Abstract

Vindhyan Basin is the largest sedimentary basin in terms of sedimentary thickness situated in the north central part of India. Gas discovery in Nohta-B from Rohtas Limestone has opened up a new spectrum for the prospectivity of Son Valley sector of Vindhyan Basin. So far, out of fourteen Exploratory Wells drilled within the Damoh-Jebara-Katni PEL Block in the Son Valley Vindhyan Basin, eleven wells have proved the presence of gas from the and more specifically, eight wells have produced gas from the Rohtas Limestone with a maximum production rate of 3897m3 /d in Nohta-C. The gas accumulations are mainly associated with the maximum concentration of fractures in view of absence of any significant porosity as the reservoir is very tight in nature. Therefore, the fracture/fault analysis are of utmost important for the identification of likely locales for hydrocarbon accumulation along fracture driven secondary porosity and the fracture patterns will be governed by major tectonic trends and paleo-stress directions. The objective of the present study is to understand the reservoir characteristics and fracture trend to assess the hydrocarbon potential of this area. The present work is an integrated and comprehensive evaluation of Rohtas Limestone, by subdividing it into different units/zones by multidisciplinary approach (i.e. sedimentology, geochemistry and logging). Rohtas Limestone is dominantly limestone in upper and lower part and generally tight in nature, whereas the middle part is mainly shaly with thin limestone bands. The primary porosity is almost negligible. The only effective porosity present is the fracture porosity. An attempt has been made to further subdivide this formation based on electrolog data and fracture identification using FMI logs.