Book Description

Geomechanical analysis plays an important role in developing and producing oil and gas from organic-rich shales through horizontal drilling and multistage hydraulic fracturing. This study aims to conduct a geomechanical analysis of Indonesian shale potentials. Laboratory analyses on Indonesian shale samples have been performed using lacustrine outcrop samples in the Central Sumatra Basin (CSB) and subsurface samples of marine deposits from the North Sumatra Basin (NSB). Indonesian shales can be classified into two different groups based on their mechanical properties. These differences can be seen as a progression of diagenesis, where the U.S. shale can be regarded as mechanically mature and Indonesian shales are relatively early-mature to immature, mechanically, due to its younger age. In-situ stress analysis of the studied wells has been carried out on a regional and borehole scale. On the regional scale, the earthquake focal mechanisms analysis and surface geological features suggest a reverse faulting (RF) environment with the direction of maximum horizontal stress (SHmax) in the northeast-southwest (NE-SW) direction. In the borehole scale, the analysis shows a near isotropic stress condition due to overpressure in the Baong Formation, suggesting a RF/Strike-slip (SS) faulting regime. In contrast, the Belumai and Bampo Formation show an anisotropic stress state in the normal fault (NF)/SS faulting regime. Two stress profiling methods, i.e., Extended Eaton (EE) and Viscous-Relaxation (VR), were carried out and compared to assess the difference in stress states at each depth. In general, both methods suggest reverse faulting (RF) regime in the upper section and Strike-Slip (SS) regime in the lower section. Having a RF environment, hydraulic fracturing in Baong Formation will result in no clear fracture barrier in preventing hydraulic fracture growth into adjacent formations. Meanwhile, for injection into the SS/NF regime in the Belumai Formation, the fracture will open against the Shmin axis and propagate to the vertical direction until it reaches a fracture barrier. As a closing remark, our study suggests that the Indonesian shale potential in NSB, where the formation is in overpressured condition and the prevailing faulting regime is RF, is not favorable for hydraulic fracturing operations.