Refraction First-beak Statics Method Under Complex Near-surface Conditions

The static corrections are essential to data acquisition, data processing and interpretation for complex near-surface areas in western China. The processing results with serious long and short wavelength static problems will lead to wrong structural interpretations directly or failing drill. So how to solve the static correction problems caused by the changes of near surface factors with refracted first-break information is a key problem for data processing in complex near-surface areas. Solving the static correction problems under complex near-surface conditions is a systematic engineering .First ,careful field weathering investigation must be done, then we have to take full advantages of refraction first-break information and field weathering investigation information to compute field static correction and large residual static corrections with various refraction first-break statics methods , finally , reflection statics methods are used iteratively to solve the residual statics problems.To solve serious static correction problems in complex near-surface areas of western China, different refraction first-break statics methods are studied in this thesis. The main study contents are as follows:1) The propagation features of refraction for horizontal layered and dip media are studied firstly, it lays a good theoretical foundation for later statics method studies.2) Forward modeling method of refraction first-break in lateral varying velocity media. For layered media, a new forward modeling method of refraction is presented. For more complex near-surface conditions such as mountain areas, a new improved ray tracing method based on shortest path assumption is studied, it has higher accuracy and faster computing efficiency than conventional ones .The method can be used for the forward modeling of complex near-surface media.3) A new statics inversion method with optimal refraction traveling time is studied. Inversion of the near surface structure can be done by the method with refraction first-break information, so it can be used to solve 2D long wavelength and short wavelength statics problems for complex near surface areas;4) A kind of 3D statics method with statistical deposition of refraction first-break traveling time in common shot domain is developed. Themethod can be used to compute large residual static corrections in complex 3D near-surface areas such as areas covered by desert and Gebi.5) Based on 2D refraction statics method in CMP domain, 3D refraction static method of CMP domain is presented. It can be used to solve both long wavelength and short wavelength statics problems in 3D CMP domain under certain preconditions.Many forward modelings and practical data computations in complex near-surface areas are carried out by the above new methods. The processing examples show that the serious statics problems in areas Hadexun and Kekeya of Tarim basin are solved with the above methods. The synthetic and real results fully prove the above statics methods are valid and effective, these new methods will play an important role in the exploration of western complex near-surface areas ,China.