Temperatures of dolomitizing fluids in the Feixianguan Formation from the Northeastern Sichuan Basin

Abstract

The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years. Because of the dolomite-hosted reservoirs in the Feixianguan Formation, these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists. Based on the homogenization temperatures of fluid inclusions, oxygen isotopic composition and their calculated temperatures, and the burial and thermal history of the typical well, it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation, Northeastern Sichuan Basin. Only a minority of dolomites are formed by high-temperature dolomitizing fluids. The ending depth interval of low-temperature dolomitizing fluids was about 1000–2500 m, of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic. The main depth interval of high-temperature dolomitizing fluids was about 3200–4500 m, of which the correspondingly main timing interval was approximately early-middle Middle Jurassic. The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation, Northeastern Sichuan Basin.