INTERNAL BLOW OUT PREVENTER

INTERNAL BLOW OUT PREVENTER

There is presented an internal blow out preventer. More precisely there is presented¹ an internal blow out preventer for use in a drill string, comprising a housing with a valve closure element and associated seals, wherein the valve closure element is configured to be moved between an open and a closed position.

The primary function of an Internal Blow Out Preventer (IBOP) is to shut off the mud (drilling fluid) passage on the inside of a drill string in the event well pressure exceeds limits during drilling operations on a drill rig.

However, the IBOP is also frequently used to prevent spillage of drilling fluids during each instance the top drive of the drill rig is disconnected from the drill string, e.g. each instance a new pipe or section of pipes is added to the drill string. This secondary function of the IBOP as a "mud saver" results in increased wear of the seals of the valve that has several un-desirable consequences.

The most obvious disadvantages are reduced service life of the IBOP valve, leakage when the valve is being used as mud saver after pressure testing, risk of rig downtime earlier than predicted, and more frequent need for seal replacements.

Although the use of two individual valves would solve the above problems, that solution would require additional space in the drill stem of the top drive (drilling machine) , space which is not always available. The length of the drill stem located between the top drive and drill string, is limited by the travel of the top drive pipe handler, which needs to be able to grip around the box of the uppermost pipe of the drill string, just below the drill stem.

A normal set up of the drill stem between the top drive and drill string includes a cross-over sub, a remotely operated IBOP, and a second IBOP, the second IOBP being used as a closing valve at the upper end of the drill string remaining in the well and disconnected from the top drive, and a saver sub that takes the wear and damage of threads when the top drive and the drill string are connected or disconnected.

The IBOP is normally a ball valve, with the advantage that sealing has a radial symmetry, making it relatively easy to manufacture .

The purpose of the invention is to overcome or limit the disadvantages of the prior art .

This is achieved according to the invention with the features as disclosed in the description below and in the subsequent patent claims.

There is presented an internal blow out preventer for use in a drill string, the internal blow out preventer comprising a housing with a valve closure element and associated seals and where the valve closure element is configured to be moved between an open and a closed position, wherein the valve closure element is provided with an inner valve closure element that is configured to be moved between an open and a closed position inside the outer valve closure element. The ^'valve body of the prior art IBOP is thus according to the present invention provided with an additional inner valve closure element which is operated independently of the outer valve closure element enabling the mud saving operation without compromising the sealing performance of the IBOP and without the need for additional length of the drill stem, i.e. between the top drive and drill string.

The flow area of the inner valve closure element may be comparable to, substantially equal to or equal to the flow through area of the outer valve closure element. Thus the inner valve closure element will not restrict flow through the IBOP when fully open.

The outer valve closure element may be separable, and a junction between a first part and a second part may be positioned so as to be out of contact with the seals during movement between the open and the closed position. This feature eliminates the risk of increased wear of the seals.

The inner valve closure element may have a spherical or cylindrical form. Shaped as a ball the inner valve closure element maintains the benefits of using flat, circular seas. However, it may be more challenging mechanically to fit a ball rather than a cylinder inside another ball. Shaped as a cylinder, the inner valve closure element requires more complex machining to accomodate seals but eases the machining of the inner valve closure element and improves the structural integrity of the outer valve closure element. It is worth mentioning that small leaks during mud saving operations are generally acceptable and may permit less stringent machining tolerances .

The outer and inner valve closure elements may be rotatable about a common axis of rotation. Thus, prior art IBOP actua- tion systems including shafts and actuators may be utilized, although using separate functions for the outer and the inner valves are required.

The present invention remedies the problem of reduced service life for the IBOP seals as the valve closure element remains stationary while the inner valve closure element is closed for the mud saving operation.

Below an example of a preferred embodyment is explained with reference to the enclosed drawings, where:

Fig. 1 shows a cross section of an internal blow out

preventer, IBOP, according to the disclosed invention;

Fig. 2 shows a larger scale cross section of IBOP parts when used as a mud saver;

Fig. 3 shows the IBOP in an exploded view;

Fig. 4 shows a cross section of the IBOP in an initial stage of closing as a blow out preventer; and

Fig. 5 shows the same as in fig. 4 in the completely closed position .

