Tight sandstone has a certain anisotropy. Using ultrasonic measurements of samples in three different directions and related matched experiments, this study systematically analyzes the pore structure and anisotropy of...Tight sandstone has a certain anisotropy. Using ultrasonic measurements of samples in three different directions and related matched experiments, this study systematically analyzes the pore structure and anisotropy of tight sandstone samples obtained from oil fields and compares results with those of shale. Results firstly show that the anisotropy of tight sandstone is mainly related to the compositional layering and thin interbedding which occur in different sedimentary environments. Tight sandstone has typical transverse isotropic medium characteristics, Young’s modulus increases in different directions with increasing confining pressure, Poisson’s ratio change is not obvious, anisotropic coefficients decrease with increasing effective pressure, and a certain linear relationship exists between ε, γ, and δ. This article finally summarizes anisotropy in different areas, thereby providing a foundation for the use of suitable appraisal models in different regions. This research can be used as an experimental reference for logging evaluation, seismic data interpretation, and fracturing develop of tight sandstones.展开更多
Brittleness analysis becomes important when looking for sweet spots in tightoil sandstone reservoirs. Hence, appropriate indices are required as accurate brittleness evaluation criteria. We construct a seismic rock ph...Brittleness analysis becomes important when looking for sweet spots in tightoil sandstone reservoirs. Hence, appropriate indices are required as accurate brittleness evaluation criteria. We construct a seismic rock physics model for tight-oil sandstone reservoirs with vertical fractures. Because of the complexities in lithology and pore structure and the anisotropic characteristics of tight-oil sandstone reservoirs, the proposed model is based on the solid components, pore connectivity, pore type, and fractures to better describe the sandstone reservoir microstructure. Using the model, we analyze the brittleness sensitivity of the elastic parameters in an anisotropic medium and establish a new brittleness index. We show the applicability of the proposed brittleness index for tight-oil sandstone reservoirs by considering the brittleness sensitivity, the rock physics response characteristics, and cross-plots. Compared with conventional brittleness indexes, the new brittleness index has high brittleness sensitivity and it is the highest in oil-bearing brittle zones with relatively high porosity. The results also suggest that the new brittleness index is much more sensitive to elastic properties variations, and thus can presumably better predict the brittleness characteristics of sweet spots in tight-oil sandstone reservoirs.展开更多
Existing seismic prediction methods struggle to effectively discriminate between fluids in tight gas reservoirs,such as those in the Sulige gas field in the Ordos Basin,where porosity and permeability are extremely lo...Existing seismic prediction methods struggle to effectively discriminate between fluids in tight gas reservoirs,such as those in the Sulige gas field in the Ordos Basin,where porosity and permeability are extremely low and the relationship between gas and water is complicated.In this paper,we have proposed a comprehensive seismic fluid identification method that combines ray-path elastic impedance(REI)inversion with fluid substitution for tight reservoirs.This approach is grounded in geophysical theory,forward modeling,and real data applications.We used geophysics experiments in tight gas reservoirs to determine that Brie's model is better suited to calculate the elastic parameters of mixed fluids than the conventional Wood’s model.This yielded a more reasonable and accurate fluid substitution model for tight gas reservoirs.We developed a forward model and carried out inversion of REI.which reduced the non-uniqueness problem that has plagued elastic impedance inversion in the angle domain.Our well logging forward model in the ray-path domain with different fluid saturations based on a fluid substitution model proved that REI identifies fluids more accurately when the ray parameters are large.The distribution of gas saturation can be distinguished from the crossplot of REI(p=0.10)and porosity.The inverted ray-path elastic impedance profile was further used to predict the porosity and gas saturation profile.Our new method achieved good results in the application of 2D seismic data in the western Sulige gas field.展开更多
Cement content of carbonate in tight sandstone near section is much the fault of well Xia503, in the Huimin sag in Linnan sub-depression higher than that of the normal sandstones far away from In order to understand t...Cement content of carbonate in tight sandstone near section is much the fault of well Xia503, in the Huimin sag in Linnan sub-depression higher than that of the normal sandstones far away from In order to understand the origin and its impact on fault sealing, analyses of the whole-rock minerals, casting thin sections, cathodoluminescence, isotope and physical properties are conducted on cores from well Xia503. It is found that c~ L3C varies from 0.1%o to 0.6%o with the average value of 0.42%o, c~ LSO varies from -13.5%o to -12.3%c with the average of-13.1%~., and C-O isotope plotting points are distributed in the low to moderate temperature area of the hydrothermal dolomite. According to the occupied relationship, cathodoluminescence, and C-O isotope feature, the carbonate cementation could be divided into four stages： calcites, dolomite, ankerite, and ferrocalcite. It is discovered that the carbonate cementation is negatively related to reservoir physical property, with the porosity of 4.8%, permeability of 0.37 roD, and displacement pressure of 1.97 MPa in the tight sandstone, which have increased by almost one order of magnitude compared to the porosity of 14.3%, permeability of 3.73 mD, and displacement pressure of 0.27 MPa in the normal sandstone, which is far away from the fault. Regardless of the lithology of the counterpart wall of the fault, only the displacement pressure difference caused by carbonate cementation between the tight sandstone and the normal sandstone could seal 41 m high oil column.展开更多
基金sponsored by the National Key Technology R&D Program for the 12th five-year plan(No.2011ZX05020-008)the China National Petroleum Corporation Logging Basic Research Project(No.2014A-3910)
文摘Tight sandstone has a certain anisotropy. Using ultrasonic measurements of samples in three different directions and related matched experiments, this study systematically analyzes the pore structure and anisotropy of tight sandstone samples obtained from oil fields and compares results with those of shale. Results firstly show that the anisotropy of tight sandstone is mainly related to the compositional layering and thin interbedding which occur in different sedimentary environments. Tight sandstone has typical transverse isotropic medium characteristics, Young’s modulus increases in different directions with increasing confining pressure, Poisson’s ratio change is not obvious, anisotropic coefficients decrease with increasing effective pressure, and a certain linear relationship exists between ε, γ, and δ. This article finally summarizes anisotropy in different areas, thereby providing a foundation for the use of suitable appraisal models in different regions. This research can be used as an experimental reference for logging evaluation, seismic data interpretation, and fracturing develop of tight sandstones.
