DME Fracing

Abstract

Herein is described a frac fluid comprising of di-methyl ether (DME) or a mixture of DME and propane to be used in hydraulic fracturing of underground formations.

Claims

1. A method for hydraulic fracturing as a well stimulation technique where a frac fluid comprising d-methyl ether (DME) is pumped into a well to create fractures in the formation. The method comprising the steps of: a. Supplying a stream of frac fluid comprising of DME from a pressurized frac fluid source into a well b. Pumping frac fluid in the well to create fractures in the formation c. Supplying proppant into the stream of frac fluid from the frac fluid source d. Pumping the proppant containing frac fluid stream into the well e. Releasing pressure from the well to allow frac fluid to vaporize and return to surface f. Collecting the frac fluid g. Separating DME from the frac fluid to be recycled for step a

2. The method in claim 1, wherein the frac fluid comprises a mixture of DME and propane.

3. The method in claim 1 or 2, wherein additives such as gelling agents, acids, gel breakers, friction reducers, chemicals for iron controls, scale inhibitors, and/or surfactants are added to the frac fluid.

4. The method in 1, 2, or 3, wherein inert gas such as carbon dioxide, nitrogen and/or flue gases are added to the frac fluid.

5. The method in claim 2, 3, or 4, wherein the volume ratio of DME to propane is 10:90 to 90:10 measured at 22° C. and 1 MPa.

6. The method in claim 5, wherein the volume ratio of DME to propane is 20:80 to 70:30 measured at 22° C. and 1 MPa.

7. The method in claim 5, wherein the volume ratio of DME to propane is 22.5:77.5 to 50:50 measured at 22° C. and 1 MPa.

8. The method in any of the preceding claims, wherein DME is manufactured from the produced on-site natural gas.

9. The method in claim 8, wherein manufactured DME is used in diesel engines to power the equipment used in fracking or production.

10. (canceled)

Description

BRIEF DESCRIPTON OF THE DRAWINGS

[0012] FIG. 1 is a drawing of an example well to help illustrate the DME fracturing process.

[0013] FIG. 2 is a graph illustrating the improved rates and cumulative production in natural gas production by using a dimethyl ether-based fracing fluid over propane-based and water-based fracing fluid in a gas field.

[0014] FIG. 3 is a schematic process flow diagram of how produced natural gas from DME fracking can be used to manufacture more DME to be used in fracking and in diesel engines to power fracking operations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Di-methy ether (DME) has a chemical formula CH.sub.3OCH.sub.3 and can be manufactured from a variety of sources, including natural gas, coal, waste from pulp and paper mills, forest products, agricultural by-products and municipal waste.

[0016] Unlike alkanes such as propane, DME when injected into a formation will increase oil and gas saturation. This will mobilize the oil and gas by reducing the relative permeability of water in the formation and increasing the relative permeability of the oil and gas. The oil in the formation will have its viscosity reduced as its components will be dissolved and diluted by DME. This will increase production rates.

[0017] One embodiment of the invention is shown in FIG. 1. FIG. 1 shows a formation penetrated by a well. A pressurized frac fluid source 10 is used to supply a stream of frac fluid comprising DME into the well 20. A frac pressure pump 30 pressurizes the frac fluid in the well to create fractures in the formation. Proppant from pressure vessel 40 is then mixed into the stream of frac fluid and pumped into the well. The proppant's role is to keep the fractures open after the pressure is released. The pressure on the well is then released to allow the frac fluid to vaporize and return to the surface. Collection at the surface may be preformed to recover the DME to be used in future fracking operations.

[0018] FIG. 2 shows the expected increase in production of a DME-based frac over that of propane-based frac, water-based frac and no frac.

[0019] Canadian Patent no 2718273 demonstrates that a mixture of DME and propane is more effective than propane in bitumen recovery. Therefore a mixture of DME and propane can be used instead.

[0020] To improve the performance of the fracture, additives are commonly added to frac fluid and may also be added to DME frac fluid. These can include, but are not limited, to gelling agents to increase viscosity, acids to further open fractures, gel breakers to decrease viscosity after fracturing is completed and aid in flowback, friction reducers, chemicals for iron controls, scale inhibitors, and/or surfactants.

[0021] Inert gases such as carbon dioxide and nitrogen and flue gases can be added to DME frac fluid. These gases will gasify into the formation and won't impede production. It also has the added benefit of reducing emissions into the air.

[0022] DME can also be produced directly from synthesis gas produced by the gasification of coal or biomass or through natural gas reforming. DME used in the frac fluid can be generated using these methods at a price competitive to that of liquefied petroleum gas (LPG) and condensate. Unlike other hydrocarbons, which may have to be pipelined/transported to the field, DME may be much more convenient and cheaper to use as it can be created on-site from various sources including produced natural gas.

[0023] As an integrated process, DME-based fracking can use the produced natural gas to manufacture more DME to be used in other fracking operations and/or to run diesel engines to provide power for fracking equipment. DME has a high cetane number and therefore works well in diesel engines.

[0024] One embodiment of this integrated process is shown in FIG. 3. Produced natural gas is converted to synthesis gas with oxygen and by-product carbon dioxide in an auto-thermal reformer (ATR).

2CH.sub.4+O.sub.2+CO.sub.2.fwdarw.3CO+3H.sub.2+H.sub.2O   (ATR)

[0025] The synthesis gas is compressed and fed to a DME slurry reactor. The effluent from the reactor is DME, by-product carbon dioxide, small amounts of methanol and unreacted synthesis gas.

3CO+3H.sub.2.fwdarw.CH.sub.3OCH.sub.3 (DME)+CO.sub.2   (DME slurry reactor)

[0026] DME and other by-products are chilled and separated as liquid from the unreacted synthesis gas. The unreacted synthesis gas is recycled to the reactor. Carbon dioxide is recycled to the ATR and converted to the synthesis gas. Methanol is also recycled to the DME reactor to be converted to DME. The overall process of converting the natural gas to DME at a DME plant can be summed as:

2CH.sub.4+O.sub.2.fwdarw.CH.sub.3OCH.sub.3 (DME)+H.sub.2O   (DME plant)

[0027] DME plants can be small or large and still be economic.