High-resolution Geochemistry in the Lucaogou Formation, Junggar Basin: An Assessment of Heterogeneous Shale Resources

Controlled by fluctuating paleoclimates and sedimentary environments, the organic and inorganic features of the Lucaogou Formation exhibit strong heterogeneity in the vertical profile, challenging conventional geological interpretation. To elucidate the possible influence of heterogeneity on resource evaluation, a high-resolution sampling approach was applied to an 86.2 cm long core from the Lucaogou Formation of the Jimsar sag in the Junggar Basin. 86 sets of samples were micro-drilled from the core and subjected to comparative Rock-Eval pyrolysis. Following the classical guidelines, the organic abundance, kerogen type, and maturity of source rocks were exhaustively analyzed. Experimental results revealed that organic richness and composition vary significantly under different sedimentary backgrounds, which in turn leads to differential hydrocarbon generation. The combination of hydrocarbon generation, transport, and expulsion results in peculiar patterns for hydrocarbon accumulation in the Lucaogou Formation. Laminated shales in the Lucaogou Formation serve as both hydrocarbon source rocks and reservoirs, with laminae being migration pathways. Organic-rich dolomites in the Lucaogou Formation have a considerable hydrocarbon-generating capacity and present the characteristics of self-generation and self-storage. However, massive mudstones act purely as hydrocarbon source rocks.