Apparatus for preventing separation of a down-hole motor from a drill string

Abstract: An apparatus is disclosed for use in a drill string 10 to prevent separation of a lower tubular member 16 from an upper tubular member 15 by a rotational force applied from a down-hole motor 22. The down-hole motor 22 is rotated by drilling fluid pumped from the surface, through a passage formed within the drill string 10, and into the down-hole motor 22. A valve 36 is positioned in the passage in the drill string 10 and has a first operating position adapted for passing the drilling fluid to the down-hole motor 22, and a second operating position adapted for substantially blocking the drilling fluid from being delivered through the down-hole motor 22. The valve is of a two piece construction, having a first body 44 connected to an upper tubular section 14 and a second body 46 connected to the down-hole motor 22. Thus, longitudinal movement between the upper tubular section 14 and the down-hole motor 22, which is a result of rotation of the lower tubular section 16 by the motor 22, causes corresponding longitudinal movement of the first and second bodies 44, 46 between the first and second operating positions.

Description: This invention relates generally to an apparatus for preventing the loss of a portion of a drill string comprising a down-hole motor if the power section of such motor rotates one drill string portion relatively to another. In the field of oil well drilling, it is often desirable to use down-hole tools that are rotatable relative to the major portion of the drill string. For example, in some wells, such as horizontally drilled wells, it is desirable that a down-hole motor rotate just the drill bit, rather than having a larger surface motor rotate a drill stem comprising the entire drill string to which the drill bit is rotationally fixed. Accordingly, it should be readily appreciated that some type of bearing is required to be positioned in the drill string so that the down-hole tool is freely rotatable relative to the drill string. However, the environment to which such down-hole motors are subjected is extremely hostile. For example, the motor and bearing arrangement is continuously exposed to very high temperatures over very long periods of time with large amounts of debris passing therethrough. Accordingly, it is common for the bearings to occasionally fail. The failed bearings prevent free rotation of the drill bit relative to the drill string portion comprising or attached to the motor housing; however, the operators of the drilling operation are ordinarily unaware of such failure and continue to pump drilling fluid through the down-hole motor. Thus, the continued rotational force applied to the drill bit by the down-hole motor power section has a tendency to rotate the portion of the motor housing below the power section. Rotation of these sections of the down hole motor housing eventually results in at least one of the sections and the drill bit being unscrewed and separated from the remainder of the down-hole motor housing and possibly being lost in the well bore. Once the motor housing and bit are lost in the well bore, time consuming and expensive "fishing" operations are necessary to attempt to retrieve the lost items. Often these relatively expensive items cannot be retrieved and continue to impede further drilling operations. It has been suggested that undesirable rotation of the down-hole motor housing can be avoided by threadably attaching the down-hole motor housing to the lower portion of the drill string with left hand threads. Thus, when the down-hole motor applies a rotating force to its own housing, the joint is actually tightened rather than loosened. However, left hand threads have the inherent drawback of being loosened during normal operation. For example, during rotation of the entire drill string, the motor housing engages the subsurface strata and resists likewise rotation, thereby unscrewing the left hand threaded joint with attendant separation. The present invention is directed to overcoming or minimizing one or more of the problems discussed above. The problem of separation of drill string portions also arises in the case of rotary drilling with the use of a surface motor to rotate a drill stem comprising an extended drill string terminating in a drill bit. In such drilling, the drill bit or lower drill string portion may encounter an increase in resistance to rotation that is suddenly overcome, thereby releasing stored torsional energy in the drill string and causing the lower portion to overun, that is, to rotate in the forwards (clockwise) sense, relatively to the upper portion of the string and possibly to an extent sufficient to unscrew a joint between these portions and permit separation thereof. The phenomenon is called "backlash" and because the drill string normally conveys a flushing or drilling fluid to the bit, even partial unscrewing of a drill string joint by backlash can cause leakage of the fluid and consequent problems. This problem of backlash has been addressed in e.g., US-A-1 796 611 that discloses apparatus for preventing separation of a first portion of a drill string from a second portion of a drill string as a consequence