Table of Content

25 June 2022, Volume 29 Issue 3

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Summary

Development Status and Prospects of In-situ Conversion Technology in Oil Shale

Li Nianyin, Wang Yuan, Chen Fei, Han Yinglong, Chen Wenbin, Kang Jia

2022, 29(3):  1-8.  DOI: 10.3969/j.issn.1006-6535.2022.03.001

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Rational and efficient development of oil shale resources is of strategic significance for energy security and economic development of China. The underground in-situ conversion technology of oil shale had unique advantages compared with surface destructive distillation technology, providing a new direction for oil shale exploitation in the future. In this paper, the development status of underground in-situ conversion technology of typical oil shale was systematically analyzed, and the process characteristics were summarized, such as electric conduction heating, thermal fluid heating, radiation heating and combustion heating. Combined with existing studies, the next study targets were proposed from the aspects of reservoir fracturing, underground reservoir space closure, efficient heating and new energy applications. The study can provide technical reference for green and efficient exploitation of oil shale.

Geologic Exploration

Study on the Difference of Pore Characteristics between Marine and Marine-continental Transitional Shale Gas Reservoirs in Upper Yangtze Region, Northwest Guizhou

Shi Miao, Zhang Jinchuan, Yuan Ye, Tao Longfeng, Liu Zhao

2022, 29(3):  9-17.  DOI: 10.3969/j.issn.1006-6535.2022.03.002

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In order to clarify the differences between the pore characteristics of marine and paralic transitional shale, in the case study of Upper Yangtze Region, Northwest Guizhou, the pore characteristics of Longmaxi Formation marine shale, Niutitang Formation shale and Longtan Formation paralic transitional shale widely distributed in the area were studied, and the types and development and distribution patterns of pores inside the shale were analyzed to further explore the causes of difference. The study showed that, the overall pore distribution pattern of marine shale was dominated by organic pores and followed by rigid intergranular pores such as quartz and carbonate minerals, with the relative content of organic pores accounting for more than 50% of the total pores; the diameter of pores in marine-continental transitional shale was greater and more variable than that of marine shale, and the pore distribution pattern was dominated by inorganic intergranular/intragranular pores and microfractures, followed by organic pores, with a large number of dissolved pores/fractures developed in carbonate minerals, and the relative content of organic pores only accounting for about 20% of the total pores. The difference of sedimentary conditions in formation period was the root cause for the difference of pore development between marine and marine-continental transitional shale, and the different preservation conditions in the later stage also had a certain influence. Differential analysis of reservoir pore characteristics provides an important guidance to the exploration and development of shale gas resources.

Logging Identification Method of Complex Lithology in Buried Hill Based on the Improved KNN Algorithm

Sun Kui

2022, 29(3):  18-27.  DOI: 10.3969/j.issn.1006-6535.2022.03.003

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Xinglongtai Mesozoic conglomerate oil and gas reservoir is a large integrated tectonic-lithological reservoir discovered in Liaohe Depression in recent years, with low proved reserve and great exploration potential. Oil pool was jointly controlled by lithofacies and tectonicss, the reservoir was highly heterogeneous, and the lithology was complex and diverse, making logging identification difficult and restricting the exploration process in this area. To this end, according to the results of core observation, cuttings logging and thin section identification, the requirements of reservoir classification and evaluation, and the principle of logging identification, the lithology of the study area is re-divided into two categories: clastic rocks and volcanic rocks, including six rock types: granitic conglomerate, mixed conglomerate, sandstone, mudstone, basalt and tuff. A crossplot of lithology was prepared on the basis of analysis of logging response characteristics of different rock types to determine the sensitive logging parameters. On this basis, the K nearest neighbor (KNN) algorithm was improved according to the characteristics of logging data, and the shear proximity machine learning algorithm (MKNN) based on the weighting of logging attributes was proposed and used for lithology prediction. The results showed that compared with the traditional K nearest neighbor (KNN) algorithm, the MKNN algorithm was more efficient, solving the problem that the imbalance of lithology sample types and the overlap of logging parameters, and the accuracy of lithology identification was increased from 82.3% to 88.7%, effectively solving the problem of fine lithology evaluation in old exploration areas. There is much for reference of the study to the improvement of logging evaluation accuracy for complex lithologic reservoirs.

