Rheological Screening of Low-Molecular-Weight Polyacrylamide/Chromium(III) Acetate Water Shutoff Gels

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractLow-molecular-weight polyacrylamides crosslinked with chromium(III) acetate are widely used in the oilfield industry to seal off watered out zones in matricial reservoirs. These products are usually mixed in surface facilities, then pumped downhole through coiled tubing and injected into the formation over a depth of several feet. For the operators, gelation time and gel consistency after well shut-in are the two most important parameters to control. The pumping time cannot exceed the gelation time and the maximum pressure drawdown sustainable by the gel is related to gel consistency (as measured, for instance, by the yield stress). Both are known to depend on temperature, polymer concentration and structure (molecular weight, hydrolysis degree), and crosslinker concentration.A systematic screening of these parameters has been undertaken by means of rheological measurements using a cone-and-plate rheometer. The procedure for determining gelation time consisted in monitoring the viscosity of the polymer and crosslinker solutions mixed at time t=0 and then submitted to shearing at a constant rate. The gelation time, which corresponds to a sudden rise in the viscosity, was observed to be independent of the applied shear rate but to strongly vary with temperature and, to a lesser extent, with polymer hydrolysis degree, concentration and molecular weight and crosslinker concentration. From the set of data obtained, simple correlations or rules of thumb for the gelation time variations are given, which can be used to optimize the formulation for a given field application.To evaluate gel consistency, some yield stress measurements were performed after a resting (shut-in) time of about 10 hours. The yield stress is related to the maximum drawdown sustainable by the gel in a formation through a simple relationship.

Rheological evaluation of a sodium silicate gel system for water management in mature, naturally-fractured oilfields

“…However, when the deformation exceeds the tolerance, the structure is destroyed and the material flows (Wang and Seright, 2006). For a gel with yield stress, τ y , under stationary (steady state) condition, Bird et al (1983), and later Broseta et al (2000) and Liu and Seright (2001), used a simple force balance to calculate the minimum pressure gradient, dP/dl, required for gel to extrude through two smooth parallel plates separated by distance w. From this minimum pressure gradient, the maximum differential pressure the formed gel can withstand is given by…”

Assessment of Pilot Water Shut Off in High Water Production Wells: Case Study in Sudan

“…Several methods were presented in the literature to determine the gel polymer properties including the bottle testing method, sealed tube method, dynamic shear method and static shear method (viscometer). [8][9][10] After suitable choice for the field appliance by injected solution can move up and down the outside well bore, to help also in fix poorly cemented high permeable sands. Cleaning in the well bore need to be done and preferable by jetting water or acid.…”

Aperture-Tolerant, Chemical-Based Methods to Reduce Channeling

“…Earlier researchers [74][75][76][77][78][79][80][81][82][83] employed rheology measurements to characterize gels and gelants that are used for water shutoff. They used dynamic viscometry measurements to monitor the gelation process and study gel properties after gelation.…”

“…When measuring rheology properties using a smooth-surface geometry, wall-slip effects could exist and diminish the measured yield stress. [81][82][83][84] Therefore, wall-slip effects must be identified and eliminated to ensure that the measured results are properties of the gels and not artifacts produced by the method of investigation.…”