Reservoir fluid identification and elastic modulus determination using AVO

AVO analysis based on the increase of reflected amplitude with increasing distance between source and receiver. This anomaly has been proved to be useful for gas identification from seismic data. A specific inversion technique has been developed to estimate the Poisson's ratio from AVO anomaly. It based on the Shuey (1985) formula and the implementation of generalized linear inversion proposed by Marquardt (1963). The technique adjusts the convergence of the iterative process in order to find the unknown parameters by considering the available observed data. Once the Poisson's ratio is obtained, the velocity of the S wave can be estimated and the elastic properties of the reservoir rock such as Young's modulus can be derived. Application of this technique to a limestone reservoir of the Cicauh area in the North West Java Basin gives the value of Young's modulus of about 23392 MPa. The porosity which derived from this value was 36.6% which is very close to well data. According to the Wren (1984) diagram the P wave velocities of 2700-3550 m/s correspond to reservoir rocks of sandstone containing fluid. In fact according to the well data, it is a limestone containing gas. Therefore, a special diagram showing the relationship between P wave velocities and Poisson's ratios should be developed. It will be useful in identification of reservoir fluid by means of AVO before drilling.