Down hole blow out preventer and method of use

Description

[0001] The invention relates to a down-hole blow-out preventer for use in drilling oil and gas wells and wells that may be drilled for recovery of geothermal energy, etc.

[0002] Surface blow-out preventers are in common use in the oil industry but so far no blow-out preventer is in commercial use which can be used successfully to block off the oil well down the drill hole and close to the drill bit.

[0003] Various proposals have been made for closing the drill hole but none has ever been used successfully commercially for various reasons.

[0004] For example US-A 3908769 shows a drill hole packer to be carried by a drill string but this packer is dependant for its operation upon a high flow rate of fluid in the reverse direction on encountering a kick. The device according to the invention works on detection of a static pressure difference.

[0005] US-A 3941 190 and 3503445 both show down hole packers but both packers are operated by tools which have to be pumped down the hole which would take several hours.

[0006] The invention provides a down-hole blow-out preventer comprising an elongate tubular housing having a through bore for the passage of drilling mud and means for connecting the ends of the housing into a drill string, a packer element arranged circumferentially around the housing and inflatable into engagement with the bore hole to seal the hole, passage means extending through the housing wall for connecting the through bore of the housing with the packer element to inflate the packer element by mud pressure from within the housing, valve means mounted inside the housing for movement between a drilling position when the valve means closes said passage means and an inflating position when the passage means is open, a one-way valve for closing the through bore of the housing on the side of the valve means to be nearer the drill bit, said one-way valve being operable to allow the passage of mud under pump pressure in a direction towards the drill bit, but not allowing flow of mud in the reverse direction, a mud circulation channel extending through the housing wall to the through bore of the housing, means being provided to open the mud circulation channel to the through bore of the housing above the valve means when the packer element is inflated to allow circulation of higher density mud through the through bore of the housing to the bore hole, and means to allow the packer element to be deflated when the hydrostatic head of the mud column above the packer element is sufficient to overbalance the pressure below it, characterised in that the said valve means is in the form of a cylindrical valve sleeve having a bore therethrough for the passage of mud and having closure valve means for closing said bore, and further characterised by means for holding open the closure valve means during the course of running in and drilling and for automatically closing the closure valve means when the pressure in the through bore of the housing is reduced to a level below the pressure in the bore hole by a predetermined amount to allow pressure in the through bore of the housing to be reapplied after closing of the closure valve means whereby to urge the cylindrical valve sleeve to its inflating position allowing inflation of the packer element.

[0007] The invention also provides a method of drilling using a surface blow-out preventer in conjunction with a down-hole blow out preventer connected into a drill string, the down-hole blow out preventer being of the kind comprising an elongate tubular housing having a through bore for the passage of drilling mud and passage means extending through the housing wall, a packer element arranged circumferentially around the housing, its inner space communicating via the passage means in the housing wall with the through bore of the housing, valve means having a bore therethrough for the passage of mud mounted in the housing for movement between a drilling position when the valve means closes said passage means and an inflating position when the passage means are open, a one-way valve for closing the through bore of the housing on the side of the valve means to be nearer the drill bit, the one-way valve being operable to allow passage of mud under pump pressure through the through bore of the housing in a direction towards the drill bit and prevent flow of mud in the opposite direction, closure valve means for closing the bore in the valve means, means for holding open the closure valve means in the course of running in and drilling and for automatically closing the closure valve means when the pressure in the through bore of the housing is reduced to a level below the pressure in the bore hole by a predetermined amount, a mud circulation channel, extending through the housing wall to the through bore of the housing, means being provided to open the mud circulation channel to the through bore of the housing above the valve means when the packer element is inflated, and means to allow the packer element to be deflated when the hydrostatic head of the mud column above the packer element is sufficient to overbalance the pressure below it, wherein, on a kick being detected, said method comprises the steps of: closing the surface blow-out preventer to seal off the bore hole at the surface, taking at the surface a measurement of the pressure in the bore hole to determine the pressure created by the kick, letting off at the surface the pressure in the drill string to allow said pressure to fall below the pressure in the bore hole by said predetermined amount whereby to cause said closure valve means to close, reapplying the pressure in the drill string whereby to cause said valve means to move to its second position allowing inflation of the packer element by mud pressure within the drill string to seal off the bottom of the bore-hole and to cause said means to open the mud circulation channel, introducing mud of an increased density into the drill string via a valve in the sur-

[0008] face blow-out preventer whereby to circulate said mud into the annulus above the packer element via said mud circulation channel, and continuing to circulate said mud until the hydrostatic head of the mud column in the annulus is sufficient to overbalance the pressure of the kick.

[0009] A specific embodiment of a down hole blow out preventer (D.H. BOP) in accordance with the invention will now be described in detail with reference to the drawings in which:

Fig. 1 shows the D.H.BOP connected in a drill pipe-string run into a hole;

Fig. 2 is a vertical sectional view of the D.H.BOP in the running-in position;

Fig. 3 is a horizontal cross-section along line III-III in Fig. 2;

Fig. 4 is a horizontal cross-section along line IV-IV in Fig. 2;

Fig. 5 is a horizontal cross-section along line V-V in Fig. 2;

Fig. 6 shows a vertical cross-sectional view of the D.H.BOP, in drilling position;

Fig. 7 is a horizontal cross-section along line VII-VII in Fig. 6;

Fig. 8 shows a vertical cross-sectional view of the D.H.BOP during a wellkick after closing the flapper valve.

Fig.9 shows a vertical cross-sectional view of the D.H.BOP, with the packer inflated;

Fig. 10 shows a vertical cross-sectional view of the D.H.BOP, with the circulating port open;

Fig. 11 is a horizontal cross-section along line XI-XI in Fig. 10;

Fig. 12 is a horizontal cross-section along line XII-XII in Fig. 10;

Fig. 13 shows a vertical cross-sectional view of the D.H.BOP, deflating the packer; and

Fig. 14 shows a horizontal cross-section on the line XIV-XIV in Fig. 13.

[0010] As can be seen from Fig. 2 the D.H.BOP comprises two barrels an outer barrel 1 and an inner barrel 2.

[0011] The inside of the outer barrel 1 and the outside of the inner barrel 2 are fine machined to the required tolerances.

[0012] The various channels and holes are milled and drilled in the inner barrel 2 and after being machined the two barrels are shrunk together by un- dercooling of the inner barrel 2.

[0013] The position of the two barrels in relation to each other must be precise.