Main Controlling Factors and Favorable Area Prediction of Deep Carbonate Gas Reservoirs in Puguang Area

Yu Jiwang, Pang Xiongqi, Zheng Dingye, Wang Xuejun, Xiao Huiyi, Zhang Pengwei, Zhuo Seqiang, Li Hongyu

2022, 29(3):  28-35.  DOI: 10.3969/j.issn.1006-6535.2022.03.004

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The deep marine strata in Puguang Area are the key targets for exploration in northeastern Sichuan. Six hydrocarbon-bearing blocks were discovered with good exploration prospects. such as Puguang and Dawan, With the successive failure of many prospecting wells, it is urgent to improve the re-recognition of characteristics and reservoir formation conditions of gas reservoirs in Puguang Area. Therefore, the types and main controlling factors of gas reservoirs in Puguang Area were analyzed according to logging data, seismic data, core description, analysis and testing data. The results showed that, there were three types of gas reservoirs in the study area: anticline, anticline-lithology, and fault-lithology. The development of gas reservoirs was mainly controlled by four factors. The source rock had high abundance of organic matters, high intensity of gas generation, and wide range of gas generation. In the sedimentary environment of rimmed platform, dolomite such as bioclast and oolite was developed in the reservoir. The dominate reservoir types were porous type, pore-fracture type and vuggy type, with sound physical properties (the average porosity was 8.20% and the average permeability was 79.50 mD). The lithology of the cap rock was mainly gypsum-salt rock, with an average thickness of more than 290 m and a wide distribution range. There were five large NE-trending faults and multiple NW-trending faults which constituted the main channel system for oil-gas migration in Puguang Area. On this basis, four types of favorable areas for accumulation were defined, with the most favorable zones located in Puguang, Maoba and Dawan blocks. The study can provide theoretical guidance and technical support for the further exploration and development of deep carbonate reservoirs in Puguang Area.

Fault Trap Evaluation and Exploration Potential in Jiangling Sag

Liu Jiandang, Lan Zhengkai, Jia Chao

2022, 29(3):  36-42.  DOI: 10.3969/j.issn.1006-6535.2022.03.005

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The complex fracture system in Jiangling Sag makes fault trapping evaluation extremely difficult, and the fault trapping performance and its combination characteristics and influencing factors bring challenges to the later exploration deployment in Jiangling Sag. According to the existing data and previous research results of Jiangling Sag and the principles of geology, the tectonic characteristics of Jiangling Sag and the evolution history of the faults were systematically analyzed, and the main fault systems were classified, the fault trapping mechanism was analyzed on the basis of studies on lateral fault trap, Jiangling Sag, and a fault trap mode of Jiangling Sag was established. The results showed that, the faults in the low-permeability zone could be trapped due to the different permeability between the fault zone and the surrounding rock, and the factors affecting fault trap included lithology joint, mudstone coating rate, rock properties, and permeability near the fault. Based on the comprehensive analysis of the fault trap in Jiangling Sag, a prospecting well was selected to the south of Well Ling 72, Jiangling Sag to making a new start for exploration in Jiangling Sag. The study results provide a theoretical basis for the role of faults in hydrocarbon accumulation and their trap characteristics, and can be used as a reference for the exploration and deployment of similar oilfields.

Distribution Characteristics and Development Potential of Single Sand Bodies in Tight Reservoirs, Well Blocks Yan 145-Yan 128

Luo Tengyue, Mi Naizhe, Wang Nianxi, Qiao Xiangyang, Du Yonghui, Zhao Pengfei, Pan Fuyou

2022, 29(3):  43-49.  DOI: 10.3969/j.issn.1006-6535.2022.03.006

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In response to the problem of rapid production decline and poor development effectiveness of the main gas reservoirs in Shan2 Member, Shan1 Member and He8 Member, Well Blocks Yan145-Yan128, Ordos Basin, a comprehensive reservoir evaluation was performed on the geological characteristics of the main gas reservoirs and the sand body contact relationship by means of refined geologic studies to further definite the distribution characteristics of sedimentary microfacies in reservoirs, characterize the distribution range of high-quality single sand body reservoirs, and identify the potential area of well deployment. The study results showed that the reservoirs in Well Blocks Yan 145-Yan 128 were delta front subfacies deposits, and the sand bodies basically were continuously developed, with a general thickness of 4 to 6 m; the vertical thickness and horizontal size of multi-layer superimposed sand bodies were large, and the connectivity of sand bodies was preferable; the vertical thickness and horizontal size of the isolated sand bodies were limited, and the connectivity of sand bodies was average; single sand bodies were isolated and superimposed in the horizontal direction; for isolated sand bodies, the unperforated production was basically at the original gas reservoirs, with abundant remaining gas, so isolated sand bodies might be the key target for further tapping the potential; according to the characteristics of residual gas distribution, measures such as infilling, re-perforating and set-out, could be taken to increase the production of reserves; it was planned to add 12 infilling wells, 15 set-out wells and 36 re-perforating wells, and it was expected to increase the recoverable reserves by 83×10⁸ m³. The study provides an important reference for the development and adjustment of similar gas reservoirs.