of backlash in a rotating drill stem comprising the drill string portions. The apparatus comprises a joint device adapted to be interposed between the drill string portions and having parts arranged for connection to the respective drill string portions and to each other by screwthreads, it being arranged that the torque required to unscrew the connection between the parts of the device is less than that required to unscrew the device parts from the respective drill string portions, or to unscrew like screw thread connections between other drill string portions in the drill stem. The parts of the device, when unscrewed from one another, are prevented from separation by engagement of mating surfaces on the respective parts and that allow only limited relative longitudinal movement of the parts. The joint device provides for the flow of drilling fluid through the device and between the connected drill string portions, without leakage even when the joint parts are unscrewed one from another. The problem of backlash in rotary drilling as above discussed and addressed by US-A-1 796 611 hardly arises in drilling systems with down-hole motors. The different, above described, problems of the latter would moreover not be solved by the arrangement disclosed in US-A-1 796 611 for reasons that are apparent, or will become apparent from the following disclosure of the invention. Thus, the present invention consists in a drilling system comprising a drill string and a down-hole motor rotatable by drilling fluid pumped from the surface through a passage formed within the drill string, and an apparatus for preventing separation of a first portion of the drill string from a second portion of the drill string by rotation of the down-hole motor, relative rotation of said drill string portions causing relative longitudinal movement thereof, said apparatus comprising a valve positioned in the passage in said drill string, said valve having a first operating position adapted for passing said drilling fluid to said down-hole motor, and a second operating position adapted for substantially blocking said drilling fluid from being delivered to said down-hole motor; said valve being responsive to said relative rotation of said drill string portions causing longitudinal separating movement of said portions, whereby said valve attains said second operating position as a result of said relative rotation. In preferred embodiments of the invention, the valve is responsive to the longitudinal relative movements of the drill string portions consequent upon relative rotation of the drill string portions. Moreover, in the preferred embodiments the valve includes first and second mating surfaces defining a drilling fluid flow path therebetween, said mating surfaces being respectively connected to said first and second drill string portions to move between spaced apart and contacting positions in response to relative rotation and longitudinal relative movement of said drill string portions. Thus the valve preferably includes a first body of generally cylindrical configuration with first and second longitudinal regions having first and second external diameters respectively, said first mating surface being formed at the intersection of said longitudinal regions, and a second body of generally tubular configuration surrounding said first body and having third and fourth longitudinal regions of third and fourth internal diameters, respectively, said second mating surface being formed at the intersection of said third and fourth longitudinal regions, said first diameter being less than said second diameter, said third diameter being less than each of said fourth and second diameters and greater than said first diameter, said first valve body being connected to said first drill string portion and said second valve body being connected to said second drill string portion. If, as is conventional, the down-hole motor rotates in a clockwise direction and the first drill string portion is connected to the second drill string portion by righthand screwthreads, the first valve body may be connected to the first drill string portion by left hand screw threads and the second valve body be integral with the second drill string portion. Alternatively, the first valve body may be integral with the first drill string portion and the second valve body be connected to the second drill string portion by lefthand screwthreads. In preferred embodiments, the valve constitutes a retainer for limiting longitudinal separating movement of the first and second drill string portions by engagement of its mating surfaces. The arrangement is preferably such that the retaining action resulting from engagement of the mating surfaces occurs following sufficient relative rotation and longitudinal separating movement of the first and second portions to disconnect these from one another. The invention is further explained and described with reference to the accompanying drawings, in which : Fig. 1 illustrates a stylized view of a drill string with a partial cross-sectional view of a bearing and down-hole motor arrangement; Fig. 2 illustrates a longitudinal cross sectional view of a section of a drill string that includes the joint formed between the down-hole motor and the drill string; and Fig. 3 illustrates a cross sectional end view of the drill string adjacent the joint illustrated in Fig. 2. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that this specification is not intended to limit the invention to the particular forms disclosed herein, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention, as defined by the appended claims. Referring now to the drawings and, in particular, to Fig. 1, a stylized view of a drill string 10 is illustrated. The drill string 10 is composed of a series of tubular members 12, 13, 14, 15, 16 threaded together to form a hollow-core cylinder. Preferably, the tubular members 12, 13, 14, 15, 16 are joined together by threaded connections that employ right hand threads. A drill bit 20 is rotatably connected at the bottom of the drill string 10 via a down-hole motor 22 located in the lowermost tubular members 15, 16. The down-hole motor 22 is schematically shown in a partial cross sectional view and includes a housing 23, a power section 24, and a bearing section 25. To effect rotation of the drill bit 20 relative to the drill string 10, the conventional down-hole motor 22 is located within the core of the drill string 10 and is operated by pumping drilling fluid therethrough to impart a rotational movement to the drill bit 20. Preferably, the drill bit 20 is rotated in a clockwise direction, as indicated by an arrow 27. Rotational directions discussed herein are conventionally referenced as viewed from a vantage point above the drill string 10. It should be appreciated that since the drill bit 20 is rotatable relative to the drill string 10, the bearing section 25 is preferably provided to reduce frictional wear therebetween. The bearing section 25 commonly includes at least two sets of bearings 26, 28 spaced longitudinally apart to reduce longitudinal wobbling of the drill bit 20 as it rotates. In the event that the bearings 26, 28 cease to operate properly so that the drill bit 20 does not freely rotate relative to the drill string 10, then the clockwise rotational force applied to the drill bit 20 is also applied to the drill string 10 through the bearings 26, 28 and, in particular, to the lower tubular member 16 of the housing 23. Since the lower tubular member 16 is attached to the upper tubular member 15 via right hand threads, the clockwise rotation of the lower tubular member 16 tends to unscrew the lower tubular member 16 from the upper tubular member 15 until they separate. Referring now to Fig. 2, a longitudinal cross sectional view of a section of the drill string 10 that includes the joint formed between tubular members 14, 15 is shown. The upper tubular member 14 has an outer sidewall 29 that includes a longitudinal section 30 having an outer diameter slightly less than the outer diameter of the remaining portion of the sidewall 29. This longitudinal section 30 has formed on its outer surface a conventional threaded portion that is of the type typically referred to as right hand threads. Conversely, the lower tubular member 15 has an outer sidewall 31 that includes a longitudinal section 32 having an inner diameter slightly less than the remaining portion of the sidewall 31. The inner diameter of the longitudinal section 32 substantially corresponds to the outer diameter of the longitudinal section 30. Moreover, the longitudinal section 32 has formed on its inner periphery a conventional threaded portion that is also of the type typically referred to as right hand threads. The threaded portions of the longitudinal sections 30, 32 are substantially similar so as to allow the tubular members 14, 15 to be joined together by counterclockwise rotation of the lower tubular member 15. During normal operation, the tubular members 14, 15, 16 remain joined together to form a substantially unitary construction with a drilling fluid passage formed in the core thereof. It should be appreciated that the drilling fluid applied to the motor 22 serves the tripartite purpose of driving the down-hole motor 22, carrying away the debris generated by the cutting action of the drill bit 20, and cooling and lubricating the bearings 26, 28. Accordingly, after the drilling fluid passes through the down-hole motor 22, a small volume passes through the bearings and exits the drill string 10, and the remaining volume is delivered through the drill bit 20. Thus, for proper operation of the drill string 10, a drilling fluid passage is formed in the core of the drill string both above and below the down-hole motor 22. A portion of the drilling fluid passage is illustrated by arrow an 34 extending past the joint formed at the junction of tubular members 14, 15. The passageway 34 extends through a valve 36, which is operable to a first operating position adapted for passing the drilling fluid to the down-hole motor 22, and a second operating position adapted for substantially blocking the drilling fluid from being delivered to the down-hole motor 22. In the diagram of Fig. 2, the valve 36 is shown biased to the first operating position. That is, the valve 36 is open and drilling fluid freely flows through the down-hole motor 22 and to the drill bit 20. Means 38 biases the valve 36 from its first to its