Boring or penetrating the earth – With below-ground tool drive prime mover – Fluid rotary type
Patent
1987-09-01
1990-03-20
Kisliuk, Bruce M.
Boring or penetrating the earth
With below-ground tool drive prime mover
Fluid rotary type
175323, 294211, 29888023, 2988972, 72 63, 72370, 418 48, E21B 402, F03C 200, B23P 1502, B21D 2602
Patent
active
049093371
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to drilling equipment and more specifically, to one of the major units of screw hydraulic downhole motors applicable for drilling oil and gas wells, viz., the rotor of a screw hydraulic downhole motor, and to a method for producing said rotor.
PRIOR ART
Known in the art presently is a downhole motor with a multi-lobe rotor made as a solid metallic multiple-thread screw, wherein the number of starts of the helical surface (helical teeth) is in excess of one (cf. USSR Inventor's Certificate No. 926,209, Int. Cl. E 21B 4/02, published on May 7, 1982).
The rotor is accommodated inside a stator featuring an inner multiple-thread helical surface, wherein the number of starts is in excess of that of the rotor by one; said helical surface is moulded on the lining made of a resilient material, such as rubber pasted to the inner surface of the stator frame. The rotor axis is offset with respect to the stator axis which aligns with the motor axis, by an amount of eccentricity equal to half the length of the rotor and stator teeth, while the ratio of the axial pitch of the rotor helical teeth to the axial pitch of the stator helical teeth equals the ratio between the number of teeth on said motor components. When the rotor teeth engage the stator teeth, spaces are formed, opening to the rotor top portion and closing over the length of the helix lead. When drilling mud is injected into the screw hydraulic down hole motor from the earth's surface along the drill string to the bottom end of which the screw hydraulic downhole motor is connected, the rotor of the motor performs planetary motion, while the rotor axis rotates about the stator axis in the counterclockwise direction at an angular velocity .omega..sub.1, and the rotor itself rotates about its own axis in a clockwise direction at an angular velocity .omega..sub.2. The magnitude of the angular velocity .omega..sub.1 is equal to that of the angular velocity .omega..sub.2 multiplied by the number of rotor teeth, while the centrifugal force acting on the rotor is proportional to its mass and to the square of the angular velocity .omega..sub.1.
However, the large mass of a solid rotor and the high magnitude of the angular velocity .omega..sub.1 of rotation of the rotor result in high centrifugal forces arising during the operation of the motor. These forces induce vigorous transverse vibrations which affect adversely the durability of the rotor, stator, hinge joints, as well as of the threaded joints of the motor and the drill string.
The multi-lobe rotor of the aforediscussed motor is manufactured by virtue of gear hobbing, i.e., cutting with a metal-cutting tool called the hob. The method is an expensive one, suffers from an inadequate productivity, fails to provide a high quality rotor teeth surface finish and involves sophisticated and costly metal-cutting machinery and tools. Furthermore, resort should be made to polishing or grinding of the rotor working surfaces to improve the quality of surface finish, which is a complicated technological task on account of the intricate configuration of the rotor and its long overall length.
In addition, it is due to a great length of the multi-lobe rotor that the cutting lips of a hob grow worn in the course of rotor machining, which affects badly the accuracy of the finished product.
Another screw hydraulic downhole motor known in the present state of the art comprises a hollow multi-lobe rotor. For the purpose of joining with a cardan or a flexible shaft, the rotor is rigidly connected, by virtue of a threaded joint, to the union coupling (cf, a textbook "Screw hydraulic downhole motors for well drilling" by M. T. Gusman et al., 1981, Nedra PH, (Moscow), pp. 125-188 (in Russian). The rotor in question is hollow-centered by removal of the metal from the central portion thereof either by virtue of a center hole drilled in the rotor or through the use of a thick-walled pipe shell.
This makes it possible to reduce to some extent the centrifugal forces applied to the rotor, thu
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Goldobin Vladimir B.
Kochnev Anatoly M.
Nikomarov Samuil S.
Vshivkov Andrei N.
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