On the drawings the reference number 1 denotes an internal blow out preventer comprising a housing 2, a spherical outer valve closure element 4 and a spherical inner valve closure element 6.

The housing 2 in this preferred embodiment is provided with internal threads 8 at its upper end portion 10 and external threads 12 at its lower end portion 14 in order to connect to a pin/box configuration of a not shown Top Drive drill stem.

'Upper' and 'lower' here refers- to the IBOP in its normal working position as shown on the drawings. A central, longitudinal bore 16 extends between the two end portions 10, 14. The bore 16 corresponds with a bore of the not shown drill string.

A shoulder 18 is formed in the bore 16 as an upper portion 20 of the bore 16 has a larger diameter than the rest of the bore 16.

The outer valve closure element 4 is positioned in the upper portion 20 of the bore 16 and connected to two hollow shafts 22 that are protruding through shaft openings 24 in the housing 4. The outer valve closure element 4 and the hollow shafts 22 are rotatable about axis 26. One of the hollow shafts 22 is connected to a not shown first actuator.

A lower ring 28 that abuts the shoulder 18, is provided with a first sealing surface 30 that is configured to seal against the outer valve closure element 4. A lower ring seal 32 provided in the lower ring 28 prevents fluid flow between the lower ring 28 and the body 2.

An upper ring 34, placed above the outer valve closure element 4, is provided with a second sealing surface 36 that is configured to seal against the outer valve closure element 4. An outer ring seal 38 provided in the upper ring 34 prevents fluid flow between the upper ring 34 and the body 2.

The first sealing surface 30 and the second sealing surface 36 constitute the outer valve sealing surfaces.

The outer valve closure element 4 has an opening 40, with an area comparable, substantially equivalent to or equal to the cross section area of the lower portion of bore 16.

The inner valve closure element 6 is positioned inside the outer valve closure element 4 and connected to two shafts 42. Each of the shafts 42 extend through a concentric bore 44 in the respective hollow shafts 22. The inner valve closure element 6 and the shafts 42 are rotatable about axis 26.

A not shown second actuator is connected to one of the shafts 42.

Seals 46 prevent fluid from flowing between the hollow shafts 22 and the housing 2 and between the hollow shafts 22 and the shafts 42.

Inner valve seals 48 positioned in corresponding

recesses 50 inside the outer valve closure element 4 prevents fluid from passing between the outer valve closure element 4 and the inner valve closure element 6.

The inner valve closure element 6 has an opening 52 of comparable, substantially equal or equal cross section area to that of the opening 40 of the outer valve closure element 4.

In one preferred embodiment shown in fig. 2, the outer valve closure element 4 is made of a first valve segment 54 and a second valve segment 56.

After the inner valve seals 48 and the inner valve closure element 6 are positioned inside the outer valve closure element 4, the first and second valve segments 54, 56 are joined at an interface 58 using bolts 60.

In fig. 3 to 5 the housing 2 is removed in order to better show the operating functions of the IBOP 1.

When used as a mud saver, the inner valve closure element 6 of the IBOP 1 is rotated about axis 26 to close the valve opening 40 thus preventing mud from flowing through the IBOP The outer valve closure element 4 is not turned and no wear is caused on the first and second sealing surfaces 30 and 36

When used as an IBOP the inner valve closure element 6 is placed in the open position, see fig. 4 and 5. The inner valve body seals 48 are thus not utilised for IBOP mode of operation .

The outer valve closure element 4 is rotated about axis 26 t a closed position, see fig. 5, preventing flow through the IBOP 1. The first and second sealing surfaces 30 and 36, not subject to wear from mud saver use, function as a reliable, leak-proof barrier against the well pressure.

The interface 58 does not pass over the sealing surfaces 30, 36 during closing or opening of the outer valve closure element 4.