Table of Content

25 December 2022, Volume 29 Issue 6

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Summary

Research Progress and Prospect of Autogenic Acid System

Li Xiaogang, Qin Yang, Zhu Jingyi, Liu Ziwei, Jin Xinxiu, Gao Chenxuan, Jin Wenbo, Du Bodi

2022, 29(6):  1-10.  DOI: 10.3969/j.issn.1006-6535.2022.06.001

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The authigenic acid acidizing technology is one of the main measures for stimulation high temperature (ultra-high temperature) and low permeability tight oil and gas reservoirs. The research progress of authigenic acid acidizing technology was comprehensively analyzed, and the acid-rock reaction characteristics of authigenic acid, the main acid-generating mechanism of authigenic acid, and the research progress of authigenic organic acid, authigenic hydrochloric acid, authigenic hydrofluoric acid and composite authigenic acids were introduced, the influence of the type of authigenic acid, hydrogen supply capacity, cost, retardation capability, corrosion inhibition capability and other factors on the field application of acidizing work fluid was analyzed, and the application of authigenic acid in acidizing operation was prospected. This study can provide a reference for the development, popularization and application of autogenic acid acidizing technology.

Eview on Study of Heavy Oil Modification Additives

Guo Hongxia, Xie Yuke, Lu Jianfeng, Jin Guangxing, Zhao Kailiang, Yang Yong, Zhang Jinbai, He Junli

2022, 29(6):  11-19.  DOI: 10.3969/j.issn.1006-6535.2022.06.002

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It is difficult to exploit the crude oil with conventional technology due to high viscosity, high flow resistance and poor flow capacity of crude oil in heavy oil reservoirs. A conclusion was made in this paper to summarize the study of heavy oil modification additives (catalysts and hydrogen donor), point out the existing problems, and outline the future study directions. The study shows that the existing heavy oil modification catalysts are disadvantaged by unclear catalytic mechanism, poor universality, high cost, regeneration difficulties, easy deactivation and environmental pollution. In addition, the uneven mass transfer and severe reaction conditions of hydrogen donor in heavy oil modification reaction will lead to limited hydrogen supply. Therefore, the future study of heavy oil modification additives is to further explore the modification mechanism of heavy oil at the molecular level, and develop modification additives with wide application scope, high activity and controllable cost in combination with complex formation conditions. The study provides a reference for studying and developing heavy oil modification additives and applying the EOR technology in oil fields.

Geologic Exploration

On Exploration and Development Potential of Shale Gas in Longyi₁⁴ Sub-bed in Luzhou Block

Zhou Anfu, Xie Wei, Qiu Xunxi, Wu Wei, Jiang Yuqiang, Dai Yun, Hu Xi, Yin Xingping

2022, 29(6):  20-28.  DOI: 10.3969/j.issn.1006-6535.2022.06.003

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In order to clarify the characteristics and exploration and development potential of shale reservoirs in Longyi₁⁴ Sub-bed, Longmaxi Formation, Luzhou Block and to realize the longitudinal three-dimensional development of the shale reservoirs in Longmaxi Formation, Southern Sichuan, Longyi₁⁴ Sub-bed is divided into three single horizons: a, b and c, and their characteristics are analyzed, including shale thickness, organic matter abundance, mineral composition, physical characteristics, reservoir pace type and hydrocarbon showing. The result shows: Class I reservoir of Longyi₁⁴ Sub-bed in Luzhou Block is featured by an average thickness of 35.6 m, a distribution area of about 1 900 km² and geological resources of more than 8 000×10⁸m³, indicating bright prospects for exploration and development. The shale reservoir at Horizon b is of a thickness of greater than 20 m, an average TOC is greater than 2.5%, a content of brittle minerals of greater than 55%, an average porosity of 4.9%, and an average gas content of 4.5 m³/t, which demonstrates superior reservoir conditions. Compared with the current main pay - Longyi₁¹ Sub-bed, the shale reservoir at Horizon b of Longyi₁⁴ Sub-bed has higher clay content and inorganic pore proportion, which requires scientific fracturing technology and shut-in and drainage measures in the exploitation process to achieve better development results. The results of the study will provide technical support for expanding shale gas exploration and development horizons and improving the production degree of shale gas resources in Longmaxi Formation, Luzhou Block.

