Patent Application
20100051288
1. Field of the Invention
The invention relates generally to devices and methods for removing water from a subterranean wellbore.
2. Description of the Related Art
The presence of water is natural gas wells is a significant hindrance to the production of gas. Water naturally migrates into a wellbore along with the natural gas. In the beginning of production, the gas flow rate is high enough that it carries the water to surface. As the well matures, the flow rate begins to drop. Eventually, water collects in the wellbore to the point where the production rate becomes very low. In some cases, the weight of the water increases pressure within the wellbore and prevents gas in the surrounding formation from entering the wellbore.
In the past, gas lift valves have been used to help lift the water out of the well. In these instances, a gas (such as compressed air) is injected into the gas lift valve from the surface to try to lift the water out of the well. This approach is problematic in that it is expensive and requires large supplies of compressed gases to maintain an acceptable flow rate of production from the well.
Prior art approaches to the removal of water from a natural gas well are discussed in U.S. Pat. Nos. 5,211,242; 5,501,279 and 6,629,566.
The invention provides methods and devices for removing water from a low rate production wellbore using gas injection. In preferred embodiments, a dewatering device is provided that can be inserted concentrically within the production tubing string of a natural gas-producing wellbore. The dewatering device includes a pressure-isolating chamber that is provided with a fluid inlet valve and a fluid outlet valve. The inlet and outlet valves are operably interconnected with a controller that controls when they are opened and closed. In a currently preferred embodiment, the controller controls the valves in accordance with a predetermined time period. In other embodiments, the controller is associated with a liquid level sensor, such as a float valve, which determines the level of liquid within the chamber. When a predetermined level of liquid is detected within the chamber, the valves are actuated.
The fluid outlet valve is interconnected with a fluid outlet line which extends to the surface of the wellbore. One or more supply lines for gas and soap (surfactant) extend from gas and soap supplies located on the surface to the chamber. In a preferred embodiment, flow of compressed gas and soap from the surface is continuous. The injected soap and compressed gas react with the water within the well to create a foamy liquid, which entraps the water.
Gas lift valves are incorporated within the gas supply line. A first gas lift valve is disposed within the pressure isolation chamber. A second gas lift valve is located above the chamber.
In exemplary operation, the dewatering device is disposed into a gas wellbore on a tool string through a production tubing string. The dewatering device is lowered to the point wherein the isolation chamber is disposed within the water in the wellbore. The fluid inlet valve is in the open position to permit water to enter the chamber. Thereafter, both the fluid inlet and fluid outlet valves are closed to isolate the volume of water. Compressed gas (e.g., air) and soap are flowed into the chamber. The compressed gas and soap mix with the water and create a pressurized liquid foam mixture. The fluid outlet valve is then opened to permit the liquid foam mixture to exit the chamber and enter the fluid outlet line. In preferred embodiments, a gas lift valve which is located above the chamber and within the fluid outlet line assists the liquid foam mixture to the surface.
In practice, the amount of compressed gases required to effectively remove water from the gas well, is significantly less than with many prior art approaches which largely require a high degree of compressed gas flow to propel a slug of liquid to the surface of the wellbore.
The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein:
A dewatering device, generally indicated at 28, is disposed within the production tubing string 20 on a tool string 30. The tool string 30 preferably comprises a string of coiled tubing or the like, of a type known in the art. A water removal conduit 31 is defined within the tool string 30.
A compressed gas supply line 44 extends from a gas supply 46 at the surface 48 and into the chamber 34. The gas supply line 44 includes a first gas lift valve 50, which is located inside of the chamber 34 and a second gas lift valve 52, which is located above the chamber 34 and within the tool string 30. In addition, a soap supply line 54 extends from a soap supply 56 at the surface 48 downwardly through the production tubing string 24 and into the chamber 34 of the housing 32. The soap supply may be any of a number of commercially available surfactants, such as F.O.A.M. products, which are available commercially from the Baker Petrolite Division of Baker Hughes Incorporated of Houston, Tex. The type and formulation of soap that is used will depend upon the composition of production fluids found in the wellbore 10. During typical operation of the dewatering device 28, soap is continuously pumped down the soap supply line 54. In addition, compressed gas is continuously pumped down the gas supply line 44.
In exemplary operation, the dewatering device 28 is assembled with the tool string 20 and both are disposed into the production tubing string 20. The tool string 30 is lowered though the production tubing string 20 until the housing 32 of the dewatering device is disposed in the water 26, as depicted in
The controller 58 then closes the fluid inlet valve 40, so that the dewatering device 28 is in the configuration shown in
In the next step of operation the fluid outlet valve 42 is opened by the controller 58, as shown in
The operation can then be repeated to flow additional water-bearing mixture toward the surface 48. The controller 58 will return the dewatering device to the configuration depicted in
In the instance where flapper valves are used for the inlet and outlet valves 40,42, there would be no need for the controller 58 to control their operation. In that case, operation of the flapper valves would occur as a result of differential pressures caused by operation of the gas lift valves 50, 52.
In practice, the devices and method of the present invention provide a significant cost savings. The use of compressed gas in conjunction with soap to form a foamy mixture which entraps the water requires less compressed gas to move the water to the surface than merely using compressed gas by itself.
In an alternative embodiment, depicted in
The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.
