Development Characteristics And Prediction Of Ordovician Fractures In Yangshuiwu Buried Hill In Jizhong Depression

The Ordovician of Yangshuiwu Buried Hill in Jizhong Depression is rich in oil and gas resources and has great exploration potential.Fractures play an important role in oil and gas storage and migration.Therefore,it is of great significance to study the development characteristics and distribution of Ordovician fractures in Yangshuiwu Buried Hill.In this paper,the development characteristics,controlling factors and prediction of Ordovician fractures in Yangshuiwu Buried Hill in Jizhong Depression are studied by means of field outcrop observation,core description,thin section analysis,conventional logging interpretation and image logging interpretation,and R/S analysis.The research shows that the fracture types developed in the Ordovician of Yangshuiwu Buried Hill in the Jizhong Depression mainly include structural fractures,diagenetic fractures and weathering fractures,mainly structural shear fractures with large dip angles,most of which are more than 50° in dip.Most of the fracture heights are below20 cm,the openings are concentrated between 0 and 20 μm,and the single-well fracture density is 0.14-0.83 fractures/m.The orientations of the fractures are mainly NEE-SWW,NNE-SSW,NNW-SSE and near E-W,and are formed in three stages.The degree of development of fractures in the study area is mainly controlled by faults,and the degree of development of fractures is higher in the densely located faults and in the hanging wall of faults.In addition,the degree of fracture development is also affected by lithology and layer thickness.Fractures are most developed in dolomite,and more developed in limestone;fractures are the least developed in mudstone.The higher the particle content and larger the particle size in the rock,the more fracture development.Within a certain thickness of a single layer,the layer thickness is inversely proportional to the degree of fracture development.According to the AC logs data,the R/S analysis method was used to predict the relatively favorable area of fractures.It was found that the relative development area of Ordovician fractures in Yangshuiwu Buried Hill is mainly distributed in strips,concentrated in the central area,and sporadically distributed in the southwest,south and northeast;fractures are relatively developed in the Xiamajiagou Formation,the Shangmajiagou Formation and the Fengfeng Formation,and the fractures in the Liangjiashan Formation are less developed.