Study And Application Of Near-Surface Modeling In Complex Areas

Complex near-surface structure is the main reason of poor shooting and recieving inseismic exploration, It makes it difficult to record high S/N data in the field acquisition aswell as badly affecting the imaging and amplitude preserve processing. Making the complexnear-surface velocity structure clear is very import for solving the problems of shooting infield acquisition, statics correction, wave field continuation and amplitude preservation indata processing.Lots of methods for near-surface modeling were developed, including one dimensionmodeling method: velocity investigation into mountain volume, shallow refraction,microseismogram log, MVSP etc. 2D and 3D methods are: interpolation, tomography,first-arrival refraction, first-arrival refraction tomography, first-arrival traveltime tomography,etc. After systematically studied the previous methods, we start the study, and achieve somedevelopments.Compared with microseismogram log, micro VSP can predict the velocity and thicknessof the undrilled layers using the upgoing wave, thus investigates into deeper layers. Because itwould not break the hole and uses the shooting wells, so can develop the high densitynear-surface investigation and establish a more accurate near-surface velocity model. In orderto take the advantage of MVSP, under hole 3C geophone array is developed and a full set ofMVSP data acquisition, processing and interpretation flow is established. Median filteringseparation for upgoing wave in micro VSP is improved. Optimized objective function topredict the velocity and thickness of the undrilled layers is established. Genetic algorithm isused to solve the optimized problem and predict the velocity and thickness of the undrilledlayers.First-arrival traveltime tomography includes first-arrival picking, initial modeling,forward modeling, inversion etc. main steps. The accuracy and efficiency of ray-racing is oneof the key parts of the tomography imaging. The hybrid-template shortest path ray-tracingmethod is proposed, and with more accuracy and efficiency. Unified objective function foroptimizing travel-time node position is established, Two order, three order and four ordertemplate are optimized, thus forms the optimized template shortest-path ray-tracing method.Some theoretical models are used to test the two ray-tracing methods. Conventionalfirst-arrival traveltime tomography only involves traveltime inversion. It can't provide astable and reasonable result. A new objective function of multi-object nonlinear first-arrivaltraveltime tomography is established to inverse the traveltime and multi-direction apparentslowness. And illustrate the solution to this method. Finally uses the theoretical data to test themulti-object nonlinear tomography. And some practical datum are processed.Interpretation of shallow refraction requires flat surface but this restricts the method to beused in the complex areas. Tomography method is adaptable to any complex areas.Tomography method is successfully applied to the inversion of shallow refraction data by simplifying the model and using virtual grid. Interpretation of microseismogram log datasupposes that first-arrival travels linearly and the tube is vertical. But things are not the same.In order to make full use of the microseismogram log data, tomography is used to inverse thedata by simplified modeling and virtual grid. Iteration tomography inversion for micro VSP isproposed, and a genetic ray-tracing algorithm is studied. Finally we uses theoretical data totest the above-mentioned methods and process the practical data.Conventional interpolation modeling method is suitable only for the layered near-surfacemodel, is difficult to be used in complex areas. The interpolation modeling method isimproved. The process of modeling is divided into three steps as velocity layering ofsurveying points, velocity interface interpolation and velocity interpolation. The methods oftomography near-surface investigation, first-break refraction, first-break tomography etc. andmodel closure are Introduced, and demonstrate the application of these methods.To verify and demonstrate the application of near-surface modeling, it is applicated in thefield data acquisition firstly, The theory of shooting in high velocity layer is consummated andthe optimum hole-depth design flow is established. Then it is applicated in the data processing.Methods such as multi-objective nonlinear tomography statics correction and wave filedcontinuation near-surface correction based on multi-objective nonlinear tomography areproposed as well. Finally the effect of the above-mentioned methods are presented.