Research On The Control Effect Of Faults On Shale Gas Accumulation In Changning Area

Southern Sichuan,which deep shale gas is abundant,that accounts for 86% of the total resources and has great potential for exploration and development.Among them,the main production effect of Changning area is better,but with the deepening of exploration process,the construction area develops to the middle and west of Ning216 well area,and the tectonic activity in this area is strong,the micro-structure and multi-stage fault develop at the bottom of Wufeng-Longmaxi Formation,and the burial depth changes rapidly to 3500 meters,so the exploration effect is not ideal.It has been proved that fault-related folds and micro-fractures are the main factors affecting shale gas accumulation in this area,but the fault-control mechanism of shale gas accumulation is not clear,which restricts the selection evaluation and exploration and development deployment in this area.In this paper,the Marine shale of Upper Ordovician Wufeng Formation in Changning area,Sichuan Basin is selected as the research object,and the existing drilling and logging data in Changning area are fully utilized,based on 3d seismic data and combined with actual production data.The detailed interpretation of the upper Ordovician Wufeng Formation fault system,the study of fault plane distribution characteristics,Typical well productivity analysis,shale gas content analysis under different structural styles,qualitative identification and quantitative characterization of faults and their related fractures,Calculation of fracture zone width of fault fracture.Through the above research work,the following research progress and understanding have been made:(1)By means of coherent body technique analysis and strike rose diagram,it is recognized that ne-SW strike,NW-SE strike and nearly EAST-W strike thrust faults are mainly developed in the study area;The main structural styles are base-involved thrust fault,imbricated thrust fault,offset thrust fault,back-thrust fault,detachment fault and wedge-shaped structure,and most of the folds are detachment fold.(2)According to the fault assemblage style in Changning area,and combined with the production data of drilling and logging,four structural styles that mainly affect the preservation of shale gas are proposed: monoclinal structural style,back-thrust anticlinal,back-thrust synclinal and thrust imbricate structural style,monoclinal structure is more conducive to the preservation of shale gas,backthrust anticlinal structure,backthrust synclinal structure and thrust imbricate structure can obtain a certain amount of shale gas after fracturing,but the production is limited.(3)The multi-scale fault sensitivity attribute is used to identify the fracture system in Changning area,and the faults and related fractures are more developed near the large faults,and the fracture density decreases with the distance from the faults;quantitative characterization of fault fractures was carried out by using the section void method(VSD),and the results were constrained by logging data.It is concluded that the porosity of fractures controlled by faults is mostly about 4%.(4)The width of fault fracture zone in Changning area was obtained by using maximum likelihood technology and VSD technology,and it was preliminatively determined that the width of fault fracture zone in Changning area was 1.5-2.0 times of the drop;The exploration distance for effective preservation of shale gas in Changning area is 300m-1000 m.In this paper,a set of methods of qualitative characterization and quantitative characterization of underground fault fracture system are established,which can effectively predict the development characteristics of fault fracture system in Changning area.The research content is closely related to production practice,and provides theoretical and technical support for further exploration and development of shale gas in this area.