Torsional Restraints For Downhole Transmissions
A noninvasive method for the affixing of a transmission in a downhole housing wherein the housing is deformed, creating an oval cross section, and inserting the transmission into the housing with the greatest cross section of the transmission being positioned along the major axis of the oval created and, thereafter, releasing pressure to cause said housing to return to its normal circular cross section.
The present invention deals, in a general sense, with the mounting of a mechanical downhole transmission within a housing and, in particular, a novel method of transferring torsional loads from the gear train to the transmission housing, to thereby resist twisting of the gear train.
BACKGROUND OF THE INVENTION FIELD OF THE INVENTIONThere are applications in the oil patch in which a mechanical transmission is mounted within a cylindrical housing. Such an application is found when used with a Geared Centrifugal Pump [GCP], such as described in Morrow U.S. Pat. No. 5,960,886. In that application, a speed increasing transmission is linked to a downhole, multistage centrifugal pump and is driven from the surface by a power source driving a rotating drive string.
The transmission is mounted within a cylindrical housing. The discharge from the pump is routed inside the transmission housing via flow tubes, which run along the side of the transmission gear train, as described in Morrow U.S. Pat. No. 8,118,089. The cylindrical housing functions as both the outer gear case for the transmission, as well as a pressure barrier between the high pressure pumped fluid in the flow tubes and the relatively low pressure in the well bore. The inside volume of the housing is kept at pump discharge pressure by a pressure compensator, so there is little to no pressure differential between the pumped fluid flowing inside the flow tubes and the inside of the housing, so as to limit potential leakage of well fluid into the transmission lubricant.
In the case of the GCP, the transmission is required to transmit significant torque between the input shaft of the transmission and the pump. This torque puts large twisting loads on the transmission gear train, which must be restrained so as not to result in deformation of the transmission internal structure and consequent misalignment of bearings, gears, shafts, etc.
The most obvious way to resist this twisting force due to the torque is to tie the transmission structure to the outer housing, which has a fairly thick wall to resist the pressure differential mentioned above and, hence, has great torsional stiffness.
OVERVIEW OF THE PRIOR ARTThe current method by which the transmission structure is tied to the outer housing is by means of a series of transverse connecting pins. Specifically, the transmission is inserted into the housing; holes are drilled along its length through the housing wall and into the structural components of the transmission. Two rows of pins are shown in the accompanying drawings at the 12:00 o'clock and 180° away at the 6:00 o'clock positions. Steel pins are then inserted into the holes and into these structural components, leaving a short length of pin engaged within the housing wall. The countersunk hole in the housing is then filled with weld to seal the hole.
This method appears to have functioned satisfactorily so far, but has several drawbacks. For example, a typical transmission using this system will employ as many as 70 pins. Each pin results in a penetration of the pressure housing and, thus, a potential point of failure.
The engagement of the pins in the housing, although small, represents a reduction in wall thickness, which reduces ultimate burst strength of the housing. The process of drilling, pinning and welding is labor intensive and, hence, expensive.
SUMMARY OF THE INVENTIONThe present invention teaches a noninvasive alternative to the pinning of the transmission components as described, and, as a principal objective, therefore, offers a novel method of keeping the torsional forces exerted on the transmission from twisting the gear train assembly, causing misalignment and accelerated failure.
With reference now to the drawings, and initially, to
Having thus illustrated the current state-of-the-art, move now to
The essence of the present invention is a novel, noninvasive method which takes advantage of the characteristics of such transmissions used in fluid production wells. The present invention has its primary use in production wells configured to draw subterranean fluids to the surface via a production well in which a power source at the surface drives a drill string having a transmission connected with the driving string which, in turn drives a pump immersed in the subsurface fluid. The method of the present intention takes advantage of certain elements of such transmissions are elongated to the extent that they are slightly longer in cross section than the cross section of the housing, or casing, in which the transmission is situate, and, when applied, offers the capacity to hold a speed increasing transmission firmly within a cylindrical housing to resist the reactive twist of the components during high torque operation.
