ANALYSIS OF OVERPRESSURE AND ITS GENERATING MECHANISM USING WELL DATA AND SEISMIC VELOCITY IN “SKW” FIELD, NORTH EAST JAVA BASIN

• Main Author: Kazainullah, Fasih
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/52741
• Institution: Institut Teknologi Bandung

North East Java Basin is known as one of the prolific hydrocarbon basins, whose drilling problems are often caused by the presence of overpressure. This study aims to predict overpressure and analyze the generating mechanism using data from two wells and 2D seismic velocity. Based on the lithology and pressure profile, there are 5 pressure zones. Zone A and C have normal hydrostatic pressures, which occurs in Lidah Formation to the upper of Mundu Formation, and Ledok Formation. Zone B is the beginning of overpressure, which occurs in the middle of the Mundu Formation to the lower Mundu Formation. Zone D has moderate overpressure, which occurs in the SKW-01 well in Wonocolo Formation, while in the SKW-02 well occurs in the upper of Wonocolo Formation to the middle of Wonocolo Formation. Zone E has high overpressure, which occurs in the SKW-01 well in Ngrayong Formation, while in the SKW-02 well occurs in the middle of Wonocolo Formation to Ngrayong Formation. The sediment thickness also controls the overpressure. The main generating mechanism of overpressure at this study field is loading, which is shown constant effective stress on the SKW-01 well, and the SKW-02 well, and is supported by a rapid sedimentation rate with average 200 m/million year. The second mechanism that generates overpressure at this study field is the transformation of smectite minerals to illite at a depth ± 4000 feet TVDSS, which is supported by geothermal gradient data of 43oC/km, so that at a depth 4000 feet TVDSS, the temperature has reached 80oC. In addition, XRD analysis also showed that the percentage of smectite minerals decreased with increasing depth, while the percentage of illite minerals minerals increased with increasing depth.