Patent Publication Number: US-2021189859-A1

Title: Method and apparatus for damping/absorbing rotational vibrations/oscillations

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a nonprovisional application which claims priority from U.S. provisional application No. 62/952,233, filed Dec. 21, 2019, and U.S. provisional application No. 62/976,898, filed Feb. 14, 2020, each of which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD/FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to damping vibrations or rotational oscillations during drilling operations using typical drilling systems, such as rotary steerable systems, and specifically to inertial damping systems converting vibration energy into heat energy, resulting in the desired damping effect. 
     BACKGROUND OF THE DISCLOSURE 
     In hydrocarbon drilling operations, boreholes are typically drilled by rotating a drill bit attached to the end of a drill string. The drill bit can be rotated by rotating the drill string at the surface and/or by a fluid-driven downhole mud motor, which may be part of a bottom hole assembly (BHA). For example, a mud motor may be used for directional drilling operations when used in conjunction with measurement while drilling (MWD) and/or logging while drilling (LWD) components. The combination of forces and moments applied by the drill string and/or mud motor and forces and moments resulting from the interaction of the drill bit with the formation can have undesirable effects on the drilling system, including a reduction in the effectiveness of the cutting action, a reduction in the life of the BHA components, damage to BHA components, and/or interference in measuring various drilling parameters. 
     SUMMARY 
     To mitigate such negative effects, BHA components such as the MWD electronics may be equipped with one or more damping systems to draw vibration energy from the BHA and thereby damping the effects associate with torsional vibration excitation. 
     According to some embodiments, a vibration damping device for use with one or more downhole electronics having a longitudinal axis, may comprise a housing mechanically coupled to the downhole electronics, the housing defining a receptacle having a volume, and an inertia element movably supported in the receptacle and having a volume, a mass, and a non-zero moment of inertia about the longitudinal axis. The volume of the receptacle may be greater than the volume of the inertia element so as to define an interstitial volume therebetween and the interstitial volume may be occupied by a fluid or an elastomer. 
     The inertia element may be supported within the receptacle in a manner that allows the inertia element to rotate about the longitudinal axis without contacting the walls of the receptacle, further including at least one of a longitudinal bearing and a radial bearing positioned between the inertia element and the housing. The housing may comprise an annular wall having an outer radius and a central bore therethrough and the receptacle may be defined in the annular wall. In some embodiments, the housing may be integral to the downhole electronics, respectively the electronics&#39; housing. 
     The inertia element may have an outer radius less than the outer radius of the annular wall and the inertia element may have an inner radius greater than the radius of the central bore, and the receptacle may be in fluid communication with the environment surrounding the housing. The device may further include a variable compensation volume, and the variable compensation volume may be in fluid communication with the receptacle. 
     The inertia element may have a shape selected from the group consisting of square toroids, tori, and azimuthally-spaced segments. 
     In some embodiments, a method for tuning a downhole torsional damping device to match at least one downhole electronics, in which the downhole torsional damping device may have a longitudinal axis and may include an inertia element and a damping fluid or elastomer, may comprise the steps of: a) calculating a set of natural frequencies and mode shapes for the downhole electronics based on the mechanical properties of the downhole electronics; b) selecting at least one desired frequency from the calculated natural frequencies; c) tuning the damping device characteristics to match the at least one desired frequency; and d) using the calculated mode shapes to place the damping device. 
     Step a) may comprise calculating a set of natural frequencies and mode shapes for a string of downhole electronics based on the mechanical properties of the downhole electronics and support members associated therewith. Step c) may comprise adjusting one or more properties selected from the group consisting of the mass of the inertia element, material density of the inertia element, moment of inertia of the inertia element to the longitudinal axis, shape of the inertia element, shape of the tool, density of the damping fluid, and viscosity of the damping fluid, and selecting a value that results in a damping tool frequency that most closely matches the desired frequency. The mode shapes may correspond to a calculated amplitude of vibration at each point along the tool and may include nodes and antinodes and step d) may include positioning a damping device at one or more antinodes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a schematic view of a drilling system in which embodiments of the current invention can be used. 
         FIG. 2  is a cutaway view illustrating a possible location for a MWD running gear inside a drill collar of a BHA. 
         FIGS. 3-5  illustrate possible locations for a damping device in a downhole electronics. 
         FIGS. 6-7  are a cross-sections illustrating embodiments of the invention. 
         FIG. 8  is a cross-section and isometric cutaway view illustrating another embodiment of the invention. 
