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Finite Element Method Simulation of Wellbore Stability under Different Operating and Geomechanical Conditions

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Fluid Dynamics & Materials Processing 2024年第1期20卷 205-218页

作者： Junyan Liu Ju Liu Yan Wang Shuang Liu Qiao Wang Yihe Du oil&gas Project Research Institute PetroChina Tarim Oilfield CompanyKorla841000China Petroleum Engineering School Southwest Petroleum UniversityChengdu610500China

The variation of the principal stress of formations with the working and geo-mechanical conditions can trigger wellbore instabilities and adversely affect the well completion.A finite element model,based on the theory of poro-elasticity and the Mohr-Coulomb rock damage criterion,is used here to analyze such a risk.The changes in wellbore stability before and after reservoir acidification are simulated for different pressure differences.The results indicate that the risk of wellbore instability grows with an increase in the production-pressure difference regardless of whether acidification is completed or not;the same is true for the instability area.After acidizing,the changes in the main geomechanical parameters(i.e.,elastic modulus,Poisson’s ratio,and rock strength)cause the maximum wellbore instability coefficient to increase.

关键词： Wellbore stability finite element acidizing operation well completion

Hydrocarbon gas huff-n-puff optimization of multiple horizontal wells with complex fracture networks in the M unconventional reservoir

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Petroleum Science 2024年第2期21卷 1018-1031页

作者： Hao-Chuan Zhang Yong Tang You-Wei He Yong Qin Jian-Hong Luo Yu Sun Ning Wang De-Qiang Wang State Key Laboratory of oil and gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu610500SichuanChina CNPC Research Institute of Petroleum Exploration&Development Beijing100083China southwest oil&gas Field company PetroChinaChengdu610051SichuanChina State Key Laboratory of Offshore oil Exploitation CNOOC Research Institute Co.LtdBeijing100027China

The oil production of the multi-fractured horizontal wells(MFHWs) declines quickly in unconventional oil reservoirs due to the fast depletion of natural energy. gas injection has been acknowledged as an effective method to improve oil recovery factor from unconventional oil reservoirs. Hydrocarbon gas huff-n-puff becomes preferable when the CO_(2) source is limited. However, the impact of complex fracture networks and well interference on the EOR performance of multiple MFHWs is still unclear. The optimal gas huff-n-puff parameters are significant for enhancing oil recovery. This work aims to optimize the hydrocarbon gas injection and production parameters for multiple MFHWs with complex fracture networks in unconventional oil reservoirs. Firstly, the numerical model based on unstructured grids is developed to characterize the complex fracture networks and capture the dynamic fracture features.Secondly, the PVT phase behavior simulation was carried out to provide the fluid model for numerical simulation. Thirdly, the optimal parameters for hydrocarbon gas huff-n-puff were obtained. Finally, the dominant factors of hydrocarbon gas huff-n-puff under complex fracture networks are obtained by fuzzy mathematical method. Results reveal that the current pressure of hydrocarbon gas injection can achieve miscible displacement. The optimal injection and production parameters are obtained by single-factor analysis to analyze the effect of individual parameter. gas injection time is the dominant factor of hydrocarbon gas huff-n-puff in unconventional oil reservoirs with complex fracture networks. This work can offer engineers guidance for hydrocarbon gas huff-n-puff of multiple MFHWs considering the complex fracture networks.

关键词： Unconventional oil reservoir Complex fracture network Hydrocarbon gas huff-n-puff Parameter optimization Numerical simulation

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Optimizing the Diameter of Plugging Balls in Deep Shale gas Wells

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Fluid Dynamics & Materials Processing 2024年第3期20卷 609-624页

作者： Yi Song Zheyu Hu Cheng Shen Lan Ren Xingwu Guo Ran Lin Kun Wang Zhiyong Zhao Shale gas Research Institute PetroChina Southwest Oil&Gasfield CompanyChengdu610056China State Key Laboratory of oil&gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu610500China National Pipe Network Group Sichuan East Natural gas Transmission Pipeline Co. Ltd.Wuhan430205China Fracturing Acidizing company Downhole Operation Company of Chuanqing Drilling Engineering Co.Ltd.Chengdu610213China

Deep shale gas reserves that have been fractured typically have many relatively close perforation holes. Due to theproximity of each fracture during the formation of the fracture network, there is significant stress interference,which results in uneven fracture propagation. It is common practice to use “balls” to temporarily plug fractureopenings in order to lessen liquid intake and achieve uniform propagation in each cluster. In this study, a diameteroptimization model is introduced for these plugging balls based on a multi-cluster fracture propagationmodel and a perforation dynamic abrasion model. This approach relies on proper consideration of the multiphasenature of the considered problem and the interaction force between the involved fluid and solid phases. Accordingly,it can take into account the behavior of the gradually changing hole diameter due to proppant continuousperforation erosion. Moreover, it can provide useful information about the fluid-dynamic behavior of the consideredsystem before and after plugging. It is shown that when the diameter of the temporary plugging ball is1.2 times that of the perforation hole, the perforation holes of each cluster can be effectively blocked.

