Tight glutenite reservoirs are widely developed in Bohai Bay Basin,East China.They are mostly huge thick and rely on hydraulic fracturing treatment for commercial exploitation.To investigate the propagation behavior o...Tight glutenite reservoirs are widely developed in Bohai Bay Basin,East China.They are mostly huge thick and rely on hydraulic fracturing treatment for commercial exploitation.To investigate the propagation behavior of hydraulic fractures in these glutenite reservoirs,the geological feature of reservoirs in Bohai Bay Basin is studied firstly,including the reservoir vertical distribution feature and the heterogeneous lithology.Then,hydraulic fracturing treatments in block Yan 222 are carried out and the fracturing processes are monitored by the microseismic system.Results show the hydraulic fractures generated in the reservoirs are mostly in X shape.The cause of X-shaped hydraulic fractures in this study is mainly ascribed to(I)the reservoir heterogeneity and(II)the stress shadow effect of two close hydraulic fractures propagating in the same orientation,which is confirmed by the following numerical simulation and related research in detail.This study can provide a reference for the research on the fracturing behavior of the deep thick glutenite reservoirs.展开更多
Detecting holes in oil–gas reservoirs is vital to the evaluation of reservoir potential. The main objective of this study is to demonstrate the feasibility of identifying general micro-hole shapes, including triangul...Detecting holes in oil–gas reservoirs is vital to the evaluation of reservoir potential. The main objective of this study is to demonstrate the feasibility of identifying general micro-hole shapes, including triangular, circular, and square shapes, in oil–gas reservoirs by adopting terahertz time-domain spectroscopy(THz-TDS). We evaluate the THz absorption responses of punched silicon(Si) wafers having micro-holes with sizes of 20 μm–500 μm. Principal component analysis(PCA) is used to establish a model between THz absorbance and hole shapes. The positions of samples in three-dimensional spaces for three principal components are used to determine the differences among diverse hole shapes and the homogeneity of similar shapes. In addition, a new Si wafer with the unknown hole shapes, including triangular, circular, and square, can be qualitatively identified by combining THz-TDS and PCA. Therefore, the combination of THz-TDS with mathematical statistical methods can serve as an effective approach to the rapid identification of micro-hole shapes in oil–gas reservoirs.展开更多
Small-scale true triaxial sand fracturing experiments are conducted on thin interbedded shale samples made from cores of Permian Lucaogou Formation shale oil reservoir in Jimsar sag, Junggar Basin, NW China. Combined ...Small-scale true triaxial sand fracturing experiments are conducted on thin interbedded shale samples made from cores of Permian Lucaogou Formation shale oil reservoir in Jimsar sag, Junggar Basin, NW China. Combined with high-precision CT scanning digital core model reconstruction technology, hydraulic fracture geometry and proppant distribution in thin interbedded shale oil reservoirs are studied. The research shows that: In thin interbedded shale oil reservoir, the interlayer difference of rock mechanics and the interlayer interface near the wellbore cannot restrain the growth of fracture height effectively, but has a significant impact on the fracture width distribution in the fracture height direction. Hydraulic fractures in these reservoirs tend to penetrate into the adjacent layer in “step-like” form, but have a smaller width at the interface deflection, which hinders the transport of proppant in vertical direction, resulting in a poor effect of layer-crossing growth. In shale layers with dense laminae, hydraulic fractures tend to form “丰” or “井” shapes. If the perforated interval is large in rock strength and high in breakdown pressure, the main fracture is fully developed initially, large in width, and supported by enough sand. In contrast, if the perforated interval is low in strength and rich in laminae, the fracturing fluid filtration loss is large, the breakdown pressure is low, the main fracture will not open wide initially, and likely to have sand plugging. Proppant is mainly concentrated in the main hydraulic fractures with large width near the perforated layer, activated laminae, branch fractures and fractures in adjacent layers contain only a small amount of(or zero) proppant. The proppant is placed in a limited range on the whole. The limit width of fracture that proppant can enter is about 2.7 times the proppant particle size.展开更多
