Thermal evolution of organic matter in the Lower Silurian Longmaxi Formation,southern Sichuan Basin and its main controlling factors
This study aims to investigate the thermal evolution characteristics of organic matter in the Lower Silurian Longmaxi Formation,southern Sichuan Basin.Data from wells,lithology,and temperature experiments is applied to examine the present-day geothermal field characteristics;Laser-excited Raman spectroscopy is employed to measure and calculate the vitrinite reflectance(RmcRo)of organic matter in shales in the Longmaxi Formation.Using Ro as a constraint and the BasinMod technique for numerical simulations of basins,we reconstruct both the heat flow history in the southern Sichuan Basin and the thermal evolution history of organic matter in the Longmaxi Formation within the basin.The results show that the bitumen in the reservoirs of the Longmaxi Formation in the southern Sichuan Basin exhibits RmcRo values varying from 2.7%to 3.9%,indicating the presence of overmature organic matter,with the maturity increasing gradually from the Weiyuan to Luzhou and then to Changning blocks.During the Caledonian,most organic matter was yet to reach the hydrocarbon generation threshold.From the Dongwu to the Indosinian orogenies,the organic matter in the northern Weiyuan and northwestern Chongqing areas featured low to medium maturity,while that in the Changning-Ningxi blocks and the southern Luzhou block was highly mature and overmature,respectively.During the Yanshanian movement,the organic matter in the Longmaxi Formation in the southern Sichuan Basin was generally overmature.The thermal evolution of organic matter in the Longmaxi Formation in the southern Sichuan Basin is jointly affected by several geological factors such as paleogeomorphology,paleo-burial depth,eruption of the Emeishan Basalt,and tectonic uplifting.Of these,the paleo-burial depth and eruption of the Emeishan Basalt are identified as the primary factors.
万方数据
维普
