Patent Application
20090079199
Not applicable.
Not applicable.
1. Field of the Invention
The invention relates generally to the field of reciprocating (walking beam) type wellbore fluid pumps. More specifically, the invention relates to electric generators and sensing systems usable therewith that are operated by such pumps.
2. Background Art
Wellbore fluid pumps include reciprocating (“walking beam” or “sucker rod”) pumps. Such pumps are operated by a prime mover, such as an electric motor or natural gas powered engine disposed at the Earth's surface. The prime mover operates a crankshaft coupled to a reciprocating beam. The beam is coupled to an assembly of pumping rods (“rod string”) extended into a wellbore drilled into the Earth's subsurface. A reciprocating pump is coupled to the lower end of the rod string and is anchored at a selected depth in the wellbore. As the walking beam reciprocates, it moves the rod string up and down, causing the movable elements of the pump in the wellbore to move correspondingly. Motion of the pump lifts fluid in the wellbore through a production tubing string to the Earth's surface. Examples of such pumps are described in U.S. Pat. No. 4,681,515 issued to Allen, U.S. Pat. No. 4,788,873 issued to Laney and U.S. Pat. No. 5,204,595 issued to Opal et al.
An issue of concern to operators of such wellbore pumps is if the rate at which the pump lifts fluid to the surface exceeds the flow capacity of the Earth formations outside the wellbore. In such cases, the pump may be operated without sufficient fluid to keep it fully submerged (called “pump off”). Pump of can cause extensive damage to the pump, requiring its removal from the wellbore for repair or replacement. Wellbore pump operators therefore go to considerable effort to operate reciprocating pumps to avoid pump off.
It is known in the art to provide sensing devices in a wellbore and to communicate signals from such sensors to the Earth's surface without hard wired connection. One such system is described in U.S. Pat. No. 6,899,178 issued to Tubel. A system disclosed in the Tubel '178 patent includes a sensor disposed near the lower end of a tubing string, and a wireless transmitter, such as an acoustic transmitter, in signal communication with the sensor. Signals representative of the sensor measurements are transmitted along the tubing string at selected times and are detected and decoded at the Earth's surface for concurrent or later use. The system disclosed in the Tubel '178 patent requires a source of electric power. Typically batteries are used for such electric power. Of course, batteries have a limited lifetime, and require that the system is periodically removed from the wellbore for battery replacement. Such removal requires removal of both the rod string and the tubing, making such battery replacement operation difficult and expensive.
It is desirable to have a source of electric power in a wellbore such that a system such as described in the Tubel '178 patent may be used with a reciprocating pump to monitor fluid level in a wellbore and to maintain battery life so that frequent replacement of batteries is not required.
An electrical system for use with a sucker rod pump according to one aspect of the invention includes an electric generator configured to be operated by motion of a sucker rod string. The rod string is configured to transfer motive power to the sucker rod pump disposed in a wellbore. The generator is disposed in the wellbore. The system includes at least one electrically powered device electrically coupled to the generator and disposed in the wellbore.
A method for operating an electrical device in a wellbore according to another aspect of the invention includes moving a sucker rod string along the interior of the wellbore to operate a sucker rod pump. Motion of the rod string is coupled to an electric generator disposed in the wellbore. Electrical power from the generator is used to at least partially power the electrical device in the wellbore.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
A reciprocating (“walking beam” or “sucker rod”) pump system including a sensing system and one example of an electric power generator is shown schematically in
The wellbore 28 typically includes a pipe or casing 30 disposed to the bottom of the wellbore 28 and retained therein by cement. The casing 30 typically includes perforations 32 at selected depths corresponding to the depth outside the casing 30 of a productive formation 34 such as may contain oil and/or gas therein. Fluid enters the casing 30 through the perforations 32. A production tubing 36 extends from a well head 48 at the Earth's surface to a selected depth in the wellbore 28. A reciprocating pump 38 is connected to the lower end of the tubing 36. The pump 38 is operated by the rod string 26.
In the example shown in
Referring to
The coils 52 are electrically connected to circuitry 60 forming part of the data telemetry system 42. Such circuits 60 may include (none of which is shown separately) power conditioners to convert the current induced in the coils 52 to direct current and energy storage devices such as a Farad size capacitors or rechargeable batteries. The circuits include devices to actuate an acoustic transmitter 62. The transmitter is actuated to send signals along the tubing string 36 corresponding to signals from one or more sensors 64 in signal communication with the circuits. In the present example, the sensor 64 may be a pressure sensor. A pressure measured by the sensor 64 will correspond to the height of the liquid column in the wellbore (28 in
Because the generator produces electric power whenever the pump system (10 in
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
