Apparatus for stripping fluid from well pipe

[57] ABSTRACT

The apparatus is used in conjunction with a rig to strip mud or oil from a tubular string as it is pulled from a well. The apparatus comprises a pair of opposed, overlapping rubber pads mounted in a container. One or more air cylinders or like means link the pads. The cylinders can be actuated from the rig floor to draw the pads together around the string as it sways laterally during tripping. The pressure with which the pads press against the string can be adjusted; this permits the unit to operate as a stripper when the string is being pulled from the well, and as a well bore cover when the string is being run back into the well.

Claims, 7 Drawing Figures

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PATENTED ΗΑΪ 22 1973

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PATENTED Μϊ 22 1973

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PATENTED Ο 22 1975

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3,733,641 and which can be actuated from the rig floor to close about the well string with a selected pressure, either when pulling out of the well or running back into it. It is a further object to provide a device which is adapted 5 to permit the passage of large diameter tools while still wiping them dry.

It is another object to provide a wiper device of this type having pads which can be closed across the well bore when the string is in the rig derrick, so as to pre10 vent foreign objects falling into the well bore.

It is another object to provide a wiper device constructed so that the passage of enlargements in the string through the wiper pads will cause the pads to move apart, but without any substantial increase in the I³ pressure with which the pads press against the string.

It is another object to provide a wiper device which is capable of stripping odd-shaped joints present in the string, such as the Kelly joint.

It is another object to provide a compact unit which will fit within the narrow confines of a rig’s substructure.

It is another object to provide a wiper device which is simple to build and maintain and which does not be₂₅ come easily jammed by the caking of drilling mud therein.

It is another object to provide a wiper device which can be adjusted to satisfactorily strip strings of substantially different outside diameters, such as drill collars ₃θ and sucker rods.

It is another object of this invention to provide a wiper device having laterally movable wiper pads and actuating means mounted on and linking the pads for opening and closing them, whereby the pads and actu35 ating means can move laterally as a unit with the well string when it sways from one side to another.

In accordance with the invention, a pair of overlapping wiper pads are positioned within a container. The container has aligned top and bottom apertures, which 40 permit of the passage of the well string therethrough.

It is adapted to be mounted on the upper end of the rig’s conductor pipe, the well pipe or the well head (all hereinafter referred to as “the well head”), and functions to trap stripped fluid so that the fluid will flow 45 back into the well head. The wiper pads are spaced from each of the container side walls and are thus free to move in a horizontal plane. Each wiper pad comprises a rubber block sandwiched between two Ushaped plates. The block has a generally horseshoe³θ shaped opening formed in its inner edge. When the pads are pressed against the well string, the opposed faces of the two block openings conform to the string surface and wipe its full circumference dry. A pair of double-acting cylinders are mounted on and link the ³³ pads. Each cylinder is disposed along one longitudinal edge of the pad structure and has its piston attached to one pad and its barrel attached to the other. Actuation of the cylinders draws the pads toward each other longitudinally or forces them apart. Flexible air hoses or ⁶⁰ conduits connect each end of each cylinder with a source of pressurized air or like fluid. A valve, preferably located on the rig floor, is provided to control the supply of air to the lines so as to direct air into either ₆₅ end of each cylinder so that they can be expanded or contracted to adjust the positions of the pads. An accumulator tank is provided in the air line for closing the pads. When an enlargement, such as the bit, forces the

APPARATUS FOR STRIPPING FLUID FROM WELL PIPE

BACKGROUND OF THE INVENTION

This invention relates to a wiper device for stripping fluid, such as drilling mud, oil or the like, from the exterior surface of a well string.

In oil field operations, a well string is usually disposed within the bore of a producing or drilling well. In the case of the well being drilled, the string may comprise a bit, drill collars and drill pipe. In the case of a producing well, the string may comprise tubing or sucker rods. The expression “well string”, as used herein, is intended to cover the various strings which may be present in a well bore and which are periodically tripped by a rig. It is to be noted that any one of these well strings is comprised of parts of different outside diameter; for example, a typical drilling string might have a 12 ½ inch O.D. bit, 6 % inch O.D. drill collars and 4 % inch O.D. drill pipe.

When the well string is drawn or tripped out of the well bore, a fluid coating usually adheres to the string’s outer surface. In the case where the well is being drilled, this fluid is usually drilling mud; in the case of a producing well, the fluid is normally oil. It is standard practice to strip or wipe this fluid from the string at the well head. If this is not done, the fluid drops on the rig floor and makes it too slippery to work on. In addition, the fluid often has substantial value and it is therefore desirable to conserve it within the well bore or mud tank system.

