Phase characteristics of hydrocarbons generated from different types of kerogen at different maturity levels in closed system

Abstract

For studying phase characteristics of hydrocarbons generated from different types of kerogen at different maturity levels, pyrolysis data of MM type-I and II kerogen (Maoming oil shale) and Coal type-III (Turpan coal) were collected and used for building phase models by PVT simulation technology. Then, phase diagrams, as well as physical properties (GOR, density, and viscosity) related to different kerogen types and along with maturity history, were output and carried out for comparative studies. The results show that three different types of kerogen perform different hydrocarbon generation processes, which form various yields and hydrocarbon compositions, leading to different petroleum types and diverse phase characteristics. The GORwt and the relative proportion of light and heavy hydrocarbons are two critical factors to shape the phase envelopes. The nature of kerogen with different maturity processes controls the changes of hydrocarbon compositions to form diverse phase characteristics. Their phase diagrams and physical properties on the ground conditions confirmed the different maturity ranges of black oils, light oils, and gas condensates generated by kerogen, respectively. Our study clarified that all types of kerogen at early generations (relatively low maturities) extensively generate black oils even though phase characteristics are different. In contrast, at a relatively high maturity by considering yields and expulsions of hydrocarbons, the MM type-II kerogen prefers to generate light oils, while the MM type-I kerogen prefers to generate black oils and the Coal/type-III kerogen prefers to generate gas condensates.