Characteristics of Upper Paleozoic Reservoirs and Its Influence on Natural Gas Accumulation in Yichuan-Huanglong Area, Ordos Basin

Shan Junfeng, Wu Bingwei, Jin Ke, Dong Desheng, Liu Yuanyuan, Cui Xiaolei, Chi Runlong, Nie Wenbin

2022, 29(6):  29-38.  DOI: 10.3969/j.issn.1006-6535.2022.06.004

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Upper Paleozoic Benxi Formation, Shanxi Formation and Shihezi Formation in Yichuan-Huanglong Area are the chief target formations for exploration and development, and the natural gas enrichment and accumulation are principally controlled by the sedimentary facies and reservoir physical properties. After the evolution of marine-marine-continental transition facies-continental sedimentary system in the Late Paleozoic, the sedimentary facies types are different and the change law of reservoir physical properties is not clear yet. Therefore, the characteristics of Upper Paleozoic reservoirs in Yichuan-Huanglong Area were comprehensively studied with sedimentary evolution analysis, field outcrops, drilling cores, micro reservoir analysis, logging curves and other data. The result shows: Benxi Formation is mainly developed with tidal-flat facies, Shanxi Formation and He₈ Member of Shihezi Formation mostly developed with meandering river-braided delta facies. Tidal channel of Benxi Formation and underwater distributary channel of Shanxi Formation and He₈ Member are the most favorable reservoir facies zones. The sand bodies of the tidal channel of Benxi Formation are lenticular in shape and limited in distribution; the sand bodies of the underwater distributary channel at the front edge of the meandering river delta in Shanxi Formation are migrated and superimposed in multiple periods, with a certain scale; the sand bodies of the underwater distributary channel at the front edge of the braided river delta in He₈ Member are superimposed vertically and connected horizontally, with a blanket-shaped distribution. The reservoir of Benxi Formation is dominated by quartz sandstone, with main pore types of primary intergranular pores and secondary dissolution pores; the reservoirs of Shanxi Formation and He₈ Member are mainly composed of lithic quartz sandstone, with main pore type of lithic dissolution pore. The lithology and pore structure of the Upper Paleozoic sandstone reservoir are the main factors affecting the hydrocarbon showing. The reservoir as a whole is characterized by extra-low porosity and ultra-low permeability, but the content of quartz in the rock gradually decreases from bottom to top, the content of rock chip and fillings gradually increases, and the lithology and pore structure of the reservoirs gradually become worse from Benxi Formation to Shanxi Formation and He₈ Member. The sand bodies of the thick tidal channel of Benxi Formation and the continuously superimposed distributary channel of Shanxi Formation and He₈ Member are lithologically pure and coarse-grained, with good physical properties and high gas abundance, and they are the dominant reservoirs, will the high-quality pores developed in Benxi Formation, which is easy to accumulate natural gas. There is much for reference of the study results to the exploration, development and reserve enhancement of Yichuan-Huanglong Area.

Lithofacies Types and Reservoir Distribution of Volcanic Rocks in Jingyan Area, Sichuan Basin

