Overpressure’s top and generating mechanism in “APR” block, North Sumatra offshore area

Abstract

The offshore North Sumatra Basin is one of the hydrocarbon-prone basins in Indonesia. The Malacca Formation acts as the reservoir in this basin. However, there are some drilling problems caused by abnormal pore pressures. Overpressure analysis is carried out so that drilling activities are avoided from drilling problems such as kicks, blowouts, stuck pipes, loss circulation, and collapse. This study aims to analyze the overpressure in the “APR” block, offshore North Sumatra Basin, which includes determine the depth of the top overpressure and the mechanism of overpressure formation. In the research area, analysis of 3 exploration wells was carried out. Overpressure is analyzed based on well log data, and pressure test data using the Eaton method (1975) supported by other data such as LOT (Leak-Off Test) data, drilling reports, mudlogs. At Well A, top overpressure depth is ± 3235 ft TVDSS (true vertical depth sub sea). At Well P, top overpressure depth is ± 3065 ft TVDSS, and at Well R, top overpressure depth is ± 2901 ft TVDML (true vertical depth mud line). The overpressure generating mechanism in the study area is caused by the loading mechanism (disequilibrium compaction) and caused by the nonloading mechanism (hydrocarbon buoyancy).