GB2215369A - Drill string circulating valve - Google Patents

Abstract

A circulating sub for a drill string has inner (16) and outer (18) coaxial subs between which a cylindrical sleeve (20) is coaxially slidable. The sleeve is retained in a first position by sheer pins (22) to close aligned ports (26, 24) in the subs (16, 18). If, for any reason, fluid pressure outside the outer sub drops below a pre-selected value the pressure differential across a piston flange (28) of the sleeve (20) rises to a level sufficient to sheer the pins (22) forcing the sleeve down and opening the ports (24, 26) to allow greater flow of fluid into the drill hole. <IMAGE>

Description

TITLE: Improvements relating to valves The present invention relates to valves.

During a deep well drilling operation a drilling fluid, which may consist of water to which certain substances held in suspension are added to increase its specific gravity and is referred to as "drilling mud", is pumped down through the hollow drill rod, passes through small nozzles in the drill bit and rises to the surface through the annular space between the drill rod and the wall of t drill hole. One function of the drilling mud is to counteract, by its specific gravity and high pressure, any gas, water or oil pressure that may build up in the hole.

The hydrostatic pressure of the drilling mud balances the pressure of formation fluids to prevent the formation fluids entering the drill hole.

However, if the drill bit penetrates a so-called loss zone which is a geological formation, such as a fissure, which cannot support the hydrostatic pressure of the drilling mud the level of the drilling mud drops dramatically. If the loss zone takes drilling mud at a sufficiently high rate the hydrostatic pressure of the drilling mud will drop to a level at which it is no longer able to prevent the influx of formation fluids into the drill hole. It is therefore essential to improve the integrity of such a loss zone as quickly as possible and this is effected by the use of special loss fluids which are pumped down the drill rod.

However, the loss fluids cannot pass through the nozzles in the drill bit without a substantial risk of blocking these nozzles. Therefore, where loss zones are expected in a drilling operation a valve known as a circulating sub is located in tne drill rod adjaent to the drill it. This valve controls large openings in the wall of the drill rod to allow loss fluid to pass into the annular space between the drill rod and the wall of the drill nole to improve the integrity of any loss zones encountered.

One known form of circulating sub suffers from the disadvantage that its method of actuation takes between 10 and 40 minutes from the time a loss zone is detected. A furtner known Form oF circulating sub includes a nozzle which restricts the flow of drilling mud to th: drill bit ond relies or tne pressure drop across t}:e nozzle when a loss zone is encountered to actuate the circulating sub.

Although this noes not have an inherent tim2 delay for actuation, the provision of a nozzle in the drill rod restricting the flow of drilling mud to the drill nit has other disadvantages.

The present invention seeks to provide an improved form of valve.

Accordingly the present invention provides a valve means having a first flow path and a second flow path extending laterally from said first flow path; closure means movable between a first position wherein said closure means closes said second flow path and a second position wherein said closure means opens said second flow path, said closure means being responsive to a pressure difference across said closure means exceeding a pre-selected value to move from said first position to said second position; and wherein said closure means is retained in its second position after actuation.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a partial section through a circulating sub incorporating one embodiment of valve according to the present invention, Fig. 2 is a side elevation of a first embodiment of tensile pin used in the sub of Fig. 1; Fig. 3 is an end elevation of the pin of Fig. 2; Fig. 4 is a further embodiment of tensile pin; Fig. 5 is a view similar to that of Fig. 1 showing the use of tensile pins; and Fig. 6 is an enlarged view in the direction of arrow B of Fig. 5.

The drawing shows a circulating sub 10 for use in a deep well drilling operation. The sub 10 is connectible to the lower end of a drill string (not shown in the drawing) and a drill bit or drill rod carrying the drill bit is connected to the other end 12 of the sub 10.

I*he sub 10 comprises a hollow, cylindrical rod 14 whose upper end is connectible to the drill string and whose lower end has a thin walled extension 16 serving as an inner sub. The inner sub 16 is surrounded by an outer sub 18 in the form of cylindrical tube which is secured at its upper end to the cylindrical rod 14 by screw threaded engagement. The central region of the outer sub 18 is spaced frorn the inner sub 16 to provide an annular, axially extending cavity in which a closure means in the form of a cylindrical sleeve 20 is axially slidable. The sleeve 20 is secured in an axially upper position to the cylindrical rod 14 hy several shear pins 22. Preferably between 6 and 12 such sheer pins are used.The outer sub 18 has a number of relatively large radial ports 24, typically between 1.25 and 1.5 inches (31.75 and 38 mm) in diameter. These ports are angularly spaced about the periphery of the outer sub 18 substantially at the same axial position and, in the absence of the sleeve 20, would communicate with the interior of the cylindrical rod 14 via co-operating ports 26 formed in the inner sub 16.

However, when secured in its uppermost position the sleeve 20 seals the ports 24.

The sleeve 20 is provided with a radially inwardly directed, annular piston flange 28 which slidably abuts the radially outer surface of the inner sub 16 and, when the sleeve 20 is in its uppermost position, lies below or adjacent to the lower edges of the ports 26. In this position, the pressure of the drilling mud acts on the 2 piston 28 (the exposed surface area being typically 2 in 2 (12.9 cm ) to urge the sleeve 20 downwardly and open the port 24. Movement of the cylinder 20 is, of course, prevented by the shear pins 22 under normal operating conditions.