Fracture Development Characteristics and Quantitative Prediction of Tight Reservoirs in Well Block Ma 2, Northwestern Margin, Junggar Basin

Li Xiaomei, Zhang Jigang, Chen Chao, Li Zhou, Liu Zhenping

2022, 29(3):  50-56.  DOI: 10.3969/j.issn.1006-6535.2022.03.007

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To address the difficulties in quantitative prediction of the development, spatial distribution and size of fractures in dense reservoirs in Well Block Ma 2, Northwest Margin, Junggar Basin, the size and spatial distribution of fractures were predicted quantitatively and the results were verified with Petrel's Kinetix fracture simulation module and numerical simulation technology based on crustal stress field, on the basis of analysis on fracture characteristics with cores, slices, imaging logging and other data. The results of the study showed that, the fractures in Well Block Ma 2 were dominated by shear fractures with a density of 5-6 fractures/m and gradually extended to the wings, and the fracture aperture was 0.00 to 0.20 mm; the fracture distribution in Well Block Ma 2 was significantly heterogeneous in longitudinal and planar direction, the fracture-concentrated sections alternated with the fracture-undeveloped sections, and fractures were well developed around most of fault zones. It is more reasonable to characterize the spatial distribution characteristics, such as length and width of fractures, with the microseismic monitoring data of horizontal wells and the results of fracture simulation. The study results provide an important basis for the implementation and optimization of development schemes for Well Block Ma 2, Mahu Oilfield.

Study on Logging Identification Method and Influencing Factors of Water-flooded Zone in Tight Sandstone Reservoir

Liu Yanhong, Luo Xingwang, Zhang Wu, Li Chen, Zhang Ruixue, Luo Qiang, Wang Bin, Zhang Yanmei

2022, 29(3):  57-63.  DOI: 10.3969/j.issn.1006-6535.2022.03.008

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In view of the complex and variable logging response characteristics of the Permian tight sandstone reservoirs in Junggar Basin, difficulty in identifying the water-flooded zones, and other challenges, a logging interpretation model was established for the parameters of the water-flooded zones according to the logging principles and methods, so as to obtain the characteristic parameters of water-flooded zone such as oil saturation and flow zone indicator. A set of quantitative characterization technologies for water-flooded zones in fractured tight sandstone oil reservoirs were developed to accurately identify the logging response characteristics of water-flooded zones. The field application results showed that the technology worked well in actual oil wells. After the implementation of the scheme, the water cut of the oil well was decreased sharply from 98% to 40%, the daily oil production increased from 0.5 t/d to 5.2 t/d, and the productivity increased nearly 10 times, with obvious development effect. The research results enrich the effective identification and quantitative characterization of water-flooded zones in Junggar Basin, and also provide a reference for the identification and effective development of water-flooded zones in similar oil reservoirs.

Reservoir Engineering

Sources and Influencing Factors of Associated Gas in Thermal Recovery of Heavy Oil

Wang Guodong

2022, 29(3):  64-68.  DOI: 10.3969/j.issn.1006-6535.2022.03.009

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In response to unclear sources of associated gas during thermal stimulation by steam injection, laboratory experiments were conducted on crude oil, core and formation water samples from Block Qi 40, Liaohe Oilfield with high-temperature and high-pressure reaction still to explore the generation mechanism and influencing factors of associated gas. The study results showed that, crude oil was the main source of associated gas in thermal recovery and mainly took place in aquathermolysis, and reservoir minerals played a catalytic role in the aquathermolysis; the starting temperature of associated gas production was 150 ℃, and its production increased with the increase of temperature, when the temperature reached 300 ℃, the joint action of aquathermolysis and heavy oil pyrolysis led to a sharp increase of associated gas production; at 250 ℃, the aquathermolysis of crude oil was basically completed after 9 days, after which there was no significant increase in associated gas production. The study is of guiding significance for the full utilization of associated gas in thermal recovery of Liaohe Oilfield by steam injection.

