Hongbin

2023, 30(3):  97-105.  DOI: 10.3969/j.issn.1006-6535.2023.03.012

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In order to study the stimulation mechanism of dimethyl ether (DME) in the development of heavy oil reservoir, reveal its mass transfer law in both oil and water phases and its swelling and viscosity reduction effect on heavy oil, a heavy oil sample from a certain block in Dagang Oilfield was selected to carry out PVT and sand-packed tube displacement experiments under high temperature and high pressure conditions. The results show that DME is a good viscosity reducer for heavy oil, easily dissolved in water and more easily dissolved in crude oil, and has strong diffusion effect in both oil and water phases; the water can be used as a carrier to inject DME into the subsurface, and the carrying capacity of DME can be increased by adding ethanol or ethylene glycol; for heavy oil with low viscosity, the DME water flooding can be carried out on the basis of water flooding, with significant oil increase effect, while for heavy oil with high viscosity that cannot form effective drive For heavy oil with high viscosity that cannot form effective displacement, the water or CO₂ can be considered as a carrier for DME huff-n-puff. The study results are of great significance for the application of DME in the production of heavy oil.

Study on CO₂ Huff-N-Puff Enhanced Recovery Technology for Jimsar Shale Oil

Cao Changxiao, Song Zhaojie, Shi Yaoli, Gao Yang, Guo Jia, Chang Xuya

2023, 30(3):  106-114.  DOI: 10.3969/j.issn.1006-6535.2023.03.013

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To address the problems of low recovery rate and poor water injection huff-n-puff effect in the depleted development of Jimsar shale oil. A study on the applicability of CO₂ huff-n-puff technology in shale oil reservoirs was carried out by means of hydrocarbon phase experiments and numerical simulation methods for reservoirs to guide the implementation of CO₂ huff-n-puff technology in the field. The results show that Compared with CH₄, CO₂ interacts better with Jimsar shale oil. Under the conditions of formation pressure and formation temperature, the solution gas-oil ratio of CO₂ in crude oil is 497.83 m³/m³, the crude oil viscosity is reduced by 70.65%, and the crude oil volume is expanded by 2.05 times; for typical shale oil wells, multi-cycle CO₂ huff-n-puff can improve the recovery rate by 9.43 percentage points and crude oil production by 31 472.40 t. With the shortening of fracture spacing and the increase of reservoir porosity, the effect of CO₂ huff-n-puff on oil enhancement gradually becomes better, and the influence of permeability and oil saturation on the effect of CO₂ huff-n-puff is relatively small. The results of the field test show that CO₂ huff-n-puff can effectively enhance the recovery rate of shale oil, and the oil enhancement effect is better under the condition of no fracture disturbance. The research results have some implications for the efficient development of shale oil.

Occurrence Characteristics and Influencing Factors of Micro Remaining Oil in Different Displacement Stages

Liu Weiwei, Chen Shaoyong, Cao Wei, Wang Li'na, Liu Zhenlin, Wang Haikao

2023, 30(3):  115-122.  DOI: 10.3969/j.issn.1006-6535.2023.03.014

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In order to further clarify the detailed description of the distribution characteristics of the micro remaining oil in the reservoir in the middle and high water-cut stage, CT nondestructive analysis was combined with conventional displacement test to analyze the distribution characteristics and influencing factors of micro remaining oil in different displacement stages by means of in-situ comparison technology. The results show that the production effect of micro remaining oil is affected by the size of micro pore throat, the connectivity of pore throat and the spatial distribution of pore throat, etc. The characteristics of remaining oil distribution and occurrence are affected jointly by the main driving force formed by various micro forces and the micro pore throat structure. In the water flooding stage, the production effect is mainly affected by the micro-pore structure, the micro remaining oil in the large pore channel with good connectivity can be migrated for a long distance, with high production effect, while the oil droplets in the small channels with poor connectivity will only be thinned slightly along the edge, with poor production effect. Polymer-surfactant composite flooding is followed by water flooding is conducted, the heterogeneity of micro-pore throat distribution is the most important factor affecting the production effect, and the production effect of low-permeability and high-permeability cores with high micro-heterogeneity is more obvious. Different injection and production strategies should be applied in different development stages of the oilfield. Homogeneous intervals with large pores should be selected for development in water flooding stage, while heterogeneous intervals with poor water flooding sweep effect should be preferentially selected for development in the polymer-surfactant composite flooding stage. The results of the study are of guiding significance for the occurrence and enhanced oil recovery of micro remaining oil in the reservoirs.

