TECHNICAL FIELD OF THE INVENTION

This invention relates, in general, to handling of drill pipe or other tubular members in a vertical position, and, in particular, to slip assemblies for pipe assemblies, such as drill pipe or production pipe, which are useful in oilfield operations for drilling, setting casing, or placing or removing any tubular member from a wellbore, for example.

BACKGROUND OF THE INVENTION

Without limiting the scope of the present disclosure, its background will be described with reference to the addition or removal of pipe from the top end of the drill string. During the addition or removal of pipe from a drill string, it is often necessary to suspend the drill string by a drill string assembly that includes a slip assembly which is mounted in the floor of the drilling rig and through which the drill string extends downwardly into a borehole. A slip bowl is included for handling drill pipe on a drilling rig. During these handling and holding operations, scratching and other deformations of the drill string become an issue at the slip assembly as the weight of the drill pipe in the drill string requires the use of teeth within the slip assembly to bite and forcefully hold the drill string. Accordingly, a need exists for improvements in oil field technology that prevent the scratching and deformation of drill strings during the holding of oil field piping and other operations.

SUMMARY OF THE INVENTION

It would be advantageous to achieve a slip assembly that would improve upon existing limitations in functionality. It would also be desirable to enable a mechanical-based solution that would prevent the scratching and deformation of tubulars, such as drill strings, during the holding of oil field piping and other operations due to the weight of the tubulars. To better address one or more of these concerns, a slip assembly for handling a tubular, such as drill pipe, is disclosed. In one embodiment, the slip assembly includes a slip bowl having slip segments inserted therein. Each of the slip segments includes a force amplifier member slidably disposed to a slip member. An amplifier is disposed within a pocket formed at the slip member, and upon actuation, the amplifier decreases the angle of inclination of the slip assembly with respect to the tubular. A pad base is secured to the force amplifier member and configured to contact the tubular. The pad base includes a frictional material. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:

Figure 1 is a front perspective view of one embodiment of a slip assembly preparing to grip a drill pipe according to the teachings presented herein;

Figure 2 is a cross-sectional view of the slip assembly depicted in figure 1 gripping the drill pipe;

Figure 3 is a front exploded view of one embodiment of a force amplifier, a pad base, and a pad element forming a portion of the slip assembly depicted in figure 1 ;

Figure 4A is a force schematic illustrating one embodiment of desired axial load and various forces with respect to a slip assembly; and

Figure 4B is a force diagram accompanying the force schematic depicted in figure

4A.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts.

The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention.

Referring initially to figure 1, figure 2, and figure 3, therein is depicted one embodiment of a slip assembly 10 for handling a tubular T, such as, for example, drill pipe on a drilling rig having a rotary table. A slip bowl 12 may be supported in the rotary table, for example, and has an upper end 14 and a lower end 16 and a tapered axial bore 18 therethrough for passage of the tubular T, which is depicted as a drill pipe having sidewall

20, for example. In one embodiment, the tapered axial bore 18 has a constant slope from the upper end 14 to the lower end 16. Multiple slip segments, including slip segments 22, 24, 26, 28, 30 are provided for insertion into the slip bowl 12. It should be appreciated that although a drill pipe is depicted, the slip assembly 10 and teachings presented herein are applicable to any type of tubular.

The slip segment 22 includes an upper end 40 and a lower end 42 and an inner surface 44 which defines the shape of the tapered axial bore 18 for passage of the tubular T. The slip segment 22 includes a body member 46 with a central bore 48 extending therethrough for receiving the tubular 20. The inner surface 44 is generally disposed at an acute angle relative to the central bore 48 such that the diameter of the central bore 48 is greater at the upper end 40 than at the lower end 42.

The slip segment 22 includes a slip member 50 having an inner-facing tapered inner slip surface 52 and an outer-facing tapered outer slip surface 54. The outer-facing tapered outer slip surface 54 is slidably disposed on the inner surface 44 of the slip segment 22 of the slip bowl 12. A pocket 56 is positioned at the inner-facing tapered inner slip surface 52.

