Quantitative Characterization And Comprehensive Evaluation Of Natural Fractures In Tight Oil Reservoirs In Yuan284,Huaqing Oilfield

Yanchang Formation Chang 6 of the upper Triassic in Huaqing oilfield,Ordos Basin is a tight sandstone reservoir.Because of its tight rock matrix,low porosity and permeability,the natural fracture system has become an important channel,reservoir space for oil and gas migration in this area.In our study,literature research,data collection and arrangement was carried out,field outcrop area and core fracture was described in detail,microscopic fracture of thin sections was described under microscope and made statistics.Combined with test analysis of fluid inclusion test,rock mechanics test,acoustic emission test,etc.,the causes and forms of fractures in the study area were systematically analyzed based on the understanding of the development of fracture oil and gas in tight sandstone reservoir at home and abroad.The fracture was quantitatively characterized.The main control factors and the formation mechanism of the cracks was analyzed.A comprehensive evaluation of the fracture distribution law was made by using the finite element numerical simulation method.The results showed that the natural fractures of Chang 6 tight reservoir in block 284 are mainly tensile fractures(71.53%).The fractures in the study area are mainly structural fractures with high angle,according to the analysis of geological genesis.The micro fracture in the study area greatly improves the pore structure and overall performance of the reservoir,which is of great value to the tight reservoir.The microscopic fracture pore structure and overall performance of the reservoir in the study area are made innovation to the most,which makes the reservoir and permeability of the tight reservoir show important value.The fractures in the study area are generally developed.Most of the natural fractures are developed in the layer and end at the lithologic interface.The filling degree of the fractures is weak,and most of them are effective fractures.The main role of seepage in the rock is macro fracture,while the permeability of micro fracture and bedding fracture is low,which mainly improves the seepage of ultra-low permeability sandstone reservoir.The degree of fracture development is controlled by factors such as lithology,formation thickness,sedimentary microfacies,diagenetic facies and rock heterogeneity.The maximum and minimum principal stresses of Yanshanian,Himalayan and present tectonic stress fields are obtained by numerical simulation.With the increase of burial depth,the maximum and minimum principal stresses tend to increase.The distribution rule of structural fracture in the study reservoir was calculated and predicted quantitatively,according to the external geological factors affecting the formation of natural fractures,the numerical simulation of paleotectonic stress field at fracture formation time,the criterion of actual rock fracture and the distribution of core fracture in oil field.As the distribution rule shows that the main fracture is tensile fracture and the development degree of fracture is controlled by the factors such as lithology,sedimentary facies and diagenesis.