The Application of Rock Physics and Pre-Stack AVO Analysis for Gas Identification in Deepwater Sediments, Rakhine Bain, offshore Myanmar

Zuo, Guoping

As geophysical exploration technologies, Rock Physics and Pre-stack AVO analysis are widely used in oil and gas exploration, it enjoys an irreplaceable position since it was first used in amplitude detection, such as bright point, flat point, etc.

Rock Physics analysis has been carried out in this research based on wells in order to prove the probability of AVO method. According to forward modeling and fluid substitution, the curve characteristics corresponding to amplitude are defined, and relevant AVO attributes are calculated, which serve as the basis for following seismic AVO attribute analysis. The findings of this research include that when reservoir contains gas, the result of forward modeling indicates that amplitude increases with offset, it belongs to class 3 AVO response, in addition, through rock physics analysis, P-wave velocity, P-wave impedance, Fluid factor, intercept × gradient (P×G) and Poisson ratio all change fast, on the other side, using fluid substitution, the gas was replaced by brine, then, the result of forward modeling indicates that amplitude changes little with offset, the rock physics attributes only show tiny changes. So, these sensitive attributes for gas reservoir can be used to detect gas reservoir.

Through AVO analysis, based on Aki & Richards equation and Shuey equation, a set of attributes are obtained from seismic data. According to rock physics analysis, the attributes sensitive to hydrocarbon are used to detect gas reservoir.

Combining those attributes with cross plot method, AVO method is much more effective to detect gas reservoir. Class 3 AVO abnormity can be distinguished easily in the cross plot of P and G. In addition, in the cross plot of far angle stack and near angle stack, it is easier to feature gas reservoir which has the characteristic of that amplitude of far angle stack is stronger than near angle stack.

In this research, P×G, fluid factor, Poisson ratio and P-wave impedance, near angel stack and far angle stack data are selected to analyze due to their sensitivity to gas layers. Through rock physics and AVO analysis, many objectives have been discovered in the study area. The application of rock physics and AVO analysis has achieved remarkable effect in gas layer identification.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013