Improved Micellar/Polymer Flooding With High-pH Chemicals

Abstract

Summary A study was made of various pre flush solutions for use in micellar/polymer flooding. The oil recovery in laboratory core floods was improved most by the use of high-pH silicate solution as a preflush and by adding chelating agents such as sodium NTA or sodium EDTA to the micellar slug. Introduction. One of the techniques which has great promise for recovering large quantities of residual, oil is micellar/polymer flooding.1–3 In this type of process, surfactants (micellar solutions) and polymers are used to recover oil left behind by waterflooding and other secondary recovery methods. Laboratory and field tests of micellar/polymer flooding processes have been conducted in the U.S., with a number of projects currently in progress.4 During this period, the reservoir' variables that affect the efficiency of the process have been more clearly identified and studied. The principal variables, which are also the most detrimental to the oil recovery efficiency of the processes, are (1) reservoir rock heterogeneity, (2) reservoir brine salinity, (3) clays arid other minerals present in the reservoir rock, and (4) multivalent cations present on the reservoir rock surfaces. Further studies have continued on how these variables affect the processes and on techniques for modifying deleterious factors and improving process efficiency. A process which uses chemicals (surfact ants and polymers) which are not affected adversely by these variables may seem to be the ideal goal; however, recognition of all the complex variables involved in micellar processes and the costs of chemicals required for such a process leads to the conclusion that this goal may not be a practical one. Since the early field tests of micellar flooding, changing and conditioning the reservoir environment has been a continuing goal. Pre flushing cores in the laboratory and the reservoir rock in field test areas with fluids that would replace or change the existing water or brine were used m many projects.5–7 Reducing flow in permeable channels, replacing high-salinity brines with fresher water, and injecting sacrificially absorbed agents ahead of the micellar fluids were the objectives of the injection of various preflush solutions. None of the attempts were completely satisfactory. At the same time, other research efforts8,9 were directed toward addition of chemicals to the micellar slug which would increase the tolerance of the surfactants to reservoir brine and/or multivalent cations and improve phase relationships of the micellar slug with the reservoir fluids.