关键词： Deep shale gas fracture propagation fluid mechanics fluid-solid coupling perforation hole abrasion

Analysis of mechanical strengths of extreme line casing joint considering geometric, material, and contact nonlinearities

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Petroleum Science 2024年第3期21卷 1992-2004页

作者： Ji-Yun Zhang Chi Peng Jian-Hong Fu Quan Cao Yu Su Jian-Yun Pang Zi-Qiang Yu Petroleum Engineering School Southwest Petroleum University Engineering Technology Research Institute of CNPC southwest oil and gas Field company

To address the challenges associated with difficult casing running, limited annular space, and poor cementing quality in the completion of ultra-deep wells, the extreme line casing offers an effective solution over conventional casings. However, due to its smaller size, the joint strength of extreme line casing is reduced, which may cause failure when running in the hole. To address this issue, this study focuses on the CST-ZT Φ139.7 mm × 7.72 mm extreme line casing and employs the elastic-plastic mechanics to establish a comprehensive analysis of the casing joint, taking into account the influence of geometric and material nonlinearities. A finite element model is developed to analyze the forces and deformations of the extreme line casing joint under axial tension and external collapse load. The model investigates the stress distribution of each thread tooth subjected to various tensile forces and external pressures. Additionally, the tensile strength and crushing strength of the extreme line casing joint are determined through both analytical and experimental approaches. The findings reveal that, under axial tensile load, the bearing surface of each thread tooth experiences uneven stress, with relatively high equivalent stress at the root of each thread tooth. The end thread teeth are valuable spots for failure. It is observed that the critical fracture axial load of thread decreases linearly with the increase of thread tooth sequence. Under external pressure, the circumferential stress is highest at the small end of the external thread, leading to yield deformation. The tensile strength of the joint obtained from the finite element model exhibits a relative error of less than 7% compared to the analytical and experimental values,proving the reliability of the finite element model. The tensile strength of the joint is 3091.9 k N.Moreover, in terms of anti-collapse capability, the joints demonstrate higher resistance to collapse compared to the casing body, which is consistent with the test results where the pip

关键词： Extreme line casing Elastic-plastic mechanics Finite element analysis Tensile strength Collapse strength

A Transient-Pressure-Based Numerical Approach for Interlayer Identification in Sand Reservoirs

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Fluid Dynamics & Materials Processing 2024年第3期20卷 641-659页

作者： Hao Luo Haibo Deng Honglin Xiao Shaoyang Geng Fu Hou Gang Luo Yaqi Li Tight oil and gas Exploration and Development Project Department PetroChina Southwest Oil and Gas Field CompanyChengdu610051China Energy College Chengdu University of TechnologyChengdu610059China

Almost all sandstone reservoirs contain interlayers. The identification and characterization of these interlayers iscritical for minimizing the uncertainty associated with oilfield development and improving oil and gas recovery.Identifying interlayers outside wells using identification methods based on logging data and machine learning isdifficult and seismic-based identification techniques are expensive. Herein, a numerical model based on seepageand well-testing theories is introduced to identify interlayers using transient pressure data. The proposed modelrelies on the open-source MATLAB Reservoir Simulation Toolbox. The effects of the interlayer thickness, position,and width on the pressure response are thoroughly investigated. A procedure for inverting interlayer parametersin the reservoir using the bottom-hole pressure is also proposed. This method uses only transient pressuredata during well testing and can effectively identify the interlayer distribution near the wellbore at an extremelylow cost. The reliability of the model is verified using effective oilfield examples.

关键词： Sand reservoir interlayer identification transient pressure analysis numerical well test

Effect of fracture fluid flowback on shale microfractures using CT scanning

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第2期16卷 426-436页

作者： Jiale He Zhihong Zhao Yiran Geng Yuping Chen Jianchun Guo Cong Lu Shouyi Wang Xueliang Han Jun Zhang State Key Laboratory of oil and gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu610500China Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education School of Energy and Power EngineeringXi’an Jiaotong UniversityXi’an710049China Drilling Test Engineering Department of Longdong oil and gas Development company Changqing OilfieldPetroChina Company LimitedQingyang745000China Tight oil and gas Exploration and Development Project Department PetroChina Southwest Oil and Gas Field CompanyChengdu610056China No.11 oil Production Plant Changqing Oilfield CompanyPetroChina Company LimitedQingyang745000China

The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.

