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Investigation of image segmentation effect on the accuracy of reconstructed digital core models of coquina carbonate

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Applied Geophysics 2020年第4期17卷 501-512页

作者： Wang Hai-Tao Wang Li Lai Fu-Qiang Zhang Jin-Yan School of Petroleum Engineering Chongqing University of Science&TechnologyChongqing 401331China National and Local Joint Engineering Research Center of Shale Gas Exploration and Development Chongqing 401120China Key Laboratory of Complex Oil and Gas Field Exploration and Development Chongqing University of Science&TechnologyChongqing 401331China The First Oil Production Plant of Changqing Oilfi eld PetroChina Company LimitedShanxi Yan’An 716000China Logging Application Research Institute CNPC LoggingShanxi Xi’An 710000China Well Logging Company Shengli Oilfi eld Service CorporationSinopecShandong Dongying 257096China

digital core models reconstructed using X-ray tomography(X-CT)enable the quantitative characterization of the pore structure in three dimensions(3D)and the numerical simulation of petrophysics.When the X-CT images accurately reflect the micro structures of core samples,the greyscale threshold in the image segmentation determines the accuracy of digital cores and the simulated petrophysical properties.Therefore,it is vital to investigate the comparison parameter for determining the key greyscale threshold and the criterion to describe the accuracy of the segmentation.Representative coquina digital core models from X-CT are used in this work to study the impact of grayscale threshold on the porosity,pore percolation,connectivity and electrical resistivity of the pore scale model and these simulations are calculated by Minkowski functions,component labeling and fi nite element method,respectively,to quantify the pore structure and simulate electrical resistivity.Results showed that the simulated physical properties of the digital cores,varied with the gradual increase of the greyscale threshold.Among the four parameters related to the threshold,the porosity was most sensitive and chose as the comparison parameter to judge the accuracy of the greyscale threshold.The variations of the threshold change the micro pore structures,and then the electrical resistivity.When the porosity of the digital core model is close to the experimental porosity,the simulated porosity exponent matches the experimental porosity exponents well.The good agreement proved that the porosity is the critical comparison parameter to describe the accuracy of image segmentation.The criterion is that the porosity of the digital core after segmentation should be close to the experimental porosity.

关键词： Porous media X-CT image segmentation digital core electrical resistivity simulation

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Study of the numerical simulation of tight sandstone gas molecular diffusion based on digital core technology

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Petroleum Science 2018年第1期15卷 68-76页

作者： Hong-Lin Zhu Shou-Feng Wang Guo-Jun Yin Qiao Chen Feng-Lin Xu Wei Peng Yan-Hu Tan Kuo Zhang Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum University Oil and Gas Engineering Research Institute Jilin Oilfield Company PetroChina Shu’nan Gas Mine Southwest Oil and Gas Field Branch Company PetroChina Co. Ltd

Diffusion is an important mass transfer mode of tight sandstone gas. Since nano-pores are extensively developed in the interior of tight sandstone, a considerable body of research indicates that the type of diffusion is mainly molecular diffusion based on Fick＇s law. However, accurate modeling and understanding the physics of gas transport phenomena in nanoporous media is still a challenge for researchers and traditional investigation（analytical and experimental methods） have many limitations in studying the generic behavior. In this paper, we used Nano-CT to observe the pore structures of samples of the tight sandstone of western of Sichuan. Combined with advanced image processing technology, threedimensional distributions of the nanometer-sized pores were reconstructed and a tight sandstone digital core model was built, as well the pore structure parameters were analyzed quantitatively. Based on the digital core model, the diffusion process of methane molecules from a higher concentration area to a lower concentration area was simulated by a finite volume method. Finally, the reservoir＇s concentration evolution was visualized and the intrinsic molecular diffusivity tensor which reflects the diffusion capabilities of this rock was calculated. Through comparisons, we found that our calculated result was in good agreement with other empirical results. This study provides a new research method for tight sandstone digital rock physics. It is a foundation for future tight sandstone gas percolation theory and numerical simulation research.

关键词： Tight sandstone gas Nano-CT digital core Molecular diffusion Numerical simulation

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Review of 3D digital core Modeling Methods and Their Applications in Oil and Gas Reservoirs

Review of 3D Digital Core Modeling Methods and Their Applica...

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作者： Xiaofang JIANG Shouchun DENG Rui LUO State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of Sciences University of Chinese Academy of Sciences

With the help of statistical physics and computer technology,the three-dimensional digital core modeling method can provide a basic model for numerical simulation of pore structure and physical properties of rocks.The digital image of the real rock sample is obtained by scanning the rock sample with appropriate resolution,and the pore structure model inside the rock is reconstructed by the numerical reconstruction method.After literature research,this paper introduces ten commonly used 3 d digital core modeling methods in physical experiment method and numerical reconstruction method respectively,and analyzes the advantages and disadvantages of these methods in modeling and the ways of combining them.For the modeling of highly heterogeneous and dense rocks in oil and gas reservoirs,especially shale,on the one hand,the combination of resolution of FIB-SEM and nano CT,as well as the combination of imaging regional scale and REV scale should be considered.The accurate differentiation of organic matter and various mineral categories with the help of RGB value still needs to be made.On the other hand,it is necessary to improve the algorithm and put forward more efficient new points in the selection of numerical reconstruction methods.For example,according to the difference of organic matter and inorganic matter,pore and crack structure and scale,more advantageous methods are used to distinguish modeling and finally superposition.The cross-scale connection between the reconstructed models is also a key problem to be solved in the future.