However, when a loss zone is encountered, the hydrostatic pressure of the drilling mud outside the drill string drops, increasing the pressure differential across the piston 28. Because the circulating sub 10 is located at or near the bottom of the drill string the differential pressure across the piston 28 is substantially equal to the pressure loss through the drill bit. If this pressure drop reaches a pre-selected value, the shear pins 22 shear and the sleeve 20 is forced axially down the cavity 21, opening the ports 24 and allowing the drilling fluid or mud to flow at a considerably higher flow rate through the ports 24 and into the drill hole to maintain a sufficiently high hydrostatic pressure in the drilling mud flowing back up the drill hole. Loss fluids can. then be pumped down the drill string to improve the integrity of the loss zone, the ports 24 and 26 being large enough to allow passage of the loss fluids without the danger of their becoming blocked.

Radial ports 30 are provided in the outer sub 18 communicating with the cavity 21 to ensure that there is little or no axial pressure differential across the sleeve itself, only across the piston 28.

A spring (not shown in the drawing) is also provided in the cavity 21 to prevent the sleeve from bouncing back towards its uppermost position after it hits the base of the cavity 21 following shearing of the pins 22.

As will be appreciated, the circulating sub 10 does not provide any restriction at all to the flow of drilling mud down the sub 10 towards the drill bit yet enables the actuating pressure differential of the sub 10 to be defined reasonably precisely by the use of particular shear pins 22. These may typically be brass of 1//8" (3.18mm) diameter requiring a shear force of typically 500 lbs for normal operations.

Fig. 2 shows a preferred form of tensile pin which may be used in preference to a sheer pin. One disadvantage of the use of a sheer pin is that it must be physically sheered between the co-operating surfaces of the sleeve 20 and the cylindrical rod 14, causing drag and frictional resistance during movement of the sleeve 20. This is avoided hy the use of tensile pins in place of sheer pins.

As can be seen from Fig. 2 one preferred form of tensile pin has a reduced diameter or "necking" portion 40 intermediate its ends. The pin itself has a head 42 formed at each end, the head being generally square or rectangular in cross-section. Fig. 3 is an end elevation of the pin of Fig. 2 showing this. The cross-sectional shape of the pin intermediate the heads can be of any suitable form although a generally circular cross-section is normally used.

Fig. 4 shows a further form of tensile pin, again having a reduced diameter portion 40' intermediate its ends, a head 42 of generally square or rectangular cross-sectional shape being formed at each end.

Fig. 5 is a partial section through a circulating sub similar to that of Fig. 1 but showing use of tensile pins of the form shown in Fig. 4 instead of sheer pins. Like parts are given like reference numbers. Fig. 6 is an enlarged view of a portion of the sub of Fig. 5 in the direction of arrow B of Fig. 5.

As can be seen from Fig. 5 each tensile pin 40' (only one of which is shown) is arranged with its axis parallel to the longitudinal axis of the sleeve 20. The lower head 42' of the pin is located in a correspondingly shaped slot 50 in the upper end region of the sleeve 20 whilst the upper head 42' is located in a correspondingly shaped slot 52 in the inner sub 16. The shape of the heads 42' and the co-operating slots are such that the heads cannot be drawn from the slots by relative axial displacement of the sleeve 20 and inner sub 16. Firstly, if the pressure differential across the piston 28 increases past a pre-selected value the tensile pins 4O' "neck" and then break allowing the sleeve 20 to be forced axially down the cavity 21, opening the ports 24. It can be seen, therefore, that the tensile pins break without contacting the sleeve or inner sub at their break points and this allows the pressure differential at which the sleeve 20 is actuated to be set more accurately than with sheer pins.

Claims (13)

1. A valve means having a first flow path; a second flow path extending laterally from said first flow path; and closure means movable between a first position wherein said closure means closes said second flow path and a second position wherein said closure means opens said second flow path, said closure means being responsive to a pressure difference across said closure means exceeding a pre-selected value to move from said first position to said second position; and wherein said closure means is retained in its second position after actuation.

2. A valve means as claimed in claim 1 wherein said second flow path extends substantially at right angles to said first flow path.

3. A valve means as claimed in claim 1 or 2 wherein said closure means is movable between said first and second positions in a direction substantially parallel to said first flow path.

4. A valve means as claimed in any of claims 1 to 3 comprising a first member through which said first flow path extends and which has a valve port from which said second flow path extends, and wherein said closure means is slidable relative to and axially of said first member between said first position wherein said closure means closes said valve port and said second position wherein said closure means opens said valve port.

5. A valve means as claimed in claim 4 wherein said closure member and said first member are substantially tubular and coaxial and said closure means has a peripheral flange means extending between said closure means and said first member, the arrangement being such that said pressure difference acts on said flange means for urging said closure member towards said second position.

6. A valve means as claimed in claim 5 wherein said closure means and said first member are substantially cylindrical and said flange means is substantially annular.

7. A valve means as claimed in claim 5 or 6 wherein said closure means coaxially surrounds said first member,and said valve port comprises an opening in a side wall of said first member through which said first flow path communicates with said flange means.

8. A valve means as claimed in any of claims 4 to 7 wherein said closure means is retained in said first position by sheering means.

9. A valve means as claimed in claim 8 wherein said sheering means comprise a plurality of sheer pins connecting said closure means to said first member and adapted to sheer in response to said pressure difference exceeding said pre-selected value.

10. A valve means as claimed in any of claims 4 to 7 wherein said closure means is retained in said first position by tensile means.

11. A valve means as claimed in claim 8 wherein said tensile means comprise a plurality of tensile pins connecting said closure means to said first member and adapted to fracture under tension in response to said pressure difference exceeding said pre-selected value.

12. A valve means as claimed in any of claims 4 to 11 for attachment to a drill rod wherein said first member is an inner sub adapted to be connected to said drill rod and further comprising an outer sub coaxially surrounding said closure means and said inner sub for receiving a drill bit.

13. A valve means substantially as hereinbefore described with reference to the accompanying drawings.