Master of Science in Petroleum Engineering (MSPE)
Surfactants have been considered for enhanced oil recovery by reduced oil-water interfacial tension. However, these surfactants may enhance oil recovery via wettability alteration as well. This study experimentally determines the influence of surfactant type and concentration on oil recovery, oil-water relative permeabilities and wettability in reservoir rocks. Several coreflood experiments were conducted using Yates reservoir fluids in Berea rocks and two types of surfactants (nonionic and anionic) in varying concentrations. A coreflood simulator was used to calculate oil-water relative permeabilities by history matching recovery and pressure drop measured during the corefloods. These relative permeability variations were interpreted using Craig's rules-of-thumb to characterize wettability alterations induced by the surfactants. The two main mechanisms behind the use of surfactants to enhance oil recovery are (1) reduction in interfacial tension and (2) alteration of wettability. To discern the relative contributions from these two mechanisms on enhanced oil recovery, two series of coreflood experiments have been conducted using a nonionic surfactant in varying concentrations. The first series used decane as the oil phase to quantify the effect of reduction in interfacial tension on oil recovery, while considering wettability effects in the decane-brine-Berea system to be negligible. The second series used Yates crude oil in place of decane to quantify the effects of reduction in interfacial tension as well as wettability alteration on enhanced oil recovery. The same two sets of experiments are then repeated with the anionic surfactant. The comparison of results of these four sets of experiments showed significantly higher oil recoveries for second series of experiments, indicating that the surfactants have altered wettability. The optimum surfactant concentration was found to be 3500 ppm. In three of the four cases studied, oil/water emulsions caused high pressure drops during the flooding experiments, strongly affecting the relative permeability curves. Craig's rules-of-thumb may not be applicable in systems containing emulsions. This study suggests that the development of a mixed-wettability state yields significantly higher oil recoveries observed in Yates crude oil systems. The significant contributions of this study are the quantification of the wettability altering capability of surfactants and the consequent enhancement of oil recovery.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Ayirala, Subhash C., "Surfactant-induced relative permeability modifications for oil recovery enhancement" (2002). LSU Master's Theses. 3629.
Dandina N. Rao