The evaluation of polymers performance as fluid diversion gelling agents in matrix acidizing

Abstract

This paper discusses the use of diversion mechanism in matrix acidizing to increase the flow resistance in highly permeable regions due to the presence of polymer temporary plugs. In this study, three polymers, namely hydroxyethyl cellulose (HEC), hydroxypropyl guar (HPG), and xanthan gum were evaluated in the laboratory to determine the best diverting agent to enhance the performance of matrix acidizing. An acidizing system was set-up using coreflooding techniques where Berea sandstone cores saturated with Sarapar were damaged by oil-based mud. Treatment fluids used were mud acid (3% HF – 12% HCl), HCl, polymer gels, and ethylene glycol monobutyl ether (EGMBE) as the mutual solvent. Polymer solutions were prepared at 40 lb/Mgal (4793 ppm) as per field formulation. The experimental results revealed that at low injection pressure, mud acid without diverting agents furnished the best performance where the improvement ratio achieved was 4.88 at 50 psi (344.7 kPa), compared with improvement ratio of 2.42 for HEC, 2.66 for HPG, and 1.35 for xanthan gum. However, at higher injection pressure, mud acid with diverting agents gave better results, where at injection pressure of 100 psi (689.5 kPa), mud acid with HEC diverting agent produced the best result with improvement ratio of 4.88 compared to 1.80 for mud acid without diverting agents. Generally, at low injection pressure, mud acid is found to stay longer in the core and has sufficient time to dissolve mud particles. Nevertheless, low injection pressure produces insufficient force to push acid deeper into the formation and fails to dissolve the viscous diverting agents completely. At high injection pressure, there is sufficient force for the acid to dissolve mud particles and viscous diverting agents, hence the diverting agents served its purpose by diverting the mud acid into low permeability zone.