Fracture Structure Characteristics And Its Controlling Effects On The Hydrocarbon Accumulation In Chexi Area

The Chexi area is located in the west of Chezhen Sag in Jiyang Depression of the Bohai Bay Basin.In recent years,with the improvement of oil and gas exploration,the deep Paleozoic buried hills are considered to be excellent exploration targets and areas for increasing reserves on the basis of the gradual implementation of the middle and shallow reserves.Buried hill reservoirs are mainly controlled by early developmental faults.Therefore,it is of great practical significance to carry out research on fracture characteristics,fault structure identification,physical analysis of fault zone and fault control of high-efficiency exploration and storage.Based on the research status of predecessors,this study implements the characteristics of fault structure;comprehensively identifies the structural characteristics of the main fault zone by means of the combination of “Well-Seismic-Core”;discusses the differences in physical properties of different structural units in the fault zone;Controlling the fracture closure of fractures.Four conclusions have been obtained:(1)The controlling faults in the Chexi depression are mainly concentrated in the two-step buried hill belt and southern stepped fracture.Affected by multi-stage tectonic stress field,the fracture is mainly composed of gridlike combination,oblique combination and parallel combination in the plane distribution.On the section,the combination of the basement and the sloping block in the steep slope of the north,and the sliding step of the development of the gentle slope in the south.(2)The structure of the fault zone in Chexi area is well developed and the log response characteristics are obvious.Through research,it is found that for a single fracture,there may be multiple sliding fracture zones inside.The width of the sliding fracture zone has a power exponential relationship with the width of the induced fracture zone.The drop of the fracture also has a power exponential relationship with the width of the fracture zone.(3)The physical properties of the internal structural unit of the fault zone are clarified.In general,the tendency of the induced fracture zone to be more porous than that of the sliding fracture zone is observed.Influenced by the development of the lithology of the fault zone,the porosity of the deep carbonate rocks is often lower than that of the shallow clastic rocks.The permeability is ranked from high to low: upper induced fracture zone > lower induced fracture zone > sliding fracture zone.(4)The fault sealing of Chexi area shows the following rules: the fault sealing is moderate-better,and the opening and closing property is greatly affected by factors such as the period of fault activity,sandstone thickness and shale content.The crack is controlled by diagenetic cementation,and the type of cement is dominated by carbonate cement.The main cementation period is the sedimentary period of the Dongying Formation and the early period of the Guantao Formation.The fracture cementation rate is mostly greater than 80%.The fracture control mode of this area can be divided into two modes: reservoir model developed in the lower part of the upper source rock and oil accumulation along a stepped fault.