Heavy End Evaluation in Oils and Associated Asphaltene Deposits from Two Adjacent Reservoirs by High-Resolution Mass Spectrometry

摘要

The formation of viscous oil and tar mats in oilfield reservoirs has substantial consequences in the production of oil. For example, aquifer sweep can be precluded in such an occurrence, impacting field development planning. Several processes can give rise to accumulations of heavy ends in reservoirs, namely, the asphaltenes and other high-molecular-weight polar compounds. Multiple, incompatible charge fluids can enter a reservoir, causing instability, migration, accumulation, and phase separation of heavy ends. Two adjacent reservoirs in Norway evidently exhibit different stages of tar formation from incompatible charge: in one reservoir, asphaltenes deposit as a result of an excess asphaltene concentration, and in the second reservoir, asphaltenes deposit from solution gas expulsion. Here, ultrahigh-resolution mass spectrometry is used to analyze heavy ends from both reservoirs in crude oils and rock core chips. The heavy ends or asphaltenes in crude oils and associated core deposits from each reservoir are analyzed and shown to be compositionally very similar. In addition, the two crude oils are examined by two-dimensional gas chromatography, confirming that the hydrocarbon liquid-phase components closely resemble one another. Importantly, there are only subtle chemical differences between heavy ends that underwent phase separation in the reservoir versus heavy ends that remained in the crude oil, a result that is consistent with heavy end chemical speciation and solvation characteristics. The combination of thermodynamic and compositional considerations proves to be very effective in elucidation of reservoir fluid geodynamic processes that have a significant impact on oil production.