The maturation of source rock in the northeastern sub-trough and the central sub-trough, Nam Con Son basin

Abstract

Exploration activities have been carried out for a long time in the Nam Con Son basin. So far, many oil and gas discoveries have been made in this area and several fields developed and put into production such as Dai Hung, Rong Doi, Hai Thach, Moc Tinh, Lan Tay… The Nam Con Son basin, especially the eastern and northeastern parts, has a complicated geological development history which strongly influences the hydrocarbon generation and migration in the area. In this paper, the authors present a geochemical model of a section through the northeastern and central sub-troughs to evaluate the hydrocarbon generation and migration processes of the source rocks.

The results of geochemical model in the studied area showed that the Middle Miocene, Lower Miocene and Oligocene fi ne rained sediments are considered as source rocks in terms of organic matter richness. Oligocene source rock contains kerogen type I/III and type III. Middle Miocene and Lower Miocene source rock contain mainly kerogen type III and a little of type II. At present, the maturity thresholds are as follows: Oil window is from 2,500 - 4,700m, wet gas and condensate window is 4,700 - 6,200m and dry gas is below 6,000 - 7,200m. The hydrocarbon component in reservoirs indicate that they were supplied from Oligocene, Lower Miocene together with Middle Miocene, in which dominant is hydrocarbon from Lower Miocene, then from Oligocene source rock, while the volume of hydrocarbon from Middle Miocene is very small. In general, hydrocarbon traps in the studied areas were not affected by uplift creating an eroded unconformity at Middle Miocene. The traps, formed in early Late Miocene and earlier, will have higher chances to trap hydrocarbon expulsion from defined matured source rocks.