Experiments on Low-temperature Oxidation, Pyrolysis and Coking of Super-heavy Oil

Zhao Shuai, Pu Wanfen, Feng Tian, Wang Wenke, Li Yibo

2022, 29(3):  69-75.  DOI: 10.3969/j.issn.1006-6535.2022.03.010

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Abstract: In response to the problem that the basic properties of oxidized carbon and pyrolysis carbon generated in the in situ combustion of super heavy oil in Block Jin 91, Liaohe Oilfield and the in-situ combustion characteristics were not well understood, experiments on low temperature oxidation and pyrolysis of super heavy oil were conducted with reaction still, the composition of produced gas and the micro morphology, element content and thermogravimetric loss of coke were analyzed by gas chromatograph, field emission scanning electron microscope, energy dispersive X-ray spectrometer and thermogravimetric analyzer, and the activation energy of coke combustion was solved by iso-conversional methods (Friedman and OFW). The results showed that, after low temperature oxidation at250 ℃, the super heavy oil was partially converted into oxidized carbon; after pyrolysis at 400 ℃, the super heavy oil was converted into pyrolysis carbon and modified oil. The relative contents of oxygen and sulfur elements in oxidized carbon were significantly higher than those in pyrolysis carbon. The surface of oxidized carbon was characterized by the inter-melted of coke particles with different particle sizes, and the porous structure of oxidized carbon became more obvious with the increase of temperature. The surface pyrolysis carbon became irregular micro blocks, and many raised particles appeared on the pyrolysis carbon surface with the increase of temperature. The formation of oxidized carbon was helpful to establish combustion front; the combustion activation energy of pyrolysis carbon was lower, conducive to maintaining the stable propagation of the combustion front. The study provides a theoretical guidance for the in-situ combustion in super heavy oil development.

Identification of High-Temperature Oxidation Zones in Cored Wells for Development with In-situ Combustion of Heavy Oil Reservoirs

Liu Qicheng, Yan Hongxing, Yang Junyin, Cheng Haiqing, Dong Xiaodong

2022, 29(3):  76-83.  DOI: 10.3969/j.issn.1006-6535.2022.03.011

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In order to accurately identify the high-temperature oxidation zones in cored wells with in-situ combustion, cores from Cored Well 1-46-K037 in Block Du 66 were used to analyze the group components, saturated hydrocarbons, functional groups and organic elements of crude oil, as well as the carbonate minerals and clay minerals in the reservoir. The study showed that, under the influence of high temperature of in-situ combustion, the contents of saturated hydrocarbons and aromatic hydrocarbons among group components of the crude oil were increased in the high-temperature oxidation zone, while the contents of non-hydrocarbons and asphaltenes were decreased; the main peak carbon in the gas chromatogram of saturated hydrocarbons was decreased, the weight ratio increased, the oxygen content in the infrared spectrum increased, and the H/C atomic ratio in organic elements increased. Due to the thermal decomposition and interconversion of minerals at high temperature, the content of carbonate minerals (dolomite, calcite and siderite) in the reservoir was decreased in the high-temperature oxidation zone, while the content of kaolinite, illite and chlorite in the clay minerals increased and the content of illite-smectite mixture decreased. The high-temperature oxidation zone identified by the characteristic parameters of crude oil should be narrower than the high-temperature oxidation zone identified by the characteristics of the reservoir minerals. The study explores the changing laws of crude oil and reservoir minerals during in-situ combustion, and improved the technical method for identifying high-temperature oxidation zones with cored wells.

A Classification Method of Tight Sandstone Gas Reservoirs Based on Improved Cloud Model

Li Xiaogang, Liu Xing, Du Jia, Yi Liangping, Wu Luofei, Xie Binghong

2022, 29(3):  84-91.  DOI: 10.3969/j.issn.1006-6535.2022.03.012

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A method of classifying dense sandstone gas reservoirs based on improved cloud model was proposed to address the difficulties in accurate classification of oil and gas reservoirs due to ambiguity and randomness. Five evaluation parameters were preferentially selected according to the characteristics of dense sandstone reservoirs, the classification and grading thresholds of each parameter were determined, the cloud numerical characteristics were calculated with an improved cloud model to generate a cloud map, the certainty of each parameter belonging to different reservoirs was analyzed, and a comprehensive model for reservoir evaluation and classification was established in combination with the weighting coefficients of the parameters. The method was applied to the evaluation of sample wells in Linxing Block, Sulige, and the classification results showed that the high-quality reservoirs of Type I and II were of open-flow capacity, while the open-flow capacity of Type III and Ⅳ reservoirs was relatively low, verifying the feasibility and effectiveness of the established reservoir classification method. The study results are both fuzzy and stochastic, improving the accuracy of reservoir classification and grading, with important guiding significance for field exploration and development.

