Valve for wellbore tubulars

Abstract

A valve 1 for controlling fluid flow in a wellbore tubular, the valve 1 comprises: a tubular body 2; a biased closing element 3 located in the tubular body 2 and configured to prevent flow in a first direction through the valve when in a closed position (Fig.4b); and a locking structure 7 for locking the biased closing element 3 in an at least partially open position, wherein the locking structure is configured to irreversibly release the biased closing element 3 in response to a fluid flow in the first direction through the valve exceeding a threshold (Fig.4a). In a preferred embodiment, biased closing element 3 is a flapper and locking structure 7 is a bracing element braced between the flapper 3 and tubular body 2. The release threshold may be increased or decreased by decreasing or increasing respectively the surface area of an extended region 11 of locking structure 7.

Description

Technical Field The invention relates to a valve for wellbore tubulars to control fluid flow through the tubular. Background Checking valves are conventionally used in drill pipes. The checking valve allows drilling fluids to circulate down the drill pipe to the drill head, whilst preventing formation fluids from flowing back up the drill pipe. A checking valve is therefore a one-way valve. A so called “float valve” has a flapper or lid and a spring to close the valve. The flapper prevents fluids from flowing up the drill pipe, whilst being easily pushed open by fluids circulated down the pipe. To equalise pressure, the drill pipe above the valve is filled from the topside during run in. However, this slows down the run in operation. Summary Convertible float valves can solve this problem by being in an open state during initial run in, allowing mud to flow upwards past the valve section in the pipe. The valve is then activated by active intervention of an operator to convert it into a standard float valve. A problem with such a convertible float valve is that it provides no protection against unexpected influx upwards during run in, prior to activation by an operator. If influx occurs when the valve is still open, formation fluids can reach the surface before an operator has the chance to activate the valve. Hence, for safety reasons, standard float valves are still often used and preferred. The present disclosure provides an improved convertible float valve, which is automatically converted to a standard float valve in response to influx. According to a first aspect there is provided a valve for controlling fluid flow in a wellbore tubular, the valve comprising: a tubular body; a biased closing element located in the tubular body and configured to prevent flow in a first direction through the valve when in a closed position; and a locking structure for locking the closing member in an open position, wherein the locking structure is configured to release [let’s make sure to back this up by structural features, how is it achieved?] the biased closing element in response to a fluid flow in the first direction through the valve exceeding a threshold. Hence, during run in, the valve can remain open, allowing mud to flow (slowly) up and fill the tubular above the valve to equalise pressure. However, if the flow up the tubular exceeds the threshold (e.g. due to influx), then the locking structure releases the biased closing element, which moves into the closed position, thereby preventing further flow up through the valve. The wellbore is filled with mud (which is a term of art for a weighted fluid used for this purpose) to prevent or reduce formation fluids entering the wellbore. The biased closing element typically comprises a flapper that is pivotally attached to the tubular body and biased to close against a lip in the tubular body. The flapper and / or the lip may comprise a seal for sealing against the other. The flapper may be biased by spring attached to the flapper and to the tubular body. The valve can be configured so that the biased closing element is released in response to a fluid flow in a second direction through the valve exceeding a second threshold, wherein the second direction is opposite to the first direction. The locking structure can be automatically disengaged in response to sufficient flow down the tubular. In the case of a convertible float valve, this allows the valve to be converted to a standard float valve by circulating drilling mud. The biased closing element can be configured to set the second threshold. For example, the second threshold can be set by the amount of bias force on the biased closing element. The locking structure can be set to hold the biased closing element in an open position that is between a fully open position and the closed position. By circulating fluids down the tubular, the biased closing element can be pushed further open against the bias force until the locking structure disengages. When the circulation then stops or the flow reverses, the biased closing element moves to the closed position. Hence, the valve is automatically activated by flow up the tubular exceeding the first threshold, and can be activated from the surface by providing flow down the tubular that exceeds the second threshold. The locking structure can comprise a bracing element that extends between the biased closing element and the inner wall of the tubular body. The bracing element may be a bar or plate or another suitable rigid structure that is pushed by the biased closing element against the inner wall of the tubular body, and is prevented from slipping by friction, or a small protrusion on the biased closing element. The bracing element may have a hinged connection against the wall, radially opposite to the hinge of the biased closing element. Another way of describing it is that the bracing element jams the valve open. The valve can be configured so that friction between the bracing element and the biased closing element and / or friction between the bracing element and the tubular body keeps the bracing element in place. However, a sufficiently strong flow upwards (in the first direction), may cause an end of the bracing element to slip and the bracing element to dislodge so that the biased closing element is released. The valve can also be configured so that a sufficiently strong flow downwards (in the second direction) causes the biased closing element to open further, thereby removing the force on the bracing element which can then be dislodged by the flow. The shape of the bracing element can further be configured to set the threshold. For example, a larger area component perpendicular to the flow direction will decrease the threshold (as the bracing element catches more of the flow), while a smaller area component perpendicular to the flow will increase the threshold. The area component perpendicular to the flow can be determined by the shape and orientation of the bracing element. The