Seismic Interpretation And Structural Feature Analysis Of Cambrian Gypsum-salt Rock In Jiannan 3D Area

Sinian system in the Sichuan basin has the characteristics of large thickness and extensive distribution,and they have superior petroleum geological conditions.In recent years,the large carbonate gas of Cambrian and Sinian reservoirs have been found in the middle Anyue area of Sichuan Province.The petroleum and natural gas geological conditions of the Yudong fold belt in the south of the Jian Nan anticline are similar to those in the central Sichuan area of Anyue.However,in Jian'anan anticline,the gypsum salt rock is relatively developed in the middle and lower part of Cambrian,and the compressional deformation of the gypsum salt rock is very complicated,which is making the seismic imaging of the subsalt structure complicated,so the understanding of the structure of under salt is not clear.This has also led to difficulties in determining the under-salt structure traps.The Jian Shen 1 well,which was built in the early stage and deployed as a target for detecting lower Cambrian-Sinian structural trap of the Jianan anticline,was not able to reach the oil and gas exploration target because of the complexity of the subsalt structure.The well met with the thick layer gypsum salt assemblage,which resulted in the completion of the accident.The drilling of Cambrian and Sinian oil-bearing formations was not successful.Finding out the trapping conditions of the Cambrian sub-salt structure has become the key to breakthrough deep oil and gas exploration in this area.Based on the 3D seismic data of Jiannan structure,the drilling-logging data of Jian Shen 1 well well,and the research results of regional geological background,this paper is guided by the theory of tectonic geology,fault-related fold model and salt-related structural model.The structural evolution and genetic mechanism of Jiannan anticline are analyzed reasonably by analyzing the fault fold model of Jiannan structure and reconstructing the deep Cambrian subsalt and upper salt tectonic pattern in the three dimensional area of Jiannan.The main achievements and understandings are as follows:(1)The main slip layer that determines the fold structure of Jiannan tectonic is the Cambrian gypsum salt rock.The structure of this area is divided into upper salt structure layer and subsalt structure layer by Cambrian gypsum salt rock.(2)The deformation of Jiannan anticline is formed by the superposition of multi-phase motion.The early Yanshanian movement has made the strata above the strata of Cambrian gypsum rock form a detachment fold structure.There was no fold deformation in the Cambrian subsalt strata.The late Yanshan-Himalayan movement continued to transform this area.In this period,basement faults are more active than the interior of the basin.The fault block structure formed in the lower Cambrian-Pres Sinian system by these basement faults.Finally Jiannan anticline formed the present structural form.(3)The drilling finish strata of the Jian Shen 1 well still belongs to the assemblage of gypsum salt rock,and the west high zone originally inferred does not exist.(4)Located directly below the east wing of the upper salt anticline in Jiannan,Fengxiangba structure is the largest fault block structural trap under salt.Fengxiangba structure that has excellent conditions for forming large carbonate gas reservoirs is the most reliable target for oil and gas exploration in this area.