Patent Application
20180128052
Downhole operations often include a downhole string, also referred to as a drill string that extends from an uphole system into a formation. The uphole system may include a platform, pumps, and other systems that support resource exploration, development, and extraction. During resource exploration operations, a drill bit is guided through the formation to form a well bore. The drill bit may be driven directly from the platform or both directly and indirectly through a flow of downhole fluid, which may take the form of drilling mud passing through a motor. A downhole motor includes a stator having a plurality of lobes and a rotor having another plurality of lobes. The stator is rotated by the downhole string and the rotor by the flow of fluid. The number of lobes on the stator is one fewer than the number of lobes on the stator. In this manner, the flow of fluid drives the rotor eccentrically while the motor drives the drill bit concentrically.
The eccentric rotation of the rotor often leads to vibrations, especially when operating the drill bit at high speeds. The vibrations produced by the downhole motor are not only detrimental to the motor itself, but may also interfere with drilling operations. The vibrations may lead to a reduced overall service life of the downhole motor. Components of the downhole motor, over time, may delaminate due to prolonged exposure to vibrations. Further, the vibrations may exist at a frequency that could lead to interferences with signals passing from the drill string to uphole operators. According, resource exploration companies would be receptive to improvements in downhole motor design and operation.
A method of operating a Moineau system to substantially eliminate vibrations, the method includes rotating a first rotational member, and rotating a second rotational member. Each of the first rotational member and the second rotational member includes a plurality of lobes. A first rotational speed of one of the first rotational member and the second rotational member is selected based on 1) a second rotational speed of the other of the first rotational member and the second rotational member and 2) the number of lobes of one of the first rotational member and the second rotational member to maintain eccentric force of one of the first and second rotational members below a predetermined threshold.
A vibrationless Moineau system includes a first downhole motor including a first stator having a first number of stator lobes, and a first rotor having a first number of rotor lobes, and a second downhole motor including a second stator operatively connected to the first rotor. The second stator has a second number of stator lobes. A second rotor has a second number of rotor lobes. The first and second downhole motors are selectively operated to substantially maintain eccentric forces on at least one of the first rotor and the second rotor below a predetermined threshold.
A resource exploration system includes a surface system, and a downhole system including a downhole string operatively connected to the surface system. The downhole string includes a vibrationless Moineau system including a first downhole motor having a first stator including a first number of stator lobes, and a first rotor including a first number of rotor lobes. A second downhole motor includes a second stator operatively connected to the first rotor. The second stator has a second number of stator lobes. A second rotor has a second number of rotor lobes. The first and second downhole motors are selectively operated to substantially maintain eccentric forces on at least one of the first rotor and the second rotor below a predetermined threshold.
Referring now to the drawings wherein like elements are numbered alike in the several Figures:
A resource exploration system, in accordance with an exemplary embodiment, is indicated generally at 2, in
Downhole system 6 may include a downhole string 20 that is extended into a wellbore 21 formed in formation 22. Downhole string 20 may include a number of connected downhole tools or tubulars 24 that may define a drill pipe 25. One of tubulars 24 may be connected with a vibrationless Moineau or downhole motor system 28 operatively connected to a drill bit 32. Vibrationless downhole motor system 28 cooperates with uphole devices (not shown) to rotate drill bit 32 creating well bore 21.
As shown in
Rotor 42 includes a number of rotor lobes 64. It is to be understood that the number of stator lobes 48 is one more than the number of rotor lobes 64. Rotor 42 is rotatably disposed inside of stator 40 and may include a rotor bore 68 that terminates at a location 70 below an upper end 74. Rotor bore 68 remains in fluid communication with drilling fluid 78 which may exit through a port 80. It is to be understood that drilling fluid 78 may take on a number of forms including drilling mud or other types of fluids, foams, gases or the like introduced into downhole motor system 28 through downhole string 20 (
Stator lobes 48 and rotor lobes 64 possess a helical angle (not separately labeled) causing a seal, such as indicated at 82 at multiple discrete locations between stator 40 and rotor 42. Seals 82 create multiple axial fluid chambers or cavities, one of which is indicated at 84. Drilling fluid 78 supplied under pressure from surface system 4 flows through axial fluid cavities 84 causing rotor 42 to rotate inside stator 40 in a planetary fashion. The number and design of stator lobes 48 and rotor lobes 64 define output characteristics of downhole motor 28. More specifically, a ratio between rotations of stator housing 44 controlled by drill string 20 and rotor 42 as controlled by drilling fluid pressure defines an output torque of downhole motor 28 that is passed to drill bit 32 through a flex shaft 90.
