Summary
A study of the formation of gel aggregates in systems containing partially hydrolyzed polyacrylamide and aluminum citrate was completed. Under certain conditions, this system forms gel aggregates, commonly referred to as colloidal dispersion gels. Systems that formed aggregates on the exit screen of a screen viscometer also developed flow resistance when displaced through slimtubes and sandpacks.
A gel system containing 1000 ppm polymer and 33.3 ppm aluminum citrate was studied in 10 darcy sandpacks 2 ft and 4 ft long. In the 2-ft sandpack, the gelant showed no significant difference in the flow resistance when compared to polymer injection when 8.7 pore volumes were injected with at residence time 0.83 hours after mixing the gelant inline prior to injection. However, a high flow resistance developed after the sandpack was shut in for 31.4 hours. The development of the high flow resistance is consistent with viscosity measurements approximately 28 hours after mixing the gelant and transistion pressures measured using the screen viscometer.
In the 4-ft sandpack, gelant was injected at an interstitial velocity of 5 ft/D so that the residence time was 19.2 hours, well beyond the time where substantial gel structure was identified in screen viscometer tests. A high flow resistance developed slowly across the sandpack, beginning at the inlet section, demonstrating the formation and retention of gel aggregates in the sandpack. Our experimental data demonstrate that gel aggregates can be formed by reaction of partially hydrolyzed polyacrylamide with aluminum citrate and propagated through sandpacks. We estimate that in-depth treatment of a 10-darcy porous matrix at interstitial velocities of 5 ft/D using this gel system is limited to approximately 12 feet because retention of gel aggregates causes the permeability to decrease leading to reduction in flowrate.
The Thermal Gelation Behavior and Performance Evaluation of High Molecular Weight Nonionic Polyacrylamide and Polyethyleneimine Mixtures for Indepth Water Control in Mature Oilfields