关键词： digital core core scale modeling Physical experiment method Numerical reconstruction method

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Calculation of oil saturation in clay-rich shale reservoirs:A case study of Qing 1 Member of Cretaceous Qingshankou Formation in Gulong Sag,Songliao Basin,NE China

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Petroleum Exploration and Development 2022年第6期49卷 1351-1363页

作者： LI Chaoliu YAN Weilin WU Hongliang TIAN Han ZHENG Jiandong YU Jun FENG Zhou XU Hongjun Research Institute of Petroleum Exploration and Development PetroChinaBeijing 100083China Exploration and Development Research Institute of Daqing Oilfield Co.Ltd. Daqing 163712China

The targeted reservoir,which is referred as the first member of Cretaceous Qingshankou Formation in Gulong Sag,Songliao Basin,NE China,is characterized by the enrichment of clay and lamellation fractures.Aiming at the technical challenge of determining oil saturation of such reservoir,nano-pores were accurately described and located through focused ion beam scanning electron microscopy and quantitative evaluation of minerals by scanning electron microscopy based on Simandoux model,to construct a 4D digital core frame.Electrical parameters of the shale reservoir were determined by finite element simulation,and the oil saturation calculation method suitable for shale was proposed.Comparison between the results from this method with that from real core test and 2D nuclear magnetic log shows that the absolute errors meet the requirements of the current reserve specification in China for clay-rich shale reservoir.Comparison analysis of multiple wells shows that the oil saturation values calculated by this method of several points vertically in single wells and multiple wells on the plane are in agreement with the test results of core samples and the regional deposition pattern,proving the accuracy and applicability of the method model.

关键词： shale oil digital core well log interpretation oil saturation Qingshankou Formation Gulong Sag Songliao Basin

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A novel pore-fracture dual network modeling method considering dynamic cracking and its applications

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Petroleum Research 2020年第2期5卷 164-169页

作者： Yukun Chen Kai Yan Jigang Zhang Runxi Leng Hongjie Cheng Xuhui Zhang Hongxian Liu Weifeng Lyu PetroChina Xinjiang Oilfield Research Institute of Exploration and DevelopmentKaramayXinjiang843000China College of Mechanical and Transportation Engineering China University of Petroleum(Beijing)Beijing102249China Institute of Mechanics Chinese Academy of SciencesBeijing100190China Department of Petroleum Engineering China University of Petroleum-Beijing at KaramayKaramayXinjiang834000China State Key Laboratory of Enhance Oil Recovery Research Institute of Petroleum Exploration and DevelopmentPetroChinaBeijing100083China

Unconventional reservoirs are normally characterized by dual porous media, which has both multi-scalepore and fracture structures, such as low permeability or tight oil reservoirs. The seepage characteristicsof such reservoirs is mainly determined by micro-fractures, but conventional laboratory experimentalmethods are difficult to measure it, which is attribute to the dynamic cracking of these micro-fractures.The emerging digital core technology in recent years can solve this problem by developing an accuratepore network model and a rational simulation approach. In this study, a novel pore-fracture dualnetwork model was established based on percolation theory. Fluid flow in the pore of two scales, microfracture and matrix pore, were considered, also with the impact of micro-fracture opening and closingduring flow. Some seepage characteristic parameters, such as fluid saturations, capillary pressure, relative permeabilities, displacement efficiency in different flow stage, can be predicted by proposedcalculating method. Through these work, seepage characteristics of dual porous media can be achieved.

关键词： Pore-fracture dual network model Micro-fracture Dynamic cracking digital core Dimensionless parameters Seepage characteristics

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Determination of multi-component content and construction of digital cores based on CT grey thresholds of altered igneous rocks

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Global Geology 2023年第3期26卷 157-166页

作者： ZHANG Naiyu GUAN Yao GUO Yuhang WANG Qinghui ZHANG Lihua PAN Baozhi College of Geo-Exploration Science and Technology Jilin UniversityChangchun 130026China China National Offshore Oil Corporation Shenzhen 518067GuangdongChina

Altered igneous reservoirs have low porosity and permeability,compact structure and certain heterogeneity.A simple digital core with certain generality and multi-parameter constraints can be con-structed to characterize the microscopic pore structure and mineral composition.In this paper,based on core X-ray,CT images and whole-rock mineral analysis,threshold segmentation of mass content and grayscale distribution of various minerals in different lithologies of igneous rocks in the buried hill of Huizhou depression is carried out to construct digital core of altered igneous rocks.The results show that after converting the mineral mass content into volume content,the minerals of altered igneous rocks in Huizhou depression can be classified into components.According to the range of grayscale value,components can be divided into six parts.Due to the difference of the content of components in different lithologies of igneous rocks,differentiated grayscale threshold segmentation is needed to obtain the digital core for a single lithology.The final digital core generation process includes two steps:building a single component digital core,and stacking and combining.This kind of universal digital core model can support the subsequent pore scale numerical simulation and comprehensive rock physics research.

