Publications

Sanga-Sanga working area has been producing for nearly 50 years. Finding new resources is a must to extend the production but the boundary of the block limits the area. Therefore, to find new resources requires getting deeper, which is associated with hard overpressure zones, where there is an opportunity to explore as shown by good production test in these zones. The potential hydrocarbon accumulation in hard overpressure zones in Lower Kutai Basin was identified and recognized by re-evaluating existing wells. Pore pressure, overburden pressure, mud weight, and drilling events of deep exploration wells were re-examined to define the overpressure, transition and hard overpressure zones. Pressure testing and production data were re-validated to identify and filter the potential zones. Vitrinite reflectance (Ro) and calculated vitrinite reflectance (Rc) from biomarker were used to determine maturity, hydrocarbon generation-migration, and overpressure generation relationships. Pore pressure analysis showed nine wells with overpressure zones and six out of these nine wells associated with hard overpressure zones. The overpressure zone could be divided into three groups based on the anticline lineament of Semberah, Lampake-Mutiara, and Badak-Nilam lineaments. Semberah and Lampake-Mutiara lineaments are characterized by long transition to hard overpressure zone, lower pressure gradient, uplifted formation, and more proximal facies. In contrary, Badak-Nilam is characterized by short transition to hard overpressure zone, higher pressure gradient, not significantly uplifted formation, and more distal facies. Hard overpressure play in Lower Kutai Basin exists in form of pressure compartments and hydrodynamic trapping as shown by Anggana-1 and Nilam-149 production test. Vertical effective stress and hydrocarbon generation-migration timing hold a significant role to accumulation. The main challenge of the hard overpressure play is seal capacity which dictates the hydrocarbon column. A dynamic pressure mechanism need to be present to keep a certain hydrocarbon column preserved from seal breach. This study has shown that the Kutai Basin has the potency of hard-overpressure play as shown by the evidence on the onshore part. The new understanding of hard overpressure resulted in several potential areas to explore the hidden resources in the hard overpressure zone that were formerly unattractive and have now turned to be more feasible for exploration.