Integrated Geochemical, Geomechanical and Geological (3G) Study of Lower Baong Shale Formation for Preliminary Shale Gas Prospectivity in the North Sumatra Basin

Abstract

Abstract The most common fallacy in evaluating shale gas potential in a basin is treated similar to those produced in the United States. In fact, each basin has unique characteristics that influence shale facies type and depositional. Lower Baong shale is responsible for source rock filled up sandstones reservoir in the oil and gas field in the North Sumatra Basin. This study reveals the data and facts from the laboratory, drilling, wireline well logs and seismic through the integrated study of geochemistry, geomechanics and geological synthesis of Lower Baong Formation. An understanding of shale geochemistry, mineralogy and geomechanics is very important to understand how the shale reservoir has the potential to reserve and produce when carried out stimulation. Geochemical laboratory analysis is used to determine the richness, maturity and kerogen type. This information is limited to a certain depth point, so that it is necessary to conduct calibrations in order to estimate the shale productive reservoir interval on a wireline log scale. Limited core data and rock mechanics laboratory analysis represented by mineralogy then also calibrated with brittleness index. Thus, geochemical and geomechanical log model tied to the seismic data, is a very useful tool for formation evaluation and broaden the understanding of shale reservoir facies distribution. Understanding shale facies needed to design fracturing horizontal hole in more detail. This study also classify shale based on organic richness, maturity, type, shale strengthness, shale brittleness and clay content. Shale facies in Lower Baong shale can be divided into 3 facies of sweet spot area. Siliceous calcareous mudstone has high potential for shale gas with 2–3.5% of TOC, II-III of kerogen type, maturity depth from 2300m, 350–425m of sweet spot thickness, 10000–18000psia of UCS, 3000–4000 psia of Young modulus, 0.18–0.22 of Poisson ratio and associated with foreland basin fill deep. Silty-shaly calcareous mudstone has medium potential for shale gas which is associated with foreland basin fill slope. Silty-shaly dolomitic mudstone is associated with foreland basin fill edge that has high potential for shale. The integrated approach for geochemistry and geomechanics is expected to reduce risk in shale gas exploration.