An organic geochemical study was performed on 22 oils from various fields within the oil field blocks of Central Sumatra. The study was conducted in order to determine if the Trough, located between the Minas and Kotabatak Fields, is an active hydrocarbon kitchen.
The oils from the study area can be subdivided into two major groups. Group 1 is comprised of oils from the Minas (Sihapas Formation), Oki, and Libo Fields, while Group 2 are oils from the Kotabatak Area, Kotagaro, Nusa, and the northwestern segment of Minas (Telisa Formation) Field.
Oils from both groups were generated from source rocks within the Pematang Formation which were deposited in a freshwater lacustrine environment. The Group 1 oils are characterized by the presence of botryococcane, heavy carbon isotopic compositions, high diasterane/sterane ratios, and relatively lower wax contents with respect to the Group 2 oils. The Group 2 oils lack of botryococcane, display light carbon isotopic compositions, and a relatively low diasterane/sterane ratios.
All of the analyzed oils were generated from source rock within the main oil generation window. There are indications that the Group 1 oils are more mature than those in Group 2. However, the observed maturity differences are very subtle; therefore, it is interpreted that the biomarker and carbon isotopic differences observed between the two groups have resulted from source rock variability that exists within the Pematang Formation rather than maturity differences.
Based on available data, there is an indication that the Trough is an active hydrocarbon kitchen. However, additional studies need to be performed in order to increase the degree of confidence in this interpretation.
Authors : Bismantoro Prabowo & Gunardi B. Sulistyo