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Influence of natural fractures on Tight Oil Migration and Production: A Case Study of Permian Lucaogou Formation in Jimsar Sag, Junggar Basin, NW China

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Journal of Earth Science 2021年第4期32卷 927-945页

作者： Yunzhao Zhang Lianbo Zeng Qun Luo Rukai Zhu Wenya Lyu Dongdong Liu Quanqi Dai Shouxu Pan State Key Laboratory of Petroleum Resources and Prospecting China University of PetroleumBeijing 102249China College of Geosciences China University of PetroleumBeijing 102249China Unconventional Petroleum Research Institute China University of PetroleumBeijing 102249China Research Institute of Petroleum Exploration and Development CNPCBeijing 100083China Key Laboratory of Oil and Gas Reservoirs CNPCBeijing 100083China National Energy Tight Oil and Gas R&D Center Beijing 100083China School of Geosciences China University of PetroleumQingdao 266580China

natural fractures,as the main flow channels and important storage spaces,have significant effects on the migration,distribution,and accumulation of tight oil.According to outcrop,core,formation micro image(FMI),cast-thin-section,and scanning electron microscopy data from the tight reservoir within the Permian Lucaogou Formation of the Junggar Basin,tectonic fractures are prevalent in this formation mainly on micro to large scale.There are two types of fractures worth noticing:diagenetic fractures and overpressure-related fractures,primarily at micro to medium scale.The diagenetic fractures consist of bedding fractures,stylolites,intragranular fractures,grain-boundary fractures,and diagenetic shrinkage fractures.Through FMI interpretation and Monte Carlo method evaluation,the macro-fractures could be considered as migration channels,and the micro-fractures as larger pore throats that function as storage spaces.The bedding fractures formed earlier than all tectonic fractures,while the overpressure-related fractures formed in the Middle and Late Jurassic.The bedding fractures and stylolites function as the primary channels for horizontal migration of tight oil.The tectonic fractures can provide vertical migration channels and reservoir spaces for tight oil,and readjust the tight oil distribution.The overpressure-related fractures are fully filled with calcite,and hence,have little effect on hydrocarbon migration and storage capacity.The data on tight oil production shows that the density and aperture of fractures jointly determine the productivity of a tight reservoir.

关键词： natural fractures tight reservoir oil migration and production Permian Lucaogou Formation Junggar Basin

The role of natural fracture activation in hydraulic fracturing for deep unconventional geo-energy reservoir stimulation

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Petroleum Science 2023年第4期20卷 2141-2164页

作者： Jun Wang He-Ping Xie Stephan KMatthai Jian-Jun Hu Cun-Bao Li Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization Institute of Deep Earth Sciences and Green EnergyShenzhen UniversityShenzhen518060GuangdongPR China Shenzhen Key Laboratory of Deep Engineering Sciences and Green Energy College of Civil and Transportation EngineeringShenzhen UniversityShenzhen518060GuangdongPR China Department of Infrastructure Engineering University of MelbourneMelbourneVIC3010Australia MOE Laboratory of Deep Earth Science and Engineering Sichuan UniversityChengdu610065SichuanPR China

The presence of sealed or semi-sealed,multiscale natural fracture systems appears to be crucial for the successful stimulation of deep reservoirs.To explore the reaction of such systems to reservoir stimulation,a new numerical simulation approach for hydraulic stimulation has been developed,trying to establish a realistic model of the physics involved.Our new model successfully reproduces dynamic fracture activation,network generation,and overall reservoir permeability enhancement.Its outputs indicate that natural fractures facilitate stimulation far beyond the near-wellbore area,and can significantly improve the hydraulic conductivity of unconventional geo-energy reservoirs.According to our model,the fracture activation patterns are jointly determined by the occurrence of natural fractures and the in situ stress.High-density natural fractures,high-fluid pressure,and low effective stress environments promote the formation of complex fracture networks during stimulation.Multistage or multicluster fracturing treatments with an appropriate spacing also increase the stimulated reservoir area(SRA).The simulation scheme demonstrated in this work offers the possibility to elucidate the complex multiphysical couplings seen in the field through detailed site-specific modeling.