second operating position in response to rotation of the lower tubular member 16 relative to the upper tubular member 15. In other words, rotation of the lower tubular member 16 unscrews the lower tubular member 16 from the tubular member 15, causing a longitudinal displacement of the lower tubular member 16 and the rotor of the down-hole motor 22. Thus, by connecting the valve between the tubular member 14, and the rotor of the down-hole motor 22, this longitudinal movement of the lower tubular member 16 is used to actuate the valve 36 and discontinue operation of the down-hole motor 22. The valve 36 has first and second mating surfaces 40, 42, which define the drilling fluid passage. It can be seen that the drilling fluid passage, as defined by the arrow 34, passes between the first and second mating surfaces 40, 42. Thus, as long as the mating surfaces 40, 42 remain in the first operating position illustrated in Fig. 2, drilling fluid continues to flow and operate the down-hole motor 22. However, if the mating surfaces 40, 42 are urged together, the drilling fluid passage is substantially sealed against continued flow of the drilling fluid and the down-hole motor 22 ceases to operate. Further, since the fluid passage 34 is now blocked, but the operators are likely unaware of this blockage, drilling fluid is still being pumped to the down-hole motor 22. Accordingly, the pressure of the drilling fluid begins to rise significantly, functioning as an indication to the operators that the bearings 26, 28 have seized and the down-hole motor 22 is no longer driving the drill bit 20. Preferably, the distance between the mating surfaces 40, 42 is less than the length of the threaded portions 30, 32 of tubular members 15, 16. Thus, the valve 36 closes before the tubular members 15, 16 separate. However, even if the length of the threaded portions 30, 32 of the tubular members 15, 16 is less than the distance between the mating surfaces 40, 42, the mating surfaces 40, 42 still engage to prevent complete separation of the tubular members 15, 16. In other words, the tubular member 16 hangs from the tubular member 14 via the mating surfaces 40, 42 to prevent complete separation. However, the valve 36 still operates properly to prevent further rotation of the down-hole motor 22, thereby causing a rise in pressure of the drilling fluid, which signals the operators that a malfunction has occurred. The valve 36 consists essentially of a first and second body 44, 46. The first body 44 is ultimately connected to the down-hole motor 22 so that it moves rotationally and longitudinally therewith. The first body 44 is generally cylindrical in configuration with a closed first end portion 48 and an open second end portion 50. The closed first end portion 48 is positioned upstream in the drilling fluid passage so that the drilling fluid has an open passage only about the annulus formed between the first body 44 and the outer walls 29, 31 of the tubular members 14, 15,. This passage, of course, extends between the first and second mating surfaces 40, 42. In some embodiments, it is desirable that a relatively small amount of fluid be allowed to bypass the valve 36 through a passage extending through the center (not shown) of the valve 36. This bypass passage allows the drill bit 20 to be rotated at a slower speed but still provide adequate drilling fluid flow to the drill bit 20 to remove the cutting debris. The first mating surface 40 is formed at the junction of first and second longitudinal portions 52, 54 of the first body 44. The first and second longitudinal portions 52, 54 have substantially different outer diameters so that the first mating surface 40 takes the form of a lower surface of a shoulder that has width equal to the difference in the radii of the first and second longitudinal portions 52, 54. The first longitudinal portion 52 has a diameter that is substantially larger than the second longitudinal portion 54. The open end 50 of the first body has a threaded portion formed on its outer circumferential surface 56, which engages with a similarly threaded portion on an interior circumferential surface 58 of the down-hole motor 22. Preferably, the threaded portions on the surfaces 56, 58 are of the type conventionally referred to as left hand threads. It should be appreciated that clockwise rotation of the down-hole motor housing 23 has a tendency to unscrew conventional right hand threads, such as those between the tubular members 15, 16. Thus, to prevent the first body 44 from being unscrewed from and separating from the down-hole motor 22 left hand threads are employed. The use of left hand threads to join the first body 44 to the down-hole motor 22 does not have the same inherent drawback as using left hand threads to join the tubular members 15, 16 together. While left hand threads in the joint between tubular members 15, 16 resist being unscrewed by rotation of the lower tubular member 16, it is inherently subject to being unscrewed by rotation of the entire drill string 10. Conversely, the left hand threads joining the first body 44 and the down-hole motor 22 are not subject to being unscrewed by rotation of the entire drill string 10 or by rotation of the down-hole motor housing 23. The