[0014] After shrinking the two barrels 1 and 2 together, the various radial holes can be drilled and the channels for the fill-up valve assembly 41, the grease bolt 1', the check valve 53, the shut-off valve 57 and the equalising valve 62 can be drilled and machined.

[0015] The top of the outer barrel 1 is provided with an external thread 4 for connection with an API threaded substitute 3 to enable the insertion of the inner parts of the D.H.BOPfrom the top.

[0016] The outer barrel 1, is provided at its lower end with an internal thread 4' to connect it with a packersleeve 5.

[0017] The packersleeve 5 is at its bottom-end provided with a threaded API box connection 6 to connect it with the drilling bit.

[0018] Inside the packersleeve 5 a chamber is machined which is nearly as long as the packersleeve 5, and in which a floatvalve assembly 7 is inserted for sliding movement from a lower to an elevated position. Floatvalve assembly 7 comprises a piston-like substantially hollow body 7' in which is mounted a conical valve 8 spring-loaded by spring 9 into sealing engagement with a valve seat, formed inside body 7'. Valve 8 is fixed to valve stem 10 which is guided for sliding up and down movement in guiding sleeve 11 mounted in bushing 12 which is fixed inside body 7' by means of a spider.

[0019] A snapring sleeve 13 is inserted into the top of packersleeve 5. The top of packersleeve 5 is provided with four pressure equalising channels 14 which communicate with four similar channels 15 in the snapring sleeve 13.

[0020] Around snapring sleeve 13 a helical spring 16 is inserted before a snapring 17 is pressed over the snapring sleeve 13.

[0021] A flappervalve sleeve 18 is pressed over the snapring 17 mounted around snapring sleeve 13 until it sits in a snapring recess 19.

[0022] Flappervalve sleeve 18 is provided with a friction cam 20 which can be forced over the snapring 17 until snapring 17 snaps into snapring slot 21 of flappervalve sleeve 18, by pump pressure when the flappervalve 22 is closed. The flappervalve 22 is pivotally mounted on top of flappervalve sleeve 18 and spring biased towards a closed position in which it is in sealing engagement with the top edge 18' of flappervalve sleeve 18. Closing movement is prevented by a flappervalve release sleeve 23 during circulating and drilling.

[0023] The flappervalve release sleeve 23 comprises a plunger holder 24 to which are fixed two plungers 25 which are received into bores formed in a plunger housing 26.

[0024] The plunger holder 24 and the plunger housing 26 are provided with four pressure equalising channels 27 and 28 respectively.

[0025] A helical spring 29 bears with its lower end against the top of the plunger holder 24 with its upper end against a retainer ring 30 by which the tension of spring 29 can be adjusted. The retainer ring 30 is also provided with four pressure equalising channels 31. A steel arresting ball 23_' biassed inwardly by a calibrated helical spring rests in a circumferential groove in plunger holder 24.

[0026] By stopring 32 upward movement of the plunger holder 24 is limited to keep the plungers 25 inside the plunger housing 26.

[0027] Against the top of retainer ring 30 bears a helical spring 33 which bears with its other end against a shut-off sleeve 34 to keep the sleeve 34 in its highest position in which a channel 35 and a fill-up channel 36 are open (see Fig. 3).

[0028] The fill-up valve assembly 41 is shown in running-in position in Fig. 2 and 3 and in circulating or drilling position in Fig. and 7. It comprises a gate 41' having a substantially rectangular cross- seciton and running in a hole 42 which hole is closed at one end by locking nut 45 having a slotted part 46 in communication with a channel 35 in the inner barrel 2. A screen 47 covers a recess, formed in outer barrel 1 which is in communication with fill-up channel 36, and an inlet 48 which opens into flappervalve release channel 49. Channel 49 extends through inner barrel 2 and opens into circumferential groove 50 formed in plunger housing 26 and ports 51 extend from groove 50 into the plunger cylinders.

[0029] The first purpose of the fill-up valve assembly 41 is to be in open position (fig. 3) to fill up the drill pipe when running the drill pipe into the hole and simultaneously to close off the flappervalve release channel 49 when running into the hole so that no pressure difference between the annulus and drillpipe can lift the plungers 25 and accidentally cause the flappervalve 22 to close.

[0030] Its second purpose is to close off the fill-up channel 36 once circulation or drilling has commenced. The greater pressure inside the drill pipe is propagated through channel 35 to gate 41' and moves the gate 41_' to close the fill-up channel 36, against the lesser pressure in the annulus as shown in Fig. 7. When the gate 41' moves it also closes the fill up channel 36 and mud will fill the fluid lock 52.

[0031] The shut-off sleeve 34 is moved downwardly when circulation is started and to increase the pressure drop an aluminium disc 37' with an orifice may be provided by means of threaded ring 37 which disc will be disintegrated during circulation. The position is shown in Fig. 6.

[0032] When the shut-off sleeve 34 moves downwardly against the tension of spring 33, the locking spring snaps into the locking groove 39 formed in the inner wall of inner barrel 2 and shuts off the channels 35 and 36. The shut-off sleeve 34 is provided with three pressure equalising channels 40.

[0033] After the shut-off sleeve 34 has moved downwardly to close channel 35 the entrapped mud in the fluid lock 52 will cause the fill-up channel 36 to be permanently closed while the flappervalve release channel 49 remains open. The plungers 25 are from now on permanently connected to and subjected to the pressure in the annulus through inlet 48 and channel 49.

[0034] Another purpose of the fill-up valve assembly 41 is to provide the possibility to calibrate the tension of the spring loaded steel ball 23' (Fig. 2) and the spiral spring 29 before running the D.H.BOP into the hole. The spring loaded steel ball 23' is there to prevent fluttering of the flapper valve release sleeve 23 by pressures lower than the setting of the spring 29 for releasing the flapper valve 22.

[0035] To enable calibration of the spring loaded steel ball 23' and the spiral spring 29 the fill-up valve gate 41' is set in the drilling position as shown in Fig. 7 whereafter a grease pump with a pressure gauge is connected to the threaded inlet 48 leading to flapper valve release channel 49. The tension set for the spiral spring 29 depends on the maximum expected penetration rate per hour, the hole size, the depth of the hole, the pump volume and the cross sectional area of the plungers 25.

[0036] Easy to read charts can be developed for this purpose.

