Research On Marine CSEM Inversion In CMP Domain Of Submarine Gas Hydrate

Since the 21st century, the emphasis of oil and gas exploration has shifted from land to ocean. As a potential new green energy, exploration and development of gas hydrate is being appreciated increasingly. Submarine gas hydrate detection will be an important part of offshore energy exploration and marine environmental protection in the future.In recent years, marine seismic exploration has been used as a main method of exploration of offshore oil and gas resources. Basing on seismic bottom simulating reflector, marine seismic exploration can determine whether gas hydrate exists or not. However, marine seismic method is ineffective in submarine salt dome, volcanic rocks covering and the carbonate reef, and drilling method is too expensive. In order to explore marine gas hydrate better and more accurately, CSEM will be a focal point on marine gas hydrate exploration.This paper begin with the forward algorithm of the marine CSEM method. First of all, the one-dimensional forward algorithm of marine CSEM method is deduced theoretically. It discuss the equivalence of marine CSEM method by analyzing the marine CSEM forward response of one-dimensional model. Then, the 2.5D adaptive unstructured finite element simulation algorithm of marine CSEM method are deduced theoretically. It realizes source-parallel algorithm of marine CSEM based on this forward approach and checking calculation of two-dimensional model. refering to the common-midpoint(CMP) method of seismic exploration, it realizes the data conversion method of marine CSEM method in CMP domain which is based on the two-dimensional forward modeling of marine CSEM. Using the CMP domain method of marine CSEM on the basis of one-dimensional inversion of marine CSEM method, it realizes marine CSEM rapid inversion method.This paper calculated one and two dimensional models of submarine gas hydrate respectively. The result shows that the marine CSEM method is sensitive to high resistivity body and it is effective to detect submarine gas hydrate. It shows that CMP domain data conversion method can better identify high-resistivity reservoirs in horizontal direction. Marine CSEM response of two-dimensional model can be expressed as one-dimensional model responses in the CMP domain cells. Through the verification of model inversion established by actual work, it shows that the CMP domain rapid inversion of marine CSEM method can effectively count out the structure of test model and electrical parameters are also in good agreement. Based on gas hydrate model whose burial depth is shallow and resistivity difference is small, the CMP domain rapid inversion of with different components and different frequencies suggest that just for this model the inversion result of multi-component is not superior to the inversion result of single component and multi-frequency inversion result are better than single frequency inversion result. The Adjacent hydrate model result shows that the CMP domain rapid inversion of marine CSEM method can effectively restore geoelectric structure of hydrate model.