advantage of the left hand threads between the first body 44 and the down-hole motor 22 is conveniently described by way of example. Assuming that the bearings 26, 28 have seized and no longer allow rotation between the drill bit 20 and the lower tubular member 16, then continued rotation of the down-hole motor 22 imparts a clockwise rotational force (see arrow 27 in Fig. 1) to the lower tubular member 16. The lower tubular member 16 is unscrewed from the upper tubular member 15 by this rotational force until the mating surfaces 40, 42 of the valve 36 engage one another, impeding the flow of drilling fluid through the down-hole motor 22 and preventing further rotation. However, as the mating surfaces 40, 42 contact one another, a force is exerted on the first body 44, which would tend to unscrew the first body 44 from the down-hole motor 22 if they were connected together by right hand threads. The left hand threaded connection, however, is simply further tightened by the force. The second body 46 of the valve 36 has a generally tubular configuration generally coaxially positioned about the first body 44. Like the first body 44, the second body 46 has first and second longitudinal regions 60, 62, which have substantially different inner diameters. Preferably, the first longitudinal region 60 has an inner diameter that is greater than the outer diameter of the first longitudinal region 52 of the first body 54 but less than the inner diameter of the second longitudinal region 62 of the second body 46. Further, the outer diameter of the second longitudinal region 54 of the of the first body 44 is preferably less than the inner diameter of the second longitudinal region 62 of the second body 46. This configuration allows the first and second bodies 44, 46 to move longitudinally within each other to space the mating surfaces 40, 42 apart or together so as to open or close the valve 36. It should be appreciated that closing the valve 36 functions as a highly detectable signal to the operators of the drilling process that the drill bit 20 has ceased to rotate properly. When the valve closes, the flow of drilling fluid from the surface is interrupted. This interruption of flow is readily identifiable by the operators as a significant and continuous rise in the pressure of the drilling fluid. The second body 46 is illustrated as being integrally formed with the outer wall 29 of the upper tubular member 14, but could readily take the form of a separate body attached to the outer wall 29 by, for example, welding or by threaded connection. Preferably, a threaded connection between the outer wall 29 and the second body 46 would take the form of left hand threads for the same reason discussed above in conjunction with the connection between the first body 44 and the down-hole motor 22. Referring now to Fig. 3, a cross sectional end view of the drill string 10 adjacent the joint illustrated in Fig. 2 is shown. In particular, the cross section through the drill string 10 is taken at a point slightly above the first body 44 so as to further illustrate the relationship of the valve 36 with the drill string 10. Two offset coordinate systems 70, 72 are superimposed over the cross section. The first coordinate system 70 represents the radial centerpoint of the drill string 10 and, in particular, the second body 46 of the valve 36. The second coordinate system 72 represents the centerpoint of the rotor of the down-hole motor 22 and is offset slightly from the centerpoint of the drill string 10. As is conventional, proper operation of the down-hole motor 22 requires that it be offset from the longitudinal axis of the drill string 10. This offset in the down-hole motor 22 requires that the diameters of the first and second bodies 44, 46 be carefully selected to ensure sufficient overlap of the mating surfaces 40, 42. The outer diameter of the first longitudinal section 52 of the first body 44 should be greater than the inner diameter of the second longitudinal section 62 of the second body 46 by a distance at least as large as the offset. Conversely, to ensure that the first and second bodies 44, 46 are free to move longitudinally within one another, the diameter of the first longitudinal section 52 of the first body 44 should be less than the diameter of the first longitudinal section 60 of the second body 46 by a distance at least as large as the offset. This same relationship should be observed between the second longitudinal sections 54, 62 of the first and second bodies 44, 46. It should be appreciated that the first and second bodies 44, 46 have been described herein as being generally or substantially coaxially arranged. However, as is apparent from Fig. 3, the longitudinal axes of the first and second bodies 44, 46 are, in fact, offset by a distance corresponding to the offset of the down-hole motor 22 from the drill string 10 longitudinal axis. Thus, the term coaxial has been used in a general sense only to describe the approximate relationship between the first and second bodies 44, 46. The axes of the first and second bodies 44, 46 can depart from precisely coaxial by a substantial distance without departing from the meaning of our use of the phrases "generally or substantially coaxial."