Study on Integrated Closed-Loop Optimal Production Allocation of Offshore Gas Field Clusters

Yan Zhenghe

2022, 29(3):  92-97.  DOI: 10.3969/j.issn.1006-6535.2022.03.013

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In order to achieve scientific and efficient production allocation of single wells and optimize gas field development decisions in the joint development of offshore gas field clusters, real-time production and monitoring data of gas field clusters were fitted by ensemble Kalman filter data assimilation method to obtain a geological model of gas field clusters with prediction results consistent with production performance. Taking the cumulative gas production of the four gas field clusters as the objective function, numerical simulation technologies and particle swarm algorithms were employed to realize intelligent optimization of production allocation for the clusters. The study results showed that the cumulative gas production in 10 years was 19.1×10⁸m³ after intelligent scheme optimization, which was 4.2% higher than that of the manual production allocation scheme, presenting a remarkable effect in productivity optimization. The study effectively improved the development efficiency, and provides technical support and case reference for the efficient development of other complex oil and gas fields and the construction of gas storage.

Fracture Modeling Method and Development Potential Prediction of Ultra-deep Gas Reservoirs with Complex Structure in Northwestern Sichuan

Zhang Lianjin, Wang Junjie, Zhuang Xiaoju, Chen Yang, Wen Wen, Lan Xuemei, Tao Jiali

2022, 29(3):  98-103.  DOI: 10.3969/j.issn.1006-6535.2022.03.014

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Aiming at the geological characteristics of marine carbonate gas reservoirs in Qixia Formation in northwest Sichuan such as complex structure, ultra-deep burial, high temperature and high pressure, thin reservoirs and well-developed fractures, an embedded discrete fracture numerical simulator was prepared with ant tracking technology and embedded discrete fracture numerical simulation method on the basis of 3D seismic data to optimize the parameters of gas reservoir development and predict the development potential of gas reservoirs. The results showed that, it was more suitable to employ ant tracking technology to predict natural fractures in the early stage of gas reservoir development, and the embedded discrete fracture numerical simulator, compared with conventional reservoir simulators, had incomparable advantages in capturing the fluid that migrated in fractures, significantly improving the numerical simulation accuracy of fractured gas reservoirs; the development well type was optimized as highly deviated well and horizontal well for Qixia Formation gas reservoirs, the reasonable spacing between development wells was 1,600 to 1,800 m, the optimal length of horizontal well was 600 m, and the optimal half-length of artificial fracture was 100 m. There is much for reference of the study results for the efficient development of similar carbonate gas reservoirs.

Experiment on Oxidation Mechanism of Crude Oil by Air Flooding in Low permeability Reservoirs

Teng Weiwei, Wu Qingxiang, Hu Xiaodie, Wang Xiaoguang, Cheng Hongjie, Zhu Guifang

2022, 29(3):  104-111.  DOI: 10.3969/j.issn.1006-6535.2022.03.015

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In order to deeply investigate the oxidation characteristics of crude oil and its influencing factors during the development by air flooding of low permeability reservoirs and evaluate its oil displacement efficiency, experiments on crude oil component analysis, oxidation characteristics of crude oil, air flooding and air-foam flooding were conducted to systematically study the oxidation characteristics and laws of crude oil under different conditions, taking the representative reservoirs of low permeability in Xinjiang Oilfield as the study object. The experimental results showed that, under the same conditions, the static oxidation reaction rate of oil sand was higher than and the reaction was more sufficient than that of pure oil sample, and the reaction rate was positively correlated with the reaction pressure, temperature and action time; at the reservoir temperature, the weight ratio of crude oil after oxidation reaction decreased, and the main peak carbon increased; the reaction temperature had a great influence on the dynamic oxidation characteristics of crude oil in air flooding, the higher the temperature, the greater the oxygen consumption and the more sufficient the reaction; the air flooding was effective in oil displacement, with gas channeling easy to occur; the foam flooding could effectively block the gas channeling channel, expand the air swept volume, and improve the air flooding effect. The study results have an exemplary significance regarding the theoretical research and application of air flooding.