Study on Mechanical Mechanism of Brittle Fracture Mode in Laminated Shale

Li Liang, Zhao Zhihong, Yang Qi, Yang Fan, Wang Peng, Liu Yongbing

2023, 30(3):  123-130.  DOI: 10.3969/j.issn.1006-6535.2023.03.015

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To address the problem of poorly understood mechanical mechanism of stress-caused brittle failure in shale, the brittle fracture model of laminated shale with longitudinal mechanical inhomogeneity was established by applying the theory of rock fracture mechanics and combining it with generalized Hooke's law on the basis of analyzing the characteristics of laminated shale, and the main influencing factors of the fracture mode of laminated shale were analyzed. The study shows that the fracture modes of laminated shale are mainly divided into shear failure and tensile failure, hard rock formations are prone to tensile failure, while soft rock formations are prone to shear failure under external stress conditions; the larger the Young's modulus of the rock formation and the smaller the Poisson's ratio, the more prone the formation is to tensile failure and vice versa; the larger the minimum horizontal principal stress and the smaller the horizontal principal stress difference, the more prone the formation is to shear failure; the variability of mechanical properties between shale layers is the fundamental reason for the brittle fracture of shale; the greater the variability between shale layers, the more brittle the rock is, and the more favorable it is for fracturing. This study can provide theoretical guidance for shale brittleness evaluation and hydraulic fracturing scheme development.

Experiment on Physical Simulation of Multi-phase Synergistic Steam Flooding in Heavy Oil Reservoirs

Liu Gang, Cao Han, Zhu Aiguo, Li Yiqiang, Yue Hang

2023, 30(3):  131-136.  DOI: 10.3969/j.issn.1006-6535.2023.03.016

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In a case study of heavy oil reservoirs in IX6 Well Block, Xinjiang Oilfiled, physical simulation test of multi-media assisted steam flooding was conducted to address such problems as prominent vertical contradiction in the late stage of steam flooding in heavy oil reservoirs and serious steam channeling in the high-permeability layer. Firstly, the gelling performance and viscosity reducing effect of gel were evaluated, and then the combination mode of multi-phase synergistic steam flooding was optimized by full-diameter core. The results show that after the high-permeability layer was plugged by gelling, the subsequently injected multi-phase media effectively entered the low-permeability layer and drove the remaining oil in the low-permeability reservoir. Nitrogen was injected after viscosity reducer injected to effectively enhance the elastic energy and fluidity of crude oil, which was conductive to expanding the sweep volume of steam. The multi-phase synergistic steam flooding development mode of plugging control, viscosity reduction and pressurization is the best combination mode, which can improve the oil recovery rate by 23.65 percentage points. The study results can provide technical reference for the improved late development effect of steam flooding in heavy oil reservoirs.