A force amplifier member 60 has a substantially tapered contour profile defining an outwardly-facing tapered outer slip surface 62 and an inwardly-facing tapered inner slip surface 64. A tail opening 66 is located on the inwardly-facing inner surface 64 and forms a portion of a dovetail joint 68 between the force amplifier member 60 and an adjacent and inner-positioned pad member 70. A downwardly-facing shoulder 72 is located on the outwardly-facing tapered outer slip surface 62 at the pocket 56. A downwardly- facing shoulder 73 is located below the downwardly-facing shoulder 72 proximate the pocket 56. An upper contact surface 74 is disposed against a limiting plate 76. The outer-facing tapered outer slip surface 54 of the slip segment 22 is slidably disposed on the tapered inwardly- facing tapered inner slip surface 64 of the force amplifier member 60.

The adjacent and inner-positioned pad member 70 includes a pad base 80 and a pad element 82 having a frictional material 84 attached thereto. In one embodiment, the friction material 84 may provide a coefficient of friction of 0.15. Further, the friction material may increase the coefficient of friction between the slip assembly 10 and the tubular T. More specifically, the pad base 80 includes an outwardly-facing outer surface 86, an inwardly- facing inner surface 88, an upper surface 90, and a lower surface 92. The outwardly-facing outer surface 86 includes a pin projection 94 that mates with the tail opening 66 to form the dovetail joint 68 between the force amplifier member 60 and the adjacent and inner- positioned pad member 70. The inwardly-facing inner surface 88 of the adjacent and inner- positioned pad member 70 includes multiple beneficially arranged die carrier projections 95, 96, 98, 100, 102 and a central elongated slot 104 for mounting the discrete pad element members 106, 108, 110, 112 thereto. The discrete pad element members 106, 108, 110, 112 include respective die carriers 114, 116, 118, 120 having rear wedge projections 122, 124, 126, 128 extending thereform. The rear wedge projections 122, 124, 126, 128 are beneficially arranged to engage in a mating relationship with the die carrier projections 95, 96, 98, 100, 102. A locking rod 130 may be received within the central elongated slot 104 and secured in place to prevent lateral movement of the die carriers 114, 116, 118, 120 relative to the pad base 80.

The die carriers 114, 116, 118, 120 may include inwardly facing teeth- like projections extending therefrom or have another form of profile presented. The die carriers 114, 116, 118, 120 may have generally arcuate inner surfaces which have corresponding curvature to the outer surface of the tubular 20 to be handled by the slip assembly 10. In another embodiment, as shown, the die carriers 114, 116, 118, 120 may include the frictional material 84 attached thereto and a substantially flat face with some or no curvature.

Further, in one embodiment, the die carrier projections 95, 96, 98, 100, 102 and the die carriers 114, 116, 118, 120 may provide for the optimization of the mechanical structure and material science. In one implementation, the design may include variations in the gap size between toothed sections, variations in the length of the toothed sections, tooth size and geometry, and depth.

In one embodiment, the slip assembly 10 may include a sensor array associated with the pad member 70 and the sensor array may indicate the relative axial position of the drill pipe with respect to the plurality of slip segments. This may be accomplished by the sensor array measuring a characteristic selected from the group consisting of vibration, shaking, weight, and holding force. The sensors may be utilized to actuate a warning signal when the tubular 20 is about to slip out of the slip assembly 10. The slip assembly 10 provided herein furnishes optimized pressure distribution along the tool length. Such optimal pressure distribution in combination with the sensor array ensures the drill string may be held firmly without scratching or drill deformation. The slip segment 24 is similar in structure and function to the slip segment 22. The slip segment 24 includes an upper end 140 and a lower end 142 and an inner surface 144 which defines the shape of the tapered axial bore 18 for passage of the tubular 20. The slip segment 24 includes a body member 146 with a central bore 148 extending therethrough for receiving the tubular 20. The inner surface 144 is generally disposed at an acute angle relative to the central bore 148 such that the diameter of the central bore 148 is greater at the upper end 140 than at the lower end 142.

The slip segment 24 includes a slip member 150 having an inner- facing tapered inner slip surface 152 and an outer-facing tapered outer slip surface 154. The outer-facing tapered outer slip surface 154 is slidably disposed on the inner surface 144 of the slip segment 24 of the slip bowl 12. A pocket 156 is positioned at the inner-facing tapered inner slip surface 152.

