SUB SURFACE SAFETY VALVE BLOCK, PARTICULARLY SUITABLE FOR THE RISERS OF OFFSHORE PLATFORMS

Abstract: Sub-surface safety valve block to be connected between a well head at sea bottom, and the lower end of a riser, in order to make it possible the production tube and/or the service tube of the completion string to be closed by means of gate valves, which sub-surface safety valve block is constituted by a valve body provided with a vertical through-bore which is tigthly closed at its upper end by a packer with which the upper portion of the completion string is connected, and at the bottom is tightly closed by a tubing hanger with which the lower portion of said completion string is connected; said packer and said tubing hanger are fastened inside the above-said through-bore by means of a mechanical hooking which can be disengaged by means of a hydraulic-­ controlled action, and are each provided with a through-­ channel in order to connect the respective production tubes with the central region of said through-bore, which can be closed by means of a gate valve, as well as with two branched channels in order to connect the relevant service tube and the relevant hydraulic-drive lines used in order to drive the SSSV safety valve, respectively with a service channel and a control channel provided inside said valve body, with a further gate valve being provided in order to make it possible this latter service channel to be closed.

Description: The present invention relates to a sub-surface safety valve block which, by making it possible for the whole completion string to be recovered and then any kind of servicing operations to be carried out on the well, as well as said completion string to be applied again with the same valve block having never to be removed, and therefore allowing the completion string and any necessary tools to pass through the same valve block, is particularly suitable for being applied to the lower end of a riser, which connects a sub-surface well head with the deck of an overhanging offshore platform, in order to independently intercept the streams flowing inside each of the tubes forming part of said completion string, i.e. the stream of hydrocarbons flowing inside the production tube and the fluid streams flowing inside the service tubes. According to the present state of the art in the sub-surface production of hydrocarbons from stationary platforms, all the borehole strings installed in a well are generally extending in the vertical direction from the sea bottom up to the deck of the platform, in order to constitute a riser provided with a plurality of concentric walls for an efficacious sheltering of said completion string inside them. Such a structure, by practically creating a continuous well, free from interruptions and safe, makes it possible for any necessary operations to be carried out inside the interior of the well, without the surrounding sea having to be taken into account and, in particular, clearly makes it possible for the completion string to be easily recovered from the sea surface, with no need for any riser recovery operations having to be carried out. But in case hydrocarbons are produced in very deep waters and thus, in particular, platforms of TLP (Tension Leg Platforms) type or single-leg platforms are used, which do not make it possible for the riser to be horizontally supported and therefore require the riser to be efficaciously put under tension from the same platform, with lower-weight risers, with as small overall dimensions as possible, having to be used, the wells are generally connected from the sea bottom to the deck of the platform by using a single rising string, or a single-wall riser per each well. This type of structure introduces hence serious safety limits, in that it is provided with one single structural barrier only, which is evidently less strong than the traditional barriers, between the external environment and the completion string, as well as with one single safety valve in order to interrupt the flowing of the fluid stream from the field, commonly denominated "SSSV (Sub Surface Safety Valve)", such a structure does not secure a complete reliability. In order to solve the above-said safety problem, one could think of using a sub surface valve block, to be interposed between the lower end of the riser and the well head at sea bottom, which valve block is provided with gate valves in order to reliably close ― when necessary ― in a discrete way each tube of the completion string. Unfortunately, this solution is affected by the serious drawback that it does no longer make it possible for the completion string to be easily removed and subsequently reinstalled, operations which have to be considered as essential during the life of a well, both in order to enable the necessary extraordinary or ordinary well maintainance to be carried out, and in order to make it possible for suitable actions to be carried out on the field for the purpose of improving the production. In fact, the above said recovery of the completion string cannot be carried out without previously removing the valve block, and, on the other hand, the recovery of said valve block implies, in its turn, the removal of the overhanging riser, as well as the reinstallation