Gravity And Seismic Simultaneous Joint Inversion Method Based On The Cross-gradient Fuctions

With the deepening of oil exploration, constantly opening up new exploration area hasbecome an inevitable demand. Meanwhile the scope of the marine regional geological surveysgradually increases and the exploration scales are shrinking. Then a new problem has been putforward to geological and geophysical exploration, namely how to deal with the difficultieswith big exploration scope and little geological and geophysical data in the early stage ofexploration? In this case, the multi-parameter joint inversion and simultaneous joint inversionof gravity and seismic data have been done in this thesis.This paper first analyzed the existing geological and geophysical modeling techniques,and found that the constant velocity constant density models are commonly used in the jointinterface inversion which can not well reflect the actual situation of the subsurface geology.Therefore, this paper adopted the variable speed variable density models changing with thevertical and horizontal coordinates which are adjusted using the speed and density gradient andachieved a major breakthrough in the modeling techniques. Second, the Langan ray tracingmethod was used for seismic forward modeling and Parker algorithm was used for gravityforward modeling to meet the need of accuracy and speed of gravity and seismic joint inversion,which laid a good foundation for the inversion of density and interface depth. Third, thetraditional gravity and seismic joint density interface inversion supposes there is a linearrelationship between density and speed and it requires a lot of prior information, and the earlystage of exploration petrophysical parameters is not easily to obtain accurate empirical formula.The cross-gradient function was taken as a constraint and introduced into the joint interfaceinversion in this paper to solve the problem. The cross-gradient constraint can be easilyintegrated with other traditional constraints to determine the appropriate target function, jointlyprocess the density data, gravity data and seismic reflection data, and acquire the model meetingthe structural similarity of these data. Fourth, the joint inversion objective function consists ofearthquake residuals term, gravity residuals term, impedance residuals term, cross-gradientconstraint term and Sobolev smoothing term was proposed and related theoretical derivationhas been done. Finally, the practical data of East Sea near Shanghai were selected to test the established joint inversion method and found that this joint explanation method integratedgravity and seismic data can well reflect the actual situation of the subsurface geology andreduce the diversity of geological interpretation.In this paper, the combined method of geological modeling, model test, theoretical analysisand practical data processing based on the cross-gradient functions has been adopted to do thesimultaneous joint inversion with gravity and seismic data and finally an effective technicalmethod is provided to look for more precise subsurface characteristics.