Development and Use of a Simulation Model for Mobility/Conformance Control Using a pH-Sensitive Polymer

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractInjection of a pH-sensitive polymer has been proposed recently as a novel deep-penetrating mobility control method, and the development of a simulation capability for its scale-up is reported here. An aqueous dispersion of polymer microgel, whose swelling property shows a strong dependence on pH, preferentially flows into high-permeability zones under acidic conditions. Since the injected fluid viscosity is low, small injection pressures are needed to inject the polymer. Geochemical reactions increase the pH, causing the polymercontaining fluid to experience a viscosity increase of several orders of magnitude thereby altering the flow pattern of subsequently injected fluid. Because the viscosity of microgel dispersions can be controlled with adjustment of pH, this process can be employed both as a deep-penetrating mobility control method (with moderate polymer viscosity) and as a conformance control method (with immobile gel generation).Polymer-bank placement design and process scale-up requires simulation of transport of microgel, acid-mineral geochemical reactions, pH changes, and the coupling between aqueous phase composition and viscosity. Such a capability has been implemented in a commercial reservoir simulator and preliminary simulations verify the operation and effectiveness of the complex new features, which can describe both the mobility and conformance control applications. Determination of reservoir mineralogy and mineral reaction rates is critical to modeling in-situ pH changes accurately. History matching of coreflood acid injection experiments was used to estimate geochemical reactions and reaction rates occurring in Berea cores. Linear and radial geometry floods in 2-layer reservoir models were carried out as preliminary scaleup simulations. Acidic fluids can be propagated farther into a reservoir in a low-pH state, using high injection velocity, an acid preflush, or weak acids. The Damkohler number was found to be a useful dimensionless quantity for characterizing acid floods with pH-sensitive polymer. Slugs of pH-sensitive polymer improve oil recovery better than continuous polymer flooding or waterflooding.The simulator was successfully used to history match coreflood experiments, to model techniques to propagate low-pH fluids deep into reservoir, and to demonstrate the effectiveness of pH-sensitive polymer slug treatments for conformance control. 1. Benson, I., "Numerical Simulation of pH-Sensitive Polymer Injection as a Conformance Control Method", M.S.

Optimizing the strength and size of preformed particle gels for better conformance control treatment

“…A pH sensitive polymer microgel uses the change in pH as an activation trigger. With increases in pH, the gel begins to adsorb water, swelling up to 1000 times its initial volume [1,12,4]. The primary differences between all of the current commercially preformed gels are the particle sizes, swelling ratios, and swelling times.…”

A critical review on use of polymer microgels for conformance control purposes

“…Choi et al's (2006) experiments and simulation matching attempts provide additional insight on geochemical characterization as well as the transport of pH-Sensitive Polymer Microgels through porous media. Benson et al (2007) coupled the microgel rheology, geochemistry, and transport through porous media, in the development and implementation of pH-Sensitive Polymer simulation capabilities in GEM-GHG (a 3D compositional reservoir simulator). Benson et al (2007) also proceeded to use the developed simulation capabilities to model simplified conformance control treatments, and found that pH-Sensitive Polymer Microgel slug treatments demonstrated positive vertical conformance improvement capabilities (above and beyond conventional polymer floods).…”

“…Benson et al (2007) coupled the microgel rheology, geochemistry, and transport through porous media, in the development and implementation of pH-Sensitive Polymer simulation capabilities in GEM-GHG (a 3D compositional reservoir simulator). Benson et al (2007) also proceeded to use the developed simulation capabilities to model simplified conformance control treatments, and found that pH-Sensitive Polymer Microgel slug treatments demonstrated positive vertical conformance improvement capabilities (above and beyond conventional polymer floods). Lalehrokh et al (2008) investigates the possible use of pHSensitive Polymer Microgels to improve sweep in fractured rocks by plugging fractures.…”

A Review of Polymer Conformance Treatment: A Successful Guideline for Water Control in Mature Fields

“…This effect makes microgel swell, serving as an effective permeability blocker (Choi et al, 2006). Furthermore, this process can be employed both as a deep-penetrating mobility control method (with moderate polymer viscosity) and as a conformance control method (with immobile gel penetration) due to their controlling of pH (Benson et al, 2007). Since the injected fluid viscosity is low, a small injection pressure is needed to inject the polymer.…”