Li Suhua, Jia Huofu, Hu Hao, Li Rong, Yu Yang

2022, 29(6):  39-46.  DOI: 10.3969/j.issn.1006-6535.2022.06.005

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A great breakthrough was made in the field of Permian volcanic rock exploration in Jingyan Area, southwest Sichuan Basin, but there are various volcanic rock types, obvious differences in seismic reflection characteristics, little coring data, thin reservoirs and unclear distribution patterns; therefore, it is important to further identify the distribution of volcanic facies and high-quality reservoirs in Jingyan Area for volcanic oil and gas exploration in the area. A forward model of volcanic reservoir was established based on the real drilling data to simulate the factors affecting the variation of seismic reflection characteristics of volcanic rock, and an identification model was established for volcanic rock facies and reservoirs. On the basis of the analysis on single well cycle, lithology, lithofacies and seismic waveforms, the types and distribution of volcanic facies were determined by seismic facies, stratigraphic thickness, coherence cube, three-dimensional visualization and other methods. After fine calibration of volcanic reservoirs, the distribution of upper and lower volcanic reservoirs was determined by wave impedance, neural network inversion and other method. Finally, the areas developed with high-quality reservoirs were delineated in combination with the favorable lithofacies, reservoir thickness, fault, and fracture distribution of volcanic rocks. The study results show that there are three types of lithofacies developed in Jingyan Area, namely, eruptive facies, volcanic channel facies and overflow facies. The distribution of volcanic rocks is relatively stable, and two reservoirs are developed in this area. The development of reservoir under the eruptive facies has an obvious effect on the seismic reflection at volcanic rock bottom. As predicted by various methods, the high-quality reservoirs of volcanic rocks are mainly distributed in the west and southwest of the work area, and the superimposed area of basement rift and fractures is the next target of favorable area exploration. There is much guiding significance of the study results for the exploration of volcanic oil and gas in Jinyan Area.

Characteristics of Mid-Deep Paleogene Sandstone Reservoirs in Baiyun Sag and Controlling Effect of Dissolution on High-Quality Reservoirs

Wen Jing, Zhao Jingzhou, Li Jun, Er Chuang

2022, 29(6):  47-55.  DOI: 10.3969/j.issn.1006-6535.2022.06.006

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To definite the characteristics of mid-deep paleogene sandstone reservoirs and the controlling effect of dissolution on high-quality reservoirs in Baiyun Sag, Pearl River Mouth Basin, South China Sea, according to the core observation, casting slice, field emission scanning electron microscopy and observation results, the lithological characteristics, reservoir space characteristics and physical characteristics of Paleogene sandstone reservoirs in Baiyun Sag were described in combination with X-ray diffraction, mercury penetration analysis and other data and technical means. In addition, a deep study was conducted on the diagenesis related to reservoir physical properties and reservoir quality. As found in the results, the reservoir sandstones in the East Sub-sag of Baiyun Sag are mainly composed of feldspathic quartz sandstone and lithic quartz sandstone. The lithology of the North Slope of Baiyun Sag is more complex than that of the East Sub-sag, primarily composed of feldspathic quartz sandstone, with a small amount of feldspathic lithic quartz sandstone. The pores of the mid-deep reservoirs in the East Sub-sag include intergranular and intragranular dissolved pores. The pore development degree of reservoirs in the North Slope is slightly higher than that of the East Sub-sag, with a higher content of intergranular dissolved pores, intragranular dissolved pores and mold pores. The reservoirs in Baiyun Sag are generally characterized by low porosity and permeability. The dissolved pore formed by the interaction of organic acids with feldspar and igneous rock debris is the most important factor that controls the physical properties of the Paleozoic sandstone reservoir in the study area. The study results can become certain reference and guidance for the exploration and development of sandstone reservoirs in Baiyun Sag, Pearl River Mouth Basin.

Study on Sedimentary Microfacies Characterization Method in Sparse Well Block with Progressive Extension

