Publications

The Tarakan Sub-Basin is situated in a passive margin, located in the northeastern part of Kalimantan. The existence of overpressure zone is indicated from drilling activities in this area. Some wells were terminated by the operator before reaching the main target due to overpressure. There are two structural styles recognized in the offshore Tarakan sub-basin. Proximal-shelf area deformation is dominated by normal-growth faults whereas distal-slope area deformation is dominated by toe-thrusts. Gravitational sliding associated with a thick layer of early Miocene shale was interpreted as the major cause of structural formation and is responsible for the appearance of structural variation in the shelf and slope area. The structural complexity within the research area has a role in controlling the distribution of pore pressure. This evidence is supported by the decreasing of overpressure magnitude distally, which is more dominated by contractional structures (toe-thrust) compared to the proximal area dominated by extensional structures (normal-growth faults). The purpose of this study is to determine the mechanism of structural development, pore-pressure prediction, over pressure distributions and understanding the relationship between pore pressure and structural style in study area. Top overpressure is predicted at a depth of 2000-3500m TVDss in Middle-Late Miocene shale interval. Change of overpressure generating mechanism is related to structural style changes within the extensional, contractional and transitional area caused by fluid expansion, disequilibrium compaction, and a combination of both, respectively. Keywords: pore pressure, overpressure, structural style, toe-thrust, growth fault, Tarakan sub-basin.