Facies Analysis and Reservoir Characterization of Rohtas Limestone in Son Valley, Vindhyan Basin, MP

Abstract

The project deals with Facies Analysis and Reservoir Characterization of Rohtas Limestone in Son Valley, Vindhyan Basin, MP. Presence of thermogenic gas has been established within Proterozoic Vindhyan sediments in the Son Valley part of Vindhyan Basin. The unconventional carbonate reservoirs of Rohtas Limestone have very low primary porosity and ultra-low permeability. The gas accumulation and the flow potential of hydrocarbons largely depend on the secondary porosity in the form of fractures. Facies analysis of the Rohtas Limestone is attempted to understand the control of facies types for entrapment of gas. The study of Facies is made through analysis of lithological data, microfacies analysis along with the study of Gamma ray log, Density log and Caliper log of few selected wells. The Rohtas Limestone has been divided in to three units, the upper, middle and lower. The Upper Rohtas Limestone comprises of thick limestone unit with very thin laminations of shale. The dominant facies consists of mudstone, dolomitic limestone and wackestone. The Middle Rohtas consists of predominant shale with thin limestone laminations. The Lower Rohtas consists of mainly limestone with interbedded shale. The main facies in the limestone comprises mudstone and dolomitic limestone. The understanding of fracture geometry of Rohtas Limestone has been also attempted by integrating the high-resolution data from an electric borehole image log and its integration with the conventional wire line logs. Xtended Range Micro Imager (XRMI) logs with improved signal to noise ratio with very high resolution borehole images, showing millimeter size features in the fabric of limestone reservoirs is useful to identify the closed fracture, open fractures, partially open fractures and the stress direction. It is also useful for identifying the Sedimentary Sequence, Reservoir Facies, Bedding Dips, which help to rationalize the choice for the next drilling location. Further it is used for identifying zones of testing and well stimulation. As a case study, XRMI and other log suites was studied for two selected wells to understand the distribution of fracture pattern in the Rohtas Limestone. The project will be helpful in understanding the Geometry of Unconventional Reservoir of the Rohtas Limestone.