locking structure may comprise a spring to hold the bracing element against the biased closing element and to retract the bracing element once the locking mechanism has disengaged. The locking structure can be configured to be displaced inside the tubular body after releasing the biased closing element to prevent the locking structure from re-engaging the biased closing element or in any way impede the movement of the biased closing element. The locking structure may comprise a spring configured to displace the locking structure inside the tubular body after releasing the biased closing element to prevent the locking structure from re-engaging the biased closing element. The spring can be located on either side of the locking structure (upstream or downstream). For example, in the case of a bracing element, the locking structure can be configured to move away the bracing element or reorientate the bracing element to prevent it from getting jammed between the biased closing element and the tubular body. The wellbore tubular can be a drill pipe, wherein the valve can be configured to be attached between two sections of the drill pipe above a bottom hole assembly (BHA) of the drill pipe. The wellbore tubular may be a casing section and the valve can be configured to be attached to an end of the casing section. The valve can be attached to the lower end of the casing section, which can provide greater protection. According to a second aspect there is provided a drill pipe comprising: a tubular section; a bottom hole assembly (BHA); a valve according to the first aspect connected between the tubular section and the BHA. According to a third aspect there is provided a casing section comprising: a tubular section; a valve according to the first aspect and connected to an end of the tubular section. According to a fourth aspect there is provided a method of providing a wellbore tubular in a wellbore, the wellbore tubular being a drill pipe according to the second aspect or a casing section according to the third aspect, the method comprising: providing the wellbore tubular with the valve in an initially open state; inserting the wellbore tubular in the wellbore; and at a target depth, circulating drilling mud through the wellbore tubular to release the biased closing element. The method may comprise, while inserting the wellbore tubular, filling the wellbore tubular with mud from the wellbore without closing the valve. The pressure is equalised without requiring filling from the surface side, which can greatly increase the speed of the run in operation. Brief Description of Drawings Figure 1 shows a schematic cross section of a valve; Figure 2 shows a schematic diagram of a valve; Figure 3 shows a schematic diagram of a bracing element; Figure 4a shows a schematic cross section of a valve being manually activated; Figure 4b shows a schematic cross section of the closed valve after being manually activated. Figure 5a shows a schematic cross section of a valve being automatically activated; Figure 5b shows a schematic cross section of the closed valve after being automatically activated; Figure 6a shows a schematic cross section of a valve; Figure 6b shows another schematic cross section of the valve; Figure 7 shows a schematic diagram of a drill pipe during a run in operation; Figure 8 shows a schematic diagram of a casing procedure for casing a wellbore; and Figure 9 shows a flow diagram of a method of inserting a drill pipe in a wellbore. Detailed description Figure 1 shows a schematic cross section of a valve 1, being an automatically convertible float valve, according to an embodiment. The valve 1 comprises a tubular body 2 and a biased closing element 3 being a flapper 4 connected to a spring 5. The cross section of tubular body 2 in radial direction of the tubular is circular, but may also be oval or have another cross section deviating from circular while still achieving the same purpose as the illustrated tubular. The flapper 4 is in a partially open position, where fluid can flow through the valve 1. The flapper is biased by the spring 5 towards a closed position, where the flapper will seal against a lip 6 in the tubular body 2. A locking structure 7 comprises a bracing element. The bracing element may be a spring-loaded bar 8. The locking structure 7 prevents the flapper 4 from closing. Figure 2 shows a schematic diagram of a valve 1. The same reference numerals are used for similar or equivalent features in different Figures to aid clarity and are not intended to limit the illustrated embodiments. The valve 1 comprises a flapper 4 that is kept open by a locking structure 7 inside a tubular body 2. The valve 1 may be the valve 1 illustrated in Figure 1. Figure 3 shows a schematic diagram of a bracing element 9 of a locking structure. The bracing element 9 comprises distal ends 10a and 10b for bracing against the biased closing element and the tubular body, respectively, and an extended region 11 between the distal ends 10a and 10b. The region 11 is extended in a direction perpendicular to the main longitudinal direction of the bracing element 9. The extended region 11 is configured to set the flow threshold at which the valve is activated. A larger area of the extended region 11 decreases the threshold, whereas a smaller area increases the threshold. A decreased threshold corresponds to a lower flow rate. Hence, the shape of the bracing element 9 is configured to set the threshold at which the valve is automatically activated. Figures 4a and 4b show schematic illustrations of the valve 1 during activation by circulating fluids down the tubular. Another way the valve can be activated is by a fluid flow from below exceeding a pre-set threshold. The valve 1 is a convertible float valve, and by activating the valve 1, it is converted to a standard float valve. In Figure 4a, the fluid 12 is circulated down through the valve 1, pushing against the flapper 4 and compressing the spring 5. The flapper 4 moves towards a fully open position, which releases the flapper from the locking structure 7. The locking bar 8 is retained into a retracted position by a retaining mechanism and as a result of the fluid flow pushing the bar downwards. In Figure 4b, circulation has stopped, and the flapper 4 is in the closed position, pushed against the lip 6 of the tubular body 2 by the spring 5, thereby preventing flow up through the valve 1. The valve 1 is configured to allow fluid to flow down through the valve 1, as the fluid flowing in the downwards direction will push the flapper 4 open. Once the valve 1 has been activated, opening the flapper 4 does not engage the locking structure 7. Before activation, as illustrated in Fig. 1, the flapper and the locking structure hold each other in a stable and fixed position as a result of carefully balanced forces. However, once the flapper and locking structure have disengaged from each other, this balanced arrangement will