[0037] The required spring tension is the tension required to overbalance the greater hydrostatic head of the mud column in the annulus caused by the presence of drilled formation cuttings when the pump is stopped. A checkvalve 53 is provided to allow mud to enter and to inflate the inflatable packer element 54 when the flappervalve 22 has been released and closed, and the flappervalve sleeve 18 has been pumped down to uncover the inflating port 55. This operation will be described later. Mud can then be pumped through port 55 and channel 56 into packer element 54. The check valve 53 closes and retains the mud in the inflatable packer element 54 when the pressure in the drillpipe drops.

[0038] It will be seen that the outside diameter of the outer barrel 1 has a partly enlarged diameter 1a, which is provided with spiral grooves 16a (Fig. 4) like an undersized solid body stabilizer.

[0039] The enlarged diameter provides protection for the packer element 54. Furthermore a steel ring 54' at the bottom end of the packer element 54 is connected to the packer sleeve 5 by means of shearpins 54". This to protect the packer element whilst running into the hole and to withstand rotational forces when drilling. The shearpins 54" are sheared when the packer 54 is inflated say at a pressure of 700 psi (48.3 bar).

[0040] The shut-off valve assembly 57 is composed of a shut-off piston 57' with 0-ring seals, a helical pressure spring 58 and a bushing 59 with a thread 59' for a grease nipple.

[0041] When running in and drilling (Fig. 5), the shut-off piston 57' is isolated from the pressure inside the tool by the flappervalve sleeve 18 with which is provided 0-ring seals (Fig. 2). It is exposed to the pressure inside the tool when in inflating the packer element 54 the flappervalve sleeve 18 is pushed downwardly and its friction cam 20 rides over the snapring 17 which then snaps into the slot 21 as will be described later.

[0042] The object of the shut-off piston 57' is to close the channel 60 while pump pressure is present within the tool, and to open the channel 60 when the pump is stopped. This is achieved by the pressure within the tool moving the piston 57' against the spring 58 to close the channel 60 from the annulus.

[0043] An equalising valve 62 is provided (Fig.5) which comprises an equalising piston 62', having a conical nose, a helical pressure spring 63 and a threaded bushing 64 in which bolt 65 is screwed.

[0044] The purpose of the equalising valve is to open the packer element to the channel 60 when the pressure in the annulus below the packer (which is fed to the valve via channel 66) is exceeded by 300 psi (20.7 bar) by the mud pressure which is above the packer. The mud pressure is present in channel 60 when piston 57' opens the channel 60 to the annulus.

[0045] When a kick is encountered and the packer element 54 has been inflated (Fig. 10) then during circulation through the circulating channels 61 the equalising channel 60 is closed and no extra circulation pressure is behind the equalising piston 62'. However when the pump is stopped and the shut-off piston 57' is pushed back by spring 58 then the equalising channel 60 is open to the mud pressure in the annulus so that the hydrostatic pressure acts on the conical nose of the equalising piston 62'.

[0046] On the opposite side of the equalising piston 62_' the formation pressure below the packer is received via equalising bushing 64 and aligned ports 67 and 68 formed in flappervalve sleeve 18 and snapring sleeve 13 respectively.

[0047] If now the mud weight is sufficiently increased to overbalance the formation porepressure and the pump is stopped then the hydrostatic head of the mud column in the annulus above the packer exerts pressure against the equalising piston 62' and moves this piston until it opens the deflating channel 69 so that the pressure inside the packer element escapes into the annulus through equalising channel 60 assisting the equalising piston 62' to remain in open position (fig. 14).

[0048] The overpressure required to move and open the equalising piston 62' can be adjusted by means of the spring loaded ball 84 resting in groove 92 and can be tested with a grease pump having a pressure gauge when the grease nipple is screwed into the threaded bushing 64.

[0049] When the flappervalve sleeve 18 is pumped down after the packer element has been inflated, the mud below the flappervalve is trapped and, although of very small volume, the closed floatvalve 7 will move downwardly and compress the gas or liquid or squeeze it back into the formation against the formation pore pressure.

[0050] After the D.H.BOP is prepared for running in, the D.H.BOP can be run into the hole, so that it reaches eventually the position as shown in Fig. 1. In Fig. 1 is shown the D.H.BOP 70, interconnected between the drillpipe-string 71 and drillbit 72 and run into hole 73 so that annulus 74 is formed. A casing 75 is cemented in the upper- portion 73' of the hole 73, while at the surface a surface blow out preventer 76 of known type is provided below rotary table 77. Mud can be pumped by pump 78 through hose 79 and swivel 80 down into drillpipe-string 71, which mud then is ejected from drillbit 72 and flows upwardly through annulus 74. With reference numeral 81 a pressure gauge is shown.

[0051] When running in, the drillpipe is empty and the floatvalve 7 is closed and in its highest position (see Fig. 2) so that no mud can enter the drillpipe through the bit nozzles and no formation cuttings can settle down inside the bit on top of the bit nozzles causing the bit to become plugged when circulation is started. The filling of the drillpipe takes place through the fill-up opening 36 and hole 42 of the fill-up gate 41' .

[0052] The mud is screened by the mudscreen 47. Fig. 1 and 3 give a clear insight on the operation and postiion of each valve and part when running into the hole.

[0053] Attention should be given to the fact that when for one reason or the other circulation has been established during running into the hole, it will be necessary that the drillpipe will be filled from the top of every stand to be run into the hole because after circulation the fill-up valve will be permanently closed as described herein above.

[0054] When the bit has reached the bottom of the hole the mudpumps are started and circulation is established through the floatvalve 7 and the bit nozzles. Fig. 6 gives a clear insight on the operation and position of each valve and part when circulating or drilling. Drilling may continue without encountering a kick and a roundtrip to change the bit is then made without having used the D.H.BOP.

[0055] When the bit is pulled and unscrewed, the floatvalve 7, the valve seat inside body 7' and the valve assembly circumferential body seals should be inspected and be in a good condition or changed for new ones before making-up a new bit.

[0056] Next, take out the threaded ring 37 from shut-off sleeve 34 with a set and pulling tool, and screw a set and pulling tool into the same thread and pull the shut-off sleeve 34 up until its highest position unscrew tool and screw in threaded ring 37 again.

[0057] The fill-up valve gate 41' has to be cleaned and to be reset after each roundtrip. Unscrew locking nut 45, put grease nipple in the thread, pump out the gate 41', clean and reinsert gate 41', use grease, set gate 41' in fill-up position with a set bolt «s» and screw in locking nut 45, take out set bolt and tighten locking nut 45. The D.H.BOP can be run again and is ready to operate again when necessary.