Nan Jinhao, Sha Zonglun, Jia Hongbing, Liu Shaoran, Xiong Xiangdong, Lin Tong

2022, 29(6):  56-64.  DOI: 10.3969/j.issn.1006-6535.2022.06.007

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In view of the low degree of well control in the sparse well block around the development area and the great gap between the accuracy of sediment characterization and the existing development area, the differences were analyzed in sandstone thickness and seismic impedance of different sedimentary microfacies, the statistics was made for the sandstone parameters of different sedimentary microfacies in the development area, and the sandstone database was established in correspondence to different microfacies; based on the control range of fan spreading on the plane predicted by seismic attributes, the development characteristics of sedimentary sand bodies in sparse well block characterized by seismic inversion were analyzed by microfacies knowledge base, and the microfacies types of sand bodies were determined; the quantitative characterization of sedimentary microfacies in sparse well block can be implemented by taking the extension range of sand bodies parallel and vertical to sediment origins as microfacies distribution range. The study shows that The development characteristics of sand bodies in different sedimentary microfacies can be effectively characterized by single sand body thickness, cumulative probability, inverse wave impedance and other parameters of braided river delta microfacies in the dense well pattern area of Block A, among which underwater distributary channel and channel mouth bar were obviously advantaged in sandstone parameters. The microfacies characterization method based on the microfacies knowledge base and seismic attribute prediction can effectively improve the accuracy of sedimentary microfacies characterization in the sparse well block, with a coincidence rate up to 91%. The favorable microfacies types in the sparse well block are mainly distributed in Well Blocks A5 and A02. The study results have been applied to the evaluation, deployment and scheme implementation of sparse well block with progressive extension around Block A, and achieved excellent results, with a cumulative production capacity of 2.35×10⁴t and proved reserves of 200×10⁴t. The study results provide strong support for stimulation and stable production of old oilfields.

Geological Characteristics and Development Potential Analysis of Linxing Tight Sandstone Gas Reservoir

Mi Honggang, Zhang Bing, Zhu Guanghui, Su Yu, Zhang Haifeng

2022, 29(6):  65-72.  DOI: 10.3969/j.issn.1006-6535.2022.06.008

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To address the technical problems of strong heterogeneity and insufficient reserves production in the Linxing Area of the Ordos Basin, the fourth member of the Shihezi Formation in the Linxing Area is taken as the research object, a method combining drilling, logging and seismic data is adopted to carry out fine characterization of three-dimensional spatial sequence stratigraphic framework, and on this basis, the fine description of sublayer sedimentary microfacies of Shihezi Formation and the qualitative and quantitative prediction of tight sandstone “sweet spot” high-quality reservoirs are carried out. The research result shows: The high-quality tight sandstone reservoirs in the Linxing Area are mainly thick tight sandstone river channel sand bodies with porosity of greater than 6%, density of less than 2.55 g/cm³, and v_P/v_S of less than 1.8, and their seismic reflection characteristics are medium-low frequency continuous medium-strong reflection; according to the prediction results of high-quality reservoir “sweet spots”, three-dimensional well locations were deployed to increase the reserves production degree of tight gas reservoirs in Linxing Block by 15.3 percentage points, and the locations of 50 wells were optimized, increasing the gas recoverable reserves by 100×10⁸m³. The research results provide favorable technical support for the three-dimensional exploration and development of unproduced reserves of tight gas reservoirs in the Linxing Area, and have important reference significance for the exploration and effective production of reserves of the same type of tight sandstone gas reservoirs.

Understanding and Practice of Oil and Gas Deepening Exploration in Mature Exploration Area of Liaohe Depression

Li Xiaoguang, Chen Chang, Han Hongwei

2022, 29(6):  73-82.  DOI: 10.3969/j.issn.1006-6535.2022.06.009

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The Liaohe Depression has already entered the high maturity stage of exploration. The deepening exploration in mature exploration area cannot be limited to the scope of geophysical technology progress, drilling level improvement and revolution of oil and gas reservior stimulation technology, but should be reflected in the accurate grasping and innovative understanding of the objective existence of subsurface geological conditions. To address the problems that the conventional oil and gas exploration is difficult to achieve oil and gas discovery on a large scale and conventional exploration ideas are difficult to adapt to new unconventional oil and gas targets, the ideas of deepening geological understanding and reconstructing reservoir formation model were applied to innovate reservoir accumulation model in the Qingshui Depression of Western Sag to newly discover oil reserves of 2 800×10⁴t in rocky oil and gas reservoirs; a new "two-element“ evaluation model was created in Leijia area, which realized the surface-to-body transformation of unconventional oil and gas target evaluation; the exploration unit was reconstructed in the Member 3, Shahejie Formation of the Eastern Sag, and a new exploration unit was discovered and the Well X47 was deployed and implemented to obtain high production gas flow. A number of achievements were made during the exploration of oil and gas in mature exploration area of Liaohe Depression, which provided ideas and methodological reference for the exploration of similar type of mature area.

