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Effects of Salt Chlorides on the Hydrocarbon Generation of Source Rocks


Former workers and we found that immature and low mature oil were widespread and most natural gas had higher dry coefficient and carbon isotope of methane, ethane and propane in the western Qaidam Basin of Northwest China, where saline lacustrine facies were developed in the Paleogene and Neogene. It was inferred that these oil and gas geochemical characteristics were related to salt minerals and salinity in the Paleogene and Neogene formations. The purpose of this work is to determine the effects of salt chlorides existed in the formations on hydrocarbon generation process. We have carried out hydrocarbon generation experimental simulations of mudstones collected from the Neogene of the western Qaidam Basin in Rock-Eval and golden tube autoclave pyrolysis systems under different salt chlorides and concentration conditions. In the Rock-Eval pyrolysis system, salt chlorides took anti-catalytic actions to decrease the hydrocarbon yields (S2) through increasing apparent activation energies. In the golden tube autoclave pyrolysis system, high concentration sodium chloride depressed hydrocarbon gas and carbon dioxide yields while raised hydrogen volumes. High concentration sodium chloride also promoted oil yield at the early period of pyrolysis while reduced oil yield at the later period. High concentration sodium chloride made apparent activation energies of C1 and C2-5 higher while that of C6+ lower. The theory of electron inducement mechanism could account for the catalyzing and anti- catalyzing action of salt chlorides.