In accordance with an exemplary aspect, rotor 42 and stator 40 may be formed of metal or alloys thereof or any other material that is suitable for downhole motor 28 in the form of a Moineau system. It is to be understood that a Moineau system has at least two rotating parts, also referred to as a first rotational member and a second rotational member. The two parts are an outer tubular part with lobes on its inner surface and an inner threaded rod part, either massive or hollow, with lobes on its outer surface.
It is also to be understood that the term “stator” as used herein refers to a slower rotating part of downhole motor 28, and the term “rotor” refers to a faster rotating part of downhole motor 28. That is, in accordance with an exemplary aspect, rotor 42 rotates faster than stator 40 in a laboratory system, while the wellbore is stationary in the laboratory system. Depending on the configuration of downhole motor 28, rotor 42 may be an inner threaded rod part arranged within an outer tubular part such as, for example, stator 40. Alternatively, stator 40 may be defined by the inner threaded rod part arranged within the outer tubular part such as, for example, rotor 42. In either example, rotor 42 is at least partially driven by fluid flow through downhole motor system 28.
In accordance with an exemplary aspect, rotation of stator 40 and rotor 42 is controlled to substantially eliminate vibrations produced by downhole motor 28. Specifically, downhole motor 28 is operated in a manner that maintains lateral accelerations of rotor 42 below about 15 g. In accordance with another aspect of an exemplary embodiment, downhole motor 28 is operated to maintain lateral accelerations of rotor 42 below about 2 g. In accordance with still another aspect of an exemplary embodiment, downhole motor 28 is operated to maintain lateral accelerations below about 0.5 g. In accordance with yet still another aspect of an exemplary embodiment, downhole motor system 28 is operated to substantially eliminate lateral accelerations of rotor 42.
Substantially eliminating lateral accelerations of rotor 42 results in substantially eliminating vibrations of downhole motor system 28. Lateral accelerations of rotor 42 may be described by formula 1. Controlling motor input through drill string 20 and establishing a selected drilling fluid pressure can establish a desired lateral acceleration of rotor 42 and thereby substantially reduce vibrations of downhole motor 28. For example, rotating downhole string 20 at about 120 RPM and delivering drilling fluid to at a flow rate causing the rotor to rotate at about 60 RM in a downhole motor having a rotor-stator lobe ratio of 2:3 will maintain lateral accelerations below about 0.5 g.
F
ecc
=m
rotor
*r
ecc*ω2ecc (1)
ωecc=ωstator−(ωrotor*nrotor lobes)=0 (2)
ωstator=ωrotor*nrotor lobes or ωrotor=ωstator/nrotor lobes (3)
ωmotor=ωstator+ωrotor (4)
P
motor
=Mω
motor
=M(ωstator+ωrotor) (5)
It is also to be understood that controlling motor inputs to reduce vibration may impose limitations on motor power. For example, downhole string 20 may be rotated only at a limited RPM due to operational limitations. In accordance with an exemplary embodiment the rotation of the downhole string determines the RPM of the stator. Table 1 presents assumed stator RPM and the rotor RPM for typical ‘rotor lobe’/‘stator lobe’ configurations to achieve a vibrationless downhole motor. Entries including a leading “x” are not applicable to a drilling operation, because of a resulting low motor power caused by a resulting low angular velocity of the motor.
In accordance with an aspect of an exemplary embodiment, motor power and angular velocity that is too low for drilling operations may be overcome by including another downhole motor in downhole string 20 with the purpose of creating another source of rotation which is different from the rotation of downhole string 20. The addition of a second downhole motor, as detailed below, would increase motor power and angular velocity to a level that is more applicable to downhole drilling operations.
A downhole motor system, in accordance with another aspect of an exemplary embodiment is illustrated generally at 150 in
It is to be understood that the terms “first” and “second” are not meant to define a particular order relative to surface system 4. That is, while second downhole motor 190 is shown positioned downhole relative to first downhole motor 180, the particular order may vary. Also, it is to be understood that first and second downhole motors 180 and 190 need not be directly adjacent. It is to be understood that first and second downhole motors may be separated by one or more intervening tubulars.