关键词： natural fractures DFM Unconventional geo-energy reservoir Fracture reactivation Hydraulic stimulation

A new-generation Embedded Discrete Fracture Model calibration workflow applied to the characterization of complex naturally fracture reservoir

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Petroleum Research 2022年第1期7卷 1-12页

作者： Hongbing Xie Mauricio Fiallos Torres Penyu Cheng Wei Yu Yuzhong Xin Jijun Miao Muwei Cheng Beijing Karst S&T Limited Beijing100083China Sim Tech LLC KatyTX77494USA RIPED Beijing100083China University of Texas at Austin AustinTX78712USA

Characterizing natural fractures has a decisive effect on production forecasts in fractured oil and gas reservoirs.Discrete Fracture Networks(DFN)constitutes the main modeling framework for fractured geosystems.However,myriads of uncertainties are enclosed prior modeling representative stochastic or deterministic DFN ensembles.This paper presents a novel methodology for DFN calibration and an efficacious field application,which incorporatesWell-testing interpretation,Embedded Discrete Fracture Model(EDFM)framework,and numerical reservoir simulation.The proposed workflow starts with the DFN generation from seismic data,imaging logging data and core data.After multiple DFNs are modeled,well-test analysis is employed to calibrate the intrinsic properties of fractures at different locations.Then,these fracture networks are characterized dynamically by EDFM,which promotes capturing the optimal fracture model quickly screened.Finally,pressure and production history match are reached for the DFN realization that honors the optimal fracture model.

关键词： DFN EDFM DFN screening Fracture networks natural fractures

Mutual impact of true triaxial stress, borehole orientation and bedding inclination on laboratory hydraulic fracturing of Lushan shale

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3131-3147页

作者： Yongfa Zhang Anfa Long Yu Zhao Arno Zang Chaolin Wang College of Civil Engineering Guizhou UniversityGuiyang550025China Helmholtz Centre Potsdam GFZ German Research Centre for GeosciencesPotsdam14473Germany

Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.

关键词： True triaxial hydraulic fracturing experiment In situ stress state Bedding planes natural fractures Wellbore orientation Shale reservoirs

Failure Patterns and Mechanisms of Hydraulic Fracture Propagation Behavior in the Presence of naturally Cemented fractures

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Computer Modeling in Engineering & Sciences 2021年第3期126卷 891-914页

作者： Daobing Wang Fang Shi Hao Qin Dongliang Sun Bo Yu School of Mechanical Engineering Beijing Key Laboratory of Pipeline Critical Technology and Equipment for Deep Water Oil&Gas DevelopmentBeijing Institute of Petrochemical TechnologyBeijing102617China Jiangsu Key Laboratory of Advanced Manufacturing Technology Huaiyin Institute of TechnologyHuaiyin223003China

In this study,we use the extended finite element method(XFEM)with a consideration of junction enrichment functions to investigate the mechanics of hydraulic fractures related to naturally cemented fractures.In the proposed numerical model,the lubrication equation is adopted to describe the fluid flow within fractures.The fluid-solid coupling systems of the hydraulic fracturing problem are solved using the Newton-Raphson method.The energy release rate criterion is used to determine the cross/arrest behavior between a hydraulic fracture(HF)and a cemented natural fracture(NF).The failure patterns and mechanisms of crack propagation at the intersection of natural fractures are discussed.Simulation results show that after crossing an NF,the failure mode along the cemented NF path may change from the tensile regime to the shear or mixed-mode regime.When an advancing HF kinks back toward the matrix,the failure mode may gradually switch back to the tensile-dominated regime.Key factors,including the length of the upper/lower portion of the cemented NF,horizontal stress anisotropy,and the intersection angle of the crack propagation are investigated in detail.An uncemented or partially cemented NF will form a more complex fracture network than a cemented NF.This study provides insight into the formation mechanism of fracture networks in formations that contain cemented NF.

关键词： Hydraulic fracturing natural fractures crack propagation unconventional reservoirs mechanical interaction joints

Fracture Network Volume Fracturing Technology in High-temperature Hard Formation of Hot Dry Rock

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Acta Geologica Sinica(English Edition) 2021年第6期95卷 1828-1834页

作者： CHEN Zuo XU Guoqing ZHOU Jian LIU Jiankun SINOPEC Research Institute of Petroleum Engineering Beijing 102206China

It is more difficult for a hot dry rock to form a fracture network system than shale due to its special lithology, physical and mechanical properties under high temperature. The essential characteristics, rock mechanics and in-situ stress characteristics of a hot rock mass have been systematically studied by means of laboratory tests and true tri-axial physical simulation. The fracture initiation and propagation characteristics under different geological and engineering conditions are physically simulated, and the main controlling factors for the formation of a complex fracture network are revealed. The technology of low displacement for enhancing thermal cracking, gel fluid for expanding fracture and variable displacement cyclic injection for increasing a fracture network has been applied in the field, and good results have been achieved. Microseismic monitoring results demonstrate that complex fractures were formed in the field test, and the stimulation volume for heat exchanging reaches more than 3 million cubic meters. The research results play an important role in the stimulation technology of an enhanced geothermal system(EGS) and realize a breakthrough for power generation.

关键词： hot dry rock granite fracture network natural fractures thermal cracking cyclic injection volume stimulation Gonghe Basin