Influence of carbonate minerals on the pyrolysis and phase behavior of oil

The concept that reservoir minerals can affect oil cracking behavior is widely accepted by geochemists. However, the role of carbonate minerals on the thermal evolution of oil is still not well understood. This is especially true for dolomite, which is one of the most important carbonate cements. To investigate its influence, a series of laboratory simulation experiments of a crude oil with various carbonate minerals, including calcite, magnesite, and dolomite was conducted. The simulation experiments were carried out using a closed system of flexible gold capsules at temperatures of 250–600°С at a heating rate of 20 °C/h and a constant pressure of 50 MPa. The results indicate that dolomite/magnesite might promote the generation of sulfate radical ion (SO42−). Subsequently, the presence of SO42− can initiate thermochemical sulfate reduction reaction with the help of minor water and H2S, resulting in the destruction of gaseous hydrocarbons. Meanwhile, the influence of dolomite on the composition of oil can further affect its phase behavior, especially in the gas window (Easy Ro range of 1.19–1.47% in the experiments). For the investigated oil, at Easy Ro of 1.47%, the presence of dolomite will increase the cricondentherm (ca. 35 °C) and decrease the cricondenbar (ca. 1.3 MPa) compared to those of pure oil.