The Formation Mechanism and the Suppression Technology Study of Multiple Wave of the South Yellow Sea Seismic Data
China has nearly 300×104km2 blue land, which is rich in oil and gas resources. However, the exploration and development of China's oil and gas resources in the ocean started late. The exploration degree of oil and gas resources in all waters is lower and the proven degree of oil and gas resources is much lower. The South Yellow Sea Basin is particularly special, which is the only sea area without oil and gas (reservoir) in China at present. According to scholars'study, the South Yellow Sea Basin is above the Yangtze block, where the upper Silurian and lower Devonian is missing, and Mesozoic and Paleozoic marine carbonate rocks develop completely. The stratigraphic development is relatively thick, and the distribution of area is wide, which has good oil and gas exploration prospects. However, due to the low level of exploration of the South Yellow Sea Basin, affected by various factors, the geological knowledge of the waters is also not clear enough. The acquired seismic data has its own particularity because of the special natural environment and geological phenomena of the area. There is all kinds of noise and deep reflection energy is weak, which is especially serious is that there are various multiple-waves that have high energy and complex wave field characteristics on seismic data of the area. It brings many difficulties to the high-quality indoor data processing and to carry out further interpretation research work is even more difficult. So it is imminent to improve the quality of seismic data of the area, which is not only to ensure the wild construction quality, but also to improve the process method to acquire high-quality processing profile. When suppressing noise in seismic data processing of the area, the most important problem is to find out that the mechanism of the complex multiple-waves on seismic data of the area, and to consider reasonable and effective multiple suppression techniques. Eliminate the false and retain the true to get well real and reliable seismic profiles and lay a solid foundation for the following interpretation work.
In recent years, with the South Yellow Sea field acquisition technology research study, we carried out a large number of indoor processing technology research to improve the processing quality of seismic data and carried out technical studies to suppress random noise, coherent noise suppression technology research and multiple suppression technology research, especially doing a lot of research on complex multiple suppression technologies which severely constrained the seismic data processing quality of the waters. The paper focuses on the South Yellow Sea complex multiple wave formation mechanism and the corresponding multiple-wave suppression technology. This dissertation relies on the National project, "Integrated geophysical supplementary investigations in Southern Yellow Sea" and the National "863" program (2006AA09Z339) study.
The thesis has made a number of innovative achievements as follows:
1. Basically found out the formation mechanism of complex multiple wave on seismic data of South Yellow Sea.
Establish a geological model by using of log data collected and other people's research results. The author analyze comparatively wave field characteristics of analog records, especially the multiple wave characteristics by using acoustic wave equation and the elastic wave equation forward modeling. By developing an integrated analysis with practical seismic data, basically find out the formation mechanism of virtual reflection, reverberation, reflection multiple wave on strong reflection interface, refraction multiple, interbed multiple and other complex multiple wave on the seismic data of this area, which provides support for the study of the reasonable multiple-wave suppression technology of the area.
2. Curvelet transform technology was used to effectively suppress the refraction multiple wave and converted multiple wave on seismic data of South Yellow Sea for the first time.
The existence of special geological phenomenon of many sets of strong reflective layers such as T2 of the sea making the incident angle easily achieve the critical angle, resulted in strong refraction and formed refraction multiple-wave. At the same time, converted wave and converted multiple-wave of the sea developed because the collection array was large, the large range of the incident angle and the complexity of the underground media, effectively suppress the refracted multiple wave and converted multiple-wave by using Curvelet Transform Technology proposed by E.J.Candes on the South Yellow Sea seismic data.
3. The high-precisionτ-R Transform technology was firstly used to effectively suppress strong multiple waves of the South Yellow Sea seismic data.
There are various multiple-waves on the South Yellow Sea seismic data, such as the virtual reflection, reverberation, the whole multiple waves of submarine and strong reflective interface, interbed multiple waves, converted waves and refracted multiple waves. The wave field characteristics are complex. There is a clear understanding of the formation mechanism of these multiple waves through the forward modeling analysis and the studies of practical data, and thus to carry out research on effective multiple-wave suppression technology. Against the special nature of the development of strong reflection multiple and interbed multiple, by the comprehensive analysis of advantages and disadvantages of current multiple suppression technology at home and abroad and the limitations of these technologies on repression of multiple waves of the waters, we proposed to suppress multiple reflections by using high-precisionτ-R transformation technology proposed by Li Qingzhong Fellow. Through the processing of theoretical analog records and the actual data, there was a good result on the repression of multiple waves of strong reflecting interface and interbed multiple waves. It has its own unique especially for the repression of interbed multiple waves.
4. Form a reasonable technical program to suppress the complex multiple wave of the South Yellow Sea seismic data.
Against the particularity that there are various multiple waves the complex wave field characteristics on seismic data of the sea. Through comprehensive study, we formed a reasonable technical solution to suppress the complex multiple wave of the South Yellow Sea seismic data:on the basic of the reasonable suppression of a variety of noise, first use the free surface multiple suppression techniques (SRME) with deconvolution to attenuate the free surface multiple reflections, and then use curvelet transform technique to suppress refracted multiple wave and converted multiple waves, followed by using high-precisionτ-R transform technique to suppress whole and interbed multiple reflections on strong reflection interface. After a variety of multiples to be suppressed, the velocity analysis precision was improved, and then use deletion fitting stacking technique to replace conventional stacking technique after normal moveout correction to further suppress the residual multiple reflections and to acquire high-quality processing profile.
The improvement of many kinds of processing technology above and the formation of a reasonable technology system and program to suppress the complex multiple wave of South Yellow Sea seismic data can effectively suppress the multiple reflections in the waters. After reasonably suppressing the multiple reflections, provide protection for obtaining high-quality seismic profiles and lay a solid foundation for the follow-up study of the geological features of the South Yellow Sea.