Micellar Flooding The Propagation of the Polymer Mobility Buffer Bank

Abstract

Abstract This study shows the factors that affect the polymer mobility buffer bank, that is, slug size and polymer mobility buffer bank, that is, slug size and concentration. The slug size is a function of polymer/chase-water mixing, polymer inaccessible polymer/chase-water mixing, polymer inaccessible pore volume (IPV), and polymer retention. The pore volume (IPV), and polymer retention. The designed polymer concentration depends on polymer apparent viscosity and, to varying degrees, on shear degradation. The polymer/chase-water mixing-zone volume at a given mobility ratio is the same for glycerine (classical miscible fluid), biopolymer, and polyacrylamide. However, the propagation rate of the polyacrylamide. However, the propagation rate of the mining zone is much higher for polymer than for glycerine because of IPV. Therefore, a larger polymer bank is required to protect the micellar polymer bank is required to protect the micellar slug than would be indicated by mixing-zone volume alone. IPV increased as polymer concentration decreased over the investigated range. A micellar fluid ahead of the polymer bank increased IPV. When polyacrylamides are used in the mobility buffer bank, their concentration should be increased to compensate for the effect of shear degradation. For each field application, shear-degradation tests should be conducted in field cores using field brine and at anticipated sand-face velocities. The loss of polyacrylamide effectiveness because of shear degradation should be determined from apparent viscosity measurement of the sheared polymer, not from polymer concentration, Brookfield viscosity, or screen factor. Introduction In a micellar flood, water-soluble polymers are used as a mobility buffer to protect the micellar slug from invasion by high-mobility chase water. In addition, polymer may be added to the micellar fluid to adjust viscosity, to improve sweep in a waterflood, as a preflush in micellar flood to improve the sweep, to control water production in producers, and for selective partial plugging of high-permeability thief zones. Biopolymers (Xanthan gum) and polyacrylamides are two classes of polymers most commonly used in oil recovery processes. processes. When designing a polymer slug for field application, proper sizing and chemical concentration are critical variables. In a micellar flood, the polymer-mobility buffer-bank size depends on polymer inaccessible pore volume (IPV), mixing, polymer inaccessible pore volume (IPV), mixing, and polymer retention. Because the primary purpose of the polymer bank is to provide adequate mobility control, a sufficient polymer concentration must be selected. However, the concentration for polyacrylamides often must be increased to account polyacrylamides often must be increased to account for losses resulting from shear degradation. This study was undertakento determine the magnitude of and variables affecting polymer inaccessible pore volume (IPV),to characterize the effect of IPV on polymer/chase-water mixing behavior, andto examine polyacrylamide shear degradation. In these IPV and mixing studies, the biopolymer is Kelzan MF TM (Xanflood); and the polyacrylamide is Dow Pusher 500. In shear polyacrylamide is Dow Pusher 500. In shear degradation studies, the polyacrylamides are Dow Pusher 500, Pusher 700, and Amoco Chemicals Pusher 500, Pusher 700, and Amoco Chemicals Sweepaid 105 (an experimental polymer). POLYMER INACCESSIBLE PORE VOLUME POLYMER INACCESSIBLE PORE VOLUME Polymers propagate through porous media more rapidly than through their carrier water. The pore space volume available for polymer flow is pore space volume available for polymer flow is less than the volume available to water. The volume in which polymer cannot flow commonly is called polymer inaccessible pore volume (IPV). The polymer inaccessible pore volume (IPV). The exact mechanism of IPV is not clear. However, it has been estimated that the polymer molecule size is of the same order as pore sizes in rock. In many cases, the smaller rock pores are not capable of transporting polymer molecules, but can transport water. Another phenomenon possibly contributing to IPV is the inability of the polymer molecule center to get near the pore wall. As a result, the average velocity of the polymer molecules is greater than that of water molecules. SPEJ p. 5