Table of Content

25 December 2021, Volume 28 Issue 6

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Summary

Advances in the Application of CO₂ Stimulation Technology

Zhang Yihe, Sheng Jiaping, Li Qingxia, Song Ping, Chen Yukun, Qin Jianhua

2021, 28(6):  1-10.  DOI: 10.3969/j.issn.1006-6535.2021.06.001

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CO₂ stimulation technology is effective in enhanced oil recovery conventional and unconventional oil reservoirs. The advances in the application of CO₂ stimulation technology was summarized from in-house laboratory investigation to application and practice in key fields, and the field tests with different technical routes were reviewed and analyzed. The application results indicated that with wide application range in different oil products and different reservoirs, CO₂ stimulation technology achieved good results in the mines at home and abroad. The reservoirs will be developed with the technologies of CO₂ composite stimulation, CO₂ synergistic stimulation, and supercritical CO₂ stimulation and nanoparticle-assisted CO₂ stimulation in the future. Supercritical CO₂ stimulation and nanoparticle-assisted CO₂ stimulation are still under the laboratory experiment. Their practicability should be further studied and verified by field application. In the context of achieving the target of carbon neutralization by 2060, the application scale of CO₂ stimulation technology will be further expanded. This study will also provide technical support for the promotion and application of CO₂ stimulation technology.

Geologic Exploration

Cenozoic Tectonic Evolution and Hydrocarbon Accumulation of Taian-Dawa Fault Zone, Liaohe Sag

Shan Junfeng, Chen Chang, Zhou Xiaolong, Fang Hong

2021, 28(6):  11-19.  DOI: 10.3969/j.issn.1006-6535.2021.06.002

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With abundant oil and gas resources, Taian-Dawa Fault Zone is one of the most important hydrocarbon-bearing zones in Liaohe Sag. The tectonic characteristics and evolution of the Fault Zone were analyzed to explore the relationship between the tectonic evolution and hydrocarbon accumulation in the Fault Zone. A study was performed on hydrocarbon accumulation mode to work out the effect of Cenozoic tectonic evolution on hydrocarbon accumulation in Taian-Dawa Fault Zone, providing guidance in the optimization of exploration fields and targets of the Fault Zone. The results of the study showed that Taian-Dawa Fault Zone was characterized by both extensional and strike-slip inversed tectonics and its tectonic evolution was divided into three stages: faulting period, dextral slip period and depression period. The tectonic evolution significantly controlled the hydrocarbon accumulation in the Fault Zone, specifically controlling the migration of subsidence center from north to south, the reservoir development, the formation of complex petroleum migration pathways, and the matching between fault activities and hydrocarbon discharge. The hydrocarbon accumulation patterns and favorable exploration areas in the north and south of the Fault Zone were identified, providing a basis for the next exploration deployment in the Fault Zone.

Study on Accumulation Conditions of Tight Sandstone Reservoirs in Huaqing Area, Ordos Basin

Shi Kanyuan, Pang Xiongqi, Wang Ke, Niu Siqi

2021, 28(6):  20-26.  DOI: 10.3969/j.issn.1006-6535.2021.06.003

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In response to severe restrictions on exploration and development by high heterogeneity and poor physical properties of sandstone in Chang₆ oil-bearing formation in Huaqing Area, Ordos Basin, the accumulation conditions of tight sandstone reservoirs in Chang₆ oil-bearing formation in the study area were studied in depth according to the theories of petroleum geology, sedimentary petrology, and petroleum accumulation dynamics, in combination of various test and analysis data. The results of the study showed that the accumulative conditions of tight sandstone reservoirs in Chang₆ oil-bearing formation in Well Block B257, Huaqing Area were controlled by high-quality source rocks, favorable reservoirs and reservoir characteristics. Finally, two favorable exploration areas were identified based on the sedimentary background, tectonic conditions, reservoir conditions, source rock conditions and production conditions of the oil-bearing formation. This study indicates the direction for the exploration and development of Chang₆ tight sandstone reservoir in Well Block B257, Huaqing Area.