First rotor 220 includes an output member 244 that operatively connects with second downhole motor 190. Output member 244 may take the form of a dampening member that restricts transmission of vibrations from first downhole motor 180 to second downhole motor 190. Output member 244 may include a seal (not separately labeled) and is rotationally isolated from first stator housing 204. Output member 244 includes a passage 250 that receives drilling fluid passing from an area (not separately labeled) between first stator 200 and first rotor 220. In the exemplary embodiment shown, first downhole motor 180 constitutes a downhole motor having a rotor-stator lobe ratio of 2:3 with the number of first rotor lobes 224 being two (2) in number and the number of first stator lobes 210 being three (3) in number.
In further accordance with an aspect of an exemplary embodiment, second downhole motor 190 includes a third rotational member defined by a second stator 250 having a second stator housing 255 and a first number of stator lobes, one of which is indicated at 258 that define a second stator lobe profile 260. A fourth rotational member defined by a second rotor 266 is rotatably supported within second stator 250. Second rotor 266 includes a second number of rotor lobes, one of which is indicated at 268 that interact with the second number of stator lobes 258. The second number of rotor lobes 268 number one fewer than the second number of stator lobes 258. A second elastomeric liner 273, see
Second stator housing 255 is mechanically linked to output member 244. In this manner rotational forces or torque developed in first rotor 220 are direct passed to second stator housing 255. Drilling fluid passing through passage 246 of output member 244 is directed into second stator housing 255. Second rotor 70 includes a first end portion 283 rotatably supported within second stator 250 through a support bearing (not shown) and a second end portion (also not shown) mechanically linked to drill bit 32.
In accordance with an aspect of an exemplary embodiment, rotational energy is imparted to first stator 200 through a drilling system (not shown) arranged at surface system 4 (
Drilling fluids at the selected pressure passing into second downhole motor 190 from passage 246 enter into second stator housing 255. Those drilling fluids interact with second rotor 266 resulting in a third rotational speed RPM 3 relative to second stator 250. The drilling fluids then pass from second downhole motor 190 through an outlet portion (not shown). In this manner, first and second downhole motors 180, 190 may be operated individually at levels below which would produce vibration but at a lower than desired speeds while the operative connection produces a much higher output, e.g., RPM1+RPM2+RPM 3 to drill bit 32. Accordingly, during operating, vibrationless downhole motor system 28 produced few if any vibrations. That is, lateral acceleration of downhole motor system 150 and, more specifically first rotor 220 and lateral accelerations of second rotor 266 are maintained below about 15 g.
In accordance with another aspect of an exemplary embodiment, downhole motor system 150 is operated to maintain lateral accelerations of rotor 42 below about 2 g. In accordance with still another aspect of an exemplary embodiment, downhole motor system 150 is operated to maintain lateral accelerations below about 0.5 g. In accordance with still another aspect of an embodiment, downhole motor system 150 is operated to substantially eliminate lateral acceleration or rotor 266. In one example, RPM 1 may be about 120 RPM, RPM 2 may be 60 RPM, and RPM 3 may be 180 RPM resulting in a combined output to drill bit 32 of 360 RPM.
In another embodiment, the downhole motor system may not be operated in a manner to reduce vibration. That is RPMs first rotor 220 and first stator 200 of the downhole motor system may not be adjusted to reduce vibration. Second rotor 266 and second stator 250 of second downhole motor system 190 may be operated in a manner to reduce vibration. More specifically, the RPM of second rotor 266 and second stator 250 may be adjusted to substantially eliminate eccentric forces. This embodiment may be beneficial with respect to reduce vibration near a vibration sensitive part of the downhole string, e.g. a bottom hole assembly. In order to damp vibration of the downhole motor system, damping elements, e.g. heavy weight drill pipes (not shown), may be included in downhole string 20 to dampen vibrations that may originate from the downhole motor system and which may propagate towards the vibration sensitive part of downhole string 20.
In accordance with an aspect of an exemplary embodiment illustrated in
A valve 324 may be arranged in bypass conduit 310 to selectively control fluid flow therethrough. More specifically, valve 324 may be selectively opened to adjust a flow of drilling fluids into second downhole motor 190 thereby providing additional control of torque developed in second rotor 266 to promote a desired output and/or further reduce vibrations. It is also to be understood that resource exploration system 2 may include a control system (not shown) operable to determine how much fluid may bypass valve 324 and a telemetry system (also not shown) that allows communication between downhole motor(s) and surface system 4. Telemetry may take the form of a mud pulse telemetry system, an acoustic telemetry system, and electro-magnetic telemetry system or a wired pipe telemetry system.