[0058] Fig. 8 gives a clear insight of the operation and the position of each valve and part when a kick is encountered and the annulus is closed in by the surface BOP 76.

[0059] If a kick is encountered during drilling then the pumps are stopped, the standard pipe valve closed, the kelly picked-up and the annular BOP closed. The closed-in drill pipe pressure is then read and recorded. As soon as the pumps are stopped the floatvalve 7 will close due to the tension of spring 9.

[0060] As the well is completely closed-in, now pressure will be built-up inside the well.

[0061] The floatvalve assembly 7 was in its lowest position when circulating. Now the pump 78 (Fig. 1) is stopped so that the closed floatvalve assembly 7 acts like a floating piston and when pressure below it is building up it can move upwardly making it possible to read the closed in drillpipe pressure (C.I.D.P.P.) from the pressure gauge 81 (Fig. 1).

[0062] The C.I.D.P.P. + hydrostatic head of the mud column in the drillpipe = formation pore pressure.

[0063] If the kick is observed at an early stage then the time required for the C.I.D.P.P. to build up should be about ten (10) minutes, depending on the column of gas already produced in the annulus 74 (compression).

[0064] The C.I.D.P.P. is recored and the required mud weight calculated with sufficient overbalance over the formation pore pressure.

[0065] Now the C.I.D.P.P. is slowly bled-off at the drillpipe. Wait a few seconds and start pump 78 slowly.

[0066] In the meantime the following occurs down- hole: When the well is closed in, the C.I.D.P.P. + hydrostatic head of the mud column in the drillpipe = closed in annular pressure + hydrostatic head of mud column in the annulus because these are communicating vessels with the floating floatvalve assembly 7 between them.

[0067] Say that the C.I.D.P.P. is 300 psi (20.7 bar) and the pressure is bled-off at the drillpipe, now the annular pressure at the bottom of the hole is 300 psi. (20.7 bar) higher than in the drillpipe. The floatvalve assembly 7 moves into its highest position and the pressure in the annulus 74 is propagated via the inlet 48 and through hole 42 in fill-up valve gate 41' through the flappervalve release channel 49 underneath the plungers 25, which are then moved upwardly lifting the flappervalve release sleeve 23 until the spring biased flappervalve 22 falls on the seat 18_' formed by the upper edge of flappervalve sleeve 18, which is then closed off (see Fig. 8). All above occurs when the C.LD.P.P. is bled-off at the drillpipe.

[0068] Now the pump 78 is started very slowly. Pressure builds up to abt. 1500 psi. (103 bar) and drops. Pump speed is increased to 100-200 gln/ min. (7.6-15 litres/S) depending on the size of the D.H.BOP and the size of the circulating channels 61.

[0069] As shown in Fig. 9 downhole the following occurs: The flappervalve 22 is already closed. Pump 78 runs slowly. The flappervalve sleeve 18 is pushed downwardly by the pump pressure .against the helical spring until the inlet 55 of the check valve 53 is uncovered and the flappervalve sleeve 18 hits the snapring 17 with the calibrated friction cam 20. Pressure is now building up and the packer element 54 is inflated through inflation channel 56.

[0070] At about 1500 psi. (103 bar) the flappervalve sleeve 18 snaps with its friction cam 20 over the snapring 17 which is locked in the snapring slot 21 and the packer 54 is set.

[0071] ' As shown in Fig. 10 when the snapring 17 is snapped into the snapring slot 21 the mud pushes shut-off piston 57' (Fig. 11) outwardly so that piston 57_' closes channel 60.

[0072] In this position of the sleeve 18 mud can be circulated through the circulation channels 61. When circulation is established the drillstring 71 is lowered to put some weight on the packer to make certain that the packer 54 is set.

[0073] The packer 54 is now isolating the producing zone from the remaining portion of the hole.

[0074] The tool is closed-off at the bottom by the float valve assembly 7 and from the top by the flappervalve 22.

[0075] When the mudweight has been increased by circulation to the required weight so that the hydrostatic pressure of the mud column above the packer 54 is overbalancing the pore pressure of the formation below the packer the pump should be stopped. The channel 60 will then be opened by the piston 57' and the equalising valve 62 so that the packer is deflated and the string can be pulled out of the hole.

[0076] As shown in Fig. 13 the following occurs down- hole when the mud is overbalancing the formation pore pressure and the pump is stopped.

[0077] When the pump 78 (Fig. 1) is stopped the shut-off piston 57' opens the equalising channel 60.

[0078] The hydrostatic pressure of the mud column above the packer 54 acts on the one side of the equalising piston 62' which normally shuts off deflating channel 69.

[0079] The other side of the equalising piston 62' is connected through channel 66 and ports 67, 68 with the space between the flappervalve 22 and the float valve assembly 7, below which the formation pore pressure acts.

[0080] If now the hydrostatic pressure of the mud column in the annulus above the packer 54 overbalances sufficiently the formation pore pressure below the packer then the equalising piston 62' moves and opens the deflating channel 69. The pressure of abt. 1500 psi. (103 bar) behind the packer element 54 is now released in the annulus through channels 69 and 60 and the packer elements deflates and the packer is free.

[0081] If the packer does not deflate then the recorded C.I.D.P.P. was not correct and the mudweight should be increased gradually and the pumps stopped at intervals.

[0082] When a well starts coming in during roundtrip- ping the same procedure should be followed as during drilling but instead of pulling out continuously one should kill the well, unseat the packer and run back to bottom decreasing the mudweight when going deeper and circulating at intervals.

[0083] Circulating takes then place through the circulating channels instead of through the bit nozzles.

[0084] When the bottom of the hole is reached, condition the mud and pull-out to inspect all parts of the D.H.BOP.

[0085] An alternative use of the D.H.BOP is when drilling on the sea bed with a surface BOP positioned on the sea bed and it is desired to suspend drilling operations e.g. when weather is bad.

[0086] The surface BOP is first closed and the mud pressure within the string is bled down. Mud under pressure is then forced into the annulus whereby the pressure in the annulus exceeds the pressure setting of the arresting ball and helical spring in the tool by at least the amount necessary to operate the D.H.BOP to close the flapper valve. The packer element can then be inflated as before and this will seal the bottom end of the casing and the drill string and the surface pipe from the sea bed to the drilling vessel can be removed.