Experiment on Optimization of Injection Parameters for Air-foam Flooding in Fractured Reservoirs

Chen Xiaodong, Guo Hongxia, Chen Lin, Wang Jin, Qu Chunxia, Cao Likun, Lu Jianfeng

2022, 29(3):  112-117.  DOI: 10.3969/j.issn.1006-6535.2022.03.016

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In order to improve the recovery efficiency of air-foam injection flooding in fractured reservoirs, experiments of early-stage water flooding, air-foam flooding and subsequent water flooding were conducted in Chang6 Member reservoirs in the west-central area of Wangyao Block to optimize gas-liquid volume ratio, foam slug volume, injection pressure, injection rate and injection time. The results showed that, after the foam was injected into the core, the water content was decreased rapidly, the recovery percent was increased rapidly, the fractured core was plugged faster than the matrix core, but the plugging effect was poor; the earlier the air and foam were injected, the higher the final recovery efficiency; the optimal gas-liquid volume ratio, foam slug volume, injection pressure and injection rate were negatively correlated with the core permeability, and the permeability change was less sensitive to the optimal injection parameters due to high fracture permeability. The results of the study provide an important theoretical basis for fine injection of air-foam flooding in low-permeability fractured reservoirs.

Development and Performance Evaluation of Foaming Agent for Air Flooding in Reservoirs with High Temperature and Salinity

Liu Ziming, Ge Jijiang, Shi Xiaojuan, Zhang Tianci, Guo Hongbin, Li Longjie

2022, 29(3):  118-123.  DOI: 10.3969/j.issn.1006-6535.2022.03.017

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To select foaming agents applicable to reservoirs with high temperature and salinity, foaming performance studies were conducted on alkyl diphenyl ether disulfonate (2A1), alpha olefin sulfonate (AOS), carboxymethyl polyoxyethylene alkyl ether (AEC10) and six betaine surfactants. The results showed that, 2A1, AOS and AEC10 had low foaming rate and poor foam stability; among betaine surfactants, the hydroxysulfobetaine with amide groups was high in foaming rate and the hydroxysulfobetainehas without amide groups was sound in foaming performance; among similar betaine surfactants, the surfactants with long carbon chain had good foam stability and the surfactants with short carbon chain had high foaming rate; the hydroxysulfobetaine with different carbon chain lengths was compounded to obtain compound foaming agents S11 and S12 with excellent foaming performance, and their thermal stability was evaluated; it was found that S11 with amide groups had better thermal stability at 110 ℃, and S12 without amide groups had better thermal stability at 130 ℃. The study results provide a theoretical guidance for the selection of foaming agents applicable to reservoirs with high temperature and salinity

Electric Heating Mechanism and Operating Parameter Optimization in the Expansion Stage of SAGD Steam Chamber

Ding Chao, Yang Zhaochen, Wu Yongbin, Wang Li, Yang Haozhe, Wang Chao

2022, 29(3):  124-130.  DOI: 10.3969/j.issn.1006-6535.2022.03.018

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To further improve the productivity of the horizontal intervals in SAGD well cluster that has entered the steam chamber expansion stage in Fengcheng Oilfield, an integrated numerical model of electric heating-assisted SAGD was established with typical reservoir parameters to study the seepage characteristics of downhole electric heating and optimize the design of operating parameters. The results showed that, downhole electric heating performed in the SAGD expansion stage had four important mechanisms: fixed-point heating, promotion of steam chamber development, fixed-point oil drainage, and improvement of effective permeability in low-permeability intervals; the reasonable steam injection rate was 158-171 m³/d, the steam chamber operating pressure was 4.9-5.4 MPa, the pressure difference between injection and production wells was 0.4-0.5 MPa, and the inter-well pressure difference between adjacent well clusters was less than 0.5 MPa; the reasonable electric heating duration was 2.0-3.0 years, the maximum surface temperature of the electric heater was 250 ℃, and the power was 800-1 000 W/m; the productivity of horizontal interval was increased from 67% to 100% after the typical well cluster was electrically heated for 3.0a, the daily oil production was increased by 2-4 m³/d,Accamulative oil-steam ratio in creased from 0.15 to 0.24, and the final recovery efficiency reached 51.3%, an increase of 8.1 percentage points. The study results can be used as a guidance for improving the development effect of SAGD.

Optimization of CO₂ Huff and Puff Scheme for Jimsar Shale Oil and Evaluation of Test Effect

Tang Weiyu, Huang Ziyi, Chen Chao, Ding Zhenhua, Sheng Jiaping, Wang Xiukun, Le Ping

2022, 29(3):  131-137.  DOI: 10.3969/j.issn.1006-6535.2022.03.019

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A method of enhanced recovery efficiency by CO₂ huff and puff was proposed in response to the low recovery efficiency in natural depletion of shale gas reservoirs in Jimsar and the difficulty of traditional recovery enhancement measures to effectively increase the production. A numerical simulation model of reservoir in the work area was established by the numerical simulation method. Test wells suitable for CO₂ huff and puff were selected according to the horizontal interval length and reservoir thickness. The decisive role of matrix energy enhancement in CO₂ huff and puff was clarified, and the working system of CO₂ huff and puff was optimized. Finally, the optimized scheme was applied to the field test. The results showed that, there was fracture channeling between the test wells, resulting in serious gas channeling in the injection stage of CO₂ huff and puff, and CO₂ did not enter the matrix sufficiently to replace the crude oil, resulting in poor overall development efficiency. The study provides a reference for enhancing oil recovery by CO₂ huff and puff in shale reservoir and for adjusting the scheme of development by CO₂ huff and puff.

