Crosswell Seismic Traveltime Tomography Technology

The crosshole traveltime tomography is an efficient way to reveal the localheterogeneity within the cross well, which has been rapidly developed and improved.The seismic tomographic image helps us to further understand the inner earthstructure, which has beneficial to the scientific development and usefulness ofecological resources.Seismic tomography is a practical method to survey and estimate underneathgeologic structure, which has been widely used in engineering and geological hazarddetection and prevention by means of geophysical exploration method. Crossholetraveltime tomography is to recover the velocity field within the wells and hence thephysical properties of the geologic body.In this thesis the main purposes and key research works are to master the variousseismic ray tracing theories and methodologies, and the popular inversion methods,and then combine the irregular shortest-path ray tracing scheme and the inversionsolver based on the conjugate gradient method to solve the damped minimum norm,and constrained least-squares problem to conduct and analyze the crosshole traveltimetomography by using the direct arrivals or the reflected arrivals. The main contentincludes (1) the principles and methodologies of several ray tracing methods;(2)theprinciples and algorithms of several popular inversion solvers;(3) crossholetraveltime tomography by means of direct arrivals;(4) crosshole traveltimetomography by means of reflected arrivals;(5) the relation between the tomographicimage and the ray density;(6) the relation between the tomographic image and thecell size in model parameterization and (7) the relation between the model smooth andtomographic image. Such discussion and analysis can give guidance to crossholetraveltime tomography, such as how to arrange the source-receiver geometry, how toefficiently parameter the velocity model, how to select the model smoothing and whatare the main factors to control the tomographic resolution.