Method for fracturing a formation using a fracturing fluid mixture

1. A method for fracturing a formation in a reservoir using a fracturing fluid mixture comprising natural gas and a base fluid, the method comprising:

(a) determining certain reservoir conditions of the reservoir comprising the formation;

(b) selecting a desired phase behavior of the fracturing fluid mixture during a fracturing operation in the formation under the determined reservoir conditions,

(c) determining properties of the fracturing fluid mixture required to achieve the desired phase behavior, the determined properties including a composition of base fluid in the mixture and a mole fraction of natural gas in the mixture;

(d) preparing the fracturing fluid mixture having the determined properties; and

(e) injecting the fracturing fluid mixture into the reservoir under the determined reservoir conditions, such that the mixture exhibits the desired phase behavior during the fracturing operation.

2. The method as claimed in claim 1 wherein the reservoir conditions comprise: reservoir pressure, reservoir temperature, fracturing pressure, and recovery pressure.

3. The method as claimed in claim 2 wherein the determined properties of the fracturing fluid mixture further comprises injection pressure and injection temperature.

4. The method as claimed in claim 1 wherein the method further comprises determining a phase envelope of the fracturing fluid mixture having the selected mole fraction of natural gas in the mixture, and injecting the fracturing fluid mixture into the reservoir at a selected injection pressure and injection temperature such that the mixture comprises a liquid phase base fluid and a gaseous phase natural gas completely dissolved in the base fluid when the injected mixture enters the formation, and wherein at least some of the gaseous phase natural gas is not dissolved in the base fluid during recovery.

5. The method as claimed in claim 4 wherein the base fluid further comprises one or both of a proppant and a viscosifier.

6. The method as claimed in claim 4 wherein the mole fraction of natural gas in the mixture is between 4 mol % to 90 mol %.

7. The method as claimed in claim 4 wherein the injection pressure and injection temperature are selected so that the mixture is below the bubble point and above the dew point of the mixture when injected into the well.

8. The method as claimed in claim 4 wherein the injection pressure and injection temperature are selected so that the mixture is above the bubble and dew points of the mixture when injected into the well.

9. The method as claimed in claim 1 wherein the base fluid comprises a hydrocarbon well servicing fluid.

10. The method as claimed in claim 9 wherein the hydrocarbon well servicing fluid comprises one or both of alkane and aromatic based hydrocarbon liquids.

11. The method as claimed in claim 1 wherein the natural gas comprises methane or blends of methane with one or more gaseous hydrocarbons selected from the group consisting of ethane, propane, butane, and pentane, or blends of methane with one or more inert gases selected from the group consisting of carbon dioxide and nitrogen.

12. The method as claimed in claim 1 wherein the method further comprises determining a phase envelope of the fracturing fluid mixture having the selected mole fraction of natural gas in the mixture, and injecting the fracturing fluid mixture into the reservoir at a selected injection pressure and injection temperature such that the mixture comprises a liquid phase base fluid and a gaseous phase natural gas at least some of which is not dissolved in the base fluid when the injected mixture enters the formation and during recovery.

13. The method as claimed in claim 12 wherein the injection pressure and injection temperature are selected so that the mixture is below the bubble point and above the dew point of the mixture when injected into the well.

14. The method as claimed in claim 1 wherein the method further comprises determining a phase envelope of the fracturing fluid mixture having the selected mole fraction of natural gas in the mixture, and injecting the fracturing fluid mixture into the reservoir at a selected composition of base fluid in the mixture and mole fraction of natural gas in the mixture that the mixture comprises a gaseous phase natural gas and a liquid phase base fluid fully dissolved in the natural gas when the injected mixture enters the formation and during recovery.

15. The method as claimed in claim 14 wherein the mole fraction of natural gas in the mixture is between 80 mol % to 99 mol %.

16. The method as claimed in claim 14 wherein the composition of the base fluid in the mixture and the mole fraction of natural gas in the mixture are selected so that the mixture is above the critical temperature when the mixture is at reservoir conditions.

17. The method as claimed in claim 1 wherein the method further comprises determining a phase envelope of the fracturing fluid mixture having the selected mole fraction of natural gas in the mixture, and injecting the fracturing fluid mixture into the reservoir at a selected injection pressure and injection temperature such that the mixture comprises a liquid phase base fluid and a gaseous phase natural gas fully dissolved in the base fluid when the injected mixture enters the formation, equilibrates to reservoir conditions and until recovery.

18. The method as claimed in claim 17 further comprising after injection and before recovery, shutting in the well for a selected period of time.

19. A method for fracturing a formation in a reservoir using a fracturing fluid mixture comprising natural gas and a hydrocarbon-containing base fluid, the method comprising:

(a) determining certain reservoir conditions of the reservoir comprising the formation;

(b) selecting at least one desired behavior of the fracturing fluid mixture during a fracturing operation in the formation under the determined reservoir conditions, the desired behavior selected from the group consisting of phase behavior, interfacial tension, viscosity and dissolved natural gas content,

(c) determining properties of the fracturing fluid mixture required to achieve the selected at least one behavior, the determined properties including a composition of a hydrocarbon-containing base fluid in the mixture and a mole fraction of natural gas in the mixture;

(d) preparing the fracturing fluid mixture having the determined properties; and

(e) injecting the fracturing fluid mixture into the reservoir under the determined reservoir conditions, such that the mixture exhibits the desired behavior during the fracturing operation.

20. The method as claimed in claim 19 wherein the selected desired behavior is viscosity, and the method further comprises determining the required mole fraction of natural gas in the mixture for a desired viscosity of the mixture during the fracturing operation.

21. The method as claimed in claim 19 wherein the selected desired behavior is surface tension, and the method further comprises determining the required mole fraction of natural gas in the mixture for a desired surface tension of the mixture during the fracturing operation.

22. The method as claimed in claim 19 wherein the selected desired behavior is dissolved gas content, and the method further comprises determining the required mole fraction of natural gas in the mixture for a desired dissolved gas content of the mixture during the fracturing operation.