The existence of high permeability features such as fissures, fractures, and eroded out permeability zones, diminishes the sweep efficiency of any water, gas, or polymer flooding. This paper presents the laboratory evaluation of three water swellable materials that can be bullheaded into the well to shut off fractures. The water swellable materials would be mixed on the fly, entering fissures and fracture systems as they swell without invading the matrix of the rock. The rate of absorption can be controlled based on the particle size, carrier fluid, and formation fluid. This conformance technology is also applicable to address loss circulation problems in production and injection wells.
The following materials were evaluated: (a) a polyacrylamide polymer, (b) a chloroprene rubber, and (c) a nitrile rubber. The polyacrylamide polymer is capable of absorbing 30 to 400 times its own weight in water while the two rubbers swell approximately 5 to 10 times their original weight. The water swellable materials were evaluated for effectiveness to: (1) provide controllable swelling rates at different conditions, (2) shut off the flow of water in synthetic cores with simulated fractures at 135°F, and (3) provide long-term thermal stability in H2S and CO2 environments.
Discussed are: (1) the methodology used for measurement of swelling properties for each material at different conditions including carrier fluid, particle size, and temperature, and (2) core flow tests with simulated fractures. These materials are nontoxic and do not contain heavy metal crosslinkers. Based on this study, these materials present an innovative technology for fracture shutoff and to control loss circulation problems. In addition, these materials are resistant to acid contamination in CO2 and H2S environments.