Research On Deep Geological Structure Of Sichuan Basin Based On Gravity And Magnetic Field Data Analysis

Sichuan Basin is one of the most essential petroliferous basins in China.Oil-gas exploration in Sichuan Basin has broadened into ultra-deep strata.The deep geological structure of Sichuan Basin predominates the formation and distribution of deep and ultra-deep oil and gas.It is of great theoretical and practicable significance to study the fine structure of the deep part of the Sichuan Basin.Gravity field analysis is one of the essential methods to study deep geological structure.In this thesis,the deep geological structure of Sichuan basin is studied by using high-precision regional gravity and magnetic data.The research contents and results of the thesis are as follows:1.Based on the multi-scale extension technique of gravity and magnetic field,the characteristics of deep structural changes in Sichuan Basin are studied.Based on the analysis of the variation characteristics of different height of gravity and magnetic field upward extension,it is considered that the deep structure of Sichuan Basin is significantly different in longitudinal direction;it is speculated that the undercutting depth of Longquanshan fault zone and Huayingshan fault zone reaches the lower part of basement.2.Based on the Parker interface inversion of regional gravity and magnetic anomalies,the folded basement and the crystalline basement of Sichuan Basin are obtained.Among them,the buried depth of fold basement is between 4km and 12 km,with the structural characteristics of shallow in the West and deep in the East;the crystalline basement has the obvious characteristics of "three parts" in the East,middle and West,with the overall trend of northeast.As a whole,the basement of Sichuan Basin is characterized by central Sichuan uplift,West Sichuan and East Sichuan depression,and there are widespread local uplift structures in them.The two sets of basement have different performance,complex basement structure,and are obviously controlled by Longquanshan fault and Huayingshan fault.3.Using density inversion imaging method based on gravity depth weighting to study the geological structure information of deep Sichuan Basin Based on gravity information.In this thesis,two main sections of gravity anomalies across Sichuan Basin are selected for deep density structure inversion.Based on the regional gravity and magnetic analysis and inversion results,Sichuan Basin has the characteristics of EastWest zoning,north-south blocking.The density structure well reveals the characteristics of Sichuan basin basement and the relationship of controlling fault distribution,and two new hidden faults that cut through the basement are identified: Nanchong-Shehong fault,Dazu-Suining fault.4.The linear structure features of the basin are obtained by using the horizontal total gradient model processing method.The linear structure reveals the development of faults in Sichuan Basin.The basin controlling structure is NE trending fault.In the later stage,it is transformed by NW trending structure.The east-west structure is still exist in parts of central and southern Sichuan.The basement of Sichuan Basin is obviously controlled by these structures,and the basement has obvious "tofu block" characteristics by structural action.Based on the research results of this thesis and previous studies on regional faults,the distribution of basement faults in Sichuan Basin is sketched.