not be retrieved, even if locking structure 7 comes into contact with the flapper during operation. The locking structure 7 can be configured to displace the locking bar 8 after activation, as illustrated in Fig. 4b. If the locking bar is displaced, so that it does not come into contact with the flapper 4 if the flapper 4 opens and closes. The displacement is achieved by a resiliently deformable element such as a spring or elastic material, which is arranged to bias the locking structure away from the flapper. The locking bar is positioned radially opposite the hinging point of the flapper and has a hinging point on a radially opposite side of the tubular compared to the hinging point of the flapper. The locking bar is initially angled in the direction of the inflow of fluids. Figures 5a and 5b show schematic illustrations of the valve 1 being automatically activated by an upwards flow (e.g. due to unexpected influx). The valve 1 is the same as described in relation to Figures 4a and 4b above. In Figure 5a, the fluid is flowing upwards through the valve 1. As the flow exceeds a threshold, the locking bar 8 is disengaged. In this embodiment, the locking structure 7 comprises a retaining spring 13, initially attached to the locking bar 8, and configured to retract the locking bar after normal operation into the position illustrated in Figs. 4. The locking structure 7 is configured so that the spring 13 breaks when the upwards flow exceeds the threshold, thereby releasing the flapper 4 because it no longer blocks flapper 4. For example, the spring 13 may comprise a weak point for a controlled failure under a predetermined force. In Figure 5b, fluid continues to flow upwards, which together with the biasing spring 5 pushes the flapper 4 into the closed position. In the closed position, the flapper 4 is pushed against the lip 6 of the tubular body 2, thereby preventing further flow up through the valve 1. The valve 1 is configured to allow fluid to flow down through the valve 1, as the fluid flowing in the downwards direction will push the flapper 4 open. Once the valve 1 has been automatically activated, opening the flapper 4 does not engage the locking structure 7 any longer. The locking bar 8 has broken away, which permanently disables the locking structure 7. The locking bar 8 hinged and is shown to be arranged against the tubular wall, but there may also be a recess to receive the locking bar 8 such that it is not in the way of the flapper. As described with reference to Fig. 3, the failure threshold can be predetermined by the shape of extended region 11 in the locking bar. A larger extended region will cause more resistance against the flow of fluid and apply a larger force onto the weak point in the spring. The weak point in the spring can also be selected to fail at a predetermined threshold, and the skilled person will be able to select the particular failure thresholds depending on the parameters of the application. Figures 6A and 6b show schematic cross sections of an alternative arrangement of valve 1, wherein the locking structure 7 is configured to be displaced after the valve 1 has been activated and the locking structure is no longer used. The locking structure comprises a bracing element 9 (e.g. a locking bar as before in Figures 4 and 5) and a displacement arm 14 for moving or reorientating the bracing element 9 after it is disengaged from the flapper 4. In Figure 6A, the bracing element and flapper 4 hold each other in place as in the previous embodiments through a combination of friction and the force of spring 5. As in the previous embodiments, the force from fluid flow in either direction can disengage the bracing element and flapper from each other if the flow exceeds a threshold in the respective direction. In Figure 6b, circulation of fluid down the valve 1 pushes the biased closing element 3 open, which thereby disengages the locking structure 7. The displacement arm 14 may comprise a spring or other means for causing displacement when the flapper 4 is released. The bracing element 9 may be held against the tubular body 2, so as to have little impact on the flow or the functioning of the flapper 4 after being disengaged. The displacement arm acts as a retraction mechanism so that the locking structure is removed from the path of movement of the flapper. Although it is very unlikely that the locking structure and the flapper come back to the same balanced position of Fig. 6a after disengagement, it is preferable to move the locking structure out of the path of the flapper to avoid impeding free movement. Figure 7 shows a schematic diagram of a drill pipe 15 during a run in operation into a wellbore 16. The wellbore is surrounded by formation 17. The drill pipe 15 comprises a plurality of tubular sections 18 (two shown for illustration) connected to a valve 1, which is in turn connected to the BHA 19. The valve 1 is an automatically convertible float valve as described herein. The arrows illustrate the direction of fluid flow as drilling mud is circulated down the drill pipe 15 and back up the annulus 20. The valve 1 may have been manually converted by circulating fluid or may have been previously automatically converted from fluid flow up the drill pipe 15 due to influx from the formation 17. Figure 8 shows a schematic diagram of a casing procedure for casing a wellbore 16. A first (upper) casing section 21 has already been set and a second casing section 22 is being run in. The wellbore is surrounded by formation 17. The second casing section 22 comprises a valve 1 directly attached to the lower end of the casing section 22. The valve 1 is an automatically convertible float valve as described herein. The valve 1 can protect the surface from unexpected influx, while still allowing normal pressure equalisation during run in by keeping the valve 1 open. Figure 9 shows a flow diagram of a method of inserting a drill pipe in a wellbore (i.e. run in) and converting the valve. The method comprises providing the drill pipe with a valve in an open position (step S1), inserting the drill pipe into the wellbore (step S2). As the drill pipe is inserted, the drill pipe is filled from the wellbore with mud (step S3). The mud was provided in the wellbore before run in. When there is no unexpected pressure spike in the wellbore, the fluid flow up the drill pipe does not exceed the threshold for disengaging the locking structure and releasing the biased closing element to automatically convert the valve. The method further comprises, at a target depth, circulating drilling mud through the drill pipe, so as to convert the valve (step S4). While specific embodiments have been described herein, it will be appreciated that the invention is not limited to those embodiments and that further embodiments falling within the scope of the claims are possible. Features of one embodiment may be appropriately combined with those of another embodiment.