Drilling & Production Engineering

Prediction Model of Equivalent Circulating Density of Drilling Fluid in Deep HPHT Wells and Its Application

Gao Yongde, Dong Hongduo, Hu Yitao, Chen Pei, Cheng Leli

2022, 29(3):  138-143.  DOI: 10.3969/j.issn.1006-6535.2022.03.020

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Deep HPHT wells have the characteristics of complex wellbore temperature field changes and large changes in the physical properties of drilling fluids, multiplying the difficulties in accurate prediction of the equivalent circulating density (ECD) of drilling fluid. To this end, based on the drilling data of deep HPHT wells in a study area in the South China Sea, the characteristics of response between the equivalent static density and rheological parameters of deep water-based drilling fluids and the temperature and pressure were investigated by means of PVT meter and rotary viscometer. The parameters of empirical model were fitted based on experimental data, while the ECD calculation model of deep HPHT wells was improved with consideration of the influence of temperature and pressure on the physical parameters of drilling fluid and the influence of subsea pressurization on the flow field and temperature field of wellbore. The study showed that, the physical properties of the water-based drilling fluid were greatly affected by high temperature and pressure, and the higher the displacement of the subsea booster pump, the higher the ECD in the wellbore. The model was used in the calculation of Well ST362-1d well in the South China Sea, and the average error was only 0.249% between the predicted value of ECD model and the measured value. The results of the study can serve as references for the optimal design of hydraulic parameters and wellbore pressure control in deep HPHT wells.

Acid Fracturing Technology for High-conductivity Unpropped Fractures in Ultra-deep Wells with High Temperature in Carbonate Reservoirs

Zhou Linbo, Liu Honglei, Li Dan, Zhang Junjiang, Zhou Jun

2022, 29(3):  144-149.  DOI: 10.3969/j.issn.1006-6535.2022.03.021

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In response to the problems of easy closure of acid-etched fractures and rapid attenuation of conductivity caused by acid fracturing in ultra-deep wells, a new acid-fracturing shielding protectant was synthesized and evaluated for its key indicators such as self-agglomeration, oil solubility and adhesion. This technology blocks the acid-rock reaction by discontinuously and temporarily shielding the surface of the hydraulic fracture, and realizes the transformation of acid-etched fractures from point support to surface support, and the effective support height of the fracture can be increased by 3 times. CFD software simulation was used to optimize the distribution pattern of shielding protective agent particles in the fractures and to determine the process parameters such as shielding protective agent dosage, injection and displacement rates, and carrier fluid type. The technology was applied to ultra-deep wells with high temperature in Tahe Oilfield. The results after fracturing showed that the adhesion and oil solubility of shielding agent at formation temperature met the design requirements, and the conductivity and service life of unpropped fractures were significantly prolonged. This technology plays an important role in the improvement of acid fracturing effect in ultra-deep wells.

Study and Application of Packer Y-tool in Dual-ESP Wells

Yu Zhigang, Zhang Dezheng, Hu Zhenchao, Mu Yongwei, Yang Bo, Ma Yaling

2022, 29(3):  150-155.  DOI: 10.3969/j.issn.1006-6535.2022.03.022

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A new packer Y-tool was developed to address the problem of ineffective fluid internal circulation due to the lost circulation at the check valve of the dual electric submersible pump (dual-ESP) in offshore oilfields. The Y-tool was designed with packer sleeve and packer sleeve locking mechanism to prevent the ineffective internal circulation of fluid in the well, ensuring the normal production of the ESP wells and reducing the workover operation caused by the lost circulation at the ESP check valve. The method was applied 15 wells in the field, with 100% efficiency rate, effectively improving the production rate of oil wells and reducing operation cost. The technology can promote the application of dual electric submersible pump in the oil recovery of offshore oilfields, with great economic and social benefits.

