QUANTITATIVE INTERPRETATION USING GEOMECHANICAL ANALYSIS, AVO MODELLING AND SEISMIC INVERSION OF SAWAN GAS FIELD CENTRAL INDUS BASIN, PAKISTAN

Abstract

The area under study is Sawan Gas Field which was discovered in 1998 by OMV (Pakistan) Exploration. Geographically the area lies in Thar Desert, Khairpur District Sind province of Pakistan. Geologically Sawan field lies on the southeastern flank of the Khairpur High which is considered as platform slope area in Middle Indus Basin. The area is characterized by normal faulting with strike slip component, with structural trap and bright spot anomaly with small four way dip closure structure. Seismic interpretation involves identification of major horizons, faults, and trap in study area. Lower Goru “C” sand interval sand having shallow marine depositional environment and restricted to the northeast–southwest trending fairway. Low impedance sandstone always difficult to image. Seismic inversion and AVO modelling study is carried out in this research to tackle this problem. Seismic inversion converts seismic amplitudes into acoustic impedance which enable us to identify low impedance individual sand packages. Model based inversion is performed and it start with an initial guess of impedance model. Initial model usually comes from wells and extrapolated away from well using horizons. The key to using AVO identification is comparison of real with a standard in this case, modelled AVO response. This is an artificial trace manufactured by assuming that some pulse through an earth model containing rock layers of given thicknesses, velocities and densities and returns to be recorded.