The Study On Multiple Suppression Technique Of Seismic Data In South China Sea

The South China Sea is rich in oil and gas resources with 230-300×109t oil and 338×1013m3 of gas, which has a very bright exploration prospects. In recent years, in order to expand the amount of resources, the seismic exploration was developing from the shallow to the deep-sea, which led to a series of disputation about the exploitation of marine resources. As the largest marginal sea, the South China Sea is the most controversial area. As for the exploitation of the disputed oil and gas resources, the regulation is shelving disputes and exploring together, which means that competition in the marine oil and gas resources depends on advanced technology. So it is important to improve the processing techniques.According to the deep-sea geological information and combining with the existing drilling information of the work area, the geological model was built. And applied the finite-difference numerical simulation of acoustic wave to simulate it. By analyzing the velocity spectrum of multiples and the time and distance relation of multiples of shot gathers, the sea velocity stacking and correlation analysis of trace gathers with the minimum offset, the features of multiple waves had been discussed. The whole multiples and interbed multiples developed in the seafloor, especially the whole multiples with a long period. It had an obvious periodicity and its periodicity was gradually weaker as offset increased. The feature of multiple waves of the actual data was similar with the model data.In the deep sea seismic exploration, near offset can be close to zero compared with the water depth, seismic waves can be approximated as normal incidence. Therefore, in the conditions of near offset, seismic wave propagation can be seen as the normal incidence in the, sea and spread into the seabed. Based on this thought, a theory formula of the seismic wave propagation was deduced. The theory considered the effect of the sea depth to the seismic wave propagation, which make the initial time of near offset department more precise than the commonly used RMS formula, and the shape of the curve is also closer to the actual wave propagation.Based on the analysis of deep-sea multiple characteristics, the multi-domain suppression technique was applied. Combined with the advantage of SRME and predictive deconvolution, the long-period and shot period multiples of near offset in the deep sea can be effectively suppressed. The parabolic Radon transform filter method can separate the multiples with the middle and far offset. When the far offset data isn't satisfied the hyperbola characteristics, there will be spatial aliasing and energy leak. According to the character that the seismic exploration array of the deep sea is longer, applying the high order NMO to the far offset data to obtain the better NMO result, which can resolve the problem that the effect is bad using Radon transform to suppress the long offset multiples. The thesis selected the method matched the actual data according to the deep sea seismic wave propagation characteristics and the problem that the various multiples developed which made the suppression effect using the single method was not perfect, by making best use of advantages and bypass the disadvantages, optimizing combination and iteration of many techniques to suppress the multiples reasonably and form the multiple suppression workflow suitable with the deep sea area of the South China sea.The combined method was applied to process the forward geological model data and the seismic data of many measure lines of Qiongdongnan basin, which had achieved good effect.