Abstract
Lab test of polymer-based in-situ gelled acids reveal that polymer and other additives separate out of the acid when these acids are prepared in high salinity water. In coreflood tests, in-situ gelled acid formed a gel inside 20". long core samples, and the acid changed its direction several times. Unexpectantly, the core's permeability was reduced at low shear rate. Wormhole length increased as the shear rate was increased, while the diameter of wormhole increased as the acid cumulative injected volume was increased. CT scan indicated the presence of gel residue inside the and around the worm hole. Gel residue increased at low shear rates. Material balance on the cross-linker indicated that a significant amount of the crosslinker was retained in the core.
Based on the results obtained from this study the in-situ gelled acids should be used only at low HCl concentrations (5 wt% HCl). Acid should be prepared in low salinity water. Acid injection rate should be determined based on the expected shear rate in the formation. A core flood experiment is recommended to confirm optimum injected rate. Flow back the well to minimize the residual gel inside the formation. The data obtained in our study can be used as a guideline for injection rate selection.
