Development and Application of Polymer Plugging Remover for Polymer Injection Well in Changqing Oilfield

Abstract

Water injection is a conventional method to maintain reservoirs pressure and improve production in low permeability oilfield. To decrease high water-cut and further enhance oil recovery, Polymers, such as polymer microsphere, preformed polymer gel, cross-linked polyacrylamide, are extensively used to control injection profile in Changqing oilfield. However, due to the low permeability and narrow pore throats of tight reservoirs, pressure in some water flooding wells increases rapidly after the polymer was injected, negatively affecting the energy supplement of the well cluster. A polymer plugging remover, composed of oxidizer, acid and chelating agent to relieve blockage, was developed with viscosity reduction and structure decomposition. The release period is more than 48 hours, which is conducive to deep-seated plugging removal. After treatment, the average diameter of polymer residue is 39-254nm and the dissolution rate is 15.76-53.42%. The permeability of the core sample plugged with polymer has increased significantly before and after treatment by polymer plugging remover, especially, it recovered by 28.67% for microsphere polymer. Five field tests have been completed successfully in the Jiyuan oilfield of Changqing. Before treatment, conventional acidification was performed in the pilot wells for two times at least, which is proved invalid. However, after polymer degraded by the plugging remover, the injection rate increased by 16.2m3/d, the pressure dropped by 3.4MPa and the validity period has exceeded 130 days on average. The polymer plugging remover provides an alternative way to increase injectability when dealing with high pressure and under-injection wells caused by polymer flooding.