Rock Mechanical Properties and Energy Evolution Characteristics of Different Shale Lithofacies in Marine-Continental Transition Facies

Liu Junjie, Wu Jianjun, Xiong Jian, Li Bing, Liu Xiangjun, Liang Lixi

2022, 29(6):  83-90.  DOI: 10.3969/j.issn.1006-6535.2022.06.010

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In view of the insufficient understanding of rock mechanical properties and energy evolution characteristics of different shale lithofacies in the marine-continental transition facies, a series of experimental studies were carried out with the downhole rock samples from the Shan₂³ sub-member of the Permian Shanxi Formation in the eastern margin of the Ordos Basin as the study object. The result shows: The mechanical properties of different shale facies are quite different. Under the uniaxial compression test, the average compressive strengths of the siliceous shale facies and clay shale facies are 58.5 and 17.9 MPa, respectively. Under the condition of uniaxial compression, different shale lithofacies have strong brittleness and split failure, with the increase of confining pressure, the plasticity increases and transforms into shear failure, and the siliceous shale facies is the most severely damaged. The energy parameters of different shale lithofacies at the peak strength point are quite different and are affected by the confining pressure to different degrees. The average total energy of siliceous shale facies, clay shale facies and mixed shale facies under uniaxial compression is 0.071, 0.016 and 0.044 J/cm³, respectively. The research results have certain reference significance for the study of wellbore stability and fracturing optimization of marine-continental transition shale reservoirs.

Reservoir Engineering

Phase State and Component Change Law of CO₂ Flooding in Low-Permeability Sandstone Reservoirs

Liu Jianyi, Yang Xue, Liu Yong

2022, 29(6):  91-96.  DOI: 10.3969/j.issn.1006-6535.2022.06.011

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To work out the phase state, changes in oil and gas components and the response of crude oil to gas injection in the gas injection development of Block W in low-permeability sandstone reservoirs, classical theories such as mass conservation and equation of state were employed to study the characteristics of crude oil component changes by gas injection expansion, gas chromatography test and PVT phase equilibrium simulation software, with CO₂ gas as injection medium. The result shows: When the CO₂ injection amount increased to 0.814 mol, the bubble point pressure increased by 0.96 times, the sample volume expanded by 2.09 times, and the CO₂ content in the fluid gradually increased from 0.6% of the background value to 81.0%, indicating that the bubble point pressure was mainly under the control from the light hydrocarbon components, and the crude oil components changed significantly due to the dissolution and separation of gas. This study technically supports the oil recovery enhancement by gas injection, the design of oil and gas transmission technology, and the preparation of development plan of low-permeability sandstone reservoirs in Dongpu Sag, as well as having important practical significance for its development.

Study and Test on Steam Flooding Technology for Thin Interbedded Ultra-Heavy Oil Reservoirs

Liu Qilu

2022, 29(6):  97-103.  DOI: 10.3969/j.issn.1006-6535.2022.06.012

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Thin interbedded ultra-thick oil reservoirs are characterized by small net total thickness ratio, strong longitudinal inhomogeneity and severe steam overlap. In order to clarify the feasibility and influencing factors of steam flooding for enhanced oil recovery in such reservoirs, a study was made on the reservoir engineering optimization design by means of numerical simulation technology and dynamic analysis, taking Xinglongtai reservoir in Block Du 80 as the target, with reference to the successful experience of steam flooding in other types of ultra-heavy oil reservoirs. As found in the results, in Xinglongtai oil reservoir of Block Du 80, the mudstone interbed of about 5 m is stably developed, which can be subdivided into 2 development layers for independent development; the wells were arranged into inverted nine-spot pattern with well spacing of 70 m, the production and injection ratio was 1.1-1.2, the steam injection rate was 1.7-1.9 t/(d·m·hm²), the downhole steam dryness was greater than 50% as the best, and the time of flooding conversion is determined as the time when the reservoir temperature is greater than 80 ℃; the perforation density was determined as 4, 8, 12 and 16 holes/m respectively according to the thickness of the sub-layer and the range limit. The field pilot test of steam flooding has achieved good results in doubling the daily oil production and oil recovery rate of single well. The study results provide technical support for the conversion of development mode after steam stimulation in thin interbedded ultra-heavy oil reservoirs.