A method of operating a Moineau system to substantially eliminate vibrations, the method comprising: rotating a first rotational member; rotating a second rotational member, each of the first rotational member and the second rotational member including a plurality of lobes; and selecting a first rotational speed of one of the first rotational member and the second rotational member based on: 1) a second rotational speed of the other of the first rotational member and the second rotational member, and 2) the number of lobes of one of the first rotational member and the second rotational member to maintain eccentric force of one of the first and second rotational members below a predetermined threshold.
The method of embodiment 1, further comprising: inputting a fluid flow at a selected flow rate into a housing of the Moineau system, the selected flow rate establishing the first rotational speed of the one of the first rotational member and the second rotational member.
The method of embodiment 2, further comprising: establishing the second rotational speed of the other of the first rotational member and the second rotational member by rotating a drill string operatively coupled to the other of the first rotational member and the second rotational member.
The method of embodiment 1, wherein operating the Moineau system includes operating a downhole motor coupled to a drill string extending into a formation.
The method of embodiment 4, wherein operating the downhole motor includes coupling the downhole motor to another downhole motor arranged uphole of the downhole motor.
The method of embodiment 5, wherein coupling the downhole motor to the another downhole motor includes connecting the downhole motor to the another downhole motor through a dampening member.
The method of embodiment 1, wherein selecting the first rotational speed of the one of the first rotational member and the second rotational member maintains eccentric forces on the one of the first and second rotational members below about 2 g.
A vibrationless Moineau system comprising: a first downhole motor including a first stator having a first number of stator lobes, and a first rotor having a first number of rotor lobes; and a second downhole motor including a second stator operatively connected to the first rotor, the second stator having a second number of stator lobes, and a second rotor having a second number of rotor lobes, wherein the first and second downhole motors are selectively operated to substantially maintain eccentric forces on at least one of the first rotor and the second rotor below a predetermined threshold.
The vibrationless Moineau system of embodiment 8, wherein the second downhole motor is arranged downhole of the first downhole motor.
The vibrationless Moineau system of embodiment 9, wherein the first rotor is operatively connected to the second stator through a dampening member.
The vibrationless Moineau system of embodiment 9, wherein a rotational speed of the second stator is selected based upon a rotational speed of the second rotor and one of the second number of stator lobes and the second number of rotor lobes.
The vibrationless Moineau system according to embodiment 8, further comprising: a bypass conduit having a first end fluidically connected to the first downhole motor and a second end fluidically connected to the second downhole motor.
The vibrationless Moineau system according to embodiment 12, wherein the first end of the bypass conduit is fluidically connected uphole of the first downhole motor.
The vibrationless Moineau system according to embodiment 12, further comprising: a valve fluidically connected with the bypass conduit, the valve being selectively controllable to allow fluid to pass from the first end to the second end.
The vibrationless Moineau system according to embodiment 8, further comprising: a drill bit operatively connected to the second rotor.
The vibrationless Moineau system according to embodiment 8, wherein the first and second downhole motors are selectively operable to maintain eccentric forces on the second rotor below about 2 g.
A resource exploration system comprising: a surface system; and a downhole system including a downhole string operatively connected to the surface system, the downhole string including a vibrationless Moineau system comprising: a first downhole motor including a first stator having a first number of stator lobes, and a first rotor having a first number of rotor lobes; and a second downhole motor including a second stator operatively connected to the first rotor, the second stator having a second number of stator lobes, and a second rotor having a second number of rotor lobes, wherein the first and second downhole motors are selectively operated to substantially maintain eccentric forces on at least one of the first rotor and the second rotor below a predetermined threshold.
The resource exploration system according to embodiment 17, wherein the first and second downhole motors are selectively operable to maintain eccentric forces on the second rotor below about 2 g.
The resource exploration system according to embodiment 17, wherein the second downhole motor is arranged downhole of the first downhole motor.
The resource exploration system according to embodiment 19, further comprising: a bypass conduit having a first end fluidically connected to the downhole string and a second end fluidically connected to the second downhole motor.
The terms “about” and “substantially” are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” can include a range of ±8% or 5%, or 2% of a given value. It is also to be understood that the term “uphole” denotes a direction along the downhole string leading to the surface and the term “downhole” denotes a direction along the downhole string leading into the formation.
While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.
