Study On Near Surface Seismic Wave Attenuation And Methods Of Quality Factor Extraction

With the advancement of oil and gas exploration, more and more researches are converted to focus on the lithologic or subtle hydrocarbon reservoirs which are much deeper and more complicated than the large-scaled structural ones. Correspondingly a much higher demand of seismic data resolution is in need if progress concerning these reservoirs to be made. Seismic wave propogation is an important sector in exploration, in which the earth's viscoelasticity-caused attenuation of energy renders a significant effect on the resolution for deep targets and is necessary to deal with.Near surface surveys are of great importance for near surface affects both the detonation and acquisition, the study of its attenuation and correspongding compensation plays a pivotal role in deep-targeted exploration. Dual borehole microlog and single borehole microlog can be used to investigate the near surface attenuation structure; zero offset VSP data can be processed to get deep layer attenuation.Based on the methodology of seismic absorption, the quality factor is abtained and clarification of its physical meaning is also presented. The great effects of near surface poses on waveform and amplitude are outlined and a series of problems due to its presence are discussed in depth. Many quality factor extraction methods are explored and commented on briefly.Enlightened by the methodology, a new approach of inverting quality factor from dual borehole microlog and single borehole microlog data is brought about. Further discussions on traditional spectral ratio method are reviewed with modifications to maximize its data potentials. By analog with average velocity, a definition of average quality factor is founded, in a bid to find a different perspective of extraction. A workflow of Quality factor extraction for zero offset VSP data processing is also given.Following theory comes to model test. Ray model and visco-acoustic models are built to test the credibility of methods in quality factor extractions both for VSP data and borehole microlog data. The results are acceptable and lead us to the field data processing. The field data, both zero offset VSP and borehole microlog data included, are processed with corresponding methods to get the specific absorption model. In the end, the energy compensation based on dynamic parameters is tested. Out of model test, we can see the compensation is very useful in data resolution enhancement. With the parameters descriptive of the attenuation known, it is necessary and rewarding to apply compensation. The field data set improves quality after the compensation, featuring a wider bandwidth and a higher dorminant frequency.