Describing matrix–fracture interaction is one of the most important factors for modeling natural fractured reservoirs.A common approach for simulation of naturally fractured reservoirs is dual-porosity modeling where...Describing matrix–fracture interaction is one of the most important factors for modeling natural fractured reservoirs.A common approach for simulation of naturally fractured reservoirs is dual-porosity modeling where the degree of communication between the low-permeability medium(matrix)and high-permeability medium(fracture)is usually determined by a transfer function.Most of the proposed matrix–fracture functions depend on the geometry of the matrix and fractures that are lumped to a factor called shape factor.Unfortunately,there is no unique solution for calculating the shape factor even for symmetric cases.Conducting fine-scale modeling is a tool for calculating the shape factor and validating the current solutions in the literature.In this study,the shape factor is calculated based on the numerical simulation of fine-grid simulations for single-phase flow using finite element method.To the best of the author’s knowledge,this is the first study to calculate the shape factors for multidimensional irregular bodies in a systematic approach.Several models were used,and shape factors were calculated for both transient and pseudo-steady-state(PSS)cases,although in some cases they were not clarified and assumptions were not clear.The boundary condition dependency of the shape factor was also investigated,and the obtained results were compared with the results of other studies.Results show that some of the most popular formulas cannot capture the exact physics of matrix–fracture interaction.The obtained results also show that both PSS and transient approaches for describing matrix–fracture transfer lead to constant shape factors that are not unique and depend on the fracture pressure(boundary condition)and how it changes with time.展开更多
A transient flow model of tree-shaped fractal reservoirs is built by embedding a fracture network simulated by a tree-shaped fractal network into a matrix system. The model can be solved using the Laplace conversion m...A transient flow model of tree-shaped fractal reservoirs is built by embedding a fracture network simulated by a tree-shaped fractal network into a matrix system. The model can be solved using the Laplace conversion method. The dimensionless bottom hole pressure can be obtained using the Stehfest numerical inversion method. The bi-logarithmic type curves for the trce-shaped fractal reservoirs are thus obtained. The pressure transient responses under different fractal factors are discussed. The factors with a primary effect on the inter-porosity flow regime include the initial branch number N, the length ratio α, and the branch angle θ. The diameter ratio β has a significant effect on the fracture radial flow, the inter-porosity and the total system radial flow regimes. The total branch level M of the network mainly influences the total system radial flow regime. The model presented in this paper provides a new methodology for analyzing and predicting the pressure dynamic characteristics of naturally fractured reservoirs.展开更多
基金Projects(51879041,51774112,U1810203)supported by the National Natural Science Foundation of ChinaProject(2020M672224)supported by the China Postdoctoral Science FoundationProject(B2020-41)supported by the Doctoral Fund of Henan Polytechnic University,China。
文摘Tight glutenite reservoirs are widely developed in Bohai Bay Basin,East China.They are mostly huge thick and rely on hydraulic fracturing treatment for commercial exploitation.To investigate the propagation behavior of hydraulic fractures in these glutenite reservoirs,the geological feature of reservoirs in Bohai Bay Basin is studied firstly,including the reservoir vertical distribution feature and the heterogeneous lithology.Then,hydraulic fracturing treatments in block Yan 222 are carried out and the fracturing processes are monitored by the microseismic system.Results show the hydraulic fractures generated in the reservoirs are mostly in X shape.The cause of X-shaped hydraulic fractures in this study is mainly ascribed to(I)the reservoir heterogeneity and(II)the stress shadow effect of two close hydraulic fractures propagating in the same orientation,which is confirmed by the following numerical simulation and related research in detail.This study can provide a reference for the research on the fracturing behavior of the deep thick glutenite reservoirs.
基金supported by the National Natural Science Foundation of China(Grant No.61405259)the National Basic Research Program of China(Grant No.2014CB744302)the Specially Founded Program on National Key Scientific Instruments and Equipment Development,China(Grant No.2012YQ140005)
文摘Detecting holes in oil–gas reservoirs is vital to the evaluation of reservoir potential. The main objective of this study is to demonstrate the feasibility of identifying general micro-hole shapes, including triangular, circular, and square shapes, in oil–gas reservoirs by adopting terahertz time-domain spectroscopy(THz-TDS). We evaluate the THz absorption responses of punched silicon(Si) wafers having micro-holes with sizes of 20 μm–500 μm. Principal component analysis(PCA) is used to establish a model between THz absorbance and hole shapes. The positions of samples in three-dimensional spaces for three principal components are used to determine the differences among diverse hole shapes and the homogeneity of similar shapes. In addition, a new Si wafer with the unknown hole shapes, including triangular, circular, and square, can be qualitatively identified by combining THz-TDS and PCA. Therefore, the combination of THz-TDS with mathematical statistical methods can serve as an effective approach to the rapid identification of micro-hole shapes in oil–gas reservoirs.
