Release of aliphatic, aromatic and sulphur compounds from Kimmeridge kerogen by hydrous pyrolysis: A quantitative study

Abstract

The results discussed in this paper form part of a larger study aimed at obtaining qualitative and quantitative data on the types and amounts of aliphatic and aromatic hydrocarbons (including biological markers) and sulphur-containing heterocyclic compounds released when kerogens, asphaltenes and the polar fractions of extracted bitumens, and crude oils, are heated in the presence of excess water. Some of the results from the experiments in which Kimmeridge kerogen was heated in the presence of excess water, at times ranging from 7 h to 3 months and at temperatures ranging from 200 to 340°C are reported here. The maximum yield of pyrolysate was obtained in experiments conducted at 330°C for 72 h, and became increasingly aromatic as pyrolysis temperatures increased. Aliphatic hydrocarbon distributions became increasingly oil-like. Interestingly, unsaturated isoprenoid hydrocarbons were present but only in the low temperature reaction mixtures. Quantitative estimates of individual hydrocarbon types showed that with increasing temperatures the n-alkanes were approximately five to tenfold more abundant than the isoprenoid hydrocarbons by that the rate of release of the latter, in the lower temperature work, was greater than for the n-alkanes. The very small amoounts of C 21 + C 22 steranes released increased for all reaction temperatures and with increased heating times; unlike the C 27–C 29 steranes, and hopanes they did not pass through a maximum yield at lower pyrolysis temperatures. Approximately five times more alkylnaphthalenes than phenanthrenes plus anthracenes were released. The most abundant sulphur containing compounds in the pyrolysates were alkylbenzothiophnes and dibenzothiophenes, the former being tenfold more abundant than the latter and almost double the total amount of alkylnaphthalenes produced at high pyrolysis temperatures. Microscopy of all of the kerogen residues indicated that vitrinite-like material had been generated in the heated kerogens and this increased in rank with increased temperatures and times of heating.