[0087] Reconnecting the surface pipe and the drill pipe and releasing the packer can be achieved by closing the drill pipe at the surface and pressurising the annulus, below the closed BOP rams at the surface, to open the equalising valve, whereafter the rams are opened.

[0088] An advantage of the D. H. BOP described is that in addition to controlling a well in a novel manner, a well can be brought under control in the conventional manner. In this case on detecting a kick the surface BOP is closed and the closed in drill pipe pressure is read. Instead of lowering the closed in pressure to close the flapper valve, the closed in pressure is maintained. The flapper valve does not close and the well can be brought under control in the normal way by the introduction of heavier mud.

Claims

1. A down-hole blow-out preventer comprising an elongate tubular housing having a through bore for the passage of drilling mud and means for connecting the ends of the housing into a drill string (71), a packer element (54) arranged circumferentially around the housing and inflatable into engagement with the bore hole (73) to seal the hole, passage means (56) extending through the housing wall for connecting the through bore of the housing with the packer element to inflate the packer element by mud pressure from within the housing, valve means mounted inside the housing for movement between a drilling position when the valve means closes said passage means and an inflating position when the passage means and an inflating position when the passage means is open, a one-way valve (8) for closing the through bore of the housing on the side of the valve means to be nearer the drill bit, said one-way valve (8) being operable to allow the passage of mud under pump pressure in a direction towards the drill bit, but not allowing flow of mud in the reverse direction, a mud circulation channel (61) extending through the housing wall to the through bore of the housing, means being provided to open the mud circulation channel to the through bore of the housing above the valve means when the packer element (54) is inflated to allow circulation of higher density mud through the through bore of the housing to the bore hole, and means to allow the packer element (54) to be deflated when the hydrostatic head of the mud column above the packer element is sufficient to overbalance the pressure below it, characterised in that the said valve means is in the form of a cylindrical valve sleeve (18) having a bore therethrough for the passage of mud and having closure valve means (22) for closing said bore, and further characterised by means (23) for holding open the closure valve means (22) during the course of running in and drilling and for automatically closing the closure valve means (22) when the pressure in the through bore of the housing is reduced to a level below the pressure in the bore hole by a predetermined amount to allow pressure in the through bore of the housing to be reapplied after closing of the closure valve means (22) whereby to urge the cylindrical valve sleeve (18) to its inflating position allowing inflation of the packer element (54).

2. A blow-out preventer device as claimed in claim 1 wherein there is means (41) to allow mud to flow through the through bore of the housing during running in whereby to allow the drill string to be filled during running in.

3. A blow-out preventer as claimed in claim 1 or claim 2 in which the closure valve means (22) is biased towards its closed position.

4. A blow-out preventer as claimed in claim 3 in which the closure valve means comprises a flapper valve (22) at the upper end of the cylindrical valve sleeve (18) and the releasable holding means comprises a flapper valve sleeve (23) within the housing, which sleeve is slidable axially within the housing between a first position in which the flapper valve is held open and a second position in which the flapper valve is released for movement to its closed position.,

5. A blow-out preventer as claimed in claim 4 in which the means to move the flapper valve sleeve (23) to its second position comprises a piston and cylinder (25, 26) device which is open to the pressure in the bore hole.

6. A blow-out preventer as claimed in any of claims 1 to 5 in which means (17, 21) are provided to retain the cylindrical valve sleeve (18) in its inflating position and there is means (62, 57) operable when the cylindrical valve sleeve is in its inflating position to deflate the packer element (54) when the density of the mud reaches a value sufficient to overcome the pressure at the bore hole below the one-way valve (8).

7. A blow-out preventer as claimed in any of claims 1 to 6 in which there is means (62) to prevent deflation of the packer element (54) when mud is being circulated.

8. A blow-out preventer as claimed in any of claims 1 to 7 in which the one way valve (8) comprises a valve body (7') which is slidably axially in the housing between end stops and in sealing engagement with the housing whereby the pressure below the one-way valve may be measured at the well head.

9. A method of drilling using a surface blow-out preventer in conjunction with a down-hole blow out preventer connected into a drill string, the down-hole blow out preventer being of the kind comprising an elongate tubular housing having a through bore for the passage of drilling mud and passage means (56) extending through the housing wall, a packer element (54) arranged circumferentially around the housing, its inner space communicating via the passage means in the housing wall with the through bore of the housing, valve means (18) having a bore therethrough for the passage of mud mounted in the housing for movement between a drilling position when the valve means closes said passage means and an inflating position when the passage means are open, a one-way valve (8) for closing the through bore of the housing on the side of the valve means to be nearer the drill bit, the one-way valve being operable to allow passage of mud under pump pressure through the through bore of the housing in a direction towards the drill bit and prevent flow of mud in the opposite direction, closure valve means (22) for closing the bore in the valve means, means (23) for holding open the closure valve means in the course of running in and drilling and for automatically closing the closure valve means when the pressure in the through bore of the housing is reduced to a level below the pressure in the bore hole by a predetermined amount, a mud circulation channel, (61) extending through the housing wall to the through bore of the housing, means being provided to open the mud circulation channel to the through bore of the housing above the valve means when the packer element is inflated, and means to allow the packer element to be deflated when the hydrostatic head of the mud column above the packer element is sufficient to overbalance the pressure below it, wherein, on a kick being detected, said method comprises the steps of: closing the surface blow-out preventer to seal off the bore hole at the surface, taking at the surface a measurement of the pressure in the bore hole to determine the pressure created by the kick, letting off at the surface the pressure in the drill string to allow said pressure to fall below the pressure in the bore hole by said predetermined amount whereby to cause said closure valve means (22) to close, reapplying the pressure in the drill string whereby to cause said valve means (18) to move to its second position allowing inflation of the packer element (54) by mud pressure within the drill string to seal off the bottom of the bore-hole and to cause said means to open the mud circulation channel, introducing mud of an increased density into the drill string via a valve in the surface blow-out preventer whereby to circulate said mud into the annulus above the packer element via said mud circulation channel (61), and continuing to circulate said mud until the hydrostatic head of the mud column in the annulus is sufficient to overbalance the pressure of the kick.

