APPLICATION OF BENZOCARBAZOLE MOLECULAR MIGRATION MARKERS IN RECONSTRUCTING RESERVOIR FILLING AT THE SOLVEIG FIELD, NORWEGIAN NORTH SEA

Abstract

Benzocarbazole (BC) migration tracers were used to investigate the complex filling of reservoir segments at the Solveig field in the Norwegian North Sea. The study suggests that the benzocarbazole ratio [a]/([a]+[c]) of crude oils and extracts decreases with inferred increasing migration distance. The complex filling history of the Solveig field is evident from the observation of variable degrees of palaeo biodegradation associated with two palaeo oil-water contacts in residual oil zones below non- to moderately biodegraded live oil columns. Live oil properties also vary significantly across the field. Benzocarbazole ratios (BCRs) obtained from oils and reservoir core extracts appear not to be affected by biodegradation and indicate a migration and filling trend from NW to SE. The BCR values were set by the initial phase of filling and do not show any overprint effects as a result of later and more mature oil charges.

BCRs from both oils and extracts of reservoir cores, particularly those composed of clean sands, helped to reconstruct migration processes in the Solveig field. Migration is construed to have first filled reservoir segment D in the NW of the field and to have continued further east towards segment C, and then via segment B and finally into segment A. Migration then continued along the southern margin of the Haugaland High to a well location to the east of the Solveig field. A fractionation effect for benzocarbazoles derived from oils versus those from extracts was noted and was attributed to differential partitioning behavior. Nevertheless, spatial trends for oil- and extract-derived BCRs were congruent. This allowed the generation of spatially more highly-resolved benzocarbazole datasets for migration assessment by combining data from both samples types (oil and reservoir extracts) if partitioning is accounted for.