Evaluation Of Natural Fractures Of Leikoupo Reservoir In Pengzhou Gas Field

Carbonate reservoir has the characteristics of low porosity and low permeability,and fracture is the key geological factor for high production of gas well.However,the development of carbonate reservoir is often very complicated and heterogeneity,which makes it difficult to describe and identify fractures.Through the analysis of core and sections cut from cores,the comprehensive identification of fractures with conventional logging data,the study of fracture period by means of experiment,the main controlling factors of analyzing fractures are all effective means to study carbonate fractures.In this paper,the fracture of carbonate reservoir of Leikoupo formation in the middle Triassic of Pengzhou gas field is studied,and the characteristics of fracture type,occurrence,fracture density and validity are analyzed through observation of core fractures.Through core location,the characteristic parameters of fractures in conventional logging are analyzed,and two methods are used to identify the fractures.The identification results are verified,and the identification patterns and standards of natural fractures are established.According to the results of observing the fracture period with core and sections cut from cores,the natural fracture formation time of Pengzhou gas field is analyzed by the analysis of the carbon-oxygen stable isotope and the temperature experiment of fluid inclusion body.The main controlling factors of natural fracture development are analyzed in combination of geological factors and core,test analysis,well profile fracture identification results,and the longitudinal and horizontal development characteristics of fractures are obtained in combination with the development of fractures in the studied area.Finally,the distribution of cracks is evaluated.By observing and describing the cores of 11 wells,vertical fractures and high angle fractures are mainly developed in the target layer of the study area,followed by reticular and irregular fractures.The study of fracture effectiveness and development density shows that vertical cracks and high angle slanting cracks in this area are the focus types.The identification pattern and standard of natural cracks are established,and the interpretation and analysis of the cracks in the work area are completed.The carbon and oxygen stable isotopic analysis of calcite filling and the experimental analysis of fluid inclusion temperature show that there are five main stages of fracture formation in the study area.Based on the analysis of the main factors controlling the development of natural fractures,it is considered that the controlling factors for the development of structural fractures in the upper segment of Lei Kou Po formation-4 in Pengzhou gas field are lithology,rock thickness,faults and structural deformation,among which faults play the most important role in controlling fractures.The structural fractures are mainly developed near the fault,and the level of fracture development decreases obviously with the increase of the distance from the fault.The fault derived fracture is the main fracture type in the study area.