Development and Evaluation of Micellar Solutions To Improve Water Injectivity

Abstract

By removing residual oil and organic skins from the vicinity of a well, water injection rates can be increased. The micellar compositions described here are highly effective for this purpose and are applicable under widely divergent field mixing and reservoir conditions. Introduction To achieve favorable oil productivity during a waterflood project, water injection rates must be maintained at a high level. Acidizing and fracturing are established techniques for increasing water injectivity. These treatments should be avoided, however, where a created fracture or channel might result in the bypassing of oil. Injectivity may be increased in some wells by removing organic deposits and residual oil from around the wellbore. Potentially y effective treatments are solvent-alcohol injection and micellar solution injection. The micellar compositions found most effective in improving injectivity are of the type described in the earlier work of Jones. These solutions, when used with special injection techniques, have been found to be effective under diverse reservoir conditions. We shall emphasize here the laboratory and developmental aspects, including both micellar composition studies and core displacement tests. Other literature discusses the use of micellar solutions in producing wells and in injection wells. Laboratory Evaluation The micellar solutions are composed of a hydrocarbon solvent (usually kerosene), a sulfonate surfactant, a cosurfactant (usually an alcohol or a modified alcohol), and water, which normally contains added amounts of an electrolyte such as sodium chloride. The micellar solutions normally are transparent and single phase. Laboratory tests show that a small slug of a micellar solution driven by water can displace all of the oil from a rock matrix. The micellar solution performs as a true solvent, similar in mechanism to that proposed by Morse. The surfactant and cosurfactant act as coupling agents to create a single-phase solution from two otherwise immiscible fluids. This mechanism may be compared to adding a mutually soluble alcohol or other solvent to a mixture of water and oil to create a single-phase, homogeneous solution. The type and amount of ingredients must be carefully selected to formulate a stable micellar solution. The surface chemistry explaining the various physical phenomena exhibited by micellar solutions physical phenomena exhibited by micellar solutions is highly complex so we shall not discuss it here. Requirements for a Versatile Composition In order that one composition may be effectively applied in many different reservoirs, the micellar fluid should exhibit the following properties.The micellar slug driven by water should be able to miscibly displace crude oils from various types of reservoir rock.It is desirable that the micellar solution be able to dissolve organic deposits, such as paraffins and asphaltenes, and to disperse solids or emulsions.The micellar solution should remain as a single-phase, homogeneous fluid over the expected range of surface and reservoir temperatures.It should be possible to prepare solutions with the various fresh waters that may be available near the treatment site. JPT P. 614

Macro- and Microemulsions in Enhanced Oil Recovery

“…Moreover, it is interesting to note that these formulations, when equilibrated with oil, produce middle phase microemulsion with very low interfacial tension (< 10" 3 dynes/cm). Similar results were also obtained using ethoxylated alcohols in surfactant formulations by previous investigators (47). It is interesting that the ethoxylated sulfonate alone (curve F in Figure 10) is unable to produce ultralow interfacial tension.…”

Surfactant precipitation in aqueous solutions containing mixtures of anionic and nonionic surfactants

“…where IS] is the concentration of added electrolyte, and /3 is the fractional counterion binding on the micelles. Note that counterion comes from both added salt and the anionic surfactant upon dissolution (left hand side of Equation [4]); the counterion from these two contributions is assumed to be of the same type. The right hand side of Equation [4] accounts for the total counterion in solution as either unassociated species, or bound on micelles.…”

“…Note that counterion comes from both added salt and the anionic surfactant upon dissolution (left hand side of Equation [4]); the counterion from these two contributions is assumed to be of the same type. The right hand side of Equation [4] accounts for the total counterion in solution as either unassociated species, or bound on micelles. The fractional counterion binding is defined as the ratio of the number of counterions bound on the mixed micelle to the number of anionic surfactant molecules in that mixed micelle.…”

“…For example, builder can be eliminated from heavy-duty liquid laundry detergent formulations by using mixtures of anionic and nonionic surfactants (1-3}. In enhanced oil recovery, mixtures of anionic and nonionic surfactants have been proposed to give the surfactant slug a greater tolerance for both salinity and hardness (4,5).…”

Physico–chemical Environment of Petroleum Reservoirs in Relation to Oil Recovery Systems

“…Dauben and Froning (14) have shown that, depending upon salt concentration, phase separation can occur at 150°F with a solution that is stable at room temperature. Dauben and Froning (14) have shown that, depending upon salt concentration, phase separation can occur at 150°F with a solution that is stable at room temperature.…”