Up to the present time, it has been conventional to use a rubber collar for stripping. This collar is brought into operation by removing the rotary bushing in the rig’s floor, threading the collar over the upper end of the string, and working it down until it seats on the annular shoulder of the bushing bore. The heavy bushing is then replaced in the bore to hold the collar in place around the string. The stationary collar tightly embraces the string and wipes it clean as it is pulled through it.

The rubber collar is characterized by some shortcomings in its role as a wiper. For example, the insertion and removal of the collar are time-consuming and expensive operations. The collar is not adapted to permit the passage of the large diameter tools, such as reamers, stabilizers and bits, which are normally present in a drilling string; hence the collar must be removed before these tools are reached. Since the collar is fixed by the bushing, it cannot move or float sideways with the string when it sways back and forth during a trip. As a result, a portion of the string’s circumference is often left unwiped. The fluid which is stripped from the string is not contained in any way and splashes on the rig substructure and blow-out preventer. This makes a mess which has to be cleaned up. When the string is out of the well, the well bore is open and metal objects can drop into it and cause future drilling problems. Along the same line, the collar is usually not used when tripping back into the well; as a result, metal objects can fall into the open annular space between the well string and bore wall.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a wiper device having enclosed wiper pads which remain permanently in place over the well head during rig operations

3,733,641 pads apart, the back flow of air is absorbed in the accumulator tank with no significant increase in pressure.

The device has certain advantageous features. More specifically, the resultant structure is operative for most well strings and yet is simple and compact enough to fit within the sub-structure of small drilling rigs. The pads, with the air cylinders mounted on them, are not restrained from lateral movement; they can “float” with the string and continuously wipe its entire circumferential surface. Because the pressure applied to the pads can be varied, the unit can be used during tripping in both directions (the pressure applied when running in with dry pipe should be less than that when pulling wet pipe). The provision of the accumulator tank permits the pads to accomodate the passage of a 4 ½ inch O.D. drill pipe or a 12 Va inch O.D. bit without damage. Without the tank, the increase in operative pressure occastioned by the passage of the bit would subject the rubber pads to severe wear and possible tearing. When the string passes out of the unit, the pads automatically move to a fully closed condition, thereby bridging the well bore and providing a hole cover. If it is desired to open the pads to a fully open position, this can easily be done by reversing the air pressure to the opposite ends of the cylinders. The container serves to catch the oil or mud which has been stripped and directs it back into the well head; the rig sub-structure is thus kept clean and there is little or no pollution due to oil or oilbase mud dropping onto the ground.

Broadly stated, in a wiper device for stripping fluid from the outer surface of a well string, which device comprises a container having side walls, a pair of horizontal wiper pads disposed within the container and slidable between an open position, wherein they are disassociated from the well string, and a closed position, wherein they press against the well string, the invention comprises the following improvement: a container having side walls which are outwardly spaced from the sides of the wiper pads to permit of lateral movement of the pads therewithin; at least one cylinder assembly mounted on and linking the wiper pads for opening and closing them; and flexible means, connected to the cylinder assembly, for supplying operating fluid to it.

DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a top view of a portion of the preferred form of the device;

FIG. 2 is a side view of the device of FIG. 1, showing a well string passing therethrough;

FIG. 3 is a side view of the device of FIG. 1 incorporated into a rig structure;

FIG. 4 is a side view of another embodiment of the device, showing it mounted on the well head;

FIG. 5 is a perspective view of part of the embodiment shown in FIG. 4; and

FIG. 6 is a side view of the device of FIG. 4 shown in place within a sub-structure of a drilling rig; and

FIG. 7 is a top view of a wiper pad used in the device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The Container

As illustrated in the drawing, the container 1 is boxlike in form and has top, bottom and side walls 2, 3 4. aligned openings 5, 6 are provided in the top and bot tom walls 2, 3. The bottom opening 6 is slightly smaller in diameter than the well head 7 so that a shoulder 8, which seats on well head 7, is provided. A skirt element 9 extends downward from bottom wall 3. This element 9 has an inwardly curved section 10, which, in combination with the well head 7, defines an annular chamber 11. An inflatable gasket 12 is disposed within the chamber 11 for sealing the device to the well head 7. A depending section 13 extends downward from the curved section 10 and has openings therethrough for receiving lock screws 15. The screws 15 fix the container 1 on the well head 7.

In operation, the container 1 functions to trap the fluid which is stripped, so that it can drop back into the well head 7.

