BACKGROUND OF THE INVENTION
The present application is based on, and claims priority to the Applicants' U.S. Provisional Patent Application Ser. No. 60/273,594, entitled “System for Lifting Water from Gas Wells Using a Propellant,” filed on Mar. 5, 2001.
1. Field of the Invention
The present invention relates generally to the field of removing water from gas wells. More specifically, the present invention discloses a method for lifting water from a gas well using a propellant charge.
2. Statement of the Problem
Gas wells typically produce some water during the course of their operation. If the gas flow is not sufficient, not all of the water produced will be lifted out of the well. Eventually, the water remaining in the well may accumulate to the point that the pressure resulting from the water column exceeds the gas reservoir pressure and gas production will cease.
Presently, water that accumulates in the production tube of gas wells is removed using nitrogen. Liquid nitrogen is pumped down the well and when the nitrogen vaporizes, the water is lifted to the surface with the nitrogen gas bubbles. However, this approach is expensive and logistically awkward due to the requirements associated with transporting and handling liquid nitrogen.
3. Prior Art
A number of devices and processes have been invented in the past relating to use of propellants to fracture the strata surrounding a well and thereby stimulate oil/gas production. The prior art in this field includes the following:
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| ||Inventor ||Patent No. ||Issue Date |
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| ||Passamaneck ||5,295,545 ||Mar. 22, 1994 |
| ||McLaughlin et al. ||5,083,615 ||Jan. 28, 1992 |
| ||Smith et al. ||5,005,649 ||Apr. 9,1991 |
| ||Austin et al. ||4,974,675 ||Dec. 4, 1990 |
| ||Trost ||4,798,244 ||Jan. 17, 1989 |
| ||Challacombe et al. ||4,757,863 ||Jul. 19, 1988 |
| ||Uhri ||4,718,490 ||Jan. 12, 1988 |
| ||Mohaupt ||4,673,039 ||Jun. 16, 1987 |
| ||Jennings ||4,711,302 ||Dec. 8, 1987 |
| ||Hill et al. ||4,633,951 ||Jan. 6, 1987 |
| ||Hill et al. ||4,683,943 ||Aug. 4, 1987 |
| ||Stowe et al. ||4,548,252 ||Oct. 22, 1985 |
| ||Wolcott ||4,522,260 ||Jun. 11, 1985 |
| ||Wolcott ||4,446,918 ||May 8, 1984 |
| ||Ford et al. ||4,391,337 ||Jul. 5, 1983 |
| ||Hane et al. ||4,329,925 ||May 18, 1982 |
| ||Mohaupt ||4,064,935 ||Dec. 27, 1977 |
| ||Godfrey et al. ||4,039,030 ||Aug. 2, 1977 |
| ||Blauer et al. ||3,937,283 ||Feb. 10, 1976 |
| ||Mohaupt ||3,313,234 ||Apr. 11, 1967 |
| ||Graham et al. ||3,170,517 ||Feb. 23, 1965 |
| ||Marx ||3,136,361 ||Jun. 9, 1964 |
| ||Riordan ||3,101,115 ||Aug. 20, 1963 |
| ||Bourne ||3,064,733 ||Nov. 20, 1962 |
| ||Hanes ||3,002,559 ||Oct. 3, 1961 |
| ||Scott ||3,001,584 ||Sep. 26, 1961 |
| ||Rachford ||2,766,828 ||Oct. 16, 1956 |
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Passamaneck discloses a method for fracturing wells in which a propellant is ignited within the well to rapidly produce combustion gases to generate pressure exceeding the fracture extension pressure of the surrounding formation. Combustion gases are generated at a rate greater than can be absorbed into any single fracture, thereby causing propagation of multiple fractures into the surrounding formation. The propellant burns in a radially inward direction in a predictable manner. A computer program is used to model the burn rate of the propellant to predict the resulting generation of combustion gases and fracture propagation, and thereby determine a suitable quantity and configuration of the propellant.
U.S. Pat. No. 4,064,935 to Mohaupt discloses a system for stimulating oil well production in which a gas-generating chemical charge is ignited to produce a gas pressure-volume pulse of known pressure-time characteristics and duration.
