Structural Fracture And Its Development Regularity In T₃x² Strata Within The Xinchang Structure, Western Sichuan Depression

The research work shows that the development of structural fracture plays an important role in the distribution of oil and gas.On the one hand,the development of structural fracture provides an access and trap for migration and accumulation of oil and gas.On the other hand, the development of structural fracture impacts the filtrate characteristics of oil and gas development.Especially, compact sandstone reservoirs with low permeability of Xinchang area in Xujiahe Formation in western Sichuan depression become available reserviors again depending on fracture network system because of the deep and super compact reservoir.So grasping the distribution of tectonic fractures becomes a focus of the study for exploration and development. This dissertation studies on fracture development in T3x2 Strata within Xinchang structure in Western Sichuan depression. This dissertation performes an advanced observation of fractures in the core, recognitions of imaging logging datas, measurements of geostress,tests of rock mechanics parameters,FEM(finite element method)numerical simulations for the geostress field,numerical calculations for the crack rate on fracture,etc..The fracture has the apparent characteristics of the group from a large number of measurements and statistics to fracture in the outcrop.Combining results of the analysis of regional tectonic dynamics,fracture of Xinchang structure is divided into three-stage(the latest Triassic,early Cretaceous,Neogene-Quaternary). Fracture of the period group has the following characteristics:1) The latest Triassic’s fracture of main NE shearing cracks developed badly and only observes a little;2) Early Cretaceous’ fracture developed integral conjugate shearing cracks and tensile fracture. The fracture at this stage was developed the most comprehensive,the largest,cutting through the largest depth and the uppermost fracture of Xinchang structure.3)Neogene-Quaternary’s fracture was developed in the most drilling cores.But development degree of the fracture is not obviously as good as early Cretaceous’.Fracture was produced relatively little. The fracture at this stage cuts through early Cretaceous’ fracture obviously.Structural fractures are generated in a certain tectonic stress condition.The geostress field of Xinchang area decides the distribution of Structural fracture.Law and analysis are obtained from FEM numerical simulation for the geostress field in Xinchang area.1)The geostress field as a whole controles the main trend of migration-accumulation of oil and gas. Oil and gas migrate and accumulate from the northwest and southeast to the central region;2)The geostress value gets small from the old to modern time.It provids the impetus for the migration of the oil and gas from deep to shallow conditions;3)It is a low stress area in or near the fault zone in plane.The stress gets small along the fault zone from deep position to shallow in a vertical section.Oil and gas is drived to migration from both sides of fault to fault zone and from the deep position to the superficial along the fault zone;4)It is advantage area for exploration and development of oil and gas in the part which is at the junction of faults,inside areas of faults,disappear department of both sides of fault and at the overlap top of tectonic structure.