Predicting oil and gas compositional yields via chemical structure–chemical yield modeling (CS-CYM): Part 1 – Concepts and implementation

The ability to predict accurately the thermal conversion of complex carbonaceous materials under a wide range of heating rates and temperatures is of value in both petroleum exploration and refining operations. Modeling the thermal cracking of kerogen and coal under basinal heating conditions improves the pre-drill prediction of oil and gas yields and quality, thereby ultimately lowering exploration risk. Modeling the chemical structure and reactivity of asphaltenes from petroleum residues enables prediction of coke formation and properties in refinery processes, thereby lowering operating cost. Previous compositional yield models based on laboratory yield measurements have been developed for specific materials, such as isolated coals and kerogens, but extrapolation to predict oil and gas generation during geologic burial is problematic. Furthermore, models based on a few reference carbonaceous materials may not simulate varying compositions of kerogen and residues seen in nature. We have developed a method to calculate the amounts and composition of products resulting from the thermal decomposition of a solid complex carbonaceous material. This procedure provides a means of using laboratory measurements of complex carbonaceous solids to construct a representative model of its chemical structure (CS) that is then coupled with elementary reaction pathways to predict the chemical yield (CY) upon thermal decomposition. Data from elemental analysis (C, H, N, O, S), solid state 13C NMR, X-ray photoelectron spectroscopy (XPS), sulfur X-ray absorption structure spectroscopy (XANES), and pyrolysis-gas chromatography (GC) are used to constrain the construction of core molecular structures representative of the complex carbonaceous material. These core structures are expanded stochastically to describe large macromolecules (>104 cores with ∼106 atoms) with bulk properties that match the experimental results. Gas, liquid and solid product yields, resulting from thermal decomposition, are calculated by identifying reactive functional groups within the CS stochastic ensemble and imposing a reaction network constrained by fundamental thermodynamics and kinetics. An expulsion model is added to the decomposition model to calculate the chemical products in open and closed systems. Product yields may then be predicted under a wide range of time–temperature conditions used in rapid laboratory pyrolysis experiments, refinery processes, or geologic maturation.