Artificial maturation of alginite and organic groundmass separated from torbanites

The two principal organic constituents-Botryococcus-related alginite and organic groundmass-were isolated by density separation from two torbanite samples (from the Stellarton Formation, Nova Scotia, Canada and the King Cannel, Utah, U.S.A.). The groundmass consisted of degraded algal, bacterial and terrestrial plant debris. Aliquots of alginite and groundmass were separately heated in gold tubes for 24 h with 70 MPa confining pressure, at fixed temperatures ranging between 250 and 375 degrees C. The 250, 300 and 325 degrees C experiments run on the alginite produced very low yields of CHCl3-extractable organic matter (EOM), indicating that very little of the generation potential had been tapped. The alginite reached the onset of generation at 350 degrees C and peaked at 375 degrees C. The groundmass exhibited a distinctly different response to heating. Its 300, 325 and 350 degrees C experiments showed a progressive increase in EOM yield with increasing temperature, producing more EOM than the corresponding alginite runs, in spite of the lower initial generation potential of the groundmass. However, EOM yields were lower at 375 degrees C, indicating that its peak generation had occurred at 350 degrees C. After heating, the CHCl3-extracted residues were analyzed by Rock-Eval and flash pyrolysis-GC-MS to determine the remaining petroleum potential and monitor the alterations in the macromolecular structure. In nature, petroleum generated from a torbanite would be a mixture of the liquids generated by each of its components, in a blend that would change as thermal alteration progressed, as the various constituents each reached their peak of generation. Such a multi-component model of torbanite composition can serve to improve predictions of oil generation from torbanites and related source rocks in sedimentary basins. Copyright (C) 1996 Elsevier Science Ltd