Insights into catalytic effects of clay minerals on hydrocarbon composition of generated liquid products during oil cracking from laboratory pyrolysis experiments

Abstract

Experiments were conducted to distinguish oil cracking in reservoir rock versus source rock. Oil and source rock samples were heated in pressure vessels at 380 °C for 72 h, which resulted in oil cracking to gas and pyrobitumen with some residual liquid. The oil samples were heated with different minerals (fine-grained quartz, calcium carbonate, montmorillonite, kaolinite and illite) employing different ratios of the oil to the mineral in each case. Heating oil with quartz or calcium carbonate was used to simulate oil cracking in reservoirs, while heating oil with clay minerals was used to simulate oil cracking within source rocks. Based on the experiments, oil cracking in reservoirs versus source rocks can be differentiated by relative concentrations of the prominent C7 hydrocarbons: n-heptane, methylcyclohexane and methylbenzene (toluene) in the liquid products. The light hydrocarbon distribution in the final cracking products is affected by the “matrix effect” from clay minerals and the surrounding medium in reservoirs and source rocks during oil cracking. No relationship between the types of marine source rock or total organic content (TOC) and the distribution of light liquid hydrocarbons generated by catalysis on clay minerals at high temperature was observed. Future studies are needed to evaluate different types of source rock (e.g., terrigenous versus marine, clastic versus calcareous), and the relationship between light liquid hydrocarbon yield and the quantity of each clay mineral.