基金supported by the National 973 project(Nos.2014CB239006 and 2011CB202402)the National Natural Science Foundation of China(Nos.41104069 and 41274124)+1 种基金Sinopec project(No.KJWX2014-05)the Fundamental Research Funds for the Central Universities(No.R1401005A)
文摘Brittleness analysis becomes important when looking for sweet spots in tightoil sandstone reservoirs. Hence, appropriate indices are required as accurate brittleness evaluation criteria. We construct a seismic rock physics model for tight-oil sandstone reservoirs with vertical fractures. Because of the complexities in lithology and pore structure and the anisotropic characteristics of tight-oil sandstone reservoirs, the proposed model is based on the solid components, pore connectivity, pore type, and fractures to better describe the sandstone reservoir microstructure. Using the model, we analyze the brittleness sensitivity of the elastic parameters in an anisotropic medium and establish a new brittleness index. We show the applicability of the proposed brittleness index for tight-oil sandstone reservoirs by considering the brittleness sensitivity, the rock physics response characteristics, and cross-plots. Compared with conventional brittleness indexes, the new brittleness index has high brittleness sensitivity and it is the highest in oil-bearing brittle zones with relatively high porosity. The results also suggest that the new brittleness index is much more sensitive to elastic properties variations, and thus can presumably better predict the brittleness characteristics of sweet spots in tight-oil sandstone reservoirs.
基金supported by the National Science and Technology Major Project(No.2016ZX05050 and 2017ZX05069)CNPC Major Technology Special Project(No.2016E-0503)
文摘Existing seismic prediction methods struggle to effectively discriminate between fluids in tight gas reservoirs,such as those in the Sulige gas field in the Ordos Basin,where porosity and permeability are extremely low and the relationship between gas and water is complicated.In this paper,we have proposed a comprehensive seismic fluid identification method that combines ray-path elastic impedance(REI)inversion with fluid substitution for tight reservoirs.This approach is grounded in geophysical theory,forward modeling,and real data applications.We used geophysics experiments in tight gas reservoirs to determine that Brie's model is better suited to calculate the elastic parameters of mixed fluids than the conventional Wood’s model.This yielded a more reasonable and accurate fluid substitution model for tight gas reservoirs.We developed a forward model and carried out inversion of REI.which reduced the non-uniqueness problem that has plagued elastic impedance inversion in the angle domain.Our well logging forward model in the ray-path domain with different fluid saturations based on a fluid substitution model proved that REI identifies fluids more accurately when the ray parameters are large.The distribution of gas saturation can be distinguished from the crossplot of REI(p=0.10)and porosity.The inverted ray-path elastic impedance profile was further used to predict the porosity and gas saturation profile.Our new method achieved good results in the application of 2D seismic data in the western Sulige gas field.
基金supported by National Basic Research Program of China(Grant No.2012CB723104)National Natural Science Foundation of China(Grant Nos.41372108,41372134)Program for Scientific Research Innovation Team in Colleges and Universities of Shandong Province,and SDUST Research Fund(Gant No.2010KYTD103)
文摘Cement content of carbonate in tight sandstone near section is much the fault of well Xia503, in the Huimin sag in Linnan sub-depression higher than that of the normal sandstones far away from In order to understand the origin and its impact on fault sealing, analyses of the whole-rock minerals, casting thin sections, cathodoluminescence, isotope and physical properties are conducted on cores from well Xia503. It is found that c~ L3C varies from 0.1%o to 0.6%o with the average value of 0.42%o, c~ LSO varies from -13.5%o to -12.3%c with the average of-13.1%~., and C-O isotope plotting points are distributed in the low to moderate temperature area of the hydrothermal dolomite. According to the occupied relationship, cathodoluminescence, and C-O isotope feature, the carbonate cementation could be divided into four stages： calcites, dolomite, ankerite, and ferrocalcite. It is discovered that the carbonate cementation is negatively related to reservoir physical property, with the porosity of 4.8%, permeability of 0.37 roD, and displacement pressure of 1.97 MPa in the tight sandstone, which have increased by almost one order of magnitude compared to the porosity of 14.3%, permeability of 3.73 mD, and displacement pressure of 0.27 MPa in the normal sandstone, which is far away from the fault. Regardless of the lithology of the counterpart wall of the fault, only the displacement pressure difference caused by carbonate cementation between the tight sandstone and the normal sandstone could seal 41 m high oil column.
