Effect of pyrolysis products phase behavior on the fluid production in the in-situ conversion of medium-low maturity shale

During medium-low maturity shale pyrolysis in-situ conversion process, dynamic temperature-field evolution affects pyrolysis products compositions. The phase model established from single product cannot accurately predict the entire development process. Through pyrolysis and phase experiments, the composition and phase equilibrium parameters of five products were obtained to establish phase models. The phase characteristics of different models were clarified and a multi-temperature-stage pyrolysis fluid coupling (MPFC) model with characterizing temperature-dependent product evolution was developed. The fluid production performance of different phase models were analyzed by numerical simulation. The results indicated that elevated pyrolysis temperatures enhance light component fractions in pyrolysis products. High-pyrolysis-temperature models exhibit lower oil-component phase equilibrium constant (K-values) and higher gas-component K-values, which enhances the retention of oil-components in oil phase, improved the stability of oil phase and oil production. Gas production rises with higher gas-components’ K-values. The influence of phase models on formation temperature and kerogen concentration is limited. Phase models control significantly the production gas-oil ratios during initial pyrolysis stages, modifying fluid composition and distribution. As the primary oil-phase component, heavy hydrocarbon's K-values obviously influence produced oil composition, lower K-values yield its higher volume fractions. Due to the gas-phase preference and phase transitions of light gases component, its lower K-values increased its fraction in produced oil. The relative ranking of K-values of all gas-components controls the composition of produced gas. The MPFC model effectively captures formation temperature temporal variation and pyrolysis products evolution, overcoming limitations of single-temperature models on describing multiple development stages.