BOTTOM HOLE BLOWOUT PREVENTER

FIELD OF INVENTION

This invention relates to blowout preventers used near the bottom of a well during drilling of the well.

BACKGROUND OF THE INVENTION

The bottom hole blowout preventer is a device used to control bac flow or displacement of drilling fluids within the drill string by high pressure gas or hydrocarbons encountered while normal drilling or well servicing activities are in progress.

Downhole blowout preventers are known which include a housing engageable in a drill string and which use a ball valve pivotally mounted in the bore of the housing, where the ball valve is rotated from an open to a closed position by means of a cooperating cam sleeve, the cooperating cam sleeve being operated by a solenoid valve in response to a signal received by a downhole unit. The solenoid valve opens up a passage into a chamber above a flanged end of the cam sleeve, and mud pressure entering the chamber forces the cam sleeve down, thus closing the ball valve. Such a downhole blowout preventer is operated from instructions from the surface, and is described, for example, in European Patent Application No. 86304179.4, published December 17, 1986.

Surface controllable rotary valves, actuated by a sleeve, have also been used in the oil industry in production. That is, in the production of well fluids, such as oil or gas from wells, it has been the practice to provide automatically closeable shut-off or safety valves which are located downhole in the

well which are held open by control fluid pressure, the valves closing automatically when control fluid pressure is purposely reduced to allow the valves to close or when damage occurs to the control fluid system at the well head or on an offshore platform. An example of such a safety valve which includes a lateral opening for ease of installing the valve, is described in United Kingdom Patent No. 1,416,085.

However, there does not exist an adeguate automatic downhole blowout preventer useable for drilling purposes. Automatic rotary valves tend to close at times when closure is. not desired, for example, from excess running-in rates, which interferes with pipe fill-up or drainage.

SUMMARY OF THE INVENTION

The inventor has provided a bottom hole blowout preventer for a drill string, the bottom hole blowout preventer having a ball valve pivotally mountable in the drill string; an actuating sleeve disposable about the ball valve within the drill string and having a flow passage, the actuating sleeve being slidable in relation to the drill string in response to downhole over pressure conditions from a first position in which the ball valve is at least partly open to a second position in which the ball valve is closed; and reset means disposable against the actuating sleeve for biasing the actuating sleeve to a chosen position; characterized in that the reset means is adjustable. As a specific example, the reset means (a spring, in this case) is adjusted to bias the ball valve to a half-open position during running in, and a fully open position during normal drilling. In another aspect, the bottom hole blowout preventer is further being characterized by including:

means connectable to the actuating sleeve to regulate the closure rate of the ball valve.

The means to regulate the closure rate of the ball valve may include a first chamber closeable by the actuating sleeve upon sliding of the actuating sleeve to the second position; * a second chamber closeable by the actuating sleeve upon sliding of the actuating sleeve to the first position; a passageway connecting the first and second chambers; and a check valve disposed in the passageway.

The reset means allows the valve to be set to a chosen position. The regulated closure, prevents the unexpected closure of the valve due to temporary over pressure conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

There will now be described a preferred embodiment of the invention, with reference to the figures in which like elements are indicated by like numerals, by way of example, and in which:

Figure 1 is a schematic section of a ball valve type bottom hole blowout preventer;

Figure 2 is a schematic section of a ^' ball valve type blowout preventer depicting a vertical cross- section at 90 degrees to the section of Figure 1;

Figure 3A is an end view of a ball valve for a bottom hole blowout preventer according to the invention; and

Figure 3B is a side view, partially broken away, of the ball valve of Figure 3A.

DESCRIPTION OF THE BEST MODE OF THE INVENTION

Referring to Figures l and 2, the bottom hole blowout preventer 10 includes a cylindrical sleeve 56 having a bore 24 for the passage of drilling fluids and suitably disposed within the drill string sub 94. The sleeve 56 has a top cap 70, and a bottom cap 28, with suitable threaded connections to enable them to be threaded onto sleeve 56. In the sleeve bore 24 there is a valve ball 40 which is rotatably mounted on pivot pins 36, which allow it to rotate on a single axis only normal to the bore 24. The valve ball pivot pins 36 fit in suitably drilled holes 76 in collets 80 fitted to either side of the ball valve 40, and facing up to flats 78 machined on either side of the ball valve 40.

The collets 80 fit into suitably machined sockets 82 in the sleeve 56. The ball valve 40 seats spherically between the upper seat 42 and the lower seat 30 in the bore 24 of the sleeve 56. The valve ball 40, and the seats 42 and 30 are retained within the sleeve 56 by the threaded bottom cap 28. There is a bore in the valve ball 40 extending perpendicular to the pivotal axis of the valve ball 40.

Machined into the flats 78 of valve ball 40 are slots 34 extending radially at 45 degrees from the vertical axis as shown in Figure 3A, and as shown in the broken away portion 35 in Figure 3B. Each slot 34 is designed to be engaged by an actuating pin 32 attached to the drill string sub 94 and travelling within a milled slot 38 in the sleeve 56. An identical set of slots and actuating pins (not shown) are on the other side of the valve to the side seen in Figure 2.