Reservoir Controlling Factors and Development Model of Middle Permian Lucaogou Formation in Chaiwopu Sag

Zhang Guanlong, Wang Yue, Zhang Kuihua, Yu Hongzhou, Xiao Xiongfei

2021, 28(6):  27-35.  DOI: 10.3969/j.issn.1006-6535.2021.06.004

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In order to work out the distribution pattern of favorable reservoirs in Middle Permian Lucaogou Formation in Chaiwopu Sag, the reservoir characteristics and controlling factors of Lucaogou Formation were systematically analyzed and the reservoir development pattern was established according to the test data such as core, rock slice, X-ray diffraction and scanning electron microscope, in combination with the characteristics of tectonic evolution and sedimentary system distribution. The study results showed that the reservoir space of Lucaogou Formation was dominated by dissolved pores and micro-fractures, and was mainly composed of reservoirs with ultra-low porosity and ultra-low permeability. In the nearshore subaqueous fan adjacent to Yilinheibiergen Mountain, the primary porosity of glutenite at the fan center was low and the reservoir was denser due to vertical and lateral compaction in the early diagenetic stage. The glutenite at the margin of the nearshore subaqueous fan was mainly subjected to the effect of vertical compression while the effect of lateral compaction was weak in the early diagenetic stage. The strong dissolution effect of acidic fluids released from source rocks in the late diagenetic stage made more inter-granular and intra-granular dissolved pores, form the most favorable sedimentary facies belt for hydrocarbon accumulation. The sandbody of turbidite fan was sandwiched in the deeper or deep lacustrine thick source rocks, developed with dissolved pores, forming a "sweet spot" reservoir for oil and gas exploration. The study results provide an important geological basis for the deployment of prospecting wells in Chaiwopu Sag.

Accumulation Mode and Development Countermeasures for Limestone-Sandstone-Shale Reservoirs in Daanzhai Member, Yuanba Block

Sun Tianli, Ou Chenghua, Guo Wei, Zhu Guo, Chen Wei, Zhang Zhiyue, Peng Shixuan, Yan Bo

2021, 28(6):  36-44.  DOI: 10.3969/j.issn.1006-6535.2021.06.005

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In order to investigate the distribution characteristics and combination patterns of the dense clast limestone-sandstone-shale mixed sedimentary reservoirs in Daanzhai Member, Yuanba Block, northeast Sichuan, the types of reservoirs and logging response characteristics of various reservoirs developed under the mixed sedimentary system in the target area were analyzed by means of core analysis, well logging interpretation, comprehensive geological study and mapping, the vertical and horizontal combination model and plane superposition model were established to characterize the distribution characteristics of the reservoirs, and the development potential and measures of natural gas in the study area were discussed. It was found in the study that Daanzhai Member in Yuanba Block is a mixed sedimentary system comprising ostracum beach, shallow lake mud, dam sand and beach sand, accompanied by the development of dense limestone, sandstone and shale reservoirs with distinct logging response characteristics, unequal quantity and strongly non-homogeneous distribution; five types of limestone-sandstone-shale reservoir assemblages and coincidence modes were identified in the longitudinal and transverse directions and planes respectively; the different reservoir assemblages had different gas resource potential; the key to the successful development of the limestone-sandstone-shale reservoir mode in Daanzhai Member, Yuanba block in northeast Sichuan was to optimize the technical combination and process flow of horizontal well drilling and staged fracturing. The results of this study can be used as a reference for the development of similar areas.

