A New Approach to Permeability Reduction
Authors: Presley C.T. , Argabright P.A. , Smith R.E. , Phillips B.L. 
Published: December 2007

Introduction

There are many published schemes for reducing the permeability of reservoir rock. The method described here permeability of reservoir rock. The method described here involves plugging interpore connections with colloidal particles. The novelty of this method is the chemistry of particles. The novelty of this method is the chemistry of the process, which enables one to pump a homogeneous solution into the reservoir before the formation of colloidal particles. The chemical basis of this process revolves around the reactions of a new class of polyelectrolytes, polyisocyanurate salt (TmPI). When 2,4-tolylene polyisocyanurate salt (TmPI). When 2,4-tolylene diisocyanate reacts with alkali metal cyanates in dipoler, aprotic solvents and the final reaction mixture is treated with methanol, a polyisocyanurate salt, TmPI (T for tolylene based, M for methanol blocked, and PI for polyisocyanurate salt), forms. polyisocyanurate salt), forms. These polyisocyanurate salts are soluble in water or in basic solution. As the pH is lowered approaching the acid region, the anionic groups are protonated, and the resulting polyisocyanuric acid precipitates from solution. Neutral or slightly basic solutions are stable for long periods of time, giving solutions with essentially the periods of time, giving solutions with essentially the viscosity of water for moderate concentrations of TmPI (less than 20 percent w/w). The reaction of TmPI used in this work is the hydrolysis reaction occurring in strongly basic solutions. In basic solution, the isocyanurate salt group is subjected to nucleophilic attack by the hydroxide ion at a position para to the charged site. The end product of the hydrolysis reaction (TMPI-B) is a complex molecule containing both salt groups and bioret groups from the hydrolysis of the isocyanurate rings. The hydrolysis reaction ceases before completion, when the number of hydrophobic bioret groups per molecule has increased sufficiently to render the molecule insoluble. The reaction is irreversible. This polymeric precipitate, TmPI-B, forms a colloidal suspension polymeric precipitate, TmPI-B, forms a colloidal suspension defying filtration. This nonfilterability suggested using in-situ hydrolysis of TmPI as the basis for a partial plugging process. plugging process. The process begins with injection of a basic, aqueous solution of a polyisocyanurate salt into a porous medium. After injection, the solution is allowed to reside in the medium until the hydrolysis reaction ceases. At this point, the TmPI-B product has precipitated uniformly throughout the porous medium. Thus, this reaction gives the capability of porous medium. Thus, this reaction gives the capability of generating particles within the pores of the medium. Subsequent flow traps these particles within the interpore flow channels, causing reduction of permeability.

Experimental Evaluation

Plugging agents were evaluated with a series of Plugging agents were evaluated with a series of coreflooding experiments. A porous medium was saturated with water containing 1.8 percent by-weight sodium chloride. The flooding sequence was initiated by injecting brine water until steady-state flow permitted measurement of the initial permeability of the medium. Once satisfactory values were obtained, an aqueous solution of the plugging agent was injected. The volume of solution plugging agent was injected. The volume of solution injected at this point was sufficient to ensure complete saturation of the porous medium. When the desired amount of plugging solution was injected, flow was stopped.

JPT

P. 592