The Occurrences of Descendant and Indigenous Hydrocarbon in Precambrian Rocks of China

Abstract

Hydrocarbon stored in Precambrian rocks is widespread in China. Hydrocarbon-bearing units are mainly associated with metamorphic and carbonate rocks of Archean and Middle-Late Proterozoic (including Sinian) age. Reservoirs are characterized by secondary porosity associated with karstification, fracturing, buried dissolution, and buried recrystallization. Hydrocarbon originated from both Phanerozoic and Precambrian source rocks, so descendant and indigenous hydrocarbon accumulation can be categorized by relation of source to reservoir rock. By volume, descendant hydrocarbon dominates. Precambrian cratons, such as the North China craton formed during Luliang tectonism (1800 Ma), and the Yangtze and Tarim cratons formed during Jinning tectonism (800 Ma), are believed to be the most common locations for hydrocarbon accumulation in Precambrian rocks. Tectonic activities on these cratons during pre-Indosinian (>235 Ma) or pre-Hercynian (>250 Ma) time were characterized by both elevation and subsidence, resulting in repeated weathering cycles causing leaching and karstification. This weathering contributed to improvement in reservoir quality, particularly within the predominant carbonate strata composing these platform deposits. Tectonism also brought younger hydrocarbon source rocks and older 297