Composite motor stator

Abstract

A hollow stator for a Moineau-style motor is constructed from a composite material such as fiberglass or graphite. A series of lobes arranged along its inner surface corresponds to the external lobes of a rotor inserted in the stator, and enables use of a constant width elastomer layer between the stator and the rotor. The composite stator includes a pair of box socket interface members at its ends to enable the stator to be attached to other components such as pipeline sections.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Not Applicable. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] Not Applicable. BACKGROUND OF THE INVENTION [0003] Referring to FIG. 1, in drilling a borehole 100 through a rock formation, such as for the recovery of oil, it is conventional practice to connect a drill bit 110 on the lower end of an assembly of drill pipe sections that are connected end-to-end so as to form a drill string 120. The drill string 120 is rotated and advanced downward, causing the drill bit to cut through the underground rock formation. A pump 130 on the surface 140 typically suctions drilling fluid (also known as drilling mud), represented by arrows 135, from a mud pit 132 and forces it down through a passage in the center of the drill string 120. The drilling fluid then exits the face of the drill bit 110, in the process cooling the face of the drill bit. The drilling mud returns to the surface 150 by an annulus located between the bo...

AI Technical Summary

Problems solved by technology

One drawback in such motors is the stress and heat generated by the movement of the rotor within the stator.

This increased temperature causes rapid degradation of the elastomer.

Also, the elevated temperature changes the mechanical properties of the rubber, weakening the stator lobe as a structural member and leading to cracking and tearing of sections 231-237, as well as portions 271-277 of the rubber at the lobe crests.

The cracking and tearing of the elastomer that comprises the stator results in fluid leakage, leading to impaired sealing and reduced motor power.

If severe enough, the cracking and tearing results in “chunking” of the rubber, potentially clogging of downstream parts such as fluid exit nozzles located on the face of the drill bit.

Another undesirable phenomenon that occurs to the motor downhole is uneven bending wear to the rubber.

Complex directional drilling programs may require severe drilling turns.

Alternately, an inexperienced or unfortunate driller may inadvertently make a series of severe turns.

This uneven pressure can lead to further cracking and tearing of the elastomer.

This approach promises a longer life motor, in that rubber degeneration in the motor can cause reduced performance and failure of the motor.

The problems of motor failure are most severe when the motor must be replaced during the drilling program.

This is difficult enough for a shallow well but for a well that extends for miles, the time and effort wasted can be substantial.

Because the operator of a drilling operation may be paying daily rental fees for his equipment, this lost time can be very expensive, especially after the cost of an additional motor.

Even where the operator is not paying these rental fees, the oil and gas industry is highly competitive and costs are constantly being squeezed from operations.

However, although composite materials are finding increasing application in the replacement of metal, composites tend to be used only for special applications.

Composite materials have not been used for Moineau-style downhole motors, perhaps because composite materials are generally more expensive than their steel counterparts.

Another drawback to use of composite materials in a downhole motor is that physical properties and characteristics of composites, such as expansion coefficient, are different from metal.

This makes a direct metal-to-composite interface difficult in the highly challenging downhole environment.

Manufacture of a downhole motor from a composite material thus presents a dilemma.

Not only does the composite construction not seem to make sense from an economic perspective, but switching to a composite motor would be a challenge because it would require a composite-to-metal interface that operates well enough to withstand the demanding downhole environment.

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