Trost discloses a fracturing tool using a cylindrical canister housing a stack of propellant modules. The propellant provides a desired burn rate when ignited to produce radial fracturing of the surrounding rock formation. A pressure monitor can be used to measure and store pressure data over time to determine when the formation has been optimally fractured.
The patents to Hill et al. disclose a method and apparatus for fracturing in which the well casing is first filled with a fracturing fluid. A gas generating unit containing shaped charges for perforating the well casing, and a propellant is suspended in the fracturing liquid within the well casing. The fracturing fluid is pressurized from the surface to a predetermined threshold value. The gas generating unit then perforates the well casing and simultaneously ignites the propellant. The propellant forces the fracturing liquid through the perforations and fractures the surrounding formation.
Rachford discloses a system for fracturing in which the well casing is first perforated. A body of propellant is suspended in the fracturing liquid within the well casing and then ignited. The propellant forces the fracturing liquid through the perforations and fractures the surrounding formation.
U.S. Pat. No. 3,313,234 to Mohaupt discloses another system for hydraulic fracturing in which the fracturing liquid is driven by a non-detonating propellant.
U.S. Pat. No. 4,673,039 to Mohaupt discloses a technique for well completion in which the well casing has incipient perforations. Propellant charges are then used to fracture the surrounding formation.
Ford et al. discuss a fracturing apparatus using a high velocity jet to first perforate the well casing. A gas propellant charge carried by the apparatus is ignited to expand the perforation and fracture the surrounding formation.
Austin et al. discloses a method of fracturing horizontal wells. A perforating gun carrying explosive charges is used to perforate the well casing. Hydraulic fracturing is then applied.
The Wolcott patents use explosive charges to create rubblized zones connecting horizontal bore holes to increase permeability.
The Scott and Riordan patents discuss the use of propellant to generate a pulse-like pressure boost to supplement the available surface pump pressure in hydraulic fracturing. This is similar in a general sense to the method discussed in U.S. Pat. Nos. 4,633,951 and 4,683,943.
The Bourne patent is another method of hydraulic fracturing in which the well casing is first perforated with shaped explosive charges carried by a perforating gun.
Graham et al. discloses a method of hydraulic fracturing in which the fracturing liquid is driven by high pressure gas pumped from the surface.
Marx discloses a method for well fracturing using a pressurized aerated liquid.
Blauer et al. disclose a method for fracturing subterranean formations using a stable foam as the fracturing fluid.
Godfrey et al. disclose a system in which both a propellant and a high explosive charge are used for fracturing. The propellant is ignited first, followed by detonation of the high explosive. The propellant serves to maintain pressure caused by the high explosive over a longer period.
Hane et al. disclose an apparatus for fracturing using multiple explosive charges.
Hanes discloses an oil well bridging plug that is “set” by means of high-pressure gas generated by burning a propellant in a closed chamber.
McLaughlin et al. disclose a gas-generating chemical reaction using aluminum alkyls to create multiple fractures in a borehole.
Smith et al. disclose a system for creating multiple fractures in a subterranean formation using pressurized gas.
Austin et al. disclose a method for fracturing horizontal wells by perforating the casing and then introducing a fracturing fluid under pressure.
Challacombe et al. disclose a system for cleaning wells using an elongated tube of combustible material that is ignited at one end to generate a pressure wave.
Uhri disclose a process for sequentially fracturing a subterranean formation by combining controlled pulse fracturing with hydraulic fracturing in the same borehole.
Stowe et al. disclose a method for controlled pulse fracturing using a stabilized hydrogen peroxide solution.
Jennings discloses a method for removing void spaces in gravel packs using a high-energy impulse device.
4. Solution to the Problem
- SUMMARY OF THE INVENTION
None of the prior art references discussed above show use of a propellant charge to lift water from a gas well. The present invention provides a system for lifting water from a gas well that is cost-effective and can be modeled using computer software to accommodate the requirements of a particular well.
This invention provides a method and apparatus for lifting water from a gas well using a propellant charge. The propellant charge with a plunger above is lowered into the well to a depth below the water level in the well. The propellant charge is then ignited to rapidly generate combustion gases that push the plunger upward to lift water from the well.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.
