Abstract

The Lopatin's time-temperature index (TTI) values, correlate with the thermal regimes needed for the generation and preservation of hydrocarbons (Waples 1980). According to the Lopatin's method, TTI 15 is believed to be the onset of the oil generation, TTI 75 to be the oil generation peak, and TTI 160 to be the end of possible oil generation.

The Northwest Java Basin is a known producing hydrocarbon area. The hydrocarbons are produced from the Jatibarang Volcanics, the Lower Cibulakan Member (Talang Akar Formation and Baturaja Formation equivalents), the Upper Cibulakan Member (Zone 16, Zone 15, Zone 14, Zone 12), and the Parigi Formation (carbonate reservoirs).

The oil window, TTI 15, is reached in Randegan (eastern part of the Northwest Java Basin), at a depth ranging between 1800 - 2000 meters, while in Cilamaya - Pamanukan - Kandanghaur areas occure between 2000 and 2300 meters. The TTI 160 is found only in the Purwakarta-1 well within the Jatibarang volcanics. The Talang Akar as a source rock in Gantar North Cilamaya areas is mature at the southern part.

The Baturaja is mature in the surroundings of Purwa-karta - Gantar, and south-ward. Only in the south of the Purwakarta areas is the lower part of the Upper Cibulakan Member sufficiently mature to generate hydrocarbons (TTI 15). The CO₂ content is believed from dissolving carbonates of the Baturaja Formation formed after the burial of the Talang Akar sediments which have a high content of carbonaceous materials.

Vertical and lateral migration seems to play a very important role on the accumulation of hydrocarbons in the upper units of the Upper Cibulakan and Parigi Formation.