         FIG. 9  is a schematic illustration of torsional vibrational nodes of part of a drill string. 
         FIGS. 10A and 10B  are plots of models illustrating damping of torsional vibration at target frequencies. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Referring initially to  FIG. 1 , a drilling system  100  in which the present apparatus may be used may include a drilling rig  101  positioned above a wellbore  102  that extends into a subsurface formation  110 . A drill string  105  may extend from drilling rig  101  into wellbore  102  and may terminate in a bottom hole assembly (BHA)  103 . Drill string  105  may be driven by the surface equipment of the rig. In some embodiments, BHA  103  may include a drill bit  107 , a motor  106 , which may be a mud motor or other downhole motor, a measurement while drilling (MWD) system, a logging while drilling (LWD) system and/or a steerable system  104 , which may be a rotary steerable system (RSS) which may include a MWD section. BHA  103  may optionally include various other devices, such as logging or measurement devices, communications devices, and the like. If present, steerable system  104  may be used to steer the bit as the wellbore is drilled. The rotational force (torque) required to rotate drill bit  107  can be provided a torque creating or applying apparatus, which may be a drill string  105 , motor  106 , or a combination thereof. 
     According to  FIG. 2 , in some embodiments, one or more downhole electronics  201  may be positioned inside a member of the drill string  105  for performing certain measurements while drilling the wellbore. In this example, a downhole electronics  201  is positioned inside a pressure barrel  202 . One or more downhole electronics  201  and their pressure barrels  202  may be combined to create a string of downhole electronics  203  which is placed inside a drill collar  204  being part of the drill string  105 . Coupling means  205  may also provide mechanical and electrical connections to pressure barrels  202 ′ and  202 ″ and the downhole electronics  201  contained therein, so as to create a string of downhole electronics  203 . Coupling means  205  may also maintain pressure barrel  202  and the contained downhole electronics  201  in a centralized position inside drill collar  204 . Coupling means  205  may have rigid and/or elastic components, such as a plurality of rubber centralizer fins. Depending on the type of coupling means  205 , undesirable effects on the drilling system  100  such as vibrations or rotational oscillations may be transmitted on to the downhole electronics  201  thereby exciting certain natural frequencies of an individual downhole electronics  201  and/or of the string of downhole electronics  203 . 
     According to  FIG. 3 , in some embodiments, one or more damping devices  300  may be positioned inside a pressure barrel  202 . Furthermore, the damping device  300  may be positioned between and affixed to both the coupling means  205  and the downhole electronics  201 . Therefore, the damping devices  300  may be equipped with mechanical connections  302  such as a lock nut, a clamp set, etc. and electrical connections  304  both matching the provided connections of the adjacent downhole electronics  201  and coupling means  205 . Coupling means  205  may also be provided with mechanical and electrical connections to combined pressure barrels  202  and  202 ″ and the downhole electronics  201  contained therein, creating a string of downhole electronics  203  as described. 
     According to  FIG. 4 , in some embodiments, one or more damping devices  300  may be positioned inside the coupling means  205  to which the downhole electronics  201  is affixed to. In this embodiment, damping device  300  may be connected to the coupling means  205  by various connection methods including, threads, glued joints, or a common form-locked and/or force-locked connection, such as a press fit between the cylindrical surface of damping device  300  and a coaxial bore in said coupling means  205 , a serration, or the like. 
     According to  FIG. 5 , in another embodiment, one or more damping devices  300  may be positioned at the opposite end of the downhole electronics  201  internal to the pressure barrel  202 , which is supported at that position but rotationally free along its longitudinal axis. 
     For  FIGS. 3-5 , the position of the at least one damping devices  300  is a matter of design preference, and/or of natural frequency and mode shape. Furthermore, the embodiments illustrated by  FIGS. 3-5  can also be combined in different ways (see for example  FIG. 8 ). Referring now to  FIG. 6 , some embodiments of damping device  300  comprise a housing  602 , a receptacle  604  defined within housing  602 , and at least one component with significant torsional inertia, illustrated as inertia element  600 , disposed in receptacle  604 . In order to be effective, inertia element  600  has certain minimum desired inertia. The minimum desired inertia depends on the energy to be dissipated and can be adapted to the specific application. 
