Characterization of B-Sands in Gambat Block using 3D Seismic Interpretation, Rock Physics Analysis, AVO Modelling & Post Stack Inversion Analysis

Abstract

Reservoir is characterized by integrating all available data to defme physical properties by using different modelling techniques. The behavior of fluids is simulated in reservoir modelling which helps asset teams of E & P companies to develop optimal production techniques. In order to characterize the reservoir accurately, different geophysical techniques such as Petrophysical analysis, Rock Physics modelling, A VO modelling, Inversion, etc. are used and the results are correlated. In the present study, B-Sands of Lower Goru Formation in Gambat Block, located in lower Indus Basin are characterized by applying all the above-mentioned techniques. Data set contains seismic data along with well data of four wells i.e. Tajjal_01 , Tajjal_02, Tajjal_03 and Tajjal_04. Among these wells, Tajjal_01 and Tajjal_04 are gas producing wells while other two are abandoned ones. In the zone of interest, saturation is changed from gas to 100% water in gas producing wells i.e. Tajjal_01 and Tajjal_04 using integrated modelling techniques and results are compared with in situ water saturated wells i.e. Tajjal_ 02 and Tajjal_ 03. Gassmann's Equation is applied to alter the saturation in the wells and VP is plotted against VS in all cases i.e. in-situ saturation conditions and modelled conditions. Results are compared and it is observed that VP is more effected by saturation as compared to VS. Amplitude analysis of reflected data is carried out by using Aki-Richard 's Equation on synthetic data and it is concluded class of reservoir sand is type IV. Post stack seismic inversion is applied to extract porosity and pore pressure of the study area. Interval velocities are computed using model based seismic inversion which is a type of deterministic inversion. Porosity of reservoir ranges between 12-18% and results of pore pressure reveal that pore pressure remains almost same in adjacent sand-shale layers. However, slight increase in the pressure is observed in Ghazij shales which is bounded by limestone at its both ends.