Swellable polymer with anionic sites
The invention is directed to stable crosslinked water-soluble swellable polymers and methods for making same. More particularly, the invention relates to a composition comprising expandable polymeric particles having anionic sites and labile crosslinkers and stable crosslinkers, said particle mixed with a fluid and a cationic crosslinker that is capable of further crosslinking the particle on degradation of the labile crosslinker and exposure of the anionic sites so as to form a gel. A particularly important use is as an injection fluid in petroleum production, where the expandable polymeric particles are injected into target zone and when the heat and/or suitable pH of the target zone cause degradation of the labile crosslinker and the particle expands, the cationic crosslinker crosslinks the polymer to form a gel, thus diverting water to lower permeability regions and improving oil recovery.
1. A method of increasing the recovery of hydrocarbon fluids from a subterranean formation comprising injecting into the subterranean formation a composition comprising water, a cationic crosslinker, and a highly crosslinked expandable hydrophilic polymeric particle having anionic sites, wherein:
i) said polymeric particle has an unexpanded volume average particle size diameter of 0.05-10 microns and a crosslinker content of about 1,000-200,000 ppm of labile crosslinker and greater than 0 to about 300 ppm of stable crosslinker,
ii) said polymeric particle has a smaller diameter than the pore throats of the subterranean formation,
iii) said labile crosslinkers break under the conditions of temperature and suitable pH in the subterranean formation to allow the polymeric particle to expand, and
iv) said cationic crosslinker then reacts with said expanded polymer to form a gel.
2. The method of claim 1 , wherein the cationic crosslinker is a complexed polyvalent cation and is injected into the subterranean formation at the same time as the highly crosslinked expandable polymeric particle.
3. The method of claim 1 , wherein the cationic crosslinker is a polyvalent cation and is injected into the subterranean formation after expansion of the polymeric particle.
4. The method of claim 1 , wherein the cationic crosslinker is PEI and is combined with the highly crosslinked expandable hydrophilic polymeric particle prior to injection into the subterranean formation.
5. The method of claim 1 , wherein the cationic crosslinker is one of more of the following: PEI, Al 3+ , Fe 3+ , Cr 3+ , Sn 4+ , and Zr 4+ .