     Housing  602  may be a solid body or have a desired shape. By way of example, in some embodiments, housing  602  may include an annular housing wall  605  defining receptacle  604  and having a coaxial bore  606  and a coaxial cylindrical outer surface  608 , where the coaxial bore  606  may serve as a wire feed through. The thickness of housing wall  605  is a matter of design preference. Inertia element  600  can be any shape having a non-zero moment of inertia about the longitudinal (rotational) axis  601  of housing  602 . By way of example, inertia element  600  may be a square toroid (as illustrated), a torus, a plurality of azimuthally-spaced segments, or other distribution of mass within housing  602 . 
     In some embodiments, receptacle  604  may be configured such that the volume of receptacle  604  is greater than the volume of inertia element  600  so as to define an interstitial volume therebetween. In such embodiments, the interstitial volume, i.e., the volume of receptacle  604  that is not occupied by inertia element  600 , may be filled with a fluid as set out in detail below. Additionally, radial and/or axial bearings may also be positioned in the volume defining specific gap(s) between the housing  602  and the inertia element  600 . Inertia element  600  can be supported within receptacle  604  in a manner that allows inertia element  600  to rotate about axis  601  without contacting the walls of receptacle  604 . Still referring to  FIG. 6 , in some embodiments, the support for inertia element  600  may include longitudinal bearings  610  and/or radial bearings  620  and a fluid. Longitudinal bearings  610  may be positioned between the end(s) of inertial element  600  and the inner surface of receptacle  604 . Radial bearings  620  may be positioned between the inside and/or outside of inertial element  600  and the inner surface of receptacle  604 . Bearings  610 ,  620  can be sliding bearings or roller bearings. If present, longitudinal and/or radial bearings  610 ,  620  can be configured such that inertia element  600  rotates around the centerline of the damping device  300 . If present, longitudinal and/or radial bearings  610 ,  620  can also be configured such that a certain predetermined gap between housing and inertia ring is maintained. In some embodiments, inertia element  600  is disposed in housing  602  in a manner that allows at least some rotation of inertia element  600  about axis  601  relative to housing  602 . In some embodiments, rotation of inertia element  600  about axis  601  is not restricted; in such embodiments, it is possible for inertia element  600  to rotate through 360 degrees. 
     Housing  602  may comprise a single element or may comprise an assembly of two or more parts, which may, by way of example only, be welded together. The embodiment of  FIG. 6  includes such a two-part housing  602 , comprising the two parts  602   a  and  602   b  being welded together (not shown). 
     In some embodiments, housing  602  may include a pressure compensation feature (not shown). If present, the pressure compensation feature may comprise a variable compensation volume. The variable compensation volume may comprise a compensation piston housing with a compensation piston moveably mounted therein. Together, the compensation piston housing and the compensation piston define a variable compensation volume. In some embodiments, the compensation volume may be in fluid communication with receptacle  604  and thus filled with the same fluid as the interstitial volume. Movement of the compensation piston inside the compensation piston housing adjusts the compensation volume so as to achieve a pressure equilibrium between the inside and the outside of damping device  300 . 
     Referring briefly to  FIG. 7 , in other embodiments, inertia element  600  may be split into two or more individual bodies, such as those illustrated at  600   a ,  600   b , and  600   c . The individual bodies may differ in their individual inertias by i) having a different volume, ii) being made of materials having different densities, iii) having different moments of inertia, or a combination of these options. Alternatively, or in addition to splitting inertia element  600  within one damping device  300 , two or more damping devices  300  may be positioned within the string of downhole electronics  203  as illustrated in  FIG. 8 . 
     Referring to  FIG. 6-7 , regardless of the configuration of the inertia element  600  and receptacle  604 , in some embodiments the interstitial volume between inertia element  600  and receptacle  604  may be filled with a fluid. In such instances, the portion of receptacle  604  that is not occupied by inertia element  600  may be occupied by a specifically selected damping fluid, such as a viscous medium including, for example, silicone oil. The damping fluid may have a high viscosity, such as for example up to 1,000,000 cSt at 25° C. In some embodiments, housing  602  and/or a pressure compensation feature may each include ports and channels (not shown) for evacuating or filling the pressure compensation feature  701  and the volume between housing  602  and inertia element  600  with damping fluid. 
     In still other embodiments, the portion of receptacle  604  that is not occupied by inertia element  600  may be occupied by an elastomer or one or more elastomeric bodies. The elastomer needs to have specific elastic and damping properties so that it can deform and dissipate energy while deforming. For both choices (a high viscosity fluid and an elastomer) it is required that the molecular chains of the material move relative to each other so as to dissipate energy. In addition, the elastomer is preferably attached to both the housing  602  and the inertia element  600  in order to transmit torque therebetween. 
