pH Triggered Gels for Water Shutoff and Conformance Control
Mukul M. Sharma
As oil fields in the US mature, the volumes of produced water requiring disposal have increased significantly. With numerous older and mature oil fields, the growing problem of water production and stricter environmental regulation of water disposal are forcing oil producers to find ways to eliminate water coning and conformance control problems. Approximately 20 billion barrels of water are reinjected in the US every year. Any technology that minimizes the amount of water or gas produced in conjunction with the produced oil would have a significant impact on the energy consumption and on the cost oil production domestically.
There are many factors, such as the presence of thief zones or high permeability zones, fractures and water coning which lead to an increase in water production. In an attempt to block out the undesired water production and increase the volumetric sweep efficiency of on-going waterfloods, the industry has used crosslinked polymer gels. The process involves strategically injecting a gelling fluid into water coning well or into a high permeability watered out zone, restricting flow in that zone and redirecting water flow into the lower permeability unswept oil zones. Thus water shut off and conformance-control treatments can be used to generate relatively large volumes of incremental oil production with low costs and selectively, targeted small volume treatments, which extends the economic lives of marginal and mature wells.
However, several, significant problems have been encountered in the application of cross-linked gel systems: Difficulty in controlling gelation kinetics, placement of the gel deep into the formation, retention and adsorption of the cross-linking agents on the rock surface, long term stability of polymers, especially at high temperatures, environmental undesirability of using cross-linking agents such as chromium, and gelation is irreversible and misplacement of these agents into undesirable zones can be disastrous to the productivity of the well.
We propose the novel use of pH-triggered gels that can be placed deep into the water bearing parts of the reservoir. The proposed gel technology is cheaper, more environmentally friendly, easily reversible and readily cleans up. The proposed polymer gel does not involve any cross linking polymer for inducing gelation and hence has significant advantages over the polymer gels being used in the industry at present. The gelation is not kinetically controlled but rather depends on the pH of the polymer solution. An increase in pH leads to gel formation while a reduction in pH reverses the gel into a low viscosity polymer solution.
The overall objectives of the proposed research are to improve the effectiveness of gel treatments in production wells for water shut-off and conformance control for water floods, through the application of pH-triggered gels. The specific objectives of the proposed work are:
- To investigate changes in rheological properties of the polymer solution as a function of polymer properties and concentration, pH, salt/brine composition, temperature and lithology.
- To assess the effectiveness of the polymer solution as a blocking agent through core flow tests, and long sand pack tests.
- Develop models for designing polymer treatments for different lithologies and conditions.
- To collaborate with service companies to test the polymer solution in the field, in wells that have water production problems, for potential commercial applications.
This research is sponsored by the Department of Energy.
Mukul M. Sharma
Center for Petroleum and Geosystems Engineering
1 University Station C0304
The University of Texas at Austin
Austin, Texas 78712-0228
Phone: (512) 471-3257 FAX: (512) 471-9605
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