Don W. Green

Development of Correlations To Predict Biopolymer Mobility in Porous Media

This paper describes the flow and rheological behavior of biopolymer solutions in sandpacks over a wide range of permeability and frontal advance rates. Empirical correlations were developed to estimate polymer mobility in porous media. The correlations are based on porous medium properties, polymer concentration, and rheological parameters for the polymer derived from steady-shear measurements.

Dissolution of lonizable Drugs into Unbuffered Solution: A Comprehensive Model for Mass Transport and Reaction in the Rotating Disk Geometry

A model has been developed to describe the mass transport and reaction of ionizable compounds where mass transfer is caused by convection and diffusion from a rotating disk. Dissolution rates of benzoic acid, 2-naphthoic acid, and indomethacin in aqueous solutions of high ionic strength (I = 0.5 with potassium chloride) at 25°C were investigated. The model includes the effects of diffusion, convection, and simultaneous acid/base reaction at all points in the region adjacent to the dissolving solid. The solution of the transport equations is obtained numerically with an iterative algorithm which uses (a) closure of all material balances and (b) equilibria at the solid/liquid surface as constraints. The model solution yields both the flux of the dissolving acid and the concentration profile of each component. Reduced values of all reaction rate constants are used in the region adjacent to the dissolving surface to allow convergence of the computation. Although nonequilibrium concentration values are calculated, it is shown that the theoretical dissolution rate determined as the solution of the model is insensitive to the magnitude of the rate constants as their maximum useable values are approached. Comparisons of the model results with experimentally determined fluxes show close agreement and confirm that the transport mechanisms in the model formulation are consistent with the measured values. Further, the inclusion of convection allows accurate calculations without utilization of an arbitrary boundary layer thickness. Accurate dissolution rates can be determined using this technique under a wide range of conditions, except at low pH.

Mathematical Model of In-Situ Gelation of Polyacrylamide by a Redox Process

Recent displacement data conclusively show that the initial permeability reduction during in-situ gelation processes does not result from a bulk gelation of the injected fluid. This paper presents a filtration-based model that correctly accounts for all physical phenomena occurring during in-situ gelation displacements

The Effect of Flow Rate on the In-Situ Gelation of a Chrome/Redox/Polyacrylamide System

Presentation of experimental data on the gelation of a polyacrylamide/thiourea/Cr(4) gel system in unconsolidated sandpacks at flow rates typical of those encountered beyond the immediate vicinity of a wellbore

Permeability reduction mechanisms involved in in-situ gelation of a polyacrylamide/chromium (VI)/thiourea system

In this paper an investigation of the in-situ gelation of a polyacrylamide/chromium(VI)/thiourea system under flow conditions in unconsolidated sandpacks is presented. High flow resistance was observed in a localized section of the sandpacks that was consistent with deep-bed filtration mechanisms. A method to measure the size of aggregates in gel solution is also presented. Results from this method showed that the gel aggregates grow with reaction time and distance traveled through the sandpack, supporting the conclusion that filtration is a dominant factor in the in-situ gelation process under flow conditions.

Fluid-Rock Interactions Between Xanthan-Chromium(III) Gel Systems and Dolomite Core Material

Gelation of chromium(III)-xanthan systems in dolomite core material was investigated. Compositional changes in the gelant caused by interactions with the dolomite core material resulted in low permeability reductions for gelants prepared with chromium chloride, chromium acetate and a chromium diamine salt. The primary cause of incomplete gelation in the dolomite material was the increase in gelant pH that resulted in precipitation of chromium.

Permeability reduction by a xanthan/chromium(III) system in porous media

This paper presents an experimental study on gelation of a xanthan/chromium(III) system in unconsolidated sandpacks at frontal velocities between 3 and 120 ft/D. High flow resistance developed at specific locations in the sandpacks in experiment conducted at velocities up to 35 ft/D; the locations correlated with velocity. No significant flow resistance developed in the sandpacks at frontal velocities of 83 and 118 ft/D. The effects of flow and shear rates and permeability on development of high flow resistance in the sandpacks are discussed. A conceptual model of the gelation process that incorporates filtration of gel aggregation is presented.

A kinetic study of the reduction of chromium(VI) to chromium(III) by thiourea

Abstract The reduction of chromium(VI) to chromium(III) by thiourea is a key aspect of the chromium(VI)–thiourea–polyacrylamide gel polymer system used in oil recovery processes. A study was undertaken to develop a kinetic model for the reduction reaction. Reaction mixtures were prepared and chromium(VI) concentrations were determined from the mixturess visible absorbance. The reaction rate was found to depend on the concentrations of chromium(VI), thiourea, and polyacrylamide and on solution pH. A kinetic model for the reactions was developed using the experimental data and previously proposed reaction mechanisms. The model accurately predicts the reaction rate in solutions that do not contain polyacrylamide and predicts a rate that is approximately correct for solutions containing polyacrylamide.

Study of Intra-Molecular Crosslinking of Polyacrylamide in Cr(III)-Polyacrylamide Gelation by Size-Exclusion Chromatography, Low-Angle Laser Light Scattering, and Viscometry

The application of crosslinked-polymer systems for permeability modification of petroleum reservoirs has received increasing attention in recent years. A crosslinked-polymer treatment, in general, involves an injection of a polymer solution into high-permeability zones or fractures which have been previously swept by the displacing fluid1. The polymer solution reacts, either before or after injection, to form a three-dimensional gel network which reduces the effective permeability of the invaded portions of the reservoir. Fluid subsequently injected is diverted to other, tighter regions of the formation, thereby improving overall volumetric sweep efficiency.

Kinetics of the chromium(VI)/thiourea reaction in the presence of polyacrylamide

The formation of chromium(III)-polyacrylamide gels was followed kinetically using spectrophotometric methods. The rate of chromium(VI) species conversion by thiourea and bisulfite was monitored to find a kinetic model for the oxidation/reduction reaction. The third order model found here shows first-order dependence on chromium(VI) concentration on thiourea and on pH. Additional results of the thiourea study show that a constant amount of chromium(VI) is consumed at gelation regardless of the initial concentration of that species, indicating that the Cr(VI) reduction reaction may be the rate-determining step in gelation. No such model or constant conversion for the bisulfite-reduced reaction could be determined.