     The presence of a viscous fluid or elastomer between the inertia element  600  and the housing  602  will result in internal friction whenever inertia element  600  moves relative to housing  602 . As a result, some of the kinetic energy of the drill string  105 , which may be transmitted by the coupling means  205  on to the string of downhole electronics  203 , is dissipated as heat. Because of the transformation of vibrational energy into heat, the damping fluid may expand, increasing pressure inside receptacle  604 . In some embodiments, housing  602  may contain the pressure and in some embodiments a pressure compensation feature  701  may be used to maintain a desired fluid pressure in receptacle  604 . Alternatively or in additionally, the gap(s) between the outer diameter of housing  602  and adjacent equipment may be eliminated or filled with a thermally conductive material so as to enhance the conductance of heat away from housing  602  and create a path for removing the generated heat. 
     In some embodiments, damping device  300  can be tuned to at least one torsional natural frequency of the downhole electronics  201  comprising component(s) it is intended to protect, which may include, for example, electronics, batteries, sensors, or the like. In these embodiments, the downhole electronics  201  or component is modeled and its natural frequency(ies) is calculated. 
     Damping device  300  can be used to increase the reliability of a downhole electronics  201 . Damping device  300  is especially advantageous in operations that have no designated vibration damping drill string member. Damping device  300  can be integrated into an individual downhole electronics  201  or a string of downhole electronics  203  as a separate device, and/or as a separate device positioned within another member of a string of downhole electronics  203 , or by integrating its components into a torque-transmitting member of the downhole electronics string  203 . 
     According to some embodiments, damping device  300  can be adapted to a downhole electronics  201  thereof using the following steps:
         a) Calculate the torsional natural frequencies, also referred to as Eigen Values or eigenfrequencies, and mode shapes (Eigen Vectors) based on the mechanical properties of the downhole electronics (ODs, IDs, Lengths, and Material Properties). The calculation may be based on a finite elements analysis or the like. In some embodiments, natural frequencies and mode shapes may be calculated for a string of downhole electronics. In such cases, the calculations could be based on the mechanical properties of the downhole electronics and any support members associated therewith.   b) Tune the damping device  300  characteristics to match the desired frequencies. Tuning the device may include varying one or more parameters including the inertia (mass, material density, lever to axis of rotation, etc.) and damping characteristics (type of fluid, fluid viscosity, shear gap width, shear gap length, etc.) of the damping device  300  and modeling or testing the device to determine its frequency response. In some instances, the target frequency may be from 30 Hz up to 3000 Hz. A system including a damping device  300  may be configured to damp vibrations at one or more frequencies. In some embodiments, damping devices tuned to different frequencies can be used to damp multiple (separate) frequencies. In other embodiments, a single damping device  300  that is capable of damping a broad range of frequencies can be used. The effective frequency range of a damping device  300  can be influenced by various parameters, as set out above.   c) Use the calculated mode shapes to position damping device  300  optimally along the string of downhole electronics so as to maximize the dampening effectiveness. As illustrated schematically in  FIG. 9 , for a given string of downhole electronics and frequency, a mathematical model can be used to calculate the amplitude of vibration at each point along the downhole electronics. As illustrated in  FIG. 9 , the amplitude will tend to vary between antinodes A 1 , A 2 , A 3  . . . , i.e. points along the Eigen Vector in which the amplitude is a local maximum or minimum, along the length of the downhole electronics, with a node N (zero value) between each pair of adjacent antinodes. Depending on the string of downhole electronics and the support within the bottom hole assembly, the antinodes may increase or diminish in amplitude along the length of the downhole electronics  201 .       

     In some embodiments, it may be advantageous to position a damping device  300  at each of one or more anti-nodes. In some instances, it may be desirable to position a damping device  300  close to or at the point with the largest absolute value of modal displacement.  FIG. 10  illustrates damping of torsional vibration measured in degrees ( FIG. 10A ) and rpm ( FIG. 10B ). 
     The purpose of the present damping device is to protect downhole electronics from drilling loads that exceed detrimental magnitudes. In some instances, the device may be used for damping loads that occur during drilling operation, such as torque peaks and/or torsional accelerations/oscillations. Downhole electronics may include one or a plurality of said damping devices in different locations. The damping device can be an integral part of the downhole electronics, where all needed elements are integrated into readily available downhole electronics. It can also be added to the downhole electronics as a separate device, where all elements are integrated into on its own.