The Wiper Pads

The upper and lower wiper pads 16a, 16b each comprise an elastic, resilient block 17 sandwiched between a pair of U-shaped plates 18, 19. The three parts are bonded together to form a solid unit.

The block 17 is suitably formed of neoprene rubber. One suitable block has a width of 18, length of 16, thickness of 1, and is made of material having the characteristics listed in Table 1.

TABLE I

Hardness, ASTM D-2240, A Durometer — 50 Tensile strength, ASTM D-412, psi — 2500 Ultimate elongation, ASTM D-412, percent — 450 Tear test, ASTM D-624, Die “C”, lbs./lin.inch —250 psi

Accelerated aging test, oven aged hrs./212°F, ASTM D-573 :

Hardness, A Durometer — max. change 15 points Tensile strength — max, change 15 percent Elongation at break — max. change 40 percent Compression set, ASTM D-395 hrs./158°F, Method “B”, percent —max. deformation 25 percent.

The block 17 defines a horseshoe — shaped groove or opening 21 in its inner edge. The opening 21 is cut so that the block 17 will conform to the surface of the well string 22 when pressed thereagainst. A pair of opposed blocks 17, having an opening 21, as shown in FIG. 7, with a radius of 2 inches are adapted to wipe almost any well string in common use at this time. As shown in FIGS. 1 and 2, the container 1 has side walls 4 which are spaced outwardly from the sides of the wiper pads 16α, 16b to permit of lateral movement of the pads.

The Cylinders

Biasing means, such as the double-acting air cylinder assembly 23, links the two wiper pads 16α, 16b. Each assembly 23 includes a piston 24 and barrel 25. The piston 24 is connected, by a pin and yoke assembly 26, with a lug 27 extending up from the lower wiper pad 16b. The barrel 25 is connected, by a collar 28, to the upper wiper pad 16α. Expansion of the cylinder assemblies 23 will slide the pads 16α, 16b apart to the open position against the side walls 4 of the container 1. Contraction of the assembly 23 will slide the pads 16α, 16b to a closed position wherein they press against the well string 22. When the well string 22 is pulled out from between the pads 16α, 16b, further contraction of the assemblies 23 will cause the pads to overlap to such an extent that they provide a closure or cover over the well bore.

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Means for Supplying Closing Force

The cylinder assemblies 23 are actuated by an air system. This system comprises a source 30 of pressurized air, first and second flexible air lines 31, 32 connecting the source 30 with the assemblies 23, and an accumula tor tank 33 connected into the first or closing air line 31. The rig is usually equipped with an air compressor to provide the air source 30. If not, a bottle of compressed air can be provided on the rig floor. A five-way valve 34 is connected to the air source 30 for directing at the rig floor. The air line 45 is suitably tied in with the air supply on the rig.

Springs 46 are attached at one end to each of the wiper pads 16α, 16b and at the other end to the rig 5 structure 47. These springs 46 act to normally urge the pads 16α, 16b to the fully open position.

In operation, the return springs 46 are set with a pressure such as 60 lbs. Pressurized air is then admitted to the air cylinder 43 to pull the member 39 down and '0 partly stretch the spring 42b so as to overcome the tension of the return springs 46 and exert a pressure with each pad 16α, 16b of about 70 lbs. The wiper pads 16α, 16b, whose weight might be about 60 pounds, tightly embrace the well string 22 and are lifted slightly off the container bottom wall 3 when the well string is passing therethrough. The pads 16α, 16b float with the string 22. When an enlargement in the string forces the pads 16α, 16b apart, the member 39 is drawn upwards. However, there is no significant increase in pressure involved, since the spring 42b stretches to accommodate this movement. When the well string 22 is lifted out from between the pads 16α, 16b, the pressure on the said pads causes them to further overlap so as to provide a closure. When the air pressure is released, the return springs 46 automatically draw the pads 16α, 16b to the fully open position.

Important Features

The device is controlled from a convenient location, such as the rig floor. The number of parts within the container are kept as small as possible so that its outside dimensions are small; as a result, it can be accomodated within the limited space available in the rig sub-structure. The wiper pads literally float with the well string so that there is little wear. The pads can undergo several inches of wear and still remain operative. There is provision for the passing of string enlargements through the pads without severe pressure increase. The mud or oil which is stripped is retained and returned to the well head. The pads can provide a closure across the well bore and prevent foreign objects falling into it. The adjustability of the closing force or pressure enables the pads to be closed when the well string is being tripped in either direction. When the string is being run in, the pads function to deflect gas kicks. By having these features in combination, the device is a practical and workable tool.