The Colloidal Structure of Crude Oil and the Structure of Oil Reservoirs

Abstract

Large sand bodies in the subsurface are shown to provide a unique laboratory for understanding both reservoirs and crude oils. Here, we treat the discovery by downhole fluid analysis of a gravitational concentration gradient of asphaltenes, the most dense component of crude oil, in a 2500-ft column of crude oil in the reservoir. The continuous trend of crude oil properties across the field implies flow connectivity of this giant sand body, addressing the single largest uncertainty in the development of deepwater oil fields todaydrainage area that can be achieved by each one of the extremely expensive wells. Consequently, downhole fluid analysis provides a new way to identify flow connectivity and to achieve significantly improved efficiency in oil production in high-cost arenas. In addition, detailed downhole and laboratory analyses of the asphaltene gravitational gradient show that asphaltenes are dispersed in crude oils of this weight as nanoaggregates. This observation agrees with the recently reported asphaltene nanoaggregates in toluene by high-Q ultrasonics and by NMR diffusion measurements. Finally, this case study suggests that resins are predominantly not associated with these asphaltene nanoaggregates, implying that the 70-year-old asphaltene−resin micelle model is in error. This asphaltene−resin micelle model, which has virtually no supporting data, appears to be substantially misleading in treating asphaltene colloidal structure.