Hydrocarbon Assessment of Zamzama Gas Field with the help of 3D Seismic Pre-stack depth migrated data

Abstract

The project area is Zamzama Gas field, located in Kirthar Fold Belt, Southern Indus Basin, Sindh province, Pakistan. Zamzama Gas field was discovered in April 1998 by BHP Billiton and started production in July 2003. Comprehensive analysis of logs, cores and production data of first discovery well Zamzama-0l/ST1 confinned Pab Sandstone as the major gas producing reservoir of Zamzama gas field and wire line logs subsequently confinned a gas column in excess of 300 meters. 3D .P.re -stack time migrated (PSTM) seismic data was acquired during appraisal program m 1999, 3D PSTM seismic was acquired over 85% of the mapped gas volume but the seismic data is 12o ~ ier due to anisotropy in the area. Client wished to improve the imaging of the data, so for this purpose seismic data was re-processed by CGG Veritas in Febmary 2012 as Pre-stack depth migrated (PSDM) seismic data with high SIN ratio. PSDM seismic and Well data for the project is requested by department of Earth Sciences, Quaid-i-Azam university, Islamabad and approved by Directorate General of Petroleum Concession (DGPC) and finally provided by LMK Resources Private Limited, Islamabad, Pakistan. The objective of the study is to understand subsurface structural trends and startigraphy of the area. Interpretation ofPSDM seismic data resulted in time and depth contour maps to understand subsurface stmctures for further exploration. Petrophysical analysis of wells resulted in estimation of hydrocarbon saturation in wells and ultimately in whole reservoir zone and also confinns the main producing zone lies in the range of about 3400-3900 m. Rock Physics analysis is used to calculate elastic properties of the reservoir rock and relate them with seismic velocities. Crossplots of Vp/Vs ratio against Poisson's ratio, Sonic log, Compressional velocity and Shear wave velocity confinns that defined zone is the zone of interest from which hydrocarbons are producing in Zamzama gas field. AVO/AVA synthetics are calculated to confirms the presence of hydrocarbons in reservoir zone. Seismic attributes are also applied on 3D PSDM seismic data to find possible reservoir characteristics and on the basis of these new hydrocarbon zones are identified for optimum field development