Hydrocarbon Accumulation Characteristics and Exploration Targets of Subu Tectonic Belt in Ulyastai Sag

Xie Jingping

2021, 28(6):  45-53.  DOI: 10.3969/j.issn.1006-6535.2021.06.006

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To address the problems of unknown oil source conditions, sandbody sedimentary patterns, effective reservoir distribution and reservoir formation patterns in Subu Area, various methods such as geochemical analysis, detailed sandbody characterization and rock-mineral analysis were employed to analyze the hydrocarbon accumulation conditions in this area from three aspects, including source rock, reservoir conditions, and facies reservoir-capping assemblage, and elucidate the reasons for the vertical development of multiple abnormal pore zones. The results of the study proved that there were three accumulation modes for reservoirs in this area, including "transverse tectonic aggregation and favorable sandbody accumulation" of conventional reservoir, unconventional "tight glutenite oil and gas reservoirs" and "shale oil and gas reservoirs", and the hydrocarbon reservoirs were middle-shallow conventional reservoir and deep unconventional reservoir longitudinally and distributed as oil reservoir belt, oil-gas mixed belt and gas reservoir belt from shallow to deep. The study results were effective in the guidance for exploration breakthroughs in the area, handover of reserves and further exploration targets of the southern subsag, Ulyastai Sag.

Characteristics and Main Controlling Factors of Primary Rhyolite Volcanic Reservoir

Huang Yun, Liang Shuyi, Yang Disheng, Ji Dongsheng, Fu Xiaopeng

2021, 28(6):  54-61.  DOI: 10.3969/j.issn.1006-6535.2021.06.007

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In recent years, the volcanic rock exploration in Junggar Basin has shown that, in addition to weathered crustal reservoirs, there are still volcanic reservoirs with sound physical properties developing below 300 m from the top of the Carboniferous volcanic rock. In order to further clarify the characteristics of these primary reservoirs and provide a basis for exploration and deployment, studies were carried out on the genesis mechanism, rock type, physical characteristics, spatial distribution, rhythmical characteristics and main controlling factors of the primary volcanic reservoirs, and the concept of "primary stratified multi-stage rhyolite reservoir", which was different from the weathered crust reservoirs of volcanic rocks, was proposed, and referred to as primary rhyolite volcanic reservoir. The distribution of primary rhyolite reservoirs was characterized by large area, large span, and vertical distribution not controlled by burial depth, and the reservoir space was mainly the primary pore associated with volatile escape at the top and bottom of each multi-stage eruption cycles; magmatic evolution and volcanic activity sequence were the main controlling factors. This achievement has expanded the longitudinal exploration depth of Carboniferous volcanic rocks, and the exploration target layer has changed from single weathered crust reservoir to primary reservoir developed in multi-stage eruption cycles, guiding the discovery of multiple Carboniferous insider oil and gas reservoirs. There is much for reference to the exploration of volcanic rocks in other basins.

Reservoir Engineering

Classification of Igneous Rock Lithology with K-nearest Neighbor Algorithm Based on Random Forest (RF-KNN)

Lai Qiang, Wei Boyang, Wu Yuyu, Pan Baozhi, Xie Bing, Guo Yuhang

2021, 28(6):  62-69.  DOI: 10.3969/j.issn.1006-6535.2021.06.008

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To address the problems that it is difficult to classify igneous rock lithology in igneous rock reservoirs and the lithology identification accuracy is greatly affected by the number of slice identification samples,the correlation between different logging curves and igneous rock lithology was analyzed by random forest (RF) algorithm,and then igneous rock lithology was classified by the the K-nearest neighbor (KNN) algorithm according to the slice sample identification.The study results were applied to the Permian igneous rock formation in Western Sichuan,and the results showed that the correlation between logging curves and lithology was decreased in order of GR, R_t, DEN,CNL and AC.The igneous rock lithology was classified with the KNN algorithm, and the value of k was controlled by two factors: the number of classifications and the number of training samples.When there were less samples,the effect of the latter was greater than that of the former.When k was 3, the backcasting accuracy of KNN algorithm was 87.5% for 24 igneous rock training samples (5 types of lithology),and the testing accuracy was 92.5% for 14 igneous rock samples (5 types of lithology).In the classification of igneous rock lithology with comparison of charts,there was less man-made influence on the KNN algorithm and the parameter adjustment was simple.This study provides an important guide to the classification of igneous rock lithology with small samples.