Ansprüche

1. Unten im Bohrloch anzuordnende, ein Ausblasen verhindernde Einrichtung, die ein längliches röhrenförmiges Gehäuse mit einer Durchgangsbohrung für Durchfluss von Bohrschlamm und Einrichtungen zum Verbinden der Enden des Gehäuses in einen Bohrstrang (71), ein Dichtelement (54), das in Umfangsrichtung um das Gehäuse herum angeordnet ist und bis zum Eingriff mit dem Bohrloch (73) aufblähbar ist, um das Loch zu dichten, Durchlassmittel (56), die sich durch die Gehäusewand erstrecken, um die Durchgangsbohrung des Gehäuses mit dem Dichtelementzu verbinden, um das Dichtelement durch Schlammdruck von innerhalb des Gehäuses her aufzublähen, Ventilmittel, das innerhalb des Gehäuses so angeordnet ist, dass es zwischen einer Bohrstellung, in der das Ventilmittel den Durchlass schliesst, und einer aufblähenden Stellung bewegbar ist, in der der Durchlass offen ist, ein Einwegventil (8) zum Schliessen der Durchgangsbohrung des Gehäuses auf der Seite des Ventilmittels, die dem Bohrmeissel näher ist, wobei das Einwegventil (8) so betätigbar ist, dass es Durchfluss von Schlamm unter Pumpendruck in einer Richtung zum Bohrmeissel ermöglicht, aber Strömung von Schlamm in der umgekehrten Richtung verhindert, ein Schlammzirkulationskanal (61), der sich durch die Gehäusewand zur Durchgangsbohrung des Gehäuses erstreckt, wobei Einrichtungen vorgesehen sind, um den Schlammzirkulationskanal zur Durchgangsbohrung des Gehäuses oberhalb des Ventilmittels zu öffnen, wenn das Dichtelement (54) aufgebläht ist, um Zirkulation von Schlamm mit höherer Dichte durch die Durchgangsbohrung des Gehäuses zum Bohrloch zu ermöglichen, und Einrichtungen aufweist, mit denen das Dichtelement (54) entleert werden kann, wenn der hydrostatische Druck der Schlammsäule oberhalb der Dichtung ausreichend ist, um den Druck unterhalb desselben zu überwinden, dadurch gekennzeichnet, dass das Ventilmittel die Form einer zylindrischen Ventilhülse (18) mit einer dadurch hindurchgehenden Bohrung für den Durchlass von Schlamm hat und Schliessventilmittel (22) aufweist, mit denen die Bohrung geschlossen werden kann, und weiter gekennzeichnet durch Mittel (23) zum Offenhalten der Schliessventilmittel (22) während des Einlaufvorganges und während des Bohrens und zum automatischen Schliessen der Schliessventilmittel (22), wenn der Druck in der Durchgangsbohrung des Gehäuses bis auf einen Pegel verkleinert ist, der um einen vorbestimmten Betrag kleiner ist als der Druck im Bohrloch, um es zu ermöglichen, dass Druck in der Durchgangsbohrung des Gehäuses wieder angelegt werden kann, nachdem die Schliessventilmittel (22) geschlossen sind wodurch die zylindrische Ventilhülse (18) in ihre aufblähende Stellung gedrückt wird, wodurch das Aufblähen des Dichtelementes (54) ermöglicht wird.

2. Ausblasen verhindernde Einrichtung nach Anspruch 1, bei der Einrichtungen (41) vorgesehen sind, um eine Schlammströmung durch die Durchlassöffnung des Gehäuses während des Einlaufvorganges zu erlauben, wodurch ein Füllen des Bohrstranges während des Einlaufvorganges ermöglicht wird.

3. Ausblasen verhindernde Einrichtung nach Anspruch 1 oder 2, bei der die Schliessventilmittel (22) in Richtung auf ihre geschlossene Stellung vorgespannt sind.

4. Ausblasen verhindernde Einrichtung nach Anspruch 3, bei der die Schliessventilmittel ein Rückschlagventil (22) am oberen Ende der zylindrischen Ventilhülse (18) aufweisen und bei der das lösbare Haltemittel eine Rückschlagventilhülse (23) innerhalb des Gehäuses aufweist, die in Axialrichtung innerhalb des Gehäuses zwischen einer ersten Stellung, in der das Rückschlagventil offengehalten wird, und einer zweiten Stellung, in der das Rückschlagventil losgelassen ist, so dass es sich in seine geschlossene Stellung bewegen kann, gleiten kann.

5. Ausblasen verhindernde Einrichtung nach Anspruch 4, in der das Mittel zum Bewegen der Rückschlagventilhülse (23) in ihre zweite Stellung eine Kolben-Zylinder-Einheit (25, 26) aufweist, die zur Druckseite im Bohrloch offen ist.

6. Ausblasen verhindernde Einrichtung nach einem der Ansprüche 1 bis 5, in der Mittel (17, 21) zum Festhalten der zylindrischen Ventilhülse (18) in ihrer aufblähenden Stellung vorgesehen sind, und dass Einrichtungen (62, 57) vorgesehen sind, die betätigbar sind, wenn die zylindrische Ventilhülse in ihrer aufblähenden Stellung ist, um das Dichtelement (54) zu entleeren, wenn die Dichte des Schlamms einen Wert erreicht, der ausreicht, den Druck am Bohrloch unterhalb des Einwegventils (8) zu überwinden.

7. Ausblasen verhindernde Einrichtung nach einem der Ansprüche 1 bis 6, in dem Einrichtungen (62) zum Verhindern der Entleerung des Dichtelementes (54) vorgesehen sind, wenn Schlamm zirkuliert wird.

8. Ausblasen verhindernde Einrichtung nach einem der Ansprüche 1 bis 7, bei der das Einwegventil (8) einen Ventilkörper (7') aufweist, der in Axialrichtung im Gehäuse zwischen Endanschlägen und in dichtendem Eingriff mit dem Gehäuse gleiten kann, wodurch der Druck unterhalb des Einwegventils am Bohrlochkdpf gemessen werden kann.

