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Petrophysical Evaluation of The Potential of Shale Gas Resource, Haenam Basin, Korea

Abstract

Test drilling, well logging and geochemical-mechanical tests for drilled core samples are performed in order to evaluate the potential of shale gas resources in Haenam Basin, Korea. Three inches diameter pilot borehole is vertically drilled to 505 meters depth, and core samples are fully taken. In situ physical properties and fractures are characterized by electric logs, radioactive logs (natural gamma, density, and neutron logs), acoustic logs, and borehole image logs. Laboratory experimentation on 32 cores is carried out using geochemical analysis (Rock-Eval), and seismic velocity and static elastic modulus are measured for cores in 17 sections. Haenam Basin is Cretaceous sedimentary rocks of Mesozoic, and our major target layers consist of shale and sandstone, partially distributed siltstone, mudstone, and conglomerate. Natural gamma intensity of the intervals of target sediments shows about 150 API. In order to identify and calculate total organic carbon in organic-rich rocks, practical method, the Passey's algorithm, has been performed using well logs. The overlaying of properly scaled sonic slowness on resistivity log show do not show clear distinction based on Passey's algorithm, and maximum total organic carbon from Rock-Eval analysis is under 2 wt%. To estimate the brittleness of sediment rocks we have evaluated the brittleness index by the averaging dynamic and static elastic modulus, respectively. The estimated brittleness index shows good trends, i.e., as Poisson's ratio decreases, Young's modulus increase. But the potential of shale gas resources from the estimated total organic carbon by Passey's algorithm and Rock Eval analysis do not reach to our expectations in this area.