Source Rock Evaluation Of Goru Shales, Gambat Latif Block, Southern Indus Basin, Pakistan

Abstract

With the increase in energy demand around the globe, hydrocarbons resources are depleting around the globe at a spiking level. Aside from conventional reservoirs, a significant amount of hydrocarbons are trapped in unconventional reservoirs. Concentration of TOC and kerogen maturation level play the key role in determining the ability of organic rich shale formation to act as a potential source rock. Our study area is Tajjal Gas field in Gambat-Latif Block which lies in Southern Indus Basin. The Gambat-Latif Block lies in extensional regime hence normal faults are found in the region. Lower Goru is the most prospective formation in the area which comprises of thin interbedded shales and sandstones and these beds act as source rock and reservoir respectively. For source rock characterization; along with seismic interpretation and well log analysis, seismic inversion and neural network method is utilized. Structural interpretation of 3D seismic data includes marking horizons, fault geometry mapping, and time and depth structural maps of Lower Goru and its sand units. The time contour map of B-Sand Interval shows that zone of interest is extending in the eastward direction. For source rock evaluation, TOC is computed using well logs. B-Sand Interval in wells Tajjal-02 and Tajjal-03 shows source rock properties with an evaluated average TOC of 1.2-2.5 wt. % and 0.2-1.5 wt. % respectively. For the impedance prediction of B-Interval, post stack inversion technique i.e. linear programming sparse spike inversion has been applied which resolves the low impedance zone in Tajjal-02 and Tajjal-03 and provides the acoustic impedance distribution across the area. Organic matter is marked by low velocity and density as compared to surrounding rock hence seismic attributes like P- impedance would respond to high “TOC” content. For computation of TOC across the study area, TOC data is superimposed and interpolated on impedance blocks using neural networks. The model created using neural network indicates an average TOC ~2.6 wt. % at Tajjal-02 and its surroundings and approximately ~0.5 wt. % in the vicinity of Tajjal-03. Such characteristics indicate that B-Sand interval possesses poor to fair source generation potential