A force amplifier member 160 has a substantially tapered contour profile defining an outwardly-facing tapered outer surface 162 and an inwardly-facing tapered inner surface 164. A downwardly- facing shoulder 172 is located on the outwardly- facing tapered outer slip surface 162 at the pocket 156. A downwardly-facing shoulder 173 is located below the downwardly-facing shoulder 172 proximate the pocket 156. An upper contact surface 174 is disposed against a limiting plate 176. The outer-facing tapered outer slip surface 154 of the slip segment 24 is slidably disposed on the inwardly- facing tapered inner slip surface 164 of the force amplifier member 160.

A force amplifier 190, including a spring 192 and a sliding cylinder 194 in one embodiment, is positioned within the pocket 56. Similarly, a force amplifier 200, including a spring 202 and a sliding cylinder 104 in one embodiment, is positioned within the pocket 156. With respect to the force amplifier 190 as an example, the force amplifier 190 is designed in a way that movement of the slip assembly 10 remains the same as on an existing slip assembly. As shown, in one embodiment, with hydraulic actuators, initial radial force is provided to the pipe member-tubular contact. This force is the same as in original tool since the force amplifier rests on the limiting plate in its upper position, which is provided by a spring and sliding cylinder, and during slips downward moving stays in that position. The initial force is therefore provided solely by the tool inclination system. After the tubular T is released, the tubular T will move the force amplifier relatively to the slip assembly 10 and much larger radial force will be provided since inclination angle may be 1° to 5° or 3°. It should be appreciated that the angle will change according to selected friction material and its minimum friction coefficient. As discussed, the force amplifier member 160 is attached to the slip assembly 10 by a dovetail connection that allows only linear movement in a predefined direction. Moreover, the force amplifier member 160 rests against the limiting plate 76 when biased by the force amplifier 190.

Referring to figure 4A and 4B, a force schematic with accompanying force diagram illustrates one embodiment of desired axial load and various forces with respect to a slip assembly 10 and a tubular T. In one oil field implementation, a friction coefficient of 0.15 is theoretically the lowest value at which the non-marking friction-based contact been the slip assembly 10 and tubular T may occur. Also, in one implementation, analysis shows that 400 MT is the maximum load that 5.5" pipe made of SM25CrW material can transfer without yielding, hence 500 MT load should not be considered as possible loading case for this particular pipe. In this example, the pad base and pad element may consist of steel or aluminum base part and a cover made of friction material, is further developed with a main objective to evaluate feasible technical solutions for the friction cover. A 750-TON Hydraulic Control Line Spider (HCLS-750) tool, manufactured by Frank's International N.V. of Houston, Texas, was taken as a reference for all loading and geometrical conditions and limitations. According to the given reference tool (HCLS-750) and desired axial load, forces on each pad element are calculated regarding the mathematical models shown in figure 4A and figure 4B. From figure 4 A, the following equation for the radial force F _r can be derived:

^F q

F _r = - (Equation 1) where F _g represents axial force (i.e., pipe weight).

If axial force is provided solely by the pipe string weight, then the axial force needs to be transferred through the contact between the tubular 20 and the slip assembly 10 or, in one embodiment, the pad element that will be connected to the slip assembly 10. The needed friction coefficient between the tubular 20 and the pad element depends on the tool angle ai and the friction coefficient between the slip assembly 10 and the slip segment, calculated as follows:

Mpipe I PAD > ^tan (« + δ) (Equation 2) Assuming the following values for the equation:

• Tool: HCLS-750

• Tool angle a = 18.4°

• Pipe: 5.5" SM25CrW (R _p0 .2 = 125M, wall = 0.415")

· Maximum PAD length L = 544mm;

then the friction coefficient between the tool and the slip: = 0.15 => = ΐ8η £ => £ = 8.53° such that the following is true:

Upipe/PAD > tan(18.4° + 8.53°) = 0.51

This calculation shows that needed friction coefficient between the pipe and the pad element in order to prevent pipe slippage has to be at least 0.51. Since this kind of friction coefficient in the presence of contaminants is practically impossible to achieve, additional radial force has to be provided somehow. To provide additional radial force the angle of inclination ai is decreased to 012 by way of the inclination I provided by the force amplifier member and force amplifier as discussed hereinabove.

The order of execution or performance of the methodologies illustrated and described herein is not essential, unless otherwise specified. That is, elements of the methods may be performed in any order, unless otherwise specified, and that the methods may include more or less elements than those disclosed herein. For example, it is contemplated that executing or performing a particular element before, contemporaneously with, or after another element are all possible sequences of execution.

While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.