The present invention relates to a device for regulating the amount of flow through a progressing cavity motor within a downhole collar and other tubular. The rotational speed of the progressing cavity motor is a direct function of the volumetric flow rate passing through the stator of the motor. By modulating this flow, the rotational speed of the system may be modulated to a predetermined rate.
A generator has been designed and constructed for creating electrical energy downhole in an oil well. The generator is driven with a progressing cavity motor as opposed to more classical methods, such as turbines. The progressing cavity motor is mechanically linked to the generator with a semi-rigid shaft. This shaft, referred to as a “flex shaft” is rigid enough to transmit a required amount of torque yet flexible enough to accommodate the eccentric neutation of the progressing cavity motor. The flex shaft in turn drives an electrical generator generally comprised of permanent magnets rotating about or within windings of an electrically conductive material such as copper wire. This results in the creation of an electrical charge capable of producing enough current to sustain electrical downhole instrumentation or other electrical devices. Further details regarding this generator are disclosed in Ser. No. 12/167,003 filed Jul. 2, 2008.
For a plurality of reasons, drilling fluid is pumped through the tubular string containing one or more drill collars from a pump located on the surface. A portion of this fluid is forced through the progressing cavity motor (pcm) located within a drill collar as the fluid travels downhole to pass to the drilling bit and return to the surface. The rotational speed of the pcm is directly proportional to the amount of fluid passing through the pcm. Under normal operations, this proportional amount is a minor portion of the total flow being supplied by the surface pump and passing through the drill collar.
In the process of drilling, the drilling mud may be pumped over a fairly wide flow range. This flow range may be 200 gallons per minute (gpm), up to and including 600 gpm. The output from the motor, however, desirably is a constant value. Flow through the pcm may be as much as 80 gpm or more.
While various designs exist for regulating fluid flow and pressure, this system modulates internal flow of drilling fluid within the motor. Substantially different yet related devices are taught in U.S. Pat. Nos. 3,974,876; 5,282,490; 5,301,713; 5,431,183; 6,053,196, and 6,129,112.
The disadvantage of the prior art is overcome by the present invention, an improved flow regulator for downhole pcm is hereinafter disclosed.
In one embodiment, a system for regulating the fluid flow through a progressing cavity motor positioned downhole within a tubular includes an annulus restriction for restricted flow through an annulus passageway radially outward of the motor, and an annular biasing member for biasing the annulus restriction toward the closed position. Fluid flowing in the annulus exerts an opening force on the annulus restriction. The system further includes a central passageway through the motor for restricting flow, and a central biasing member for biasing the central restriction toward an open position, with fluid flow in the central passageway exerting a closing force on the central restriction. The system is particularly well-suited for providing a constant rpm for a downhole motor to power an electrical generator.
These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.
The present invention provides a system to achieve modulation of flow through a downhole motor while the flow outside the motor may vary.
The inner, smaller spring 26 and its flow restriction 28 are designed such that once a steady state flow is established, flow through the motor 10 is at a substantially constant rpm, thereby applying a constant rpm to electrical generator 40 powered by the motor. As shown in
The outer larger spring 24 is used to create a usable pressure drop across the motor for a spectrum of flow rates of drilling mud. The inner, smaller spring 26 is used to regulate the rpm of the pcm. Both springs are designed to act synchronously to produce a steady state flow condition.
As shown in
Each of the annular restriction and the central restriction are biased axially in a selected direction, and preferably the axial bias is provided by a coil spring. Each of the annular restriction and the central restriction thus move axially relative to a conical shaped member to vary the flow past the restriction. More particularly, as shown in
According to the present invention, the annular biasing element provides a biasing force proportional to the opposing mildly movable due to the flow rate through the annulus passageway acting on the axially movable annulus restriction 22, so that the biasing force increases with increased flow through the annular passageway. Similarly, the central biasing element provides a biasing force which is proportional to the force due to the flow rate through the central passageway acting on the axially movable central restriction 24, so that the central biasing force will increase with increased flow through the central passageway. The annulus biasing member 24 biases the annular restriction or valve member 22 upward toward the conical seat 38, although in alternate embodiments an inward protrusion could be provided on the interior of the drill collar 8, in which case an annular biasing member may bias the valve member toward a seat which has a larger diameter than the largest restriction of the valve member.
The present invention is considered significantly better than concepts which utilize a more traditional governor with spinning weights to control fluid flow. In this application, such a governor concept would be difficult to achieve with the available diametrical space of a downhole progressing cavity motor, and the reliability of such a system would be questionable in view of acessibility and bearing problems associated with a spinning weight design.
A significant advantage of the present invention is that the system generates a substantially constant rpm for the output of progressing cavity motor which then results in a substantially constant voltage output from the electrical generator. Downhole tools which are powered by the electrical generator have a known voltage requirement, and thus a substantially constant voltage may be obtained from the generator without driving the motor at an excess speed, which may cause excessive, premature wear, as well as producing a higher than desired voltage. In the latter case, the additional voltage would have to be discarded, and may present significant problems with respect to heating down hole.
Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.
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Number | Date | Country | |
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20110174499 A1 | Jul 2011 | US |