thereof, with the obvious consequences that long dead times and laborious handling procedures, and hence high operating costs, become necessary. The purpose of the present invention is hence of obviating the above said drawback, and therefore of supplying a sub surface safety valve block to be applied between the sub surface well head and the lowermost end of the riser which connects said well head with the deck of an overhanging offshore platform, which not only makes it possible for the production tube and the service tubes of the completion string to be selectively closed by means of hydraulic-driven gate valves, as well as to make it possible for the hydraulic control line, which is provided for actuating the SSSV safety valve (which acts inside the production tube contained inside the lower portion of the completion string installed inside the well) to pass, but also enables all of said completion string to be recovered, without said valve block having to be removed. The above purpose is substantially achieved in that said completion string can be recovered by having it run through a suitable vertical through-bore provided in said valve block, wherein the upper end of the lower portion of the completion string installed inside the well, and the lower end of the upper portion of the same completion string installed inside the riser are respectively connected to a sub surface tubing hanger and to a packer, which are in their turn fastened, with a tight sealing by means of gaskets and a mechanical hooking disengageable by means of a hydraulic-controlled action, to both ends of said through-bore, and are each provided with a through-channel which connects the production tubes of respectively said lower portion and said upper portion of said completion string with the central region of said through-bore, which can be closed by means of a hydraulic-driven gate valve supported by the body of said valve block, as well as with branched channels in order to substantially connect with each other the service tube and the hydraulic control line for the hydraulic drive of the SSSV safety valve of said two portions of the completion string, through a respective service channel and a respective control channel provided inside said body of the valve block, with a further hydraulic-driven gate valve ― also supported by said valve block body ― making it possible for said service channel inside said valve block body to be closed, and said service channel provided inside said packer being equipped with a nonreturn valve. On the other hand, said packer is provided, at its upper end, in correspondence with said channels thereof, with flares for housing under tight-sealed conditions the ends of the elements of said upper portion of the completion string, i.e. of the production tube and of the service tubes, as well as of the SSSV safety valve control line. It is at once evident that in order to recover the whole completion string, it is now enough to lift said upper portion of the completion string by sliding its elements out from said flares provided in the packer, lift said packer after hydraulically disengaging it, and finally lift said tubing hanger, with which the elements of the lower portion of the completion string are integral, after said tubing hanger being hydraulically disengaged from the well head as well, by making it slide through said through-bore of said valve block, which action can be carried out without removing the valve block, and hence the riser, with the closure of the production tube and/or of the service tubes being achieved by hydraulically actuating said gate valves. Summing up, the sub surface safety valve block, is particularly suitable for being applied between a well head at the sea bottom and the lower end of a riser which connects said well head with the deck of an overhanging offshore platform in order to selectively close the production tube and/or the service tubes of a completion string by means of hydraulic-drive gate valves supported by the body of said valve block. It also makes it possible for the hydraulic control line of said completion battery, which is provided in order to control a safety valve (better known as an "SSSV"), which acts on the production tube of the lower portion of said completion string, installed inside the well, to be passed through said valve body. A sub-surface safety valve block of this type is known from DE-A-2832678. It is further characterized according to the present invention in that the body of said valve block is provided with a vertical through-bore wherein the upper end of said lower portion of the completion string is connected to a sub surface tubing hanger which is fastened, with a tight sealing, inside the bottom end of said vertical through-bore by means of gaskets and a mechanical hooking means disengageable by means of a hydraulic-controlled action, and which is provided with a through-channel which connects the production tube of said lower portion of said completion string with the central region of said through-bore, which through-bore can be closed by means of one of said hydraulic-driven gate valves, the tubing hanger as well being provided with branched channels in order to respectively connect the service tube and the hydraulic