关键词： Shale Flowback of fracturing fluid Microfracture Lattice Boltzmann method(LBM)

Acid-rock reaction kinetics in a two-scale model based on reaction order correction

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Petroleum Science 2024年第3期21卷 2089-2101页

作者： Xue-Song Li Ning Qi Ze-Hui Zhang Lian Liu Xia-Qing Li Xu-Hang Su School of Petroleum Engineering China University of Petroleum(East China) Key Lab of Unconventional oil & gas Development Ministry of Education China University of Petroleum(East China) sinopec Northwest oilfield Branch company Petroleum Engineering Technology Research Institute SINOPEC Shengli Oilfield Company

The reaction order plays a crucial role in evaluating the response rate of acid-rock. However, the conventional two-scale model typically assumes that the reaction order is constant as one, which can lead to significant deviations from reality. To address this issue, this study proposes a novel multi-order dynamic model for acid-rock reaction by combining rotating disk experimental data with theoretical derivation.Through numerical simulations, this model allows for the investigation of the impact of acidification conditions on different orders of reaction, thereby providing valuable insights for on-site construction.The analysis reveals that higher response orders require higher optimal acid liquid flow rates, and lower optimal H+diffusion coefficients, and demonstrate no significant correlation with acid concentration.Consequently, it is recommended to increase the displacement and use high-viscosity acid for reservoirs with high calcite content, while reducing the displacement and using low-viscosity acid for reservoirs with high dolomite content.

关键词： Reaction order Two-scale model Wormhole propagation Carbonate rocks Numerical simulation

A phase-field model for simulating the propagation behavior of mixed-mode cracks during the hydraulic fracturing process in fractured reservoirs

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Applied Mathematics and Mechanics(English Edition) 2024年第5期45卷 911-930页

作者： Dan ZHANG Liangping YI Zhaozhong YANG Jingqiang ZHANG Gang CHEN Ruoyu YANG Xiaogang LI State Key Laboratory of oil and gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu 610500China State Key Laboratory of oil and gas Reservoir Geology and Exploitation Chengdu University of TechnologyChengdu 610059China Tarim oilfield company PetroChinaBayingolin Mongolian Autonomous Prefecture 841000Xinjiang Uygur Autonomous RegionChina Wuqi oil Production Plant Shaanxi Yanchang PetroleumXi'an 716000China Exploration Division of Petrochina southwest oil and gasfield company Chengdu 610041China

A novel phase-field model for the propagation of mixed-mode hydraulic fractures,characterized by the formation of mixed-mode fractures due to the interactions between fluids and solids,is proposed.In this model,the driving force for the phase field consists of both tensile and shear components,with the fluid contribution primarily manifesting in the tension driving force.The displacement and pressure are solved simultaneously by an implicit method.The numerical solution's iterative format is established by the finite element discretization and Newton-Raphson(NR)iterative methods.The correctness of the model is verified through the uniaxial compression physical experiments on fluid-pressurized rocks,and the limitations of the hydraulic fracture expansion phase-field model,which only considers mode I fractures,are revealed.In addition,the influence of matrix mode II fracture toughness value,natural fracture mode II toughness value,and fracturing fluid injection rate on the hydraulic fracture propagation in porous media with natural fractures is studied.

关键词： mixed-mode crack hydraulic fracturing poro-elasticity phase-field method(PFM)

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Effect of proppant sizes and injection modes on proppant transportation and distribution in the tortuous fracture model

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Particuology 2024年第1期84卷 261-280页

作者： Jun Li Xu Han Siyuan He Mingyi Wu Xin Huang Nianyin Li State Key Laboratory of oil and gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu610500China Chongqing Industry Polytechnic College Chongqing401120China Sichuan Particles Energy and Technology Co. LtdChengdu611630China Engineering Technology Research Institute of Petrochina southwest oil and gas Field company Chengdu610017China

Particle-fluid transport and placement mechanism in tortuous fracture played a crucial role in uncon-ventional reservoirs.Currently,most studies focused on mono-size proppant with fluid transport pro-cesses in tortuous fractures.However,the mixture-size proppant with fluid movement mechanism in tortuous fracture was still uncommon.Therefore,this study designed and applied a series of experiments with a physical analog model of a tortuous fracture with 120°and 90°-angled bends and combined high-speed camera-based equipment.This experimental system was used to track different-mixture-sized proppant particle motion trajectories for a series of proppant injection schemes;The following conclu-sions were drawn from this study:1.The pile-up processes mechanism in all investigated schemes were similar and could be reduced to four main stages.2.The packing structure at both sides of the fracture wall had different variation rates,which were controlled by the mix ratio(change from 1∶1-1∶5)of proppant size.3.Some new packing patterns,such as Zebra Stripe,had occurred,controlled by the different proppant injection sequences.4.Small-sized mono-proppant(30/50 mesh)had the highest transport efficiency in the tortuous fracture,followed by the mixed-sized multi-proppant(10/20 mesh:30/50 mesh),large-sized proppant(10/20 mesh)was the worst.5.An optimized alternating in-jection mode was recommended as injecting small-sized proppant first(30/50 mesh)and followed by mixed-sized multi-proppant(10/20 mesh:30/50 mesh),which could contribute to obtaining the optimal both proppant packing height and travel distance in tortuous fracture.6.Two correlations were devel-oped for predicting the proppant packing height and transportation distance.

关键词： Tortuous fracture model Mixed-sized proppant Multi-sized proppant injection mode Proppant motion and distribution Packing mechanism