Rheology and Transport in Porous Media of New Water-Shutoff/ Conformance-Control Microgels

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 93254, “Rheology and Transport in Porous Media of New Water-Shutoff/Conformance-Control Microgels,” by D. Rousseau, SPE, G. Chauveteau, M. Renard, R. Tabary, and A. Zaitoun, SPE, Institut Français du Pétrole; P. Mallo and O. Braun, Seppic; and A. Omari, Bordeaux U., prepared for the 2005 SPE International Symposium on Oilfield Chemistry, Houston, 2–4 February. The performance of new microgels specifically designed for water shutoff and conformance control was investigated extensively at laboratory scale. These microgels are preformed, stable, fully water soluble, size controlled with a narrow size distribution, and nontoxic. They reduce water permeability by forming adsorbed layers sufficiently soft to be easily collapsed by oil/water capillary pressure, so that oil permeability is not affected significantly. Because the manufacturing process of these new microgels makes it possible to vary chemical composition, size, and crosslink density, they can be designed to meet the requirements of a given field application. Introduction In a global context of growing energy needs, extending the life of hydrocarbon reservoirs will be a real challenge for decades to come. Reducing water production significantly and improving oil-recovery efficiency are important goals for the oil industry. Thus, the development of more-reliable techniques that use “green” products for water shutoff, conformance, and mobility control is of crucial interest. Injection of a gelling system composed of a polymer and a crosslinker has been used widely to reduce water production. In this process, the gel is formed in situ. Because gelling properties depend on gelling time and final gel strength, gel penetration depth is quite difficult to predict. This difficulty results from uncertainties concerning shear stresses both in surface facilities and in the near-wellbore area and concerning the physicochemical environment around the well. Moreover, both polymer and/or crosslinker adsorption in the near-wellbore region and dilution by dispersion during placement can affect treatment effectiveness. In 1999, a completely new concept was introduced that consisted of injecting fully water-soluble, nontoxic, soft, stable, and size-controlled microgels into the reservoir. A first type of microgel, using an environmentally friendly zirconium crosslinker, was studied extensively in past years. More recently, a second type of microgel that is covalently crosslinked was introduced. These microgels, now available at industrial scale, have been shown to have very attractive properties for both water-shutoff and conformance-control operations. Experimental Materials. The new microgels presented in this study are colloidal particles of acrylamide-based polymeric gels with neutral organic covalent crosslinkers. Such compounds are 100% nontoxic. Properties of these microgels depend on their manufacturing conditions, polymer-chain chemistry, and crosslink density. This study focuses mainly on three microgel samples with different crosslink densities referred to as high, medium, and low. The high-crosslink-density sample is the same as the one studied in in an earlier study. To show the differences between microgels and linear polymers, experiments also were performed with a high-molecular-weight linear polymer with a chemical com-position very similar to that of the microgels.