In-Situ Gel Calculations in Complex Reservoir Systems Using a New Chemical Flood Simulator

Abstract

Scott, T., SPE, U.K. Atomic Energy Authority, Winfrith Roberts, L.J., U.K. Atomic Energy Authority, Winfrith Sharp, S.R., U.K. Atomic Energy Authority, Winfrith Clifford, P.J., U.K. Atomic Energy Authority, Winfrith Sorbie, K.S., SPE, U.K. Atomic Energy Authority, Winfrith Summary. This paper presents results for a series of calculations on the deep emplacement of a polymer gel in a stratified reservoir model. These calculations were performed with a new chemical flooding simulator that has the facility to describe generalized chemical reactions between components. This code is described, and preliminary calculations on an in-situ gel treatment in a large model reservoir are presented. We find that to obtain significant amounts of incremental oil while avoiding very large pressure buildup, the polymer gel system must have the correct combination of long gelation times and good permeability-reducing properties in the high-permeability streak (residual resistance factor FR 10 to 40 in the cases studied here). No commercial polymer/crosslinker systems are currently available that have the very long gel times required to obtain deep emplacement in a large reservoir system. Introduction During recent years several chemical systems have been suggested for blocking off very-high-permeability channels in heterogeneous petroleum reservoirs. These systems involve the injection of petroleum reservoirs. These systems involve the injection of polymer [either polyacrylamide (PAM) or xanthan polymer] and polymer [either polyacrylamide (PAM) or xanthan polymer] and a crosslinking-ion or redox system to form a suitable gel. Reactants may be mixed just before injection into the reservoir, or they may be injected as alternating slugs of the two materials. To date, no calculations have appeared in the literature that attempt to quantify the flow patterns and oil recoveries expected when a polymer gel system is injected into a heterogeneous reservoir. In this paper, such calculations are presented, assuming a simple model of the gel kinetics and behavior in the porous medium. These calculations have been carried out with a new chemical flood simulator, Simulator for Chemical Oil Recovery and Polymer Injection (SCORPIO), developed at Winfrith. SCORPIO is a general-purpose, multiphase, multicomponent chemical-flood simulator that may be applied to polymer, surfactant, or caustic flooding on either the field or polymer, surfactant, or caustic flooding on either the field or laboratory scale. This paper includes a description of the simulator's underlying mathematical formulation, amplifying those features that deal with in-situ gelation. Results from in-situ gel calculations are discussed in some detail, particularly the effects of gel formation rate and pore blocking on oil recovery efficiency. Simulation Model SCORPIO is based on the method of finite differences and is designed to be flexible enough to handle a wide range of petroleum engineering problems. Up to 10 chemical components may be included. and these can be distributed among up to three liquid phases (aqueous, oleic, and micellar). Flow may be treated as either compressible or incompressible, making due allowance for rock compressibility. Two new features for a chemical flood simulator are included in SCORPIO:a generalized model of chemical reaction that defines the rates and stoichiometry for any series of coupled chemical reactions between components within a given phase anda heat-balance equation that allows calculation of temperature fronts and contours within a reservoir caused by injection of cool water into a hot reservoir. Heat flow across reservoir boundaries is treated with aquifer-type models. The calculated temperature may feed back onto such physical properties as fluid viscosity and reaction rates. Some calculations properties as fluid viscosity and reaction rates. Some calculations that use facilities of this type have been presented previously in a study of the effects of temperature on the chemical degradation of polymer in a stratified reservoir system. This module is used to describe the chemical reactions that take place in gel formations. In addition, modules are available to model the influence of coupled adsorption of components and the effects of frontal spreading through velocity dispersion and molecular diffusion. The code can accommodate several different rock types for relative permeability, adsorption, polymer residual resistance, and capillary pressure, in addition to allowing for regional variations in rock permeability. Injection and production wells can be operated under either pressure or rate constraints and may be completed in any number of layers of the reservoir. The compositional formulation used in SCORPIO is an extension of that introduced by Acs et al. and subsequently used by others in their code development work. This approach has been adapted to chemical flooding and has proved a good foundation on which to establish the framework of the simulator. Simulator Equations. In this section, the differential equations that govern fluid flow in the reservoir are presented, together with a statement of the physical significance of the various terms representing important phenomena. The corresponding difference equations and the solution strategy used to solve for the primary variables of the system are described later. SPERE P. 634

Experimental and Theoretical Investigation of Time-Setting Polymer Gels in Porous Media

“…The experimental and modeling study presented here is in support of previous work at this laboratory on field-scale simulations of in-situ gelation. 39 The main conclusions of the work presented here are as follows.…”

Gel Performance Simulations and Laboratory/Field Studies to Design Water Conformance Treatments in Eastern Venezuelan HPHT Reservoirs

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