A NEW UNDERSTANDING OF HYDROCARBON GENERATION MECHANISM OF CARBONATE ROCKS

The mechanism of hydrocarbon generation in carbonate rocks are studied by step heating extraction and simulation. The authors found that (1) carbonate minerals have the influence of condensation and dehy-drogenation on kercgen,and can promote its degradation into liquid hydrocarbon under low temperature, thus increase the yield of gaseous hydrocarbon, (2) Montmorillonite is capable of promoting the breakage of carbon chains and the transformation of liquid hydrocarbon into gaseous hydrocarbon under low temperature; (3) The existence of clay mineral in carbonate rocks affects the condensation and dehydrcgenation of carbonate minerals over kerogen, thus the hydrocarbon generating rate is reduced; (4) The peak of gas generation for carbonate source rocks is later than that for muddy source rocks. Furthermore,based on the measurements of residual gas generating rates in carbonate source roeks, and simulations on samples with low maturation from different sequences in various areas of China, the migrating rate for liquid hydrocarbon in carbonate rocks during gee-history is considerable higher than that in mudstone, and it can reach as much as 60% for pure limestone, but only 25% for marlites.