Organic geochemistry and hydrocarbon potential of source rocks from the Mohe Formation of the Upper Jurassic in the Mohe Basin, northeast China

Abstract

The Mohe Formation is one of the important source rocks for oil-gas and gas hydrates in the Mohe Basin. In this paper, mudstone from cores of the M-1 and M-3 wells and argillite from cores of the MK-2 well of the Mohe Basin were studied. The depositional environment, organic matter source, thermal maturity, kerogen type, and hydrocarbon generation potential of the core samples were determined using organic and inorganic geochemistry. The dual sources of organic matter were terrestrial plants and aquatic organisms. The organic matter was deposited in a reducing lacustrine environment. The lake water salinity was higher when argillite was deposited. The late stage of the sedimentary filling of the lacustrine basin was characterized by high sulfate contents. The source rocks primarily contained Type II2–III kerogen. The present-day thermal maturity parameters reveal that the organic matter of the Mohe Formation is mature to overmature, indicating that this unit is capable of generating gas condensate and dry gas. In addition, we compared the organic geochemistry characteristics of mudstone and argillite. The results indicate that TOC, S1 + S2, and HI are lower in argillite than in mudstone. Although the biomarker maturity parameters cannot reflect the thermal evolution of the source rocks, they reflect the source of the organic matter and the depositional environment. The results provide important constraints for the evaluation of the hydrocarbon potential of lacustrine source rocks of the Mohe Formation from the Upper Jurassic and for the location of petroleum resources in the Mohe Basin.