Abstract

Aqueous solution properties of special concern in oil recovery processes are compared for several water-soluble polymers of the polysaccharide type. This article highlights gel-free dissolution requirements, viscosity dependence upon solution temperature, and solution filterability through sequentially decreasing pore diameters. A slurry-sequence mixing approach is described which minimizes the energy input necessary to achieve good dissolution of hydrophilic W-SPs without gel formation. The temperature dependence of solution viscosities is observed to be affected by W-SP concentration but not by solution salinity for most polysaccharides investigated. The results are polysaccharides investigated. The results are considered in terms of solution conformational differences. Formation penetration and impairment by W-SP solutions which have been sequentially filtered through decreasing pore diameters are discussed in terms of macromolecular steric blockage mechanisms arising from hydrodynamic volume and molecular aggregation phenomena.

Introduction

Water-soluble polymers (W-SPs) find application in almost every aspect of oil recovery. In primary recovery processes W-SPs are used in drilling (as clay modifiers in high solids muds, in foam drilling, as the primary viscosifying component in low solids muds, etc.), in completion and workover and in fracturing applications. In improved recovery techniques W-SPs find utility as flow diversion agents and in mobility control buffer solutions. The performance of polysaccharide type W-SPs in three areas related to these processes will be discussed:

  1. ease of dispersion and factors effecting premature gel formation in aqueous solutions,

  2. the dependence of solution viscosities upon temperature at different salinities and W-SP concentrations, and

  3. the filterability of variously thickened aqueous solutions, with consideration of the influence of hydrodynamic volume and aggregation of macromolecules on formation penetration and impairment.

EXPERIMENTAL

Polysaccharide aqueous solutions were prepared by the addition of a polymer slurry to a baffled mixing vessel with two impellers (Fig. 1). Glyoxal surface treated hydroxyethyl cellulose (HEC) slurries (8 parts water to 1 part polymer) were prepared in a low-energy mixing vessel (upper prepared in a low-energy mixing vessel (upper left-hand section of Fig. 1). The non-surface treated polysaccharides (e.g., in particular microbial product) were slurried in a high-energy intensive Waring blender prior to introduction into the baffled mixing vessel. The several suppliers of microbial Xanthomonas campestris polysaccharide (XCPS) are identified by letter; A - Abbott, C. CECA, G - General Mills, P - Pfizer, K - Kelco. The polysaccharide produced by the fungus belonging to polysaccharide produced by the fungus belonging to the genus Sclerotium (SRPS) is manufactured by CECA. Hydroxyethyl cellulose (HEC) is a product (CELLOSIZEK) of Union Carbide; the Guar gum derivatives (Jaguar HP-1 and HP-11) are manufactured by Stein Hall. The cellulose sulfate ester (Colloid Ho) was synthesized in the laboratories of Stauffer Chemical. Solution viscosities were determined with Brookfield, Fann, Rheometrics Mechanical Spectrometer (RMS) and Ferranti-Shirley viscometers. Low concentration solution data for determining the onset of macromolecular interactions as well as intrinsic viscosities were obtained with Cannon-Fenske capillary viscometers.

The low shear rate viscosity data dependence upon solution temperature were determined with the Brookfield viscometer in insulated baths, using Honeywell Dialatrol controller units (+ 0.1 deg. F). The viscosity data obtained at 150 deg. F over a wide shear rate spectrum with the RMS were approximate temperature (+ 5 deg. F) studies.

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