Abstract: With the development of petroleum exploration,lithologic and low-relief structure reservoirs become more and more important. For low-relief structure,besides the inherent factor of stratigraphic lithology,the key factor that influences low-relief structures is the long-wavelength statics. The main reasons resulting in the longwavelength statics are the relative low precision of the near-surface velocity model and the inaccurate space depiction of low-velocity bottom interface in complex surface area. The near-surface velocity model was built using stratified constrained model building method. Firstly,the accurate low-velocity layer model was built using micrologging data,and then the descending-velocity layer model was built using short-refraction and vertical seismic profile(VSP) data,so as to obtain the initial model of global optimization nonlinear near-surface tomography. Nearsurface velocity model with high precision can be built by using the stratified constrained tomography method. Based on the VSP and measured well depth constraints,the space morphology of the interface of the descending-velocity layer was optimized by cokriging method. Through the above two strategies,the long-wavelength static correc tion problems in complex surface area were well solved,and good application results were achieved in litho-logic reservoir exploration in X area of Mahu Sag,Junggar Basin.

Key words: complex surface, long-wavelength statics, stratified constraint, velocity structure, constrained tomography inversion