Prestack Fracture Prediction Based On Tectonic Stress Field Analysis

Fractures within the earth's crust are distributed everywhere, they are constructured within the long perod of tectonic movements and other geological forces, fractured reservoir beds on earth are widely developed. With the improvement of oil and gas exploration technology, more and more fractured reservoir beds have been discovered in recent years, such as fractured shale oil and gas reservoirs of the Qaidam Basin, the Ordovician fractured carbonate oil and gas reservoirs, tight sandstone cracks in oil and gas reservoirs in Sichuan, and so on. The exploration of fractured reservoirs is increasingly becoming an important oil-gas exploration strategy to take over the outproduced area. The key point is how to solve the prediction problem of that kinds of lithologic reservoir, especially fracture prediction has gradually become one of the main exploration direction of fractured and non-structural exploration of oil and gas reservoirs in China.The paper combines theory and methods tectonic stress field in recent years, integrates preecessors' study, summarizes the regional geology general situation of puguang gas field which is located in northwest of Sichuan firstly, and then use prestack seismic data to numerical simulation of tectonic stress field, so that prediction the density and direction of fracture.The main work of this paper, summarized as follows:(1) systematically to sort out the basic conceptions and principles about stress, tectonic stress, tectonic stress field, fracture reservoir and fracture;(2) analysis of structure characteristic of fracture development and characteristic of tectonic stress field within the puguang gas field;(3) using the different Angle of prestack gathers data, logging data and geological data to prestack inversion, that obtain p-wave and s-wave impedance, Poisson's ratio, Lame coefficient, shear modulus etc. elastic parameters; which process using using nonlinear modeling technology;(4) using the finite element analysis method and FRgeoMech module of FRS software to simulate the tectonic stress field of study area, analysis the relationship between stress and fracture, prediction the density and direction of fracture;(5) using seismic discontinuity detection methods based on local structural entropy to prediction faluts and fractures' density, and compare with the result of tectonic stress field numerical simulation analysis.Paper do the work about prestack fracture prediction based on tectonic stress field analysis achieve the following understanding:(1) using the different Angle of prestack gathers data, obtain p-wave and s-wave impedance, Poisson's ratio, Lame coefficient etc. elastic parameters, which that provide the basis of geological modeling in tectonic stress field numerical simulation;(2) according to the result of numerical simulation of stress field, the puguang gas field development two groups of fracture systems, namely NNE direction, and NN direction supplement;(3) the seismic coherence analysis and pretection the density of fracture, but it can not accurate description of fracture development compare with tectonic stress field numerical simulation.