Permeability Modification Simulator Studies of Polymer-Gel-Treatment Initiation Time and Crossflow Effects on Waterflood Oil Recovery

Abstract

Summary A 3D, three-phase (oil/water/gas) permeability modification simulator was developed by incorporating an in-situ gelation model into a black-oil simulator(BOAST). Several important features that describe gel-system transport in aporous medium were considered. Simulation results showed that the effectiveness of a gel treatment in either an injection or production well or in an injection and a production well together production well or in an injection and a production well together decreased as kV/kH increased. The best gel treatment initiation time in the injection well only or the injection and production wells together was approximately when water breakthrough occurred. The new simulator is useful to simulate and to optimize any combination of primary production, waterflooding, polymer flooding, and permeability modificationtreatments. Introduction Permeability heterogeneity is the main factor that leads to low Permeability heterogeneity is the main factor that leads to low sweep efficiency in oil recovery from petroleum reservoirs. A mobility-control method based on use of various viscosifying agents, such as dilute polymer solutions, has been used to improve sweep efficiency. This method has been successful in many field tests;however, it may leave large areas unswept and may provide few benefits in reservoirs with a severe permeability contrast between horizontal strata. Someform of permeability modification is necessary to divert injected fluids from highly permeable zones to previously unswept zones in these reservoirs. Many laboratory and previously unswept zones in these reservoirs. Many laboratory and field studies have addressed this problem. Colloidal suspensions, precipitates, emulsions, acrylic/epoxy resins, and crosslinked precipitates, emulsions, acrylic/epoxy resins, and crosslinked polymers are some of the systems reported to have provided polymers are some of the systems reported to have provided significant fluid diversion away from thief zones. Crosslinked polymer systems involve injection of a polymer (polyacrylamide or biopolymer)and a crosslinking agent with or without a reducing agent or injection of alternate slugs of polymer and crosslinker to form suitable polymer gels to block off highly permeable zones. In either case, the injected gel system must have permeable zones. In either case, the injected gel system must have a low viscosity. Gels are formed either on the surface before injection or in situ(by controlled release of an ionic crosslinking agent or by buildup of crosslinked polymer layers). A simulator is useful to facilitate the treatment design and to assess potential fields for permeability modification treatments with crosslinked polymers. Such a simulator must be able to describe the chemical species transport and reaction kinetics of the gelation system instratified reservoirs. It must also be able to account for such phenomena asinaccessible PV (IPV) to macromolecules, adsorption of chemical species on rock surfaces, and retention of crosslinked gels on the rock matrix. Attempts to simulate profile modification using crosslinked polymers have recently appeared in the literature. 11–13 Calculations based on a simplified in-situ gelation model have also been made. 12.14 These simulators are all based on chemical flood simulators and are not applicable to reservoirs that contain gas. In this work, a 3D, three-phase permeability modification simulator was developed that incorporates these features into a BOAST simulator. The effects of selected parameters on oil recovery exceeding that from waterflooding were investigated with the new simulator.