Evaluation of reservoir wettability and its effect on oil recovery. Annual report, February 1, 1996--January 31, 1997

We report on the first year of the project, {open_quotes}Evaluation of Reservoir Wettability and its Effect on Oil Recovery.{close_quotes} The objectives of this five-year project are: (1) to achieve improved understanding of the surface and interfacial properties of crude oils and their interactions with mineral surfaces, (2) to apply the results of surface studies to improve predictions of oil production from laboratory measurements, and (3) to use the results of this research to recommend ways to improve oil recovery by waterflooding. During the first year of this project we have focused on understanding the interactions between crude oils and mineral surfaces that establish wetting in porous media. Mixed-wetting can occur in oil reservoirs as a consequence of the initial fluid distribution. Water existing as thick films on flat surfaces and as wedges in comers can prevent contact of oil and mineral. Water-wet pathways are thus preserved. Depending on the balance of surface forces-which depend on oil, solid, and brine compositions-thick water films can be either stable or unstable. Water film stability has important implications for subsequent alteration of wetting in a reservoir. On surfaces exposed to oil, the components that are likely to adsorb and alter wetting can divided into two main groups: those containing polar heteroatoms, especially organic acids and bases; and the asphaltenes, large molecules that aggregate in solution and precipitate upon addition of n-pentane and similar agents. In order to understand how crude oils interact with mineral surfaces, we must first gather information about both these classes of compounds in a crude oil. Test procedures used to assess the extent of wetting alteration include adhesion and adsorption on smooth surfaces and spontaneous imbibition into porous media. Part 1 of this project is devoted to determining the mechanisms by which crude oils alter wetting