The present invention can be more readily understood in conjunction with the accompanying drawings, in which:
FIG. 1 is a vertical cross-sectional view of the present apparatus in a well.
FIG. 2 is a side elevational view of the present apparatus corresponding to FIG. 1.
FIG. 3 is an exploded perspective view of the propellant charge 20, inhibitor coating 22, and propellant casings 24.
FIG. 4 is a detail cross-sectional view of a barometric firing device 40 and the igniter 30.
FIG. 5 is a detail cross-sectional view of the barometric firing device 40 and igniter 30 corresponding to FIG. 4 after the tensile stud 46 has broken to release the firing head 44.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 6 is a top view of the igniter 30 showing the scoring 36 on the top of the igniter 30.
Turning to FIG. 1, a vertical cross-sectional view is provided of the present apparatus in a well 70. FIG. 2 is a corresponding side elevational view of the present apparatus. The major components of the assembly are a plunger assembly 10, a propellant charge 20, and an igniter 30 to ignite the propellant charge 20.
The plunger assembly 10 is located at the upper end of the apparatus, as illustrated in FIGS. 1 and 2. Any of a wide variety of configurations could be employed. The embodiment shown in the drawings has upper and lower ribbed metal plungers 12 and 14 mounted on a mandrel extending upward from the upper end of the propellant assembly 20. A number of rubber packers or swab cups 16 can be included to provide a closer and more flexible fit against the interior surface of the well casing 70. The diameter of the elements of the plunger assembly 10 should be chosen to provide a loose fit with the inside diameter of the well casing 70 so that the plunger assembly 10 will effectively lift water from the well, as will be described below.
The propellant charge 20 can be any solid or liquid propellant capable of generating large quantities of combustion gases when ignited. Solid propellants are preferable due to their simplicity and ease of handling. In addition, many solid propellants remain relatively impervious to water at the high pressures commonly encountered at well depths. For example, Arcite 479 or Arcite 386M manufactured by Atlantic Research Corporation can be used as the propellant. In the preferred embodiment of the present invention, the ignition method chosen produces a relatively slow axial burn of the propellant 20 (i.e., a “cigarette” burn). For example, this can be accomplished by using an igniter 30 placed on the bottom of the propellant 20.
The cylindrical side wall of the propellant charge 20 is covered with an inhibitor coating 22 and tightly covered by a protective metal casing 24, as illustrated in FIG. 3, to prevent combustion along the side wall of the propellant 20. The casing 24 also helps to protect the propellant from damage in transit and while the apparatus is being lower into place in the well. In the preferred embodiment of the present invention, the propellant casing 24 is formed from two semi-circular halves that are clamped around the propellant charge 20 by semi-circular straps 25, as depicted in the exploded perspective view of FIG. 3. However, other casing configurations could be readily substituted or the casing 24 could be omitted.
The diameter of the propellant charge 20 is selected based on the inside diameter of the well casing 70. For example, if the production tubing has an inside diameter of 1.995 inches, a propellant can have an outside diameter of up to about 1.5 inches. Other combinations of production tubing inside diameters and propellant outside diameters could be used as appropriate. Propellant lengths of up to 30 feet can be handled using conventional well-head equipment.
After the apparatus has been lowered into the well 70, a firing device 40 triggers the igniter 30, which is used to ignite the propellant charge 20. The igniter 30 shown in the drawings is a closed housing containing an incendiary material 34, such as magnesium Teflon. When the igniter 30 is activated by the firing device 40, the incendiary material 34 ruptures the igniter housing and strikes the exposed end of the propellant charge 20, thereby igniting the propellant. The top of the igniter 30 can be scored 36, as shown in FIG. 6, so that segments of the top of the igniter will be folded outward in a predetermined pattern by the force of the incendiary material 34. This helps to ensure that incendiary material 34 will be spewed against the bottom end of the propellant 20. An internal structural support may be required within the igniter 30 to prevent the scorings 36 from breaking inward due to well pressure prior to activation of the firing device 40.
The igniter 30 can be suspended beneath the bottom of the propellant charge 20 by means of a perforated igniter holder 32, as shown in FIGS. 1, 4, and 5. The perforations in the igniter holder 32 allow combustion gases to escape as the propellant 20 burns.
