Gravity And Magnetic Anomaly Study Structures In Central Yili Basin And Forecast The Prospect Of Oil And Gas

Yili basin is a superimposed basin,which is clamped in the Tianshan orogenic belt,central Asia.Within Yili basin,the region centered Baishidun subarch is one of the prospective areas of oil and gas.Combining with existing studies,this thesis focuses on two-dimensional gravity and magnetic wavelet domain de-noising and human-computer interaction(HCI)inversion method to probe the subsurface structure of the study area and provides the basis for further oil and gas exploration.The measured potential field data inevitably contains noise.Without de-noising the measured potential field data,it may lead to some deviation of the subsequent processing and interpretation,or even cause errors.This thesis has studied the de-noising method of potential field data based on energy distribution in wavelet domain.There are four key issues in the algorithm: determining the scale of signal-noise separation,choice of wavelet function,choice of threshold,determining the truncating energy value.This thesis has introduced the corresponding solutions.To verify the reliability of the de-noising method,the thesis conducts model test and compares it to two methods in the frequency domain.The result of model tests shows that the de-noising method of potential field data based on energy distribution in wavelet domain is stable and reliable.Two-dimensional gravity and magnetic HCI inversion considers the subsurface as 2D model of density and magnetic susceptibility.Human is allowed to draw the model shape and set the physical parameters.The computer can real-time update the response of gravity and magnetic model and visualize the results.Compared with automatic gravity and magnetic inversion,HCI inversion method can be more convenient to add a variety of geological constraint information to obtain a reliable explanation.This thesis selects a number of typical profiles to carry out HCI inversion,quantitatively interpret density,magnetic susceptibility characteristics of the geological cross-section.Combining with existing studies,this thesis gets the following structure understanding: the study area is located in the intersection of several structural units in Yili basin.Baishidun subarch lies in the central study region.The Mesozoic and Permian strata are relatively shallow and thick,and its Paleozoic basement is shallower than depression in east and west,deeper than arch in north and south.Eastern study area belongs to Gongnaisi depression,in which massively develops igneous rock and strong tectonic activity occurrs.Northwest study area belongs to Yining depression.The Mesozoic and Permian strata are deep and thick,and its Paleozoic basement is the deepest of study area.Large area of southwest study area belongs to Wusunshan area.Its Paleozoic basements is the shallowest of the area or even directly exposes.Northern study area belongs to Awulale.The southern boundary of it may be overthrust on Baishidun subarch.Based on those understanding,this thesis has delineated 2 oil and gas favorable storage areas,relatively in Baishidun subarch and Yining depression.