Crosslinked swellable polymer
The invention is directed to stable crosslinked water-soluble swellable polymers, methods for making same, and their various uses in the hygiene and medical arts, gel electrophoresis, packaging, agriculture, the cable industry, information technology, in the food industry, papermaking, use as flocculation aids, and the like. More particularly, the invention relates to a composition comprising expandable polymeric microparticles having labile crosslinkers and stable crosslinkers, said microparticle mixed with a fluid and an unreacted tertiary crosslinker that is capable of further crosslinking the microparticle on degradation of the labile crosslinker so as to form a stable gel. A particularly important use is as an injection fluid in petroleum production, where the expandable polymeric particles are injected into a well and when the heat and/or pH of the well cause degradation of the labile crosslinker and when the particle expands, the tertiary crosslinker crosslinks the polymer to form a stable gel, thus diverting water to lower permeability regions and improving oil recovery.
1. A method of increasing the recovery of hydrocarbon fluids in a subterranean formation comprising injecting into the subterranean formation a composition comprising water, an unreacted tertiary crosslinker, and a highly cross linked expandable hydrophilic polymer particle, wherein:
i) said polymer particle has an unexpanded volume average particle size diameter of 0.05-10 microns and a crosslinker content of about 9,000-200,000 ppm of labile crosslinker and about greater than 0 to 300 ppm of stable crosslinker,
ii) said polymer particle has a smaller diameter than the pores of the subterranean formation, and
iii) said labile crosslinkers break under the conditions of temperature and pH in the subterranean formation to allow the polymer particle to expand and said tertiary crosslinker then reacts with said polymer to form a stable gel.
2. The method of claim 1 , wherein the unreacted tertiary crosslinker is injected into the subterranean formation at the same time as the highly crosslinked expandable polymer particle.
3. The method of claim 1 , wherein the unreacted tertiary crosslinker is injected into the subterranean formation after expansion of the polymer particle.
4. The method of claim 1 , wherein the polymeric particle comprises a copolymer of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate, the stable crosslinker comprises methylene bisacrylamide, the labile crosslinker comprises a polyethylene glycol diacrylate, and the tertiary crosslinker comprises phenol and formaldehyde.