control line for the hydraulic drive of the SSSV safety valve of said lower portion of said completion string with a corresponding service channel and a corresponding control channel provided inside said body of the valve block, with a further one of said hydraulic-driven gate valves making it possible for said service channel inside said valve block body to be closed, and with the lower end of the upper portion of said completion string, installed inside said riser, is connected with a packer, which in its turn is fastened under tight sealing conditions inside the upper end of said vertical through-bore by means of gaskets and a mechanical hooking means disengageable by means of a hydraulic-controlled action, and which packer is provided as well with a through-channel which connects the production tube of said upper portion of said completion string with said central region of said through-bore, as well as with two branched channels in order to respectively connect the service tube and the hydraulic control line for the hydraulic drive of the SSSV safety valve of said upper portion of the completion string with said corresponding service channel and control channel provided inside said body of the valve block, with said branched channel provided inside said packer and which corresponds to the service tube being equipped with a nonreturn valve. Then, according to a preferred embodiment of the present invention, said bottom end of said upper portion of said completion string is connected with said packer by means of housing flares provided in the top portion of said packer, inside which the lower ends of the production tube and of the service tubes, as well as of the SSSV safety valve control line, which constitute the upper end of said completion string, enter under tight-sealing conditions, with said flares being in correspondence with said channels provided in said packer. On the other end, in order to provide for said packer and said tubing hanger to be easily installed inside said vertical through-bore provided inside the body of said valve block, with no need arising for their branched channels having to be exactly aligned with the corresponding service channel and control channel provided inside said valve block body, according to a further feature of the present invention said branched channels, both provided in the packer and in the tubing hanger, open into corresponding annular chambers provided around the peripheral surface of said packer and of said tubing hanger, opposite to said corresponding service channel and control channel in said body in said valve block. Finally, in order to accomplish a further protective barrier between the inside of the well and the external marine environment, according to a further feature of the present invention said tubing hanger is provided in correspondence of its bottom side, with a protruding part which enters, under tight-seal conditions accomplished by means of a gasket, the collar of the borehole string which bounds said well. The invention is now explained in greater detail by referring to the hereto attached drawings, which illustrate a preferred form of practical embodiment of the same invention, given for merely exemplifying, non-limitative purposes, in that technical variants and structural modifications may be always supplied without departing from the scope of the present invention. In said drawings: Figure 1 shows a general view of an offshore platform in which safety valve blocks according to the present invention are used; Figure 2 shows a perspective, enlarged-scale, view of one of the safety valve blocks of Figure 1; Figure 3 shows a sectional view made according to path AA of Figure 2; Figure 4 shows a partially sectional, magnified front view of the valve block of Figure 2; Figure 5 shows a magnified, sectional, front view of a detail of the valve block of Figure 4. Referring to the figures, the reference numeral 1 indicates an offshore platform of TLP (Tension Leg Platform) type, anchored to sea bottom 2 by means of the tension legs 3, and the reference number 4 indicates a set of risers which connect the deck 5 of said platform with corresponding well heads 6 at sea bottom, from which the borehole strings 7 leave. Between each well head 6 and the bottom end of each riser 4, a sub surface safety valve block 8 is then applied. In a more specific way, the block 8 is constituted by a valve body 9 provided with a vertical through-bore 10, and ending, at its top end, with a male fitting 11 to which a connector bowl 12 integral with the bottom end of the corresponding riser 4 is connected, by known means. The above said connector bowl 12 furthermore contains the control lines 14 and 15 for the hydraulic actuators, respectively driving the gate valves 16 and 17 of the valve block 8, with said lines respectively leading to annular chambers 18 and 19 (specifically see Figure 5) secure that the relevant connection is always accomplished, without any need for orienting operations having to be carried out, with the corresponding control lines 14′ and 15′ running through said male fitting 11, with the tight sealing being secured by the gaskets 13. At its bottom end, said valve body 9 ends, on the contrary, with a connector bowl 118, by means of