GEO-STATISTICS BASED RESERVOIR MODELLING FOR HYDROCARBON RESOURCE POTENTIAL IN ZAMZAMA BLOCK, SOUTHERN INDUS BASIN, PAKISTAN

Abstract

The research area for the Zamzama gas field is located in Sindh's Dadu district, within the Zamzama block. The investigation region lies in Pakistan's Southern Indus basin's Kirthar foredeep. The geologic succession ranges from Jurassic to modern times. The Zamzama structure is a massive north-south thrusting anticline with an eastward trending. To interpret its structure and tectonic regime, seismic and borehole data are presented. The general geology, stratigraphy, and tectonics of the area is thoroughly investigated in order to better comprehend the tectonic evolution since Pangea's formation. Two horizons of interest are marked, and no fault is encountered in the given 3D seismic cube, then interpreted to determine the depth, extension, and orientation of subsurface structure. The petrophysical analysis is run to investigate reservoir formation in order to determine rock type and hydrocarbon potential. Different logs, such as LLS and LLD form various cross overs, indicating the presence of fluid in porous and permeable rocks. Porosities, shale volume, water saturation, and hydrocarbon saturation are estimated, indicating that the reservoir rock has sufficient conventional reservoir rock potential for oil and gas production. Seismic post stack inversion is applied on a seismic line integrated with well data to understand the reservoir response on large scale. Model-based inversion is used which shows the low impedance at the depth of reservoir indicating presence of porous and permeable rock. Rock physics modeling is performed to distinguish the facies by plotting different cross plots between various rock parameters. Hence, Zamzama is a potential gas-producing field in the lower Indus basin, where the Pab sandstone in Zamzama - 03 is a producing field. Bayesian classification is run on 3D seismic data cube to predict the lithologies and fluid present in the reservoir. For Bayesian classification different cross plots are used for the prediction of lithology and fluid, with density plotted on Z axis. The cross-plots clearly separated and delineated the Litho-fluid classes (hydrocarbon sand, gas sand, and brine sand) with specific orientation/patterns.