基金National Natural Science Foundation of China(NO.51974332)Strategic Cooperation Project Between PetroChina and China University of Petroleum(Beijing)(NO.ZLZX2020-07)。
文摘Small-scale true triaxial sand fracturing experiments are conducted on thin interbedded shale samples made from cores of Permian Lucaogou Formation shale oil reservoir in Jimsar sag, Junggar Basin, NW China. Combined with high-precision CT scanning digital core model reconstruction technology, hydraulic fracture geometry and proppant distribution in thin interbedded shale oil reservoirs are studied. The research shows that: In thin interbedded shale oil reservoir, the interlayer difference of rock mechanics and the interlayer interface near the wellbore cannot restrain the growth of fracture height effectively, but has a significant impact on the fracture width distribution in the fracture height direction. Hydraulic fractures in these reservoirs tend to penetrate into the adjacent layer in “step-like” form, but have a smaller width at the interface deflection, which hinders the transport of proppant in vertical direction, resulting in a poor effect of layer-crossing growth. In shale layers with dense laminae, hydraulic fractures tend to form “丰” or “井” shapes. If the perforated interval is large in rock strength and high in breakdown pressure, the main fracture is fully developed initially, large in width, and supported by enough sand. In contrast, if the perforated interval is low in strength and rich in laminae, the fracturing fluid filtration loss is large, the breakdown pressure is low, the main fracture will not open wide initially, and likely to have sand plugging. Proppant is mainly concentrated in the main hydraulic fractures with large width near the perforated layer, activated laminae, branch fractures and fractures in adjacent layers contain only a small amount of(or zero) proppant. The proppant is placed in a limited range on the whole. The limit width of fracture that proppant can enter is about 2.7 times the proppant particle size.
文摘Describing matrix–fracture interaction is one of the most important factors for modeling natural fractured reservoirs.A common approach for simulation of naturally fractured reservoirs is dual-porosity modeling where the degree of communication between the low-permeability medium(matrix)and high-permeability medium(fracture)is usually determined by a transfer function.Most of the proposed matrix–fracture functions depend on the geometry of the matrix and fractures that are lumped to a factor called shape factor.Unfortunately,there is no unique solution for calculating the shape factor even for symmetric cases.Conducting fine-scale modeling is a tool for calculating the shape factor and validating the current solutions in the literature.In this study,the shape factor is calculated based on the numerical simulation of fine-grid simulations for single-phase flow using finite element method.To the best of the author’s knowledge,this is the first study to calculate the shape factors for multidimensional irregular bodies in a systematic approach.Several models were used,and shape factors were calculated for both transient and pseudo-steady-state(PSS)cases,although in some cases they were not clarified and assumptions were not clear.The boundary condition dependency of the shape factor was also investigated,and the obtained results were compared with the results of other studies.Results show that some of the most popular formulas cannot capture the exact physics of matrix–fracture interaction.The obtained results also show that both PSS and transient approaches for describing matrix–fracture transfer lead to constant shape factors that are not unique and depend on the fracture pressure(boundary condition)and how it changes with time.
基金supported by the National Science Fund for Distinguished Young Scholars of China(Grant No.51125019)supported by the 2014 Australia China National Gas Technology Partnership Fund Top Up Scholoarship
文摘A transient flow model of tree-shaped fractal reservoirs is built by embedding a fracture network simulated by a tree-shaped fractal network into a matrix system. The model can be solved using the Laplace conversion method. The dimensionless bottom hole pressure can be obtained using the Stehfest numerical inversion method. The bi-logarithmic type curves for the trce-shaped fractal reservoirs are thus obtained. The pressure transient responses under different fractal factors are discussed. The factors with a primary effect on the inter-porosity flow regime include the initial branch number N, the length ratio α, and the branch angle θ. The diameter ratio β has a significant effect on the fracture radial flow, the inter-porosity and the total system radial flow regimes. The total branch level M of the network mainly influences the total system radial flow regime. The model presented in this paper provides a new methodology for analyzing and predicting the pressure dynamic characteristics of naturally fractured reservoirs.
