Master of Science (MS)
The improvement or increase of oil recoverable from discovered reservoirs has always been a very important issue as this helps to meet ever growing energy demand. Several methods have been put forward as means of achieving this objective. Chemical flooding, using surfactants has been considered in enhanced oil recovery processes. Surfactants are used primarily to lower oil-water interfacial tension (IFT) and thus improve production. However, surfactants possess the ability to alter rock wettability and hence increase oil production. Previous investigations were performed at ambient conditions using stocktank oil. Extrapolation of the findings from the ambient conditions testing to reservoir conditions may be erroneous. Thus, reservoir condition investigations have been carried out using Yates live crude oils and Yates synthetic brine. Several coreflood experiments have been conducted at live reservoir conditions using two types of surfactants (anionic and nonionic) in varying concentrations. A core flood simulator based on JBN technique has been used to calculate oil-water relative permeabilities by history matching recovery and pressure drop measured during the corefloods. The simulated relative permeabilities have been used to infer wettability alteration based on Craig’s rule of thumb to characterize wettability. The contact angle measurements, from previous investigations conducted at LSU, have been used to compare wettability alterations inferred from relative permeabilities. Furthermore, this study includes imbibition experiments as another means to infer wettability alterations by surfactants. Initial wettability has been established for the Yates field using the Amott’s wettability index and changes in the wettability indices with varying surfactant concentration have also been measured. These changes have been interpreted to infer wettability alteration. The use of nonionic ethoxy alcohol surfactant at different concentrations with Yates live crude oil in corefloods experiments showed significantly higher oil recoveries indicating that the surfactant has altered wettability. The optimum surfactant concentration has been established at 1500 ppm. Other experiments conducted using the anionic ethoxy sulphate surfactant have not shown a favorable wettability alteration as Yates core was altered from weakly water-wet to weakly oil wet consequently lowering oil recoveries. Analysis of the experimental results in terms of capillary number for the live oil floods at reservoir conditions demonstrated the significance of including measured water-advancing contact angle in definition of the capillary number. The ambient imbibition tests and reservoir condition coreflow experiments conducted in this study have provided an insight into effect of surfactants on wettability alteration at both ambient and reservoir conditions using stocktank oil and live reservoir fluids and the improvement in oil recoveries as a result of wettability alteration.
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Abe, Ayodeji Adebola, "Relative permeability and wettability implications of dilute surfactants at reservoir conditions" (2005). LSU Master's Theses. 2660.