9. Bohrverfahren unter Verwendung einer an der Oberfläche angeordneten ein Ausblasen verhindernder Einrichtung in Verbindung mit einer unten im Bohrloch anzuordnenden ein Ausblasen verhindernden Einrichtung, die mit einem Bohrstrang verbunden ist, wobei die im Bohrloch anzuordnende ein Ausblasen verhindernde Einrichtung der Art ist, die ein längliches röhrenförmiges Gehäuse mit einer Durchgangsbohrung für den Durchlass von Bohrschlamm und mit einem Durchlass (56), der sich durch die Gehäusewand erstreckt, ein Dichtelement (54), das in Umfangsrichtung um das Gehäuse herum angeordnet ist, dessen Innenraum über den Durchlass in der Gehäusewand mit der Durchgangsbohrung des Gehäuses in Verbindung steht, ein Ventilmittel (58), das eine dadurch hindurchgehende Bohrung für den Durchlass von Schlamm aufweist und im Gehäuse so befestigt ist, dass es sich zwischen einer Bohrstellung, in der das Ventilmittel den Durchlass schliesst, und einer aufblähenden Stellung bewegen kann, in der der Durchlass offen ist, ein Einwegventil (8) zum Schliessen der Durchlassbohrung im Gehäuse auf der Seite des Ventilmittels, die dem Bohrmeissel näher ist, wobei das Einwegventil so betätigbar ist, dass Strömung von Schlamm unter Pumpendruck durch die Durchlassbohrung des Gehäuses in einer Richtung zum Bohrmeissel ermöglicht ist und Strömung von Schlamm in der entgegengesetzten Richtung verhindert ist, Schliessventilmittel (22) zum Schliessen der Bohrung im Ventilmittel, Einrichtungen (23) zum Offenhalten der Schliessventilmittel während des Einlaufvorgangs und während des Bohrens und zum automatischen Schliessen der Schliessventilmittel, wenn der Druck in der Durchgangsbohrung des Gehäuses bis auf einen Pegel verringert ist, der um einen vorbestimmten Betrag kleiner ist als der Druck in dem Bohrloch, einen Schlammzirkulationskanal (61), der sich durch die Gehäusewände zur Durchlassbohrung des Gehäuses erstreckt, wobei Einrichtungen zum Öffnen des Schlammzirkulationskanals zur Durchgangsöffnung des Gehäuses oberhalb des Ventilmittels, wenn das Dichtungselement aufgebläht ist, vorgesehen sind, und Einrichtungen vorgesehen sind, die es ermöglichen, dass das Dichtelement entleert wird, wenn der hydrostatische Druck der Schlammsäule oberhalb des Dichtelementes ausreicht, den Druck unterhalb desselben zu überwinden, wobei, wenn ein Schlag festgestellt wird, das Verfahren die Schritte aufweist: die an der Oberfläche angeordnete, ein Ausblasen verhindernde Einrichtung zu schliessen und so das Bohrloch an der Oberfläche zu schliessen, an der Oberfläche eine Messung des Drucks im Bohrloch zur Bestimmung des Druckes durchzuführen, der durch den Schlag oder das schlagförmige Ereignis erzeugt ist, an der Oberfläche den Druck im Bohrstrang abzulassen, so dass dieser Druck bis auf einen Wert abfallen kann, der um den vorbestimmten Betrag unterhalb des Drucks im Bohrloch liegt, wodurch ein Schliessen der Schliessventilmittel (22) bewirkt wird, Druck wieder an den Bohrstrang anzulegen, wodurch eine Bewegung des Ventilmittels (18) in seine zweite Stellung bewirkt wird, wodurch ermöglicht wird, dass das Dichtelement (54) durch Schlammdruck innerhalb des Bohrstranges aufgebläht wird und wodurch die Sohle des Bohrloches abgedichtet wird und wodurch durch die genannte Einrichtung der Schlammzirkulationskanal geöffnet wird, Schlamm höherer Dichte in den Bohrstrang über ein Ventil in der an der Oberfläche angeordneten ein Ausblasen verhindernden Einrichtung einzuführen, wodurch der Schlamm in den ringförmigen Raum oberhalb des Dichtelementes über den Schlammzirkulationskanal (61) gebracht wird, und mit diesem Einbringen oder Zirkulieren des Schlamms fortzufahren, bis der hydrostatische Druck der Schlammsäule im ringförmigen Raum ausreicht, den Druck des Schlags oder schlagförmigen Ereignisses zu überwinden.

Revendications

1. Obturateur anti-éruption de fond de puits comprenant un corps tubulaire allongé présentant un alésage traversant pour le passage de boue de forage et des moyens pour raccorder les extrémités du corps au sein d'un train de tiges (71), un élément de garniture d'étanchéité (54) disposé circonférentiellement autour du corps et pouvant être gonflé pour porter contre le trou de forage (73) pour étancher le trou, un moyen de passage (56) traversant la paroi du corps pour relier l'alésage traversant du corps à l'élément de garniture d'étanchéité pour gonfler l'élément de garniture d'étanchéité par la pression de boue provenant de l'intérieur du corps, un moyen de commande d'écoulement monté à l'intérieur du corps pour se déplacer entre une position de forage où le moyen de commande d'écoulement ferme ledit moyen de passage et une position de gonflage où le moyen de passage est ouvert, une soupape de retenue (8) pour fermer l'alésage traversant du corps du côté du moyen de commande d'écoulement destiné à être le plus proche du trépan, ladite soupape de retenue (8) agissant pour laisser la boue passer sous l'effet de la pression de pompe dans le sens allant vers le trépan, mais ne permettant pas l'écoulement de boue dans le sens opposé, un canal de circulation de boue (61) allant à travers la paroi du corps jusqu'à l'alésage traversant du corps, un moyen étant prévu pour ouvrir le canal de circulation de boue à l'alésage traversant du corps au-dessus du moyen de commande d'écoulement quand l'élément de garniture d'étanchéité (54) est gonflé pour permettre la circulation de boue à plus haute densité à travers l'alésage traversant du corps jusqu'au trou de forage, et un moyen pour permettre de dégonfler l'élément de garniture d'étanchéité (54) quand la charge hydrostatique de la colonne de boue située au-dessus de l'élément de garniture d'étanchéité est suffisante pour l'emporter sur la pression régnant au-dessous de lui, caractérisé en ce que ledit moyen de commande d'écoulement se présente sous la forme d'un manchon cylindrique (18) de commande d'écoulement traversé par un alésage pour le passage de boue et comportant un moyen de commande d'écoulement de fermeture (22) pour fermer ledit alésage, et caractérisé en outre par un moyen (23) pour maintenir ouvert le moyen de commande d'écoulement de fermeture (22) au cours de la descente du train de tiges et du forage et pour fermer automatiquement le moyen de commande d'écoulement de fermeture (22) quand la pression régnant dans l'alésage traversant du corps est réduite à un niveau inférieur d'une quantité déterminée, à la pression régnant dans le trou de forage pour permettre à la pression régnant dans l'alésage traversant du corps de se ré-appliquer après la fermeture du moyen de commande d'écoulement de fermeture (22) de façon à solliciter le manchon cylindrique (18) de commande d'écoulement vers sa position de gonflage permettant le gonflage de l'élément de garniture d'étanchéité (54).