Test and Application of Regenerative Nitrogen Foam Flooding in Low-Permeability Reservoirs

Cheng Hongjie, Chen Yukun, Li Tieshuan, Zhang Hanqing, Zhang Jipeng, Wu Yongbin

2022, 29(6):  104-110.  DOI: 10.3969/j.issn.1006-6535.2022.06.013

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The conventional nitrogen foam is difficult to re-foam after defoaming in the formation, which severely restricts the effect of foam flooding, laboratory tests were conducted to select an economical and efficient regenerative nitrogen foam flooding formulation system in terms of foaming capacity, re-foaming performance, salt resistance and temperature resistance and pressure resistance with a multi-factor evaluation method. One-dimensional core displacement test was conducted under simulated reservoir conditions to confirm the feasibility of regenerative foam and select the reasonable injection parameters: the gas-liquid ratio was 3∶1, the injection rate was 0.3-0.4 mL/min, and the gas and liquid were injected simultaneously. Pilot tests were conducted in two well clusters in SN well block, Xinjiang Oilfield. The regenerative nitrogen foam plug of 0.43 times of pore volume was injected cumulatively, and the daily oil increase was more than 8 t/d, and the water cut of the well cluster decreased by 6.6 percentage points. In the subsequent water flooding, the oil production was enhanced by re-foaming to 4 947 t, and the input-output ratio reached 1.0∶1.6. It is found in the study that regenerative nitrogen foam flooding can effectively improve the oil production and recovery, with important application potential in similar reservoirs.

Microfracturing-based Expansion Technology and Application in Shallow Ultra-heavy Oil Horizontal Wells

Shen Tingting

2022, 29(6):  111-118.  DOI: 10.3969/j.issn.1006-6535.2022.06.014

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A microfracturing-based expansion technology for horizontal wells was proposed to improve the seepage conditions around the horizontal wellbore, because the infill horizontal wells were not connected to the original wells in composite well pattern under steam flooding and gravity drainage in the heterogeneous reservoirs, Qigu Formation, F Oilfield, Xinjiang Oilfield. The feasibility of microfracturing-based expansion technology and the change characteristics of expanded reservoir were analyzed by laboratory core test, geomechanical finite element simulation and thermal numerical simulation. The results show that he reservoir was high in high quartz while low in clay mineral content, and well developed with pores, which was favorable for water flooding for expansion; in the process of stable pressurization, the spread range of the injection fluid was expanded to reduce the effective confining pressure of the surrounding reservoir and significantly improve the expansion effect; the displacement and porosity of the expanded reservoir in longitudinal direction were obviously better than that in transverse direction, which is conducive to the connection of upper and lower injection-production wells. After five rounds of steam stimulation for preheating after microfracturing-based expansion, the oil wells were connected quickly. In the preheating period, the periodic oil production and oil-steam ratio were significantly improved, and the productivity of horizontal section was greatly enhanced. The study results provide a reference for improving the connectivity among injection and production wells in composite well pattern under steam flooding and gravity drainage.

A Review of Unconventional Gas Well Production Decline and EUR Prediction Methods

Cui Yingmin, Guo Hongxia, Lu Jianfeng, Yang Yong, Zhang Jinbai, Liu Wei, Jin Guangxing, Zhao Kailiang

2022, 29(6):  119-126.  DOI: 10.3969/j.issn.1006-6535.2022.06.015

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In view of the problems of production decline of unconventional gas wells, large differences and low accuracy in the EUR (predicted ultimate recovery factor) results, the theoretical basis and advantages and disadvantages of the various methods such as Wattenbarger linear flow method, PLE power exponential decline model method, and SEPD extended exponential decline model method were compared and analyzed to evaluate the objects of use, required data and applicable conditions of various methods. At the same time, the prediction results of the four models of PLE, SEPD, Duong and LGM in the linear flow stage and the quasi-boundary flow stage were compared with the prediction results of the numerical simulation well, and practical applications were carried out. The research result shows: Various commonly used production decline methods for unconventional gas wells are suitable for different formation flow regimes; Wattenbarger linear flow, quasi-constant flow pressure, and horizontal well multi-stage fracturing model are more suitable for flow conditions with variable production and variable bottom-hole pressure. PLE and Duong models are more accurate for prediction within 2a. This study provides a reference for production prediction of unconventional gas wells.

