Well treatment fluids and methods
View Patent ↗A well treatment fluid includes an aqueous-based fluid, a crosslinked CMHEC polymer, and a crosslinker. The CMHEC polymer exhibits a DS of 0.2 to 0.6 and a MS of 2.0 to 2.5. The well treatment fluid exhibits a viscosity of at least about 100 cP. A well treatment method includes crosslinking a CMHEC polymer in an aqueous-based fluid at a pH of at least about 6. The crosslinking increases a viscosity of the well treatment fluid to at least about 100 cP. A well is treated with the well treatment fluid at a temperature of at least about 200° F. Another well treatment method includes forming a well treatment fluid from produced water that has a TDS content of at least about 150,000 ppm. The crosslinking increases a viscosity of the well treatment fluid to at least about 100 cP.
1. A well treatment method comprising:
forming a well treatment fluid by combining ingredients including an aqueous-based fluid, a carboxymethyl hydroxyethyl cellulose (CMHEC) polymer, and a crosslinker, the aqueous-based fluid containing produced water, the well treatment fluid having a total dissolved solids (TDS) content of at least 100,000 ppm, and the CMHEC polymer exhibiting a degree of substitution (DS) of 0.3 to 0.5 and a molar substitution (MS) of 2.0 to 2.5;
crosslinking the CMHEC polymer in the aqueous-based fluid at a pH of at least about 6 using the crosslinker, the crosslinking increasing viscosity of the well treatment fluid to a sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 ; and
treating a well with the well treatment fluid at a temperature of at least about 200° F. while the well treatment fluid exhibits the sustained viscosity, the well treatment fluid exhibiting a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 1 hour when at the temperature of at least about 200° F.
2. The method of claim 1 wherein the pH is from about 6 to less than 7.
3. The method of claim 2 wherein the well treatment fluid has a total dissolved solids (TDS) content of at least about 150,000 ppm.
4. The method of claim 1 wherein the well treatment fluid has a divalent cation content as CaCO 3 of at least about 10,000 ppm.
5. The method of claim 1 wherein the well treatment fluid exhibits a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 2 hours when at the temperature of at least about 200° F.
6. The method of claim 5 wherein the temperature is at least 250° F.
7. The method of claim 1 wherein the well treatment fluid further comprises Mg(OH) 2 .
8. The method of claim 1 wherein the pH is from greater than 7 to about 11.
9. The method of claim 1 further comprising combining MgO as an additional ingredient before the crosslinking and maintaining the pH of at least about 6 at least up to when the crosslinking occurs.
10. The method of claim 1 wherein the temperature is at least about 300° F.
11. The method of claim 1 wherein the well treatment fluid exhibits a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 2 hours when at a temperature of at least about 275° F.
12. The method of claim 1 wherein the well treatment fluid exhibits a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 1 hour when at a temperature of at least about 300° F.
13. A well treatment method comprising:
forming a well treatment fluid by combining ingredients including an aqueous-based fluid, a carboxymethyl hydroxyethyl cellulose (CMHEC) polymer, and a crosslinker, the aqueous-based fluid being formed from produced water, the well treatment fluid having a total dissolved solids (TDS) content of at least about 150,000 ppm, and the CMHEC polymer exhibiting a degree of substitution (DS) of 0.3 to 0.5 and a molar substitution (MS) of 2.0 to 2.5;
crosslinking the CMHEC polymer in the aqueous-based fluid using the crosslinker, the crosslinking increasing viscosity of the well treatment fluid to a sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 ; and
treating a well by fracturing a subterranean formation with the well treatment fluid at a temperature of at least about 200° F. while the well treatment fluid exhibits the sustained viscosity, the well treatment fluid exhibiting a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 1 hour when at the temperature of at least about 200° F.
14. The method of claim 13 wherein the well treatment fluid has a divalent cation content as CaCO 3 of at least about 25,000 ppm.
15. The method of claim 13 wherein the well treatment fluid has a divalent cation content as CaCO 3 of at least about 10,000 ppm.
16. The method of claim 13 wherein the well treatment fluid exhibits a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 2 hours when at the temperature of at least about 200° F.
17. The method of claim 16 wherein the temperature is at least 250° F.
18. The method of claim 13 wherein the well treatment fluid exhibits a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 2 hours when at a temperature of at least about 275° F.
19. The method of claim 13 wherein the well treatment fluid exhibits a property of stabilizing the sustained viscosity of greater than or equal to about 100 cP at a shear rate of 100 sec −1 for a time of at least about 1 hour when at a temperature of at least about 300° F.