AVO Forward Modeling and Gassmann Fluid Substitution Analysis of Sanghar Area, Lower Indus Basin, Pakistan

Abstract

This dissertation contains the study and interpretation of 2D seismic reflection data of selected seismic lines of Sanghar area, Lower Indus Basin, Pakistan. The main objective of this research was delineation of subsurface structures favorable for hydrocarbon accumulation and attributes analysis. This area is situated in the Sanghar District of Sindh Province and is licensed to Oil and Gas Development Corporation Limited (OGDCL). The seismic data for this dissertation was provided by the Land Mark Resources (LMKR) by the permission of Directorate General of Petroleum Concessions (DGPC). The data comprised six seismic lines, well tops of well Sono-2, and Sono-5. The names of lines obtained are: (872-SGR-510, 862-SGR-140, 862-SGR-161, 862- SGR-162, 862-SGR-163 and 872-SGR-509). Three horizons are marked and named after correlating with well tops of Sono-2 and 5, after well to seismic tie these horizons are correlated in whole area. In time structure maps, it was found that the area is under the Extensional Tectonic Regime which produced the Normal faulting in the region. Major Horst and Graben structures are formed due to the process of rifting. Time and depth contours were generated for structural delineation. Petrophysical analysis confirms that Lower Goru formation are acting reservoirs in Sono-2 and Sono-5. Seismic inversion helps to determine the acoustic impedance for the interested formations. The acoustic impedance for Lower Goru formation lies between 9554 & 9525 ((m/s)*(g/cc)). Gassmann fluid substitution is applied for discrimination of fluid within the interested reservoirs of Sono-2. By using Zoeppritz calculator, reflection coefficient curves as a function of angle of incidence for Zoeppritz and its approximations Shuey 3 terms giving a clear indication of oil and gas reservoirs.