Nanogels for delayed gelation
The instant application relates to nanogels or compositions that hold multivalent metal ions until some level of nanogel degradation has occurred, then slowly release the multivalent metal ions for gelation with carboxylate containing polymers. Compositions comprising such nanogels, together with polymers that can be crosslinked with multivalent metal ions, allow the deployment of such mixtures in various applications, and greatly increased gelation times.
1. A degradable composition comprising a polymer having releasable carboxylate groups bound to a multivalent metal ion, said degradable composition lasting at least 5 days at 85° C. in a brine solution having 23 g/l NaCl, and thereafter degrading and releasing said multivalent metal ion, wherein said composition is in the form of a nanogel, wherein said polymer is polyvinyl alcohol succinate (PVAS) or polyaspartate (PAsp) and said multivalent metal ion comprises chromium or zirconium, wherein said composition comprises:
a) 135 mg PVAS-25 kDA and 1500 ppm Cr;
b) 101 mg PVAS-25 kDA and 1500 ppm Cr;
c) 68 mg PVAS-25 kDA and 1500 ppm Cr
d) 143 mg PVAS-6 kDA and 1500 ppm Cr
e) 794 mg PVAS-6 kDA and 3600 ppm Cr;
f) 368 mg PVAS-25 kDA and 3600 ppm Cr;
g) 328 ppm PVAS-6 kDA and 4463 ppm Zr; or
h) 921 ppm PAsp and 6837 ppm Cr.
2. The composition of claim 1 , wherein said nanogel has an average particle size of less than one micron.
3. The composition of claim 1 , wherein said nanogel has an average particle size of 200-600 nm.
4. The composition of claim 1 , wherein said nanogel has an average particle size of 400 nm.
5. The composition of claim 1 , comprising PVA succinate and chromium or zirconium.
6. The composition of claim 1 , comprising polyaspartate and chromium or zirconium.
7. A delayed gelling composition comprising the composition of claim 1 admixed with an injection fluid admixed with a carboxylate containing polymer.
8. An improved method of sweeping for oil or gas, said method requiring blocking thief zones with a polymer, and sweeping a reservoir for oil or gas, the improvement comprising injecting the composition of claim 7 into a reservoir, aging said composition until the viscosity increases, and sweeping the reservoir for oil or gas.
9. An improved method of producing oil or gas, said method requiring injecting a polymer into a reservoir and producing an oil or gas, the improvement comprising injecting the composition of claim 7 into a reservoir, aging said composition until the viscosity increases, and producing said oil or gas.