OVERPRESSURE ANALYSIS AND ITS RELATIONSHIP TO HYDROCARBON ACCUMULATION IN NUNUKAN BLOCK, TARAKAN SUBBASIN

• Main Author: Wicaksono, Andika
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/56937
• Institution: Institut Teknologi Bandung

Overpressuring has created drilling problems for most operators in the Tarakan Subbasin. Kick, loss, shale caving and stuck pipe are common encountered while drilling in this overpressured zone, especially for exploration drilling. Several drilling projects even prematurely terminated before reaching the proposed total depth due to this overpressuring problem. Therefore, only a small of hydrocarbon accumulations have been proven and bring question about the possibility of large accumulation beneath the overpressured zone. Seven wells and approximately 30 km of 2D interval seismic velocity have been evaluated to identify the characteristic of overpressure. Eaton’s sonic pore pressure prediction was used in this research to estimate pore pressure profile and to identify top overpressure and top hard overpressure. Velocity-density crossplot and velocity-effective stress crossplot were used to identify the overpressure mechanism. Integrated evaluation of pore pressure prediction and hydrocarbon indicators from wells and seismic can estimate the possibility of hydrocarbon accumulation beneath the overpressured zone. Overpressure distribution within this research area varies with the shallowest top overpressure is in the eastern area, which correlates with high shale contain. Both loading and unloading overpressure mechanisms exist. The unloading mechanism was predicted as the hydrocarbon generation. There is a positive indication that the transition zone from top overpressure to top hard overpressure could potentially be the largest hydrocarbon accumulation up to 14.000 feet.