The scientific principle, broadly stated, employs an external force to deform the housing elastically with the external force so that the transmission can be inserted and positioned inside the housing, then squeezing, or compressing, the housing until it becomes oval in cross section, positioning the transmission and releasing the pressure on the housing, which results in frictional engagement with the transmission and thereafter releasing the force to allow the housing to return to its cylindrical shape, clamping the transmission firmly in position. This is the procedure shown in
One such method of applying force is by the use of hydraulic jacks 25 against the casing, or housing, 27 as seen in
Once the transmission is positioned within the deformed housing, the external force is released, and the housing will return to its circular shape, shown in
The bearing surface of the transmission components that contact the inner wall of the housing can be textured, e.g., either by knurling or with machined shallow grooves, 30, that create sharp ridges aligned with the principal axis of the housing, to grip the inside of the housing more securely, as shown in
It some instances, the components of the device being held do not have sufficient stiffness in those areas where they will be squeezed by the housing after the deforming force is released and may be deformed inward, excessively. In those cases, stand-off spacers which have a larger diameter than the transmission components, can be spaced appropriately to carry the squeezing force of the undeformed housing (
In summary, in order to accomplish the objectives of the present invention, one must first distort the casing, and that is accomplished by the application of external pressure in a uniform manner and in an amount sufficient to distort the casing without exceeding its elastic limit.
Next, the transmission gearing, supported by its cradles, is inserted into the distorted casing such that the major diameter of the transmission components are situate along the distorted axis of the casing.
Finally, the surfaces of selected transmission components, clearly those components which are stationary, such as the cradles, are roughened such as by knurling, or grooving, such that when external pressure on the casing is released and it returns to its circular cross section, the contact between the knurled, or grooved, surfaces and the inner diameter of the casing provides a rigid connection. In this manner, the objectives of the present invention are achieved.
The present invention contemplates an alternative to the structure previously described. Referring to
It will be understood that those skilled in the art, may, upon reading of the detailed description, think of various ways to accomplish the invention other than those specifically set forth. It will be appreciated that such variations are within the contemplation of the invention as illustrated by the forthcoming claims.
Claims
1. In a well for the production of subsurface fluids wherein a cylindrical housing, said housing having an interior wall surface and an exterior wall surface, extends from a power source at the surface to a pump immersed in the subsurface fluid;
- a method of affixing a transmission within the housing, comprising the steps of:
- applying pressure to compress said housing so as to distort its cross section to an oval configuration;
- positioning said transmission within said housing at a predetermined level;
- releasing pressure on said housing so as to permit its return to its circular inside diameter whereby said internal diameter of said housing frictionally engaged with at least a portion of said transmission firmly holding the same in its predetermined position.
2. In a well for the production of subsurface fluids wherein a cylindrical housing, said housing having an interior wall surface and an exterior wall surface, extends from a power source at the surface to a pump immersed in the subsurface fluid;
- a method of affixing a transmission within the housing, comprising the steps of:
- applying pressure to compress said housing so as to distort its cross section to an oval configuration;
- roughening the surface of the interior diameter of said housing;
- positioning said transmission within said housing at a predetermined level;
- releasing pressure on said housing so as to permit its return to its circular inside diameter whereby said internal diameter of said housing frictionally engaged with at least a portion of said transmission firmly holding the same in its predetermined position.
3. The method of claim 1, comprising the step of introducing hydraulic jacks 180 degrees apart against the exterior surface of said housing and using said jacks to distort said housing.
4. The method of claim 1, wherein spacers are provided intermittently throughout said transmission.
5. The method of claim 2, wherein said hydraulic jacks providing a uniform radial pressure to said housing.
6. The method of claim 1, wherein said interior wall of said housing being textured.
7. The method of claim 2, wherein said interior wall of said housing being knurled.
8. The method of claim 1, wherein said interior wall being knurled.
9. The method of claim 2, wherein said interior wall of said housing being textured.
Type: Application
Filed: Mar 25, 2014
Publication Date: Oct 2, 2014
Inventors: William Bruce Morrow (Santa Barbara, CA), Edward Hahlbeck (Pewaukee, WI)
Application Number: 14/224,347