Claims

1. A valve for controlling fluid flow in a wellbore tubular, the valve comprising:a tubular body;a biased closing element located in the tubular body and configured to prevent flow in a first direction through the valve when in a closed position; anda locking structure for locking the closing member in an at least partially open position, wherein the locking structure is configured to release the biased closing element in response to a fluid flow in the first direction through the valve exceeding a threshold.

2. A valve according to claim 1, wherein the biased closing element comprises a flapper pivotally attached to the tubular body and biased to close against a lip in the tubular body.

3. A valve according to claim 1 or 2, wherein the valve is configured so that the biased closing element is released in response to a fluid flow in a second direction through the valve exceeding a second threshold, wherein the second direction is opposite to the first direction.

4. A valve according to claim 3, wherein the biased closing element is configured to set the second threshold.

5. A valve according to any one of the preceding claims, wherein the locking structure comprises a bracing element that is braced between the biased closing element and the tubular body.

6. A valve according to claim 5, wherein a shape of the bracing element is configured to set the threshold.

7. A valve according to claim 5 or 6, wherein the locking structure comprises a spring to hold the bracing element against the biased closing element.

8. A valve according to any one of the preceding claims, wherein the locking structure is configured to be displaced inside the tubular body after releasing thebiased closing element to prevent the locking structure from re-engaging the biased closing element.

9. A valve according to any one of the preceding claims, wherein the locking structure comprises a spring configured to displace the locking structure inside the tubular body after releasing the biased closing element to prevent the locking structure from re-engaging the biased closing element.

10. A valve according to any one of the preceding claims, wherein the wellbore tubular is a drill pipe and the valve is configured to be attached between two sections of the drill pipe above a bottom hole assembly (BHA) of the drill pipe.

11. A valve according to any one of claims 1 to 9, wherein the wellbore tubular is a casing section and the valve is configured to be attached to an end of the casing section.

12. A drill pipe comprising:a tubular section;a bottom hole assembly (BHA);a valve according to any one of the preceding claims connected between the tubular section and the BHA.

13. A casing section comprising:a tubular section;a valve according to any one of claims 1 to 11 and connected to an end of the tubular section.

14. A method of providing a wellbore tubular in a wellbore, the wellbore tubular being a drill pipe according to claim 12 or a casing section according to claim 13, the method comprising:providing the wellbore tubular with the valve in an initially open position;inserting the wellbore tubular into the wellbore; andat a target depth, circulating drilling mud through the wellbore tubular to release the biased closing element.

15. A method according to claim 14, further comprising:while inserting the wellbore tubular, filling the wellbore tubular with mud from the wellbore without closing the valve.

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