Hydrocarbon-generation in Cambrian-Silurian high- to over- mature source rocks, middle and upper Yangtze region, China

Two main Cambrian-Silurian high- to over-mature hydrocarbon source rocks occur in the Middle and Upper Yangtze region: the Lower Cambrian Niutitang Formation (mostly shale), and the Lower Silurian Longmaxi and Upper Ordovician Wufeng formations (mostly graptolite shale). Due to several complicated tectonic events occurred in the study area, the source rocks experienced inhomogeneous uplift, deformation, and burial, resulting in discontinuous and episodic hydrocarbon generation evolution. Based on a detailed study of the tectonic burial history and an analysis of the current degree of thermal evolution of the source rocks, this paper studied the burial history, the thermal history, and the hydrocarbon-generation history of the Cambrian-Silurian source rocks. It used basin modeling technology and thermal simulation tests on source rocks to reveal the process and the regional regularity of the hydrocarbon-generation evolution, and to expound the tectonic phases and the time-spatial distribution of hydrocarbon generation. It shows that the region from western Hubei to eastern Chongqing is the major source area of Lower Cambrian rocks, and the region from southeastern Sichuan to central Guizhou is the major source area of Lower Silurian rocks. Reconstruction of hydrocarbon-generation history allows simulated estimation of the remaining hydrocarbon-generation potential of the high-over mature marine source rocks.