Recognition of Variation Law of Active Hydrogen Component of Fire-Flooded Crude Oil

Yang Hong, Su Rigu, Chen Lijuan, Wang Xusheng, Chen Long, Pan Jingjun, Guo Yong

2022, 29(6):  127-132.  DOI: 10.3969/j.issn.1006-6535.2022.06.016

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In order to enrich the methods for identifying whether high temperature oxidation occurs and the degree of high temperature oxidation during the fire flooding development, the real boiling point distillation method was applied to separate the crude oil before and after the effectiveness of fire flooding in Hongqian Area of Xinjiang Oilfield, the corresponding real boiling point distillation curves were plotted, and the acid value of each fraction was measured. The high-resolution mass spectrometry was used to analyze different types of acidic compounds under the condition of electrospray ionization source in negative ion mode, and the equivalent double bond index (DBE) and carbon number distribution of O2-type components were classified in details. The results show that although the fluctuation range of the acid value of crude oil before and after the effectiveness of fire flooding is less than 1.0 mg/g, the content of low and medium boiling point components in the effected crude oil and the yield of real boiling point distillation mass are significantly improved, some components of the effected crude oil are oxidized to generate compounds containing active hydrogen functional groups, and two peaks appeared in the boiling point range of 200-250 ℃and 300-420 ℃. The mass spectrometry analysis shows that the relative abundances of DBE 3 and 4 in the O2 components of the fire flooding effected crude oil increases, and the proportion of two-membered and three-membered naphthenic acids increases. The research results can provide guidance for the analysis of crude oil fire flooding process and the refining of distillate products.

Analysis of Influencing Factors on the Development Effect of CO₂ Assisted Gravity Flooding

Lei Meng, Qu Yaguang, Wan Cuirong, Yang Bo, He Denghui, Ma Guoqing, Gong Xu

2022, 29(6):  133-140.  DOI: 10.3969/j.issn.1006-6535.2022.06.017

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To address the problem that the effect of various geological parameters on the development of CO₂-assisted gravity flooding technology is still unclear, taking a medium and low permeability oil reservoir as the research object, a number of theoretical models of one-injection and one-recovery mechanism were established to study the influence of the formation sedimentary rhythm, dip angle, permeability, porosity, ratio of vertical permeability to horizontal permeability, and permeability max-min ratio on the effect of the CO₂-assisted gravity flooding. The result shows: The CO₂-assisted gravity flooding is more suitable for positive rhythm sedimentary strata than negative rhythm strata; there is a certain formation dip, which is conducive to gravitational differentiation and formation of gas caps; the CO₂-assisted gravity flooding is carried out in medium-low permeability and low-porosity oil reservoirs, which has a certain effect on the inhibition of gas channeling breakthrough. The smaller the ratio of vertical permeability to horizontal permeability, the more conducive to inhibiting the rapid vertical diffusion of gas. The permeability max-min ratio has little effect on CO₂-assisted gravity flooding. The influence of different geological factors on the recovery degree is the ratio of vertical permeability to horizontal permeability, formation dip angle, formation permeability, formation porosity, formation permeability max-min ratio in descending order. The field test of the A Reservoir shows that CO₂-assisted gravity flooding can increase the stage cumulative oil production by more than 3 times, and can achieve a significant increase in production. The research results can provide theoretical guidance for the development of CO₂ flooding in similar oilfields.

