Experimental study and modeling of interactions between H₂S and hydrocarbons. Formation of sulfur compounds and kinetic effects in reservoirs

H₂S can be a dominant gas in carbonate petroleum reservoirs. However, researches on the influence of H₂S on the oil stability are limited in literature. In this thesis, interactions between hydrocarbons (oils, model compounds) and H₂S were studied by confined pyrolysis in gold cells from 310 to 350 deg. C under 700 bar. Results of pyrolysis of oil (free of sulfur) in presence of H₂S lead to highlight a new pathway of formation of organic sulfur compounds in oils. Pyrolysis of binary mixtures n-octane/H₂S and alkylbenzene/H₂S allowed to propose different radical reactions for the generation of main sulfur products, namely, thiophene, thiols, thiolanes, alkyl-thiophenes in the first case; thiol-aromatics, alkyl-benzothiophenes in the second. Results obtained in the mixture n-octane/H₂S led to construct and validate a detailed mechanistic model. The mechanism shows that pyrolysis of n-octane/H₂S occurs in long chain and H₂S has an inhibition effect on the consumption of n-octane at temperatures above of 320 deg. C, but accelerate the reaction rate strongly at low temperatures. Extrapolation of the kinetic model to geological temperatures and pressures (150-200 deg. C, 700 bar) shows that H₂S can significantly influence the composition and stability of hydrocarbons. It is also proposed to apply the model to study the reactivity of H₂S under conditions of enhanced recovery (steam injection, pyrolysis) or of geological storage in depleted petroleum reservoirs. (author)