Surfactant flooding of carbonate reservoirs is still a difficult proposition due to the harsh brine conditions and pore structure of carbonates. The first part of the work presented in this paper establishes the effect of the ionic composition, Then synthetic brines consisting of NaCl. CaCl2. NaHCO3, and Na2SO4 are employed, on the interfacial tension of pure hydrocarbon-water systems. Toluene, hexane and cyclohexane are the hydrocarbons studied over a range of temperatures. It has been found that the interfacial tension decreases with increasing temperature and increases with increasing ionic concentration.
In the second phase of the work some potentially useful surfactants have been screened for a range of conditions including ionic concentration, pH, temperature, and surfactant concentration. The primary criteria were the formation of stable phases, absence of emulsions or precipitates and development of low interfacial tension as measured by the spinning drop method. The surfactants were screened for low concentrations that would make them suitable for continuous waterfloods. The interfacial tension has been correlated with some of these variables. Results are analysed and the suitability of the surfactants for the proposed conditions discussed.
The use of surfactants in enhanced oil recovery has been studied extensively in the past and has been reviewed in several volumes [1,2]. The use of surfactants in carbonate formations has had limited application [3] due to fractures, low matrix permeability, dead pore volume, high hardness and salinity, heterogeneity and adsorption. The use of surfactants at low concentrations has also found limited application in carbonate reservoirs, although it seems to have been more extensively studied in sandstones [4,5] The majority of studies have been on microemulsion formulations that utilize relatively high concentrations' of surfactants in a slug of limited pore volume. Many previous studies of the IFT behaviour of surfactants have also concentrated on rather low concentrations of NaCl, with little or no divalent ion present, whereas our survey of Canadian carbonate reservoirs indicates that monovalent and divalent ion concentrations are both high and quite variable. These conclusions are substantiated by surveys of connate water compositions of Canadian and United States reservoirs [6,7]. As a first step in the investigation of surfactant enhanced waterflooding of carbonate reservoirs, the effect of various ions on the interfacial tension of toluene, cyclohexane or hexane and water was investigated. Toluene, cyclohexane and hexane and water were chosen as examples of aromatic, naphthenic, and paraffinic hydrocarbons. The concentration range selected was 0–15% wt/wt NaCl for hexane, cyclohexane. and toluene. Toluene was measured against 5% Na22SO4 to indicate the effect of varying the Anion. N-hexane was measured against individual 5% CaCl2, 5% Na2SO4, and is NaHCO3 concentrations compare different anions and cations.
The hydrocarbons used were Fisher Scientific Co. ACS grade toluene. cyclohexane, and n-hexane. Fisher ACS grade NaCl, CaCl22H2O, Na2SO4, and NaHCO3 were the sources of the ions used. Solutions were made up using distilled water.
