Research Of Joint Inversion Methods For Cross-well And Surface Seismic Data

The key problem of geophysical inversion is how to predict the physical parameters which are related with surface observation signal. Joint inversion of multi data is the gross tendency of geophysical inversion in keeping with developing of exploration. It has two advantages by contrast with the single inversion: higher resolution and less non-uniqueness. This joint inversion is to combine cross-well (or VSP data, borehole geophysical data, etc.) and surface seismic data to solve the rock formation spatial structure and physical properties with the geological, drilling, and well logging regularity.Inversion algorithms can be classified into linear and nonlinear algorithms. The seismic inversion problem is usually vehemently nonlinear and has multi minimum solutions. So the linear algorithm based on method of derivation is generally trapped into local minimum solutions and can't get to the global optimal solution. We must adopt the global optimum algorithm to resolve the nonlinear inversion problems efficiently and enhance the reliability of inversion results.The paper discusses the principles of matching and calibration of seismic and logging data, wavelet extraction, initial model establishment, and impedance inversion comprehensively, which are the fundament of joint inversion of cross-well and surface seismic data. This joint inversion uses the impedance inversion based on modeling method. Firstly, we integrate the well logging data to inverse the impedance of surface seismic data and cross-well seismic data separately, and then extract pseudo wells from the impedance inversion results of cross-well data. Secondly, we combine the pseudo wells and virtual wells together to establish the 2D or 3D geologic structure model, and then inverse the lower band impedance and relative impedance separately. Finally, we merge the two impedances above together and generate the ultimate high resolution impedance model which is the result of the joint inversion.The technique of pseudo wells is the bridge truss of correlating the cross-well data of higher resolution and the surface seismic data of lower resolution. It can resolve the problem that how to improve the lower accuracy of model building and interpolating because of the un-homogeneous distribution of virtual wells in only surface seismic data condition.