Tectonostratigraphic evolution of Mesozoic sequence Miano gas field, Central Indus basin, Pakistan (T-1433) (MFN 8116)

Abstract

Geologically, study area is located in Pannu-Aqil Graben which is located in between Mari-Kandhkot High in the north and Jacobbabad-Khairpur high in the south. The main objective of this thesis is to understand the tectono-stratigraphic evolution of the Mesozoic Sequence by analyzing subsurface structural and stratigraphic framework, petroleum system elements and depositional modeling. 2 D seismic and well log data set was used to carry out detailed structural and stratigraphic analysis by generating time/depth contour maps, depositional model, petroleum system elements and correlating the results with previous studies. The area under investigation displays a combination of major (Type-1) and minor (Type-II) normal faults with a dominant strike slip component (wrench faults). Two higher order sequences (alternative TST and HST packages) are identified within Sembar Formation of Early Cretaceous which marks the early rift phase of Indian plate. Whereas the Goru-A sand has one complete sequence comprising of LSW (Lowstand Wedge), TST (Transgressional System Tract) and HST (Highstand System Tract). Goru-B sand has a combination of TST and HST named Force Regressive Wedges (FRW) which indicate ongoing rifting of Indian plate in middle and late Cretaceous. Areas for the potential plays are identified within Goru Formation, slope fans and shelfal sand bodies are interpreted as potential site for reservoir quality sands. Sembar Formation is acting as a source rock with an evaluated TOC between 2.1 to 2.56 wt. % which lies in realm of good generation potential,Vitrinite reflectance in the range of 1.3-1.5% and temperature of 150oC. The formation is a mature source rock based on geothermal gradient variation, overburden thickness and presence of hydrocarbon fluid on log suite. Petrophysical analysis showed that one reservoir zone of significant thickness and hydrocarbon saturation in each well is potentially sound enough to produce commercially. Reservoir mineralogical variation depict quartz grains are coated with mixed layer clays minerals. Depositional environment is shoreface barrier island, transitional between reducing and oxidizing conditions. As a whole, the Mesozoic sequence was deposited and evolved in a basinal configuration which was the result of several rift and drift phases of Indian plate. Each phase played a major role in the development of a complete petroleum system in Cretaceous Formations.