THE ANALYSIS OF OVERPRESSURE CHARACTERISTIC IN OFFSHORE AREA OF TARAKAN BASIN, NORTH KALIMANTAN

• Main Author: Rowin Pardamean, Daniel
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/57757
• Institution: Institut Teknologi Bandung

The study is conducted in the offshore area of Tarakan Basin, North Kalimantan. Based on the drilling report, overpressure is present in the offshore area of Tarakan Basin. If overpressure is well estimated, financial and technical losses can be prevented. The stratigraphy in the offshore area of Tarakan Basin consists of Bunyu, Tarakan, Santul, and Tabul formations which are Middle Miocene to Recent in age. The lithology in the offshore area of Tarakan Basin is dominated by fine-grained deposit. The fine-grained deposit will tend to form a closed system that will keep the pore fluid from dewatering and causing overpressure. The pore pressure analysis is carried out to determine the top of overpressure, estimate pore pressure magnitude, analyse overpressure generating mechanism, and analyse the relationship between geological condition in study area and overpressure. The data processing was performed in three wells (BUN-1, BUN-2, and BUN-3) using wireline log data, well report, temperature data, and pressure data. The geological condition of the study area is used as the reference to estimate the pore pressure. Results from the data processing and analysis show that there are three pore pressure conditions in the study area, i.e. hydrostatic, loading overpressure, and non-loading overpressure. All analysed wells penetrate the overpressure zone located in the Santul and Tabul formations. The depth of the top of overpressure ranges from 2114.32 – 2283.36 m, with the magnitude of overpressure around 3054 – 6709,56 psi. The temperature at the top of overpressure is sufficient for clay mineral diagenesis, but further analysis is needed to explain the process causing the non-loading overpressure. Meanwhile, the loading overpressure is caused by disequilibrium compaction.