Research on a temporary plugging agent based on polymer gel for reservoir acidification

A temporary plugging agent based on polymer gel was successfully prepared for temporary plugging in acidizing treatment. The gelation time, gel-breaking time, viscosity changes, temporary plugging capacity, and permeability recovery capacity were investigated. Increasing the polymer and cross-linker concentration reduced the gelation time of the polymer gel and temporary plugging agent, but caused difficulties in breaking the temporary plugging agent. Ammonium persulfate (APS) could be the driving force for the differences of gelation time between the polymer gel and temporary plugging agent. Additionally, increasing APS concentration made the temporary plugging agent break easily. Viscosity changes are the most important feature of a temporary plugging agent. According to the viscosity changes, the whole process can be divided into two major stages: the cross-linking reaction stage and the degradation reaction stage. The temporary plugging agent had a good plugging capacity which could effectively plug the high permeability zones. By temporary plugging, the pollution near wellbore was removed without damaging non-target zones. As a result, the permeability of the low permeability zones was greatly improved, and the permeability of the high permeability zones was effectively recovered.