Prediction Method and Application of Single Shale Gas Well Production in Weiyuan Block, Sichuan Basin

Han Shan, Che Mingguang, Su Wang, Xiao Yuxiang, Wu Zhongbao, Chen Jianyang, Wang Libin

2022, 29(6):  141-149.  DOI: 10.3969/j.issn.1006-6535.2022.06.018

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To address the problem that the main controlling factors of single shale gas well production in Weiyuan Block, Sichuan Basin are unknown, based on the geological and engineering data and production data of 132 gas wells which have been put in production for more than a year in the area, an analytical study was conducted by the gray correlation method. The study shows that, the main controlling factors affecting the first-year cumulative production of a single shale gas well are proppant dose, number of fracturing stages, median vertical depth of horizontal wells, fracturing section length, fracturing fluid volume, porosity, pressure coefficient and sanding intensity. It was clear that the machine learning method was higher in accuracy after comparison of the machine learning method and the traditional empirical formula method to predict the first year's cumulative output and initial output. Meanwhile, based on the analysis of the main controlling factors, the machine learning method applicable to the study area was preferably selected as the support vector machine method, and its prediction accuracy was higher than 90%. The study has an important implication to the productivity evaluation of similar shale gas blocks.

Drilling & Production Engineering

Analysis on Key Influencing Factors of Proppant Migration in Tortuous Fractures Based on CFD-DEM Method

Wang Xuefei, Wang Suling, Hou Feng, Wang Ming, Li Xuemei, Sun Dandan

2022, 29(6):  150-158.  DOI: 10.3969/j.issn.1006-6535.2022.06.019

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The migration and displacement of proppant in fractures is the key to maintain fracture opening and enhance fracture conductivity, but the mechanism of proppant migration in tortuous fractures remains unclear. According to the principle of computational fluid dynamics, a numerical model of proppant migration in tortuous fractures was established by the discrete unit method to study the effects of proppant-carrying fluid injection rate, fracturing fluid-proppant ratio, proppant particle size and other factors on the migration and displacement of proppant in tortuous fractures. The result shows: The greater the tortuosity of the fracture, the shorter the proppant displacement distance and the greater the flow rate loss; at 20 mm from the fracture entrance, the flow rate loss rate in the fracture with tortuosity of 1.2, 1.5 and 2.0 was increases by 2.2, 3.7 and 4.5 times compared with that in the fracture with tortuosity of 1.0; the proppant displacement distance in the tortuous fracture increased with the increase of proppant injection rate, and decreased with the increase of fracturing fluid-proppant ratio and proppant particle size. This study can theoretically guide the study of proppant migration in tortuous fractures.

Development and Application of Polymer Thickener for Fracturing Fluid with High Temperature and Salt Resistance and Low Damage

Zhang Wei, Ren Dengfeng, Zhou Jin, Liu Shuang, Wang Yan, Wang Qiao

2022, 29(6):  159-164.  DOI: 10.3969/j.issn.1006-6535.2022.06.020

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The Kuqa Piedmont Block in Tarim is an ultra-deep high temperature and high pressure block with the characteristics of deep burial, high temperature and high formation pressure, so conventional fracturing fluids are not favoralole for the construction requirements of this block. To this end, acrylamide (AM), trimethyl (3-acrylamidopropyl) ammonium chloride (APTAC), 3-acryloylethanol-3-methylpropanesulfonic acid (AEMS) were used as monomers to synthesize the polymer thickener JAS-3 with temperature resistance, salt resistance and low damage through the optimization of additives dosage and reaction parameters, and the properties of such polymer thickener were evaluated. The research shows: The polymer fracturing fluid prepared with JAS-3 has good temperature and shear resistance, sand-carrying performance and low damage to the reservoir. After adding NaBr with a mass fraction of 30% to 40%, its viscosity can still be maintained above 85 mPa·s at a temperature of 180 ℃ and a rotation speed of 170 r/s. The polymer fracturing fluid has a large elastic modulus, a small viscosity modulus, a larger rigidity, good sand-carrying performance, and meanwhile it has low residue content after gelout, causing small damage to the reservoir. The fracturing fluid has been tested in 6 wells in the Kuqa Piedmont Block in Tarim, and has achieved good stimulation effects. The development of the thickener has important reference significance for the fracturing of ultra-deep high temperature and high pressure blocks.