which it is anchored, in a known way, to said well head 6 containing the collars 119 of said borehole strings 7, wherein the smallest-diameter tubing string 7′ (see Figure 4) bounds the true well 20, inside which the lowermost portion of the completion string 21, substantially consisting of the production tube 22, on which the safety valve of SSSV type 23 acts, and of the hydraulic line 24 for the hydraulic drive of said valve 23, is installed. The upper end of said lower portion of the completion string 21 is then connected with a sub surface tubing hanger 25, which is fastened inside the bottom portion of said vertical through-bore 10 by means of a mechanical hooking device 26 disengageable by means of a hydraulic-controlled action, and is substantially constituted by radially expanding sectors, which can radially expand into a corresponding circular groove provided in the body 9 of the valve, with the tight sealing between the tubing hanger and the through-bore being secured by annular gaskets 27. Said tubing hanger 25 is furthermore provided with a through-channel 28 which connects said production tube 22 with the overhanging central area of the through-bore 10, which can be closed by means of the gate 29 of the above-said hydraulic-driven gate valve 17, which is mounted on the body 9 of the valve block, and, in case inside said control line 15′ the actuation pressure is absent, automatically returns back into its closure position, owing to the action of its return spring 30. Inside the tubing hanger 25 also a branched channel 31 is provided, in order to connect said control line 24 for the SSSV valve 23, with a corresponding control channel 32 provided in said valve body 9, as well as a second branched channel 33 is provided, in order to act as the service tube for said lower portion of the completion string 21, to be connected with a corresponding service channel 34 also provided in the valve body 9, and which can be closed by means of said gate valve 16, which is analogous to said gate valve 17. Then, according to a further feature of the present invention, the above-said branched channels 31 and 33 are caused to lead to annular chambers, respectivaly indicated by the reference numerals 53 and 54, provided around the peripheral surface of the tubing hanger 25, a feature this, which secures that they are always respectively connected with the channels 32 and 34, with no need for orienting operations having to be carried out. On the other hand, according to a preferred form of practical embodiment of the present invention, said tubing hanger 25 is provided, at its lowermost side, with a protruding part 35 (see Figure 4) which, by means of a ring-shaped gasket 36, creates a further tight seal between the well 20 and the marine environment, besides the tight seal created by the ring-shaped gasket 37 between the connector bowl 118 and the well head 6. On the contrary, the upper portion of the completion string 38, installed inside the riser 4, and constituted by the production tube 39, the service tube 40 and the hydraulic control line 41 for the SSSV safety valve 23, is connected with a packer 42 and said connection, according to a preferred form of practical embodiment of the present invention, is accomplished by means of three housing flares 43 (see Figure 5) provided in the upper portion of said packer 42, inside which the bottom ends of said tubes 39 and 40 and of said control line 41 respectively enter, with the tight sealing being secured by the gaskets 44. Said packer 42 is then fastened, under tight sealed conditions, inside the upper portion of said vertical through-bore 10 in a way perfectly analogous to as already done for said tubing hanger 25, i.e., by means of a mechanical hooking device 45, disengageable by means of a hydraulic-controlled action, and the annular gaskets 46. In an analogous way, said packer 42 is furthermore provided with a through-channel 47 in order to connect said production tube 39 with the underlying cental region of the through-bore 10, with a branched channel 48 in order to connect said service tube 40 with said service channel 34, and with a further branched channel 49 in order to connect said control line 41 with said control channel 32. Also in this case, said branched channels 48 and 49 are then caused to lead into annular chambers, respectively indicated by the reference numerals 50 and 51, in order to facilitate the connection with said channels 34 and 32; and furthermore in said branched channel 48 a nonreturn valve 52 (see Figure 5) is provided, in order to make sure that the fluid inside the service line flows in one single direction.

Claims: 1. Sub surface safety valve block (8) particularly suitable for being applied between a well head (6) situated at sea bottom (2) and the lowermost end of a riser (4) which connects said well head with the deck of an overhanging offshore platform (1), in order to selectively close the production tube (22; 39) and/or the service tubes (40) of a completion string by means of hydraulic-driven gate valves (16, 17) supported by the body (9) of said valve block (8), which also makes it possible for the hydraulic control line (24, 41) of said completion string to pass, which is provided for driving a safety valve (SSSV-