A Trinomial Deliverability Calculation Method for Shale Gas Wells Considering the Effect of Adsorbed Gas

Fang Dazhi, Liu Hong, Pang Jin, Gu Hongtao, Ma Weijun

2023, 30(3):  137-142.  DOI: 10.3969/j.issn.1006-6535.2023.03.017

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To address the problem of the unclear effect law of the shale gas adsorption-desorption on the deliverability of production wells, based on the seepage characteristics and deliverability equation of tight gas wells, a deliverability model considering shale gas adsorption-desorption was established with reference to the gas seepage differential equation and in combination with the Langmuir isothermal adsorption equation; the deliverability and open flow capacity of shale gas wells under different desorption time were calculated based on the drilling and completion and dynamic monitoring data of shale gas wells, and the effect of adsorbed gas was transformed into additional resistance coefficients based on the information of back-pressure well testing to form a trinomial deliverability calculation equation, and this equation was used to study the effect of adsorbed gas on shale gas deliverability calculation. The results show that the adsorbed gas will cause a higher initial deliverability calculation value of shale gas wells, and the calculated open flow capacity is relatively stable after 10 d of desorption; the adsorbed gas content has a greater influence on the deliverability of shale gas wells, and the adsorption pressure has a smaller influence on the deliverability; the error between the results of the trinomial deliverability calculation and the analytical method model calculation is less than 12%, and the results are more reliable. The research results can be used as a reference for the deliverability evaluation of shale gas wells.

Drilling & Production Engineering

Evaluation of Adaptability of Fracturing Fluid System for Tight Sandstone Gas Reservoirs in the Denglouku Formation of CL Block

Xiao Hangzhou

2023, 30(3):  143-147.  DOI: 10.3969/j.issn.1006-6535.2023.03.018

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To further evaluate the adaptability of fracturing fluid and proppant to the dense sandstone reservoir in the Denglouku Formation of CL block, the commonly used fracturing fluid and proppant in the target formation were selected for core permeability testing experiments, flowback experiments, CT reconstruction experiments and reservoir conductivity experiments to comprehensively evaluate the effects of different types of fracturing fluid and proppant on the permeability of rock samples. The study shows that there is still some damage to the core after fracturing fluid flowback, and the damage rate of guar gum fracturing fluid is larger than that of slickwater fracturing fluid, mainly manifested as water-sensitivity damage, water-locking damage and residue damage, and the mechanism is that the pore structure of rock samples treated with guar gum fracturing fluid changes significantly, and the percentage of micropores with pore throat radius of 7-22 μm increases; the permeability of dense sandstone reservoir is affected by proppant embedding, and the conductivity is negatively correlated with the particle size and closure pressure. The research results can provide theoretical guidance for the preferential selection of fracturing fluid system for dense sandstone gas reservoirs in Denglouku Formation of CL block.

Exploration of the Longitudinal and Transverse Sand Production Law in the Full Life Production Cycle of Dina 2 Condensate Field

Liu Hongtao, Wen Zhang, Tu Zhixiong, Zhang Bao, Jing Hongtao, Yi Jun, Kong Chang'e, Yu Xiaotong

2023, 30(3):  148-154.  DOI: 10.3969/j.issn.1006-6535.2023.03.019

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The Dina 2 condensate field in Tarim Oilfield is a fractured sandstone gas reservoir with characteristics such as high temperature and high pressure, low porosity and low permeability, and medium-high cementation strength, and the traditional view is that there is no sand production problem for this type of reservoir, but since the start of production in 2009, sand samples have been taken from 21 wells and the sand production is common, which has become a key technical problem affecting the stable production of the gas field. To this end, a porous elastic-plastic 3D sand production fluid-solid coupling model was established, and a numerical simulation method was adopted to carry out a full range of sand production rate prediction for the Dina 2 Gasfield. The study shows that the sand production process in Dina 2 Gasfield can be divided into four stages according to the sand production rate: small amount of sand production, incremental sand production, intensifying sand production and stable sand production; the area of heavy sand production is around Wells X-6, X-7 and X-8, and the amount of sand production gradually decreases from the middle of the gas field to the surrounding area, and the key sand production layer is located in E1-2 km² Formation of Kumugeliemu Group. It was verified on the basis of the field measurement data that the prediction error of the sand production rate is within 15%, indicating the practicality of the prediction method. This study can provide technical support for the formulation of reasonable sand control measures and efficient development of the oilfield.