Any of a variety of types of firing devices 40 can be used to trigger the igniter 30. For example, a timer can be used to trigger the igniter 30 at a predetermined time after the apparatus has been inserted into the well. This approach can be based on a calculation of the time required from the apparatus to drop from the well opening to a desired depth in the well.
The preferred embodiment of the present invention uses a barometric firing device 40, as shown in FIGS. 4 and 5, to trigger the igniter 30 at a predetermined depth. FIG. 4 is a detail cross-sectional view of the barometric firing device 40 prior to firing. The chamber containing the tensile stud 46 is subject to the surrounding well pressure, due to a series of openings extending through the firing device housing 42 of the firing device 40. However, in contrast, the upper chamber of the firing device housing 42 remains substantially at surface pressure due the seal between the firing head 44 and the interior surface of the firing device housing 42. This places a tensile stress on the tensile stud 46 that is directly proportional to the difference between surface pressure and well pressure. Thus, the tensile stud 46 can designed to fail at a predetermined depth in the well 70.
FIG. 5 is a detail cross-sectional view of the barometric firing device 40 and igniter 30 corresponding to FIG. 4 after the tensile stud 46 has broken to release the firing head 44. The pressure difference across the face of the firing head 44 causes it to quickly more upward and strike the primer in a rifle cartridge 48. The resulting detonation of the primer and powder in the cartridge 48 is released into the interior of the igniter 30 to ignite the incendiary material 34, which in turn, ignites the propellant charge 20, as previously described.
A perforated basket 50 is attached below the propellant charge 20 and encloses the igniter 30 and firing device 40. Here again, the perforations allow combustion gases to escape, but prevent large debris from accidentally being left in the well.
A computer simulation can be employed to model the combustion and water lifting processes. This allows each application to be optimized before a job is undertaken. For example, the appropriate amount of propellant for a specific job can be modeled using the assumption that a certain percentage of the potential chemical energy of the propellant will be converted into useful work in lifting water. If the propellant is Arcite 386M with a diameter of 1.5 inches, propellant lengths of 10, 20, and 30 feet have potential energy in the form of chemical bond energy of approximately 19.0, 38.0, and 57.0 million ft-lbs, respectively. The energy required to lift 1000 feet of water from a depth of 12,000 feet to the surface is 15.56 million ft-lbs, which is the most severe requirement. It can seen that if 10 feet of propellant is used it would take 81.9% of the potential chemical energy, if 20 feet is used 40.9%, and if 30 feet is used 27.3%. Undoubtedly, viscous dissipation and heat transfer effects will be present, which will prevent all of the potential chemical energy in the propellant from being available to lift water out of the well. However, from past work that has been done fracturing wells using propellants, it has been found that between 40% to 60% of the energy is available to do useful work. This can be used as a rough estimate for the purpose of determining the appropriate amount of propellant for a specific job.
In operation, the propellant charge 20 and plunger assembly 10 are lowered or dropped into the well to a predetermined depth below the water level in the well. In the embodiment shown in the drawings, the propellant charge 20 and plunger 10 are combined in a single assembly. However, the propellant charge 20 and plunger 10 could lowered into the well as separate units, with the plunger 10 being placed into the well above the propellant charge 20. The firing device 40 is triggered at a predetermined depth to ignite the igniter 30, which in turn, ignites the propellant charge 20. As the propellant charge 20 burns upward from its lower end, the resulting combustion gases push the plunger 10 upward to lift water from the well. This process can be repeated, if necessary, until the desired amount of water has been removed from the well 70.
Optionally, a bridge plug 60 can be placed in the well 70 below the propellant/plunger assembly. The propellant/plunger assembly is then lowered down the well to the bridge plug 60. As previously discussed, the igniter 30 is then lit by the firing device 40 and the gases produced by the burning propellant 20 push the plunger 10 upward to lift water up and out of the well. The bridge plug 60 serves as a backstop so that water will not be pushed back into the surrounding formation 80 by the increased pressured produced by the combustion gases.
The above disclosure sets forth a number of embodiments of the present invention. Other arrangements or embodiments, not precisely set forth, could be practiced under the teachings of the present invention and as set forth in the following claims.