Green coal bed methane fracturing fluid compositions, methods of preparation and methods of use
Coal friendly, non-toxic, green fracturing compositions, methods of preparing fracturing compositions and methods of use in various fracturing applications are described. The compositions are characterized as non-toxic compositions enabling effective use of the fracturing compositions in coal bed methane (CBM) formations and particularly shallow CBM formations. The compositions include a liquid component (water-based component) and a gas component in proportions that can support a proppant under turbulent conditions and that promote the formation of a mist.
1. A method of fracturing a coal bed methane formation from a well comprising the steps of:
a. preparing a non-toxic and coal bed methane friendly liquid component at surface in a blender, the liquid component including:
i. a viscosified water component having a viscosity sufficient to temporarily support proppant admixed within the viscosified water component; and,
ii. a breaker for relaxing the viscosity of the viscosified water component within a pre-determined period;
b. testing the non-toxic and coal bed methane friendly liquid component to verify non-toxicity;
c. mixing the proppant into the liquid component in the blender;
d. introducing the proppant/liquid component into a high pressure pump and increasing the pressure to well pressure;
e. introducing a gas component into the high pressure pump and increasing the pressure to well pressure;
f. mix the gas component with the proppant/liquid component under high turbulence conditions; and
g. pumping the combined gas and fluid from step f) at a high rate down the well,
wherein the combined gas and fluid in step g) is characterized as a mist or slug at the formation.
2. A method as in claim 1 wherein the gas component is carbon dioxide or nitrogen or a mixture of carbon dioxide and nitrogen.
3. A method as in claim 1 wherein the combined gas and fluid in step f) is 3 -15 vol % liquid component and 85-97 vol % gas component exclusive of the proppant.
4. A method as in claim 1 wherein the pre-determined period is less than 30 minutes.
5. A method as in claim 1 wherein the pre-determined period is less than 10 minutes.
6. A method as in claim 1 wherein the initial viscosity of the viscosified water component is 15 -100 centipoise (cP) at 170 sec −1 (20 ° C) prior to mixing with proppant or gas component.
7. A method as in claim 1 wherein the mass of proppant mixed in step c) is 1.0 -5.0 times the mass of the liquid component.
8. A method as in claim 1 wherein the concentration of breaker within the liquid component is sufficient to relax the initial viscosity of the liquid component to less than 10 cp at 170 sec −1 (20 ° C) within 30 minutes.
9. A method as in claim 1 wherein the concentration of breaker within the liquid component is sufficient to relax the initial viscosity of the liquid component to less than 10 cp at 170 sec −1 (20 ° C) within 10 minutes.
10. A method as in claim 1 wherein the viscosified liquid component includes 0.1 to 2.0 wt % gelling agent.
11. A method as in claim 10 wherein the liquid component is prepared in step a) by mixing the gelling agent and liquid component in a hydration unit.
12. A method as in claim 10 wherein the gelling agent is hydroxyethyl cellulose (HEC) or a derivative thereof.
13. A method as in claim 10 wherein the gelling agent is PAC (poly anionic cellulose) or a derivative thereof.
14. A method as in claim 1 wherein the breaker is hemicellulase enzyme.
15. A method as in claim 1 further comprising the step of mixing less than 1 vol % buffer with the liquid component.
16. A method as in claim 15 wherein the buffer is an organic acid.
17. A method as in claim 16 wherein the organic acid is formic acid.
18. A method as in claim 1 further comprising the step of mixing less than 1 vol % clay control agent with the viscosified liquid component.
19. A method as in claim 1 wherein proppant is partially supported within the liquid component at surface by turbulence.
20. A method as in claim 1 wherein the process is continuous.
21. A method as in claim 1 wherein the well injection of high ratio proppant slurry is preceded by a 100% gas pad.
22. A method of preparing a non-toxic fracturing fluid composition and fracturing a coal bed methane formation from a well comprising the steps of:
a. preparing a non-toxic and coal bed methane friendly liquid test component at surface in a blender, the liquid component including:
i. a viscosified water component having a viscosity sufficient to temporarily support proppant admixed within the viscosified water component; and,
ii. a breaker for relaxing the viscosity of the viscosified water component within a pre-determined period;
b. subjecting the test component to toxicity testing to verify non-toxicity;
c. preparing a field-size liquid component based on the test component at surface in a field-size blender;
d. mixing the proppant into the liquid component in the field-size blender;
e. introducing the proppant/liquid component into a high pressure pump and increasing the pressure to well pressure;
f. introducing a gas component into the high pressure pump and increasing the pressure to well pressure
g. mix the gas component with the proppant/liquid component under high turbulence conditions; and
h. pumping the combined gas and fluid from step g) at a high rate down the well.