Study on Polymer Plugging Mechanism and Plug Removal Method in Sandstone Reservoirs

Zhao Lin, Gao Shenling, Chen Yuan, Mei Dongfeng, Hou Baofeng, Wang Rui, Li Xindan

2022, 29(3):  156-161.  DOI: 10.3969/j.issn.1006-6535.2022.03.023

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In order to solve the problem of severe polymer plugging in polymer flooding process in sandstone reservoirs, the polymer plugging radius was determined by the displacement experiment with multi-point pressure measurement of long sand-packed pipe and the reservoir engineering method, and the polymer plugging mechanism was studied by scanning electron microscopy, CT scanning, nuclear magnetic resonance and other methods. The results showed that, polymer plugging mainly occurred at 0-1/4 near the injection end of the sand-packed pipe; a large amount of polymer was adsorbed on the surface of the high-permeability cores, and polymer plugging was mainly caused by adsorption; the pore size of the low-permeability core was small and a great amount of polymer was mechanically captured at the pore throat, and polymer plugging was mainly caused by mechanical capture; compared with that before polymer flooding, the average pore throat radius and average throat coordination number of core after polymer flooding were reduced, with the average pore throat radius reduced from 42.2 μm to 39.9 μm and the average throat coordination number reduced from 3.36 to 3.19. Based on the study results of plugging radius and location, the field test of plug removal was implemented. The apparent water injectivity index after plug removal was 10.5 times that before plug removal, meeting the injection requirements. The results of the study provide theoretical guidance for studying the polymer plugging mechanism in sandstone reservoirs and the field test of polymer flooding.

Lost Circulation Mechanism and Main Controlling Factors in Deep Brittle Shale Wells

Li Wenzhe, Yu Xingchuan, Lai Yan, Liu Houbin, Wen Wen, Zhang Zhen, Wu Shenyao

2022, 29(3):  162-169.  DOI: 10.3969/j.issn.1006-6535.2022.03.024

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In spite of abundant shale gas resources in Changning Block, Sichuan Province, the severe lost circulation of drilling fluid in horizontal well drilling is prominent restricts the exploration and development of shale gas resources in Changning Block. Based on single-well logging data and seismic interpretation data, a distribution model of shale gas formation fractures, crustal stress and formation pressure of shale gas reservoirs, Changning Block was established, and a study was conducted on the response relationship between them and lost circulation. The results showed that, the fracture density was high in the high position of the tectonic anticline in Changning Block, the formation was buried shallowly, the crustal stress was low, the critical pressure of opening and extension of closed fractures was low, the formation pore pressure was low, and the lost circulation of drilling fluid was severe; the fracture density in the low position of the tectonic syncline was lower than that in the high position, the formation was buried deeply, the crustal stress was high, the critical pressure of opening and extension of closed fractures was low, the formation pore pressure was high, the formation pore pressure was high, and the lost circulation of drilling fluid was subtle. The faults and fractures were developed in Changning Block, and the lost circulation of drilling fluid was mainly caused by pressure difference and closed fracture expansion. The results of the study disclose the lost circulation mechanism of drilling fluid in deep shale in Changning Block, and clarify the main influencing factors, which can be used as a scientific basis for lost circulation prevention and efficient development of shale reservoirs in Changning Block.

Optimization of Fracture Parameters for Staged Fracturing with Temporary Fiber Plugging and Diversion in Highly Deviated Wells and Horizontal Wells in Deep Carbonate Reservoirs

Zhu Wenzhao, Miao Juan, Chen Siyun, Lei Lei, Liu Ju

2022, 29(3):  170-174.  DOI: 10.3969/j.issn.1006-6535.2022.03.025

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To further increase the number of stages of staged fracturing and achieve full-well staged fracturing of highly deviated wells and horizontal wells in Types II and III reservoirs in Gaoshiti-Moxi Area, Sichuan Basin, a laboratory experiment was conducted for physical simulation of temporary plugging and turnaround staged fracturing to optimize staged fracturing parameters. The study showed that, the mass fraction of temporarily plugged fibers and the construction displacement are the key factors affecting the diversion effect; the plugging pressure reached the pressure limit of 15 MPa at a mass fraction of 2.5% and a displacement of 120-250 mL/min for fiber combinations with fiber length of 3-12 mm, forming a stable plug without breakout. The results of the study were applied to multi-stage fracturing of highly deviated wells and horizontal wells in Types II and III reservoirs, Gaoshiti-Maoxi Area, confirming the feasibility of the technology. The test production was increased by 46% compared to similar reservoirs where staged fracturing was not implemented. The study provides a reference for promoting the effective prediction of low-grade resources in carbonates.