Petrophysical Interpretation of Early Cretaceous Sequence, Lower Indus Basin, Pakistan (T-1436) (MFN 6899)

Abstract

The main objective of this research work is to evaluate source rock and its geomechanical properties through petrophysical interpretation of well Khajari-01 and Buzdar South Deep-01, which are in Sanghar-south and Badin-II block respectively, Thar Platform, Lower Indus Basin, Pakistan. Thar Platform is in south of Mari-Kandhkot High, bounded by Indian Shield to the east, marginal zone of Indian Plate to the west and Offshore Indus to the south. It is comprised of faulted and tilted blocks of Mesozoic rocks which form structural traps. Petrophysical results of source rock and geomechanical properties evaluation for Sembar Formation in both wells demarcated that it has a fair to good generation potential on the bases of calculated TOC between 0.5 to 1.4 wt. %. Effective source interval out of entire Sembar Formation is encountered at depth 1900 to 2120 m and 2767 to 3120 m for well Khajari-01 and Buzdar South Deep-01 respectively. The formation is an immature source rock based on geothermal gradient variation, overburden thickness and absence of hydrocarbon fluid on log suite. On the bases of well location, less thickness and shallowness of Sembar Formation in Khajari as compared to Buzdar South Deep, it has been concluded that basin development took place toward south west and sediment input is from south east. Its lithological variation i.e. quartz clay substitution depicted sandy shale interval at depth 1723 to 1900 m and 3120 to 3220 m for well Khajari-01 and Buzdar South Deep-01 respectively. Mineralogical variation depicted mixed layer clays including chlorite, smectite/montmorillonite and illite as dominant minerals and transitional environment i.e. in between reducing and oxidizing depositional environment. These clays are dispersed and laminar in origin and comprises of flatten pores geometry of isolated intra-granular or isolated organic matter pores. These results of Sembar Formation are founded to be same in well agreement with the geomechanical properties evaluation results of rock physics template. Other rock physics template results depicted that the brittleness of Sembar Formation decreases with the increase of porosity and the change varied with difference of fluid saturation and rock matrix i.e. clay content or quartz-clay substitution. Sembar Formation founded to be of medium to high ductile based on computed Brittleness Index. This high ductility of Sembar Formation is due to clay lamination as depicted from high poisons ratio.