The Expulsinator versus conventional pyrolysis: The differences of oil/gas generation and expulsion simulation under near-natural conditions

Abstract

Abstract The Expulsinator provides a new technique to simulate generation and expulsion of hydrocarbons under near-natural conditions. This is realized by application of lithostatic pressure onto an intact source rock disc with undisturbed mineral matrix and kerogen network and by hydrous pyrolysis, conducted in open flow-through mode. Conventional pyrolysis methodologies serve well in generation kinetics assessment but are only of limited use for investigation of primary migration and expulsion due to destructive sample preparation, inappropriate pressure regimes and pyrolysis in closed mode and/or in the absence of water. However, comparison of results generated with conventional pyrolysis with Expulsinator experiments is important to assess the performance of the generation and expulsion simulation carried out with the Expulsinator. Thus, the generation and expulsion behaviour of this new methodology has been compared with established pyrolysis methodologies, like HyPy and closed small vessel pyrolysis (CSVP) and has been assessed by Rock Eval pyrolysis. Expulsinator experiments released higher amounts of bitumen than CSVP. This has been attributed to increased cross-linking reactions of bitumen in case of the classic pyrolysis, favouring formation of pyrobitumen. Differences in yields and composition of n-alkanes were controlled not by generation (kinetics) exclusively but also by expulsion effects, in particular delayed expulsion caused by geochromatography. Expulsinator conversion rates of TOC exceeded 81%, whereas those of hydrous CSVP remained at 65%. Higher Expulsinator TOC conversion was accompanied by lower gas generation compared to CSVP. This is attributed to the open setup of the expulsion experiment, which by rapid removal of products generated prevents their secondary alteration, particularly polymerization to pyrobitumen and oil to gas cracking at higher temperatures. HyPy of Expulsinator pyrolysis residues verified a low generation potential remaining after the expulsion experiment. The Expulsinator-device delivers oil and gas generation data, which can be applied in numerical modelling exercises.