TOTAL ORGANIC CARBON CONTENT AND POROSITY ESTIMATION USING 3D POST STACK SEISMIC INVERSION AND WELL LOGS ANALYSIS WITHIN TALHAR SHALE OF GAMBAT AREA, SOUTHERN INDUS BASIN, PAKISTAN

Abstract

In this study, Post stacks seismic inversion have been utilized for inverting a 3D seismic data into acoustic impedance volumes for the computation of TOC and porosity content for the Gambat area. Gambat block, located approximately 42 km southwest of the Sawan gas field. The Sands (Lower Goru Formation) is acting as a “reservoir” while Talhar shale is acting as a source of the area. The primary purpose of this research is to describe the structural settings of the study area using seismic interpretation. Seismic interpretation transforms seismic data into a geological picture. Structural interpretation maps the faulting in the area and seismic horizon interpretation delineates the subsurface extent of the reservoir. Seismic interpretation confirms the presence of normal faults. The time contour of C-Interval shows that reservoir is deepening in the eastward while shallowing toward the westward direction. Source Rock Evaluation was done for computation of TOC from well logs using the Passey’s “∆logR” method. Talhar shale is acting as a source rock with an evaluated average TOC of 3.69 wt. % and Total porosity of approximately 9 %. Post stack inversion techniques including sparse spike inversion and model based inversion have been applied for impedance prediction of C-Interval and Talhar shale in Gambat area and the relative performance of each technique has been investigated. Both inversion techniques resolve the reservoir low impedance. “Total organic carbon” (TOC) is the most important parameter used for identifying “unconventional shale” reservoir potential. Seismic attributes like Pimpedance would respond to high “TOC” content due to the low “velocity” and “density” of organic matter. Sparse spike inversion and model based inversion is applied for the calculation of “total porosity” and “total organic carbon” (TOC) because it provides the acoustic impedance distribution (variation) across the area. The TOC and porosity models indicate an average porosity > 9 % and Average TOC > 3 %. Such characteristics indicate that Talhar Shale possesses the capacity to produce oil and gas.