Mechanical properties of Indonesian organic-rich shales from the Central Sumatra and North Sumatra Basin, and comparison with US shales

Abstract

Mechanical characterization of shales is a fundamental requirement in optimizing shale resource development and transferring development strategies between shale plays. Here we report the laboratory-based mechanical properties of Indonesian shale potentials located within Tertiary basins in active margin settings. Samples from surface-outcrops of lacustrine sediments in the Central Sumatra Basin (CSB) and subsurface-cores of marine deposits in the North Sumatra Basin (NSB) were examined in a series of experiments for their mechanical properties including rock strength, elastic properties, and creep compliance. Results show that the Indonesian shales studied here are generally more compliant than Mesozoic/Paleozoic U.S. shales reported in the literature. Within the context of a binary mixture model (stiff and soft components) used to explain shale elastic properties, these differences in mechanical properties imply that the soft and stiff end-members are more compliant in Indonesian shales. We interpret these differences as the difference in mechanical maturity, which reflects the degree to which mechanical properties have evolved due diagenesis. CSB and NSB samples are considered to be early mature, mechanically, compared to the mechanically mature U.S. shales. Particularly, the Baong Formation samples from the NSB studied here come from a hard-overpressured interval and are mechanically immature, despite their moderate thermal maturity based on vitrinite reflectance. Laboratory results also show no significant differences in mechanical properties between shales deposited in lacustrine (CSB samples) and marine (NSB samples) environments.