Claims: A drilling system comprising a drill string (10) and a down-hole motor (22) rotatable by drilling fluid pumped from the surface through a passage formed within the drill string, and an apparatus for preventing separation of a first portion (16) of the drill string from a second portion (15) of the drill string by rotation of the down-hole motor, relative rotation of said drill string portions causing relative longitudinal movement thereof, said apparatus comprising a valve (36) positioned in the passage in said drill string, said valve having a first operating position adapted for passing said drilling fluid to said down-hole motor, and a second operating position adapted for substantially blocking said drilling fluid from being delivered to said down-hole motor; said valve being responsive to said relative rotation of said drill string portions (16,15) causing longitudinal separating movement of said portions, whereby said valve attains said second operating position as a result of said relative rotation. System according to Claim 1, wherein said valve (36) is responsive to longitudinal relative movements of said drill string portions (16,15). System according to Claim 1 or 2, wherein said valve (36) includes first and second mating surfaces (40,42) defining a drilling fluid flow path (34) therebetween, said mating surfaces being respectively connected to said first and second drill string portions (16,15) to move between spaced-apart and contacting positions in response to relative rotation and longitudinal relative movement of said drill string portions. System according to Claim 3, wherein said valve (36) includes a first body (44) of generally cylindrical configuration with first and second longitudinal regions (52,54) having first and second external diameters respectively, said first mating surface (40) being formed at the intersection of said longitudinal regions, and a second body (46) of generally tubular configuration surrounding said first body (44) and having third and fourth longitudinal regions (60,62) of third and fourth internal diameters, respectively, said second mating surface (42) being formed at the intersection of said third and fourth longitudinal regions (60,62), said first diameter being less than said second diameter, said third diameter being less than each of said fourth and second diameters and greater than said first diameter, said first valve body (44) being connected to said first drill string portion (16) and said second valve body (46) being connected to said second drill string portion (15). System according to Claim 4, wherein said down-hole motor (22) rotates in a clockwise direction, said first drill string portion (16) is connected to said second drill string portion (15) by righthand screwthreads, said first valve body (44) is connected to said first drill string portion (16) by lefthand screwthreads, and said second valve body (46) is integral with said second drill string portion (15). System according to Claim 4, wherein said down-hole motor (22) rotates in a clockwise direction, said first drill string portion (16) is connected to second drill string portion (15) by righthand screwthreads, said first valve body (44) is integral with said first drill string portion (16), and said second valve body (46) is connected to said second drill string portion (15) by lefthand screw-threads. System according to Claim 3 or any claim dependent thereon wherein said valve (36) constitutes a retainer for limiting longitudinal separating movement of the first and second drill string portions (16,15) by engagement of its said mating surfaces (40,42). System according to Claim 7, wherein said first and second drill string portions (16,15) have a screwthread connection and said mating surfaces (40,42) are so disposed as to engage following relative rotation and longitudinal separating movement of the first and second drill string portions sufficient to disconnect said portions one from the other.

Inventors: BEASLEY THOMAS R, BEASLEY, THOMAS R.
Applicants: DAILEY PETROLEUM SERVICES, DAILEY PETROLEUM SERVICES CORP.
Application year: 1991
Main classification: E21B17
IPC codes: E21B17, E21B47, E21B21, E21B4