Fitted over the upper outside diameter of sleeve 56 is a retainer 58 with a machined collar 84 on its inside diameter, made to have a close tolerance fit over the sleeve 56 and with an O-ring seal 86 between the sleeve outside diameter and the retainer inside diameter. The retainer 58 limits the vertical movement of the sleeve 56. For high pressure applications, the surface of the shoulder 57 on the sleeve 56 and the surface of the corresponding shoulder 59 on the retainer 58 should be pre-finished to produce a metal to metal high pressure seal.

Two drilled channels 88 in the retainer 58 connect a lower hydraulic chamber 44 to an upper hydraulic oil chamber 66 through a ball check valve 90 that meters oil flow in the upper direction (towards chamber 66) and allows free oil passage in the opposite direction. The size of the orifice in the check valve may be varied according to the desired closure rate of the ball valve 40. The two channels 88 and the chambers 44 and 66 comprise means to regulate the closure rate of the ball valve 40. They are hydraulically connected to the actuating sleeve 56 and it will be understood that "connected* ¹ as used in the claims includes hydraulic connection. The outside diameter of the retainer 58 is threaded at 52 over the lower half of its length and has O-ring seal grooves 22 in its outside diameter above and below the threads 52. The retainer 58 threads into a sub 94 or other sub that becomes an integral part of the drill string and retains the entire blowout preventer assembly in place within the sub.O-ring seals 14 on the sleeve 56 and moulded lip seals 16 on the bottom cap 28 help seal the chambers

44 and 66. Opposing compression springs 50 and 62 preferably bias the sleeve 56 to a ready position (not shown) in which the valve ball 40 is neither fully

closed nor fully open. Pressure from drilling fluid during drilling forces the sleeve 56 to the first position shown in Figure 1, in which the valve ball 40 is fully open. Alternatively, the valve can be pre- set to be fully open during running in by appropriate adjustment of the compression springs 50 and 62, for example for use with stuck pipe conditions and fishing tools. Adjustment of the springs may be accomplished by changing the lengths of the springs. The spring 62 is held between shoulder 60 of the retainer 58 and the shoulder 64 of the sleeve 56. The spring 50 is held between shoulder 46 of the sleeve 56 and shoulder 54 of the retainer 58. Together the springs 50 and 62 constitute reset means disposed against the actuating sleeve 56 for biasing the ball valve to a chosen position.

The manner of operation of the bottom hole blowout preventer is as follows. Forces resulting from a bottom hole over pressure condition act on the lower surfaces 20 of the sleeve 56 and cause it to move vertically within the drill string sub 94 and retainer 58. This upward motion causes the actuating pins 32 to move downward within the milled slots 38 of sleeve 56. The engagement of the actuating pins 32 with the machine slots 34 and the valve ball 40 causes the valve ball 40 to rotate 90 degrees around the pivot pin 36 between the open position shown in Figure l and the closed position shown in Figure 2.

As the sleeve 56, top cap 70 and bottom cap 28 traverse vertically up within the sub 94, a chamber 66 is created between the bottom shoulder 68 of the top cap and the top shoulder 72 of the retainer 58. At the same time, the lower hydraulic fluid chamber 44 closes, and forces hydraulic fluid through channel 88 and the check-valve 90, into the top chamber 66. As these chambers 44 and 66 are sealed to ensure fluid tight integrity one from the other, and from the outer

well fluids, the flow of hydraulic oil 96 from the lower chamber 44 through the metering effect of check valve 90 inhibits the rotating closure rate of the valve ball 40. In the event of a well kick or blowout, pressure forces acting on the lower blowout preventer surfaces force valve closure at a predetermined rate, and ensure a delayed closure. In the case of closure during running in, the delayed closure allows a controlled amount of bypass before closure is initiated. As pressure is egualized across the valve, the valve is automatically reset by the springs 50 and 62 to a chosen position such as an open position. By allowing limited flow at the surface, resulting from the delayed closure, the bottom hole pressures can readily be taken.

If the drill string is run in the hole at an excess rate, bottom hole pressures will tend to urge the valve ball 40 towards closure, but will re-open as the drill pipe fills. The metering effect of the check valve 90 avoids unwanted closure due to variable pressure conditions, including those resulting from drill pipe fill up during running in.

Drilling ahead procedures retain the valve in the fully open position with fluid pressures acting upon the upper surfaces of the sleeve 56. During normal running in procedures, the ball valve 40 will normally stay in the half-open position.

In summary, in the absence of forces from pressure on either of the top or bottom surfaces of the sleeve 56, the compression springs 50 and 62 preferably bias the ball valve 40 in a central half- open position. Forces acting on the upper surfaces of the sleeve, for example during drilling, will bring the valve to a fully open position. Forces acting on the lower surfaces of the sleeve 56 will bring the ball valve 40 to a fully closed position at a rate

that is regulated by the metered closure system. With the relaxation of either the upward or downward force, the blowout preventer will always return to the ready position. The bottom hole blowout preventer as described may be run anywhere in the drill string, and is not restricted to bottom hole operations, although it is most commonly used in bottom hole operations.

Immaterial modifications can be made to the invention described here and these are intended to be covered within the scope of the invention.