Thermal Evolution Patterns and Primary Controlling Factors of Sinian‐Lower Paleozoic Source Rocks in the Sichuan Basin, Southwestern China

Abstract

AbstractThermal evolution is an essential part of evaluation to source rocks as well as of research of hydrocarbon dynamic accumulation in oil‐gas‐bearing basins. The purpose of this work is to use the Easy%Ro chemical kinetic model to simulate the thermal evolution history of source rocks of Sinian‐Paleozoic ages in the Sichuan basin. It is based on analysis of styles of stratum deposition, recovery of thermal history of the basin, and the data from 86 representative drilling boreholes and more than 200 man‐made wells. The results show that the varied tectonic units of the basin have distinct feature of thermal evolution of the Lower Cambrian and Lower Silurian source rocks. Thus four models of thermal evolution are established: (1) Being mature during the Caledonian epoch and rapidly developed and shaped up in the early Late Permian period, as represented by the Lower Cambrian source rocks in the southern basin; (2) Not being mature during the Caledonian epoch and rapidly developed and shaped up in the early Late Permian period, as represented by the Lower Cambrian source rocks in the southwestern basin and Lower Silurian source rocks in the southern basin; (3) Being mature during the Caledonian epoch and mature again in the Late Hercynian‐Yanshanian epochs, as indicated by the Lower Cambrian source rocks in the northern basin; and (4) Not mature during the Caledonian epoch and steady maturity in the Late Hercynian‐Yanshanian epochs, as shown by the Lower Cambrian source rocks in the central basin and Lower Silurian source rocks in the eastern and northern basin. By comparison of relationship among the deposition rate heat flow and temperature increase rate, we infer the controlling factors of the thermal evolution of the source rocks above. For the southwestern and local southern Sichuan basin, the mantle plume and abnormal heat effect of basalt at the Emeishan during the early Late Permian period had exerted an major influence on the source rocks. In the rest of the basin, heating of sediments at depth and heat flow of the basin has a joint effect, especially the former had greatly increased the temperature of source rocks.