Abstract:

With well development of cementation, carbonate hydrocarbon source rocks would be consolidated into rocks quite earlier, therefore, compaction effect is not merely chief one instead of multi-effects existence in hydrocarbon expulsion. Different evolution stages with various ways of hydrocarbon expulsion, in the higher-over maturation stage, micro-fissure hydrocarbon expulsion and molecular diffusion are believed to play a chief role. A mathematical model of diffusively hydrocarbon expulsion and micro-fissure hydrocarbon expulsion can be established quantitatively in line with the principle of mass conservation of hydrocarbon generation and expulsion on the basis of one dimensional geological model. Modeling results from this model indicate that Majiagou Formation in the Ordovician in Ordos basin had entered hydrocarbon generation threshold by the end of the earlier Permian and reached the peak of hydrocarbon generation in the Triassic, and began getting into the over saturation-dry stage in the earlier Cretaceous; Accumulative total hydrocarbon expulsion rate is 60%-80%, of which compactively hydrocarbon expulsion, diffusively hydrocarbon expulsion and micro fissure hydrocarbon expulsion are predominant whereas water soluble facies hydrocarbon expulsion occupies a small proportion.

Key words: carbonate source rock, hydrocarbon expulsion, microfissure, Majiagou Formation, Ordos basin