Experimental study of swelling and rheological behavior of preformed particle gel used in water shutoff treatment

Production of water effluents in mature reservoirs subjected to water flooding face many difficulties that might, ultimately, lead to their abandonment. Gel shutoff treatment of such reservoirs using preformed particle gel (PPG) is a technique used to block fracture channels and to insulate highly permeable zones. The technique not only reduces water production but leads also to successful conformance control. The present study introduces a novel type of PPG with an extremely high swelling ratio. The PPG is made up of polyacrylamide and Aluminum nitrate nanohydrate, which acts like a superabsorbent to absorb water equivalent in weight to 1000-2000 times the dry weight of the gel. Tests were conducted in the present experiment to investigate the effects of polymer and crosslinker concentrations, temperature, salinity, and pH on the swelling of PPG. Results showed that increasing polymer and crosslinker concentrations as well as enhanced salinity led to declining PPG swelling ratio. While PPG swelling ratio was not considerable outside the pH range of 5-9, its rate within this range was relatively high. Moreover, PPG swelling ratio increased only slightly with increasing temperature by up to 100 degrees C, beyond which the 3D network structure of PPG collapsed. Rheological tests were performed to determine PPG strength in three samples selected based on least salt sensitivity factor values. In addition, the core flooding test was performed to evaluate the blocking efficiency and the performance of the three samples in reducing water production in sandpacks. The test results revealed that PPG reduced water effluents in the sandpack by 30%-65%.