Research On Complex Near-surface Velocity Building And Static Correction In Kuqa Area

The complex near-surface structure in the Kuqa area severely restricts the survey of the near-surface and the following velocity building.As a result,the problem of static correction becomes prominent and further restricts the development of the seismic exploration in this area.There are many methods for survey and velocity building for the thick weathered layer at home and abroad,and most methods adopt the shallow layer refraction and the microlog technology as well as small reflection.But using microlog in thick weathered layer is restricted by the rig drilling capacity,production efficiency and exploration investments.Only three to five ultra-deep microlog can work in a wide range of thick Gobi gravel region and sparse micrologs can not meet the requirements of near-surface velocity building accuracy.Generally,the shallow refraction used in thinner layered media has higher accuracy.However,the shallow refraction used in thick and continuous Gobi gravel area has a poor accuracy.Small reflection near-surface survey seldom can be generally carried out in production because it requires specialized seismic acquisition crew and the exploration investment is higher.Therefore,it is difficult to conduct the survey and velocity building of the near-surface layer in the front of the thick Gobi gravel area in Kuqa piedmont.At the same time,due to the complex near-surface conditions of Kuqa area,the speed and thickness of shallow geological structure change rapidly in the different direction of the plane.It is difficult for the single near-surface model static correction method,refraction static correction method based on first arrival or tomographic static correction method based on first arrival to completely solve the static correction problem in this region and it needs to carry out targeted research to improve the accuracy of static correction to improve the imaging.This paper starts with investigation of shallow layer tomography and properly determines specific survey parameters through modeling,trace gathering,shot points and the application condition and scope by comparing the forward and inverse interpretation models under different conditions.After the implementation in the field,combining the data acquired from the 2D seismic exploration and the microlog interpretation in the mountainous area,a near-surface model whose precision can meet the needs of exploration is built by means of pseudo three-dimensional tomographic modeling.This near-surface model can analyze the near-surface structure of the thick Gobi gravel area in front of the Shenmu three-dimensional mountain.In this context,it further analyzes the applicability of different static correction methods.The advantages of first arrival tomography and refraction static correction are combined through near-surface model splicing and this improves the static correction accuracy of in the complex surface area.This paper has solved the problem of surface survey and modeling of the thick zones of weathered layer.Joint tomography and refraction static correction effectively improves the imaging and works out economic and practical near-surface velocity building and statics correction under the conditon of complex surface and this provides the necessary technical reserves for the seismic exploration of the complex surface area in the future.