Development of Selective Water Plugging Interfacial Gel

Li Jun, Wang Li, Li Yong, Chen Qilong, Wang Sha, Lu Hongsheng

2023, 30(3):  155-160.  DOI: 10.3969/j.issn.1006-6535.2023.03.020

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In response to the disadvantages of poor oil-water selectivity and high injection pressure of high polymer selective water plugging gels, small-molecule gel factors were synthesized through the acid-amine neutralization reaction between N,N-dimethylcyclohexylamine and stearic acid, arachidic acid and behenic acid respectively, which can spontaneously form interfacial gels at the oil-water interface. The microscopic appearance and rheological properties of the interfacial gels were investigated by polarizing microscope and rheometer, and the selective water plugging performance of the small-molecule gel factor at the oil-water interface was investigated by displacement experiments. The results show that the viscosity of the interfacial gel formed by the small-molecule gel factor at the oil-water interface can reach 105 mPa·s or more, and the yield stress is as high as 100 Pa; the displacement experiment proves that the small-molecule gel factor can selectively block the water channel, the breakthrough pressure gradient is up to 2.74 MPa/m, and the recovery rate is enhanced by 21.3 percentage points. The small-molecule gel factor has good oil-water selectivity and can effectively enhance the recovery of crude oil, so it is worth to be promoted and applied.

Study and Test on Self-pressurized Oil Transmission Technology of Associated Gas Cap in SAGD Production Station

Gao Zhongmin

2023, 30(3):  161-167.  DOI: 10.3969/j.issn.1006-6535.2023.03.021

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Generally the oil between SAGD oil production station and the joint station is transmitted by pumping, with high energy consumption, significant loss and safety hazards. At the stage of steam chamber expansion in SAGD development, there is a great amount of associated gas stably generated, which make it possible to realize self-pressurized oil transmission. Therefore, a study was conducted on the self-pressurized oil transmission technology for SAGD production station. The original gathering and transmission technology was optimized on the basis of high and stable gas cap pressure of the buffer tank in SAGD production station, and self-pressurized oil transmission was enabled without any external force. The technology can bring about such economic and social benefits as low cost, high profit, staff reduction and improved efficiency. This technology has been stably applied in three stages of SAGD development: steam chamber expansion, stable oil drainage and initial steam chamber decline, providing technical support for the promotion and application of SAGD development technology.

Optimized Design of Fracturing Parameters for New Wells in Formation Deficit Zone of Tight Conglomerate Reservoir

Li Jie, Ma Mingwei, Yang Shengfeng, Wang Song, Li Yunzhe, Xu Peng, Li Jiye

2023, 30(3):  168-174.  DOI: 10.3969/j.issn.1006-6535.2023.03.022

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To address the problem that the energy deficit of the old well formation has an impact on the reservoir stimulation and production of the new well, a numerical model of the reservoir is established on the basis of a three-dimensional geological and ground stress model, the dynamic change law of the stress field of the old well is studied in combination with the production data, the characteristics of the fracture pattern of the new well are predicted based on the fracture propagation model, and the fracturing design parameters are optimized. The study shows that the ground stress area caused by the development of old wells has an induced effect on the fracture propagation of neighboring wells, and optimizing the ratio of the front fluid in new wells can compensate for the formation energy deficit, avoid the artificial fracture in new wells from extending excessively in the deficit direction, so that the reservoir stimulation is more adequate and post-fracturing capacity is more desirable. The example application of Well Group H1 in the Mahu conglomerate reservoir shows that the preferred cluster spacing is 25-30 m, the fluid intensity used is 18 m³/m, and the single cluster pad fluid volume is 400 m³, which can effectively inhibit the induction of artificial fractures in new wells by low stress zones and improve the proppant placement concentration. This study has important guidance for the development of similar conglomerate reservoirs.