The potential of bound biomarker profiles released via catalytic hydropyrolysis to reconstruct basin charging history for oils

Catalytic hydropyrolysis performed in a fixed bed reactor using high hydrogen gas pressures (>10 MPa) has the unique ability to release high yields of biomarker hydrocarbons from macromolecular organic fractions in petroleum source rocks and crude oils whilst minimising alteration to their isomeric distributions. One potential application of such bound biomarker profiles, which is the subject under investigation here, is to act as molecular tracers to aid the reconstruction of secondary migration pathways of oils in basins as well as reservoir filling histories. Our hypothesis is that bound biomarker compounds released from the adsorbed asphaltenes from core petroleum samples along a known migration pathway reveal the maturity and source characteristics of the first oil that came into contact with the carrier substrate. The primary investigation was performed on the Blake Field (Outer Moray Firth, UK North Sea, blocks 13/24 and 13/29), where the solvent-extractable biomarker hydrocarbon distributions exhibit no significant variations throughout the reservoir, offering little information as to reservoir filling events. Bound biomarker characterisation obtained by the hydropyrolysis of the adsorbed asphaltene fractions not only displayed lower overall maturities than the hydrocarbon biomarkers, but significantly exposed a discrete positive trend of maturity emanating from a location in the northwest part of the field which, if the original hypothesis is correct, possibly indicates the location where oil first entered the reservoir. Supplementary information obtained from laboratory experiments where two oils of subtly different composition (in terms of bound biomarker profiles) were consecutively passed through core substrates under anhydrous and hydrous conditions, and eluted with solvents of increasing polarity, revealed that the most strongly adsorbed asphaltenes exhibited bound biomarker distributions indicative of approximately 70 wt% of asphaltenes from the original oil retained on the core substrate, which is compatible with the hypothesis.