2. Obturateur anti-éruption selon la revendication 1 dans lequel il existe un moyen (41) pour permettre à la boue de traverser l'alésage traversant du corps pendant la descente du train de tiges de façon à permettre au train de tiges de se remplir pendant la descente.

3. Obturateur anti-éruption selon la revendication 1 ou la revendication 2 dans lequel le moyen de commande d'écoulement de fermeture (22) est sollicité vers sa position de fermeture.

4. Obturateur anti-éruption selon la revendication 3 dans lequel le moyen de commande d'écoulement de fermeture est constitué par un clapet de retenue (22) situé à l'extrémité supérieure du manchon cylindrique (18) de commande d'écoulement et le moyen de maintien libérable est constitué par un manchon à clapet de retenue (23) situé dans le corps, lequel manchon peut coulisser axialement à l'intérieur du corps entre une première position dans laquelle le clapet de retenue est maintenu ouvert et une seconde position dans laquelle le clapet de retenue est libéré pour passer dans sa position de fermeture.

5. Obturateur anti-éruption selon la revendication 4 dans lequel le moyen de mise du manchon à clapet de retenue (23) dans sa seconde position est constitué par un dispositif de piston-cylindre (25, 26) ouvert à la pression régnant dans le trou de forage.

6. Obturateur anti-éruption selon l'une quelconque des revendications 1 à 5 dans lequel des moyens (17, 21) sont prévus pour maintenir le manchon cylindrique (18) de commande d'écoulement dans sa position de gonflage et il existe des moyens (62, 57) agissant quand le manchon cylindrique de commande d'écoulement est dans sa position de gonflage pour dégonfler l'élément de garniture d'étanchéité (54) quand la densité de la boue atteint une valeur suffisante pour triompher de la pression régnant dans le trou de forage au-dessous de la soupape de retenue (8).

7. Obturateur anti-éruption selon l'une quelconque des revendications 1 à 6 dans lequel il existe un moyen (62) pour empêcher l'élément de garniture d'étanchéité (54) de se dégonfler pendant la circulation de boue.

8. Obturateur anti-éruption selon l'une quelconque des revendications 1 à 7 dans lequel la soupape de retenue (8) comprend un corps de soupape (7') qui peut coulisser axialement dans le corps entre des butées d'extrémité et est en contact d'étanchéité avec le corps de sorte que la pression régnant au-dessous de la soupape de retenue peut être mesurée en tête de puits.

9. Procédé de forage utilisant un obturateur anti-éruption de surface conjointement avec un obturateur anti-éruption de fond de puits incorporé à un train de tiges, l'obturateur anti-éruption de fond de puits étant du genre comportant un corps tubulaire allongé présentant un alésage traversant pour le passage de boue de forage et un moyen de passage (56) traversant la paroi du corps, un élément de garniture d'étanchéité (54) disposé circonférentiellement autour du corps, son espace intérieur communiquant par la voie du moyen de passage prévu dans la paroi du corps avec l'alésage traversant du corps, un moyen de commande d'écoulement (18) traversé par un alésage pour le passage de boue monté dans le corps de façon à être mobile entre une position de forage où le moyen de commande d'écoulement ferme ledit moyen de passage et une position de gonflage où le moyen de passage est ouvert, une soupape de retenue (8) pour fermer l'alésage traversant du corps du côté du moyen de commande d'écoulement destiné à être le plus proche du trépan, la soupape de retenue agissant pour permettre le passage de boue sous l'effet de la pression de pompe à travers l'alésage traversant du corps dans le sens allant vers le trépan et pour empêcher l'écoulement de boue dans le sens opposé, un moyen de commande d'écoulement de fermeture (22) pour fermer l'alésage du moyen de commande d'écoulement, un moyen (23) pour maintenir le moyen de commande d'écoulement de fermeture ouvert au cours de la descente du train de tiges et du forage et pour fermer automatiquement le moyen de commande d'écoulement de fermeture quand la pression régnant dans l'alésage traversant du corps est réduite à un niveau inférieur d'une quantité déterminée à la pression régnant dans le trou de forage, un canal de circulation de boue, (61) allant à travers la paroi du corps jusqu'à l'alésage traversant du corps, des moyens étant prévus pour ouvrir le canal de circulation de boue à l'alésage traversant du corps au-dessus du moyen de commande d'écoulement quand l'élément de garniture d'étanchéité est gonflé, et des moyens pour permettre de dégonfler l'élément de garniture d'étanchéité quand la charge hydrostatique de la colonne de boue surmontant l'élément de garniture d'étanchéité est suffisante pour l'emporter sur la pression régnant au-dessous de lui, dans lequel, lors de la détection d'une poussée («kick»), ledit procédé comprend les opérations consistant à: fermer l'obturateur anti-éruption de surface pour étancher le trou de forage en surface, procéder en surface à une mesure de la pression régnant dans le trou de sondage pour déterminer la pression engendrée par la poussée, laisser s'échapper en surface la pression régnant dans le train de tiges pour permettre à ladit pression de devenir inférieure, de ladite quantité déterminée, à la pression régnant dans le trou de forage de façon à amener ledit moyen de commande d'écoulement de fermeture (22) à se fermer, ré-appliquer la pression dans le train de tiges pour amener ledit moyen de commande d'écoulement (18) à passer dans sa seconde position permettant le gonflage de l'élément de garniture d'étanchéité (54) par la pression de boue régnant dans le train de tiges pour étancher le fond du trou de sondage et pour amener ledit moyen à ouvrir le canal de circulation de boue, introduire de la boue de densité accrue dans le train de tiges par la voie d'une soupape prévue dans l'obturateur anti-éruption de surface de façon à envoyer ladite boue à l'intérieur de l'espace annulaire surmontant l'élément de garniture d'étanchéité par la voie dudit canal de circulation de boue (61), et continuer à faire circuler ladite boue jusqu'à ce que la charge hydrostatique de la colonne de boue présente dans l'espace annulaire soit suffisante pour l'emporter sur la pression de la poussée.

Drawing