关键词： CT threshold segmentation digital core mineral

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Wormholes propagation for fractured-vuggy formation:Laboratory tests,numerical simulation and field application

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Petroleum 2017年第4期3卷 438-446页

作者： Fei Liu Yu Sang Nanxing Xie Li Li Li Ran Weihua Chen Engineering Technology Research Institute Southwest Oil&Gas Field CompanyPetroChinaChengdu610017China Research and Development Center of the National Energy High Sulfur Gas Reservoir Southwest Oil&Gas Field CompanyPetroChinaChengdu610017China

The propagation of wormhole is vital important for matrix acidizing and acid fracturing in carbonate reservoirs.While the formation of acid dissolved wormhole is derived from heterogeneous physical and chemical transportations and reactions.Alveolate dissolved pores,krast caves,and natural fissures are the major reservoir spaces for the Sinian dolomite formation in the Anyue gas field of the Sichuan Basin.There were four categories of formation,which are matrix dominated,inter-breccia dissolved pore dominated,dissolved pore and cave dominated,and fissure and cave dominated,based on the development intensity and connectedness of caves and fissures.The caves and fissures make the wormhole formation and propagation particularly complicated.Firstly,the 3-D topological structure of dissolved pores,vugs,fissures and throats inside cores is quantitatively scanned by CT imaging technology for its feature of vivid and damage-free.Secondly,3-D patterns of wormhole are obtained with CT scanning after core flooding by acid.Additionally,the porethroat network model is reconstructed with digital cores technology.Then,the size and ratio of pore and throat before and after core flooding by acid is analyzed and the absolute permeability of pore scale flow is numerically simulated to understand the fundamental influence of pores and vugs distribution and connectedness on wormhole propagation.Lastly,the wormhole pattern gained by CT scanning and simulating with two-scale model is compared.Meanwhile,the corrected two-scale model is utilized to simulate the wormhole propagation for matrix acidizing and acid fracturing of Sinian fractured-vuggy dolomite in Anyue gas field,Sichuan Basin.The optimized injection rate and volume were in agreement with the characteristic matrix acidizing operating curve,which indicates that the two-scale model was suitable for matrix acidizing optimization design of such formations.In addition,the simulated acid etched fracture length with considering the dynamic wormhole leakoff was consistent with the we

关键词： CT scanning digital core Dolomite Wormhole Fractured-vuggy reservoir Matrix acidizing Acid fracturing

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3D characterization of porosity and minerals of low-permeability uranium-bearing sandstone based on multi-resolution image fusion

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Nuclear Science and Techniques 2020年第10期31卷 115-134页

作者： Bing Sun Shan-Shan Hou Sheng Zeng Xin Bai Shu-Wen Zhang Jing Zhang School of Civil Engineering University of South ChinaHengyang 421001China School of Resource Environment and Safety Engineering University of South ChinaHengyang 421001China School of Resources and Safety Engineering Central South UniversityChangsha 410083China

In the process of in situ leaching of uranium,the microstructure controls and influences the flow distribution,percolation characteristics,and reaction mechanism of lixivium in the pores of reservoir rocks and directly affects the leaching of useful components.In this study,the pore throat,pore size distribution,and mineral composition of low-permeability uranium-bearing sandstone were quantitatively analyzed by high pressure mercury injection,nuclear magnetic resonance,X-ray diffraction,and wavelength-dispersive X-ray fluorescence.The distribution characteristics of pores and minerals in the samples were qualitatively analyzed using energy-dispersive scanning electron microscopy and multi-resolution CT images.Image registration with the landmarks algorithm provided by FEI Avizo was used to accurately match the CT images with different resolutions.The multi-scale and multi-mineral digital core model of low-permeability uranium-bearing sandstone is reconstructed through pore segmentation and mineral segmentation of fusion core scanning images.The results show that the pore structure of low-permeability uranium-bearing sandstone is complex and has multi-scale and multi-crossing characteristics.The intergranular pores determine the main seepage channel in the pore space,and the secondary pores have poor connectivity with other pores.Pyrite and coffinite are isolated from the connected pores and surrounded by a large number of clay minerals and ankerite cements,which increases the difficulty of uranium leaching.Clays and a large amount of ankerite cement are filled in the primary and secondary pores and pore throats of the low-permeability uraniumbearing sandstone,which significantly reduces the porosity of the movable fluid and results in low overall permeability of the cores.The multi-scale and multi-mineral digital core proposed in this study provides a basis for characterizing macroscopic and microscopic pore-throat structures and mineral distributions of low-permeability uranium-bearing sandstone and can better

关键词： Low-permeability uranium-bearing sandstone digital core Micro-CT SEM–EDS Image fusion

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