Discussion on Heavy Oil Formation Mechanism in the T Block, Oriente Basin, Ecuador

Hu Ying et al.(2010) used gas chromatography (GC) finger mark, seismic inversion and oil-oil correlation to suggest that the southern kitchen had contributed to the hydrocarbon accumulation and API differential distribution in northern part of P-O-M basin. In this discussion, we refute their arguments and conclusions. We show that: 1) There exist one EW extended arch between the Northern oil and gas accumulation area and southern kitchen according to basin gravity map which formed a barrier for further migration of oil and gas from southern kitchen; 2) The API plane distribution shows that there is a EW extended low API (10-17API) value belt developed between the southern kitchen and northern accumulation area, just on the way for oil migration from southern kitchen to northern part of the basin, whose API should be higher according to the theory of secondary mature oil migrated from southern kitchen; 3) According to Goncalves et al.(2002) and Dashwood and Abbotts (1990), due to the development of larger thrust faults in the thrust belt which provide vertical migration pathway and damaged the lateral migration carrier, the secondary oil migration mainly happened in the foothill belt which results in mixed oil accumulated in the foothill belt rather than in eastern slop in P-O-M basin; 4) The GC feature in T block is different from the mixed oil in Goncalves et al.(2002) but more similar with the differential biodegradation oil in Dashwood and Abbotts (1990). Finally, we propose a model for hydrocarbon accumulation in P-O-M basin, and prefer that the API differential distribution is the result of early accumulated oil differential biodegradation.