Abstract
The Sanga-Sanga working area consists of brown fields that have been produced for nearly 50 years. The production is declining rapidly from anticlinal trap fields. Finding new resources is a must in order to extend the production life. Therefore, the exploration requires getting deeper targeting reservoirs associated with hard overpressure zones.
The methodology used to identify and recognize the potency of hard overpressure zone is the integration of geology, geophysics, and geochemistry data. Normal compaction trend and pore pressure analyses were performed to determine top of overpressure zones. The geochemical data from biomarker provide calculated vitrinite reflectance (Rc) to complement vitrinite reflectance (Ro) when evaluating relationship between hydrocarbon origin and overpressure generation. Finally, the seismic integrates all the data in structural reconstruction framework.
Pore pressure analysis showed 9 wells have overpressure zones. The overpressure occurrence can be grouped based on anticlinal lineaments. The Badak-Nilam lineament is characterized by a sharp change in overpressure to hard overpressure zone, distal facies, relatively normal deposition and showing higher pressure gradient. The Semberah and Lampake-Mutiara lineament are characterized by long transition zone, proximal facies, strongly uplifted and folded, and showing lower pressure gradient. Ro and Rc data showed that there are two periods of hydrocarbon charging into the reservoir, prior to and after the hard overpressure zone occurred. Vertical effective stress, dynamic mechanism, and the timing hydrocarbon generation-migration and overpressure generation hole significant role to accumulation.
The evaluation of hard overpressure zone play requires the integration of geology, geophysics and geochemistry to get the understanding of the timing sequence between hydrocarbon generation-migration and overpressure generation. Calculated vitrinite reflectance data from biomarker gave an advantage to this timing relationship that could lead to the exploration of the hidden resources in the hard overpressure zone becomes more feasible.