Low-velocity Seepage Characteristics of Single-phase Fluid in Shale Reservoir

Li Lei, Hao Yongmao, Wang Chengwei, Xiao Pufu, Zhao Chunpeng

2021, 28(6):  70-75.  DOI: 10.3969/j.issn.1006-6535.2021.06.009

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There are obvious differences in the effective production conditions and recoverability evaluation methods between shale oil and gas and conventional oil and gas. In order to investigate the seepage characteristics of shale oil in micro and nano pores, low-velocity seepage experiment was conducted to study the low-velocity non-Darcy seepage patterns of single-phase fluids in Qianjiang Sag, Jiyang Sag and Eagle Ford reservoirs in typical shale blocks at home and abroad. The results of the study showed that the low-rate seepage characteristics of shale oil were mainly affected by the liquid-solid boundary layer effect, slip length and seepage channel. The seepage curve of Qianjiang Sag was concave. The smaller the pressure gradient, the stronger the fluid-solid interface force, and the more obvious the non-linear section; Jiyang Sag was obviously affected by the development of rock core microfractures, and big pores such as inorganic pores and microfractures were the main flow channels at low pressure gradients, with low surface roughness and tortuosity; as the pressure gradient increased, fluid flowed in the small pores and organic pores; Eagle Ford reservoirs were influenced by the mineral composition and pore structure of the block, and the seepage characteristics presented two linear sections with different slopes, and the resistance to seepage increased as the pressure difference increased. The study clarifies the main characteristics and influencing mechanisms of low-velocity seepage of shale oil in nano and micron pores, providing a theoretical basis for formulating shale oil development plans and guiding the efficient development of shale oil.

Optimization of Gas Injection and Production in Gas Storage Based on Large Depleted Gas Reservoir with Consideration of Safe and Stable Operation

Zhou Jun, Peng Jinghong, Luo Sha, Sun Jianhua, Liang Guangchuan, Peng Cao

2021, 28(6):  76-82.  DOI: 10.3969/j.issn.1006-6535.2021.06.010

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Usually there are multiple injection-production blocks in large depleted gas reservoirs, and too high formation pressure difference between blocks can destabilize the reservoir. In order to achieve balanced variation of formation pressure during the injection and production, an optimization model was established with the minimal variance value of formation pressure between periodic blocks as the objective function. The model combined the mathematical optimization technology with the safety and stability of the gas storage, and takes the number of production wells in each block and the injection and production volume of single well as the decision variables, and takes the total amount of gas injection and production of the gas storage, the maximum injection and production volume of single well, and the maximum formation pressure of the block as constraints. The optimization model was applied to Wen23 gas storage based on a large depleted gas reservoir, and the optimized injection-production solution for the gas storage was successfully solved under the condition of an annual gas working volume of 30×10⁸ m³/a. The results of the study showed that the optimized injection-production scheme can not only reduce the formation pressure difference between blocks and achieve a balanced change in the overall formation pressure in the gas storage, but also effectively avoid the occurrence of extremely high pressure blocks and further guarantee the safe and stable operation of the gas storage, on the premise of meeting the requirements of gas injection-production rate in the gas storage. There is much for reference of the study results for the design of the injection- production solution of the gas storage.

Design Optimization and Productivity Prediction of Horizontal Wells in Low-permeability Conglomerate Reservoir in Well Block Ma18

Li Haonan, Shi Yaoli, Yao Zhenhua, Li Xiaomei, Song Ping, Tan Long

2021, 28(6):  83-90.  DOI: 10.3969/j.issn.1006-6535.2021.06.011

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In response to the problems of low recoverable reserves and poor commercial benefits of single well with vertical well fracturing in low-permeability conglomerate reservoir in Well Block Ma18, Aihu Oilfield, the parameter design and productivity prediction of multi-stage fractured horizontal wells were investigated by numerical reservoir simulation, reservoir engineering method, economic limit method and mine field test method. The results indicated that the "sweet spot" depth in Well Block Ma18 was 3 876 to 3 881 m, the horizontal well strike should be in north-south direction, the recommended length of horizontal interval in horizontal well was 1 200 to 1 400 m, the well spacing was 500 m, the fracture half-length was 150 m, and the fracture spacing was 50 m. Six multi-stage fractured horizontal wells were designed with optimized parameters, achieving an average daily oil production of 29.0 t/d in the first year, which was consistent with the predicted production of 25.0 to 33.0 t/d. This study developed an oil saturation prediction method for conglomerate reservoir, and developed a method of parameter design and productivity prediction for multi-stage fractured horizontal wells in conglomerate reservoir, providing a reference for similar reservoirs.

Evaluation and Optimization of Energy Supplement Methods for Tight Sandstone Reservoirs

Li Binhui, Yuan Shengwang, Dong Dapeng, Fu Lanqing, Wang Ruihan, Shi Xiaodong

2021, 28(6):  91-97.  DOI: 10.3969/j.issn.1006-6535.2021.06.012

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In view of the difficulties in energy supplement after large-scale fracturing by stimulated reservoir volume of tight sandstone reservoirs, a large artificial three-dimensional core physical model and a physical simulation lab module designed and manufactured by ourselves were used to study the optimization of the energy supplement methods for tight sandstone reservoirs. The experimental results showed that during the fracturing development of tight sandstone reservoirs, the formation energy was greatly lost and could be supplemented by water or gas injection effectively; the larger the fractures in the formation, the more conducive to crude oil seepage and the wider spreading scope of the subsequent supplemented energy, which was helpful to further improve the oil recovery; CO₂ was better than active water in terms of being used as imbibition medium which was selected in terms of improving flooding efficiency and the sweep efficiency; the CO₂ stimulation has achieved a significant oil recovery enhancement in the field test. Therefore, CO₂ stimulation, as an effective way of energy supplement, has a good application prospect in the development of tight oil reservoirs. In this paper, the seepage law of horizontal well fracturing in tight sandstone reservoirs was analyzed and the best imbibition medium after large-scale fracturing in tight sandstone reservoirs was preferably selected, providing an important theoretical basis for the development design of tight sandstone reservoirs.

Quantitative Characterization Technology and Application of Dominant Injection-Production Direction in Low-permeability Sandstone Reservoirs

Zhou Liguo

2021, 28(6):  98-104.  DOI: 10.3969/j.issn.1006-6535.2021.06.013

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For low-permeability sandstone reservoirs with poor reservoir physical properties and strong heterogeneity, it is easy to form ineffective water injection cycle in the dominant injection-production direction in the moderate and high water-cut stages, resulting in low utilization of injected water and poor development effect. Therefore, based on the similar principle of seepage mechanics and hydroelectricity of the well group and the dynamic monitoring data acquired in the development process, a weighted calculation method was established to split the water injection rate in the longitudinal and planar directions. Three parameters, cumulative water intake rate per unit oil layer thickness in the injection-production direction, cumulative water intake ratio in the injection-production direction and water intake volume in the injection-production direction, were constrained to determine the quantitative characterization parameters on the plane in the dominant injection-production direction and their differentiation standard. The application proved that the quantitative characterization technology of the dominant injection-production direction had significant effect the fine water injection control in the ultra-high water-cut stage. After the water injection control of 177 wells, the water injection rate was reduced by 3 115 m³/d in the dominant injection-production direction and increased by 5 376 m³/d in the low water absorption direction, and the proportion of ineffective water injection decreased from about 20% to less than 10%. This study plays a guiding role in fine water injection control and remaining oil exploitation in the same reservoir.

Indoor Evaluation of Foaming Agent for New High-temperature Flue Gas Displacement with Function of Profile Control and Oil Displacement

Deng Hongwei

2021, 28(6):  105-112.  DOI: 10.3969/j.issn.1006-6535.2021.06.014

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With significant potential, the technology of displacing reservoir oil with high-temperature thermal fluids such as waste flue gas from steam injection boiler can not only reduce carbon emission,but also improve oil recovery efficiency.However, the higher outlet temperature and complex composition of flue gas seriously affect the performance of foaming agent,and there are few studies on foaming agent suitable for flue gas displacement.In this connection, a terpolymer foaming agent (PNCAS) for high-temperature flue gas displacement with function of profile control and oil displacement was developed,the performance of foaming agent was studied with high-temperature and high-pressure foam tester,and the effects on foaming performance from foaming agent concentration,temperature, pressure an gas components were also analyzed.The sealing performance was evaluated by using the sand-packed tube displacement experimental device,and the resistance factor of the foaming agent solution was tested,and the dual-pipe parallel displacement and microscopic visualization experiments were conducted.The experimental results proved that PNCAS foaming agent had high resistance and low oil-water interfacial tension after aging at 300 ℃,which significantly reduced the flow rate of flue gas and steam,reduced gas channeling, increased the steam sweeping area, and thus improving the recovery efficiency of heavy oil.The study results play a great guiding role in the heavy oil development with flue gas-assisted thermal recovery.

Study on Factors Influencing the Displacement Pattern of Hydraulic Fracturing Proppant

Zhang Xiao, Liu Xinjia, Tian Yongdong, Zhang Suian, Lian Haoyu, Zheng Weibo, Ma Xiongqiang

2021, 28(6):  113-120.  DOI: 10.3969/j.issn.1006-6535.2021.06.015

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In order to improve the proppant displacement in the fracture and enhance the fracturing stimulation effect, the experiment on proppant carrying capacity of fracturing fluid was conducted with experimental simulation method and visual-panel fracture device, the formation of in-fracture sand bank was characterized in combination with the microscopic movement trajectory of the proppant particles and the macroscopic shape of sand bank, the difference in sand carrying modes was analyzed between of viscous and non-viscous fracturing fluids, and the effects on the displacement pattern of sand dike was studies in terms of fracture inter-perforation disturbance, fracturing fluid displacement, fracturing fluid viscosity and construction sand ratio. The results indicated that the proppant in fractures migrated under the joint action of fluidization and sedimentation, mainly dragged and transported under the action of fluidization; an immobile thin layer of fluid was formed between the fluidized layer and sand bank in viscous fracturing fluid to support the particles, reducing the friction and collision between the fluid and the particles; the formation of the sand bank includes four stages, that is, sand bank formation, development, balancing and piston-like forwarding, the formed sand bank could be characterized by accumulating angle, balancing height and advancing angle under the joint effect of perforation disturbance and fluid erosion, and there were no sand zones in the fractures near the wellbore and in the direction of fracture height; the balancing height of the sand bank mainly depended on the movement speed of proppant particles, inversely proportional to the construction displacement and the fracturing fluid viscosity and directly proportional to the sand ratio. This study provides a reference for the optimization of fracturing operation parameters.

Pilot Test of CO₂ Miscible Displacement for Extra High Water Cut Reservoir in Xishanyao Formation of Block Cai 9

Zhang Yanmei, Wan Wensheng, Li Chen, Luo Hongcheng, Liu Yantong, Zhang Huili, Zhang Ruixue

2021, 28(6):  121-128.  DOI: 10.3969/j.issn.1006-6535.2021.06.016

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At present, the oil reservoir in Xishanyao Formation in Well Block Cai 9, Cainan Oilfield is high in water cut and low in production, with a well development rate of only 23.0%, and it will be abandoned and shut down. In order to improve the productivity and reduce the water cut of the ultra-high water-cut reservoir in this well block, analogy method, reservoir engineering and numerical simulation method were employed to analyze the feasibility of CO₂ miscible displacement, develop reservoir engineering design, and perform pilot test. The results showed that Well Block C2576 in inverted seven-spot pattern with small spacing was selected as the pilot test area, Sublayer J₂x₁^2-2 rich in remaining oil was selected as the injection layer, the reasonable injection rate was 0.3 times the pore volume (the CO₂ injection rate on ground was 10 500 t ), the gas injection velocity was 30-40 t/d, and the injection-production ratio was 1.1-1.2. The field test proved that after 4 529.7 t CO₂ injected cumulatively into this well block, the cumulative oil increase reached 1 269 t, and the oil displacement efficiency was 0.27 t/t after CO₂ injection, achieving a good stimulation effect. This research provides technical support for the pilot test, overall adjustment and development of CO₂ miscible displacement in Cainan Oilfield.

Reservoir Evaluation Method and Development Countermeasures for Fracture-Vuggy Reservoir

Geng Tian, Lyu Yanping, Wu Bo, Zhang Xiao, Wen Huan

2021, 28(6):  129-136.  DOI: 10.3969/j.issn.1006-6535.2021.06.017

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The fracture-vuggy reservoir in Tahe Oilfield is highly inhomogeneous, and the complex oil-water relationship and uneven reserve production in the middle and late development stages will lead to great difficulty in exploring remaining oil. In response to the problem that the existing reserve classification method is not applicable to effective guidance in the fine development of the main area, volume carving method was adopted for reserve recalculation, the accuracy of fracture-cavern carving was improved through attribute optimization, the accuracy of reserve calculation was enhanced by differential assignment of parameter partitioning, the reserve classification criteria were refined according to the fracture-cavern connectivity characteristics and reserve utilization, and the reserves were classified into three categories: unconnected reserve, connected nonproducing reserve and connected producing reserve. Development adjustment measures were taken for different types of reserves, for example, new well deployment and well pattern improvement were mainly adopted for unconnected reserve and connected nonproducing reserve, and injection-production adjustment between wells for connected and producing reserve. Reserve evaluation technology was employed to guide new well deployment and injection-production adjustments. Since 2018, 31 new wells have been put into production in Tahe Block 4, and oil-water well adjustment measures were implemented in 25 wells, and the daily oil production was increased from 270 t/d to 700 t/d, showing remarkable comprehensive improvement effect. The research results have implications for efficient adjustment in the intermediate and late stages of fracture-vuggy reservoir development.

Drilling & Production Engineering

Study on Rock Breaking Rules of Axe-shaped PDC Cutter with Numerical Simulation

Zou Deyong, Chen Yahui, Zhao Fangyuan, Cui Yudong

2021, 28(6):  137-143.  DOI: 10.3969/j.issn.1006-6535.2021.06.018

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Axe-shaped PDC cutter is of special shape and presents better breaking performance in rock breaking experiment. However, the rock breaking rules of axe-shaped PDC cutter and the optimization method of its working parameters and shape are ambiguous. Therefore, a three-dimensional finite element model of cutting rock with axe-shaped PDC cutter was established with ABAQUS software, and the effects of back dip angle and axe edge angle on the rock breaking effect of axe-shaped PDC cutter were analyzed by finite element numerical simulation method. The results showed that the rock breaking efficiency of the axe-shaped PDC cutter was the highest when the back dip angle was 15 °; with the same back dip angle, the smaller the axe edge angle was, the easier the tangential crack was to propagate inside the rock, and the optimal axe edge angle was 110 °. According to the simulation results, the shape parameters of the bit with axe-shaped PDC cutter were optimized, and good results were obtained in the field test. The results of the study provide an important basis for the optimal design of the bit with axe-shaped PDC cutter.

Study on Prevention of Micro-Annulus in Cement Sheath by Prestressed Cementing Method

Xi Yan, Li Fangyuan, Wang Song, Liu Mingjie, Xia Mingli, Zeng Xiamao, Zhong Wenli

2021, 28(6):  144-150.  DOI: 10.3969/j.issn.1006-6535.2021.06.019

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The annulus pressure is more common in deep shale gas horizontal wells, which is mainly caused by the micro-annulus at the interface between casing and cement sheath. To address this problem, the generation and propagation of micro-annulus under prestressed cementing were analyzed by mechanical experimental means and numerical simulation methods, and the number of fracturing-resistant sections of cement sheath under different prestress was determined. The results showed that the lower the pressure inside the casing, the more times that the cement sheath withstood the cyclic loads on the premise of keeping the seal integrity; the micro-annulus width of 30.89 μm under cyclic load was the critical value for gas channeling. The prestressed cementing significantly reduced the initial plastic deformation and increased the plastic deformation increment; taking into account the radial prestrain generated by the casing under prestress, the prestressed cementing technology significantly reduced the micro-annulus width and increased the number of fracturing-resistant sections for cement sheath seal integrity in the multi-stage fracturing process. The higher the prestress value, the more fracturing-resistant sections before the micro-annulus appeared; with the same number of fracturing sections, the higher the prestress the smaller the micro-annulus of cement sheath. The field application results indicated that the annulus pressure of casing in deep shale gas horizontal wells was effectively reduced by prestressed cementing technology and cement slurry with low elasticity modulus. The results of the study provide technical support for the cementing of shale gas horizontal wells.

Study and Application of High-temperature Channeling Blocking System Based on Multi-group Cross Linked Gel for Heavy Oil Reservoirs

Wang Jie, Fu Meilong, Xian Ruokun, Zhang Zhiyuan, Chen Lifeng

2021, 28(6):  151-157.  DOI: 10.3969/j.issn.1006-6535.2021.06.020

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In order to address the serious problem of steam channeling in the reservoir development by steam flooding, a high-temperature channeling blocking system based on multi-group cross linked gel was developed. An evaluation was made on its temperature resistance, steam plugging capability, and erosion resistance. It was found in the study that the high-temperature channeling blocking system based on multi-group cross linked gel could stably generate gel under high temperature of 130 ℃, and the gel had a good stability after 120 d at 250 ℃, and excellent plugging performance; the plugging rate of the gel-based channeling blocking system was as high as 99.63% at high temperature when the injection speed was 1 mL/min and the plugging agent volume injected was 0.8 time the pore volume, and the breakthrough pressure gradient was 7.35 MPa/m; at 250 ℃, the channeling blocking system was completely gelling in the sand-filled pipe, and the plugging rate was maintained above 98% after high-temperature steam flushing (30 times the pore volume), with good flushing resistance. The channeling blocking system has proven to be highly effective in plugging with steam by on-site application, effectively solving the problem of steam channeling in the development with steam flooding of heavy oil reservoir, and it can provide a technical support for the efficient development of heavy oil reservoir.

Study on the Mechanism of the Asymmetry Effect of SRV Fracturing on Casing Damage

Lin Zhiwei, Zhong Shouming, Song Lin, Wang Xuegang, Lin Tiejun, Yu Hao, Shi Tao

2021, 28(6):  158-164.  DOI: 10.3969/j.issn.1006-6535.2021.06.021

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To address the problem of casing damage in the SRV fracturing of tight oil and gas reservoirs, a full-sized three-dimensional casing-cement sheath-formation coupled finite element analysis model was established according to the theories of elastoplastic mechanics and contact mechanics and the actual construction conditions of SRV fracturing, with SRV fracturing asymmetric zones characterized by different elliptic cylinders and ABAQUS solver intervened and secondly developed with Fortran subroutine, in order to simulate the dynamic evolution of physical properties and the analysis of mechanical properties of hydration-induced swelling in the SRV fracturing zones. The results showed that the loads outsides the perimeter of the wellbore were more nonuniform with the increase of the ratio of the long and short axes in the elliptical stimulated zone, and the non-uniformity transmitted to the casing through the cement sheath increased first and then tended to be stable; the non-uniformity of the external load on the casing increased with the increase of the volume expansion rate; the increase of the non-uniformity of the external load on the casing exerted more stress on the casing, easily leading to casing failure. This study provides a theoretical basis for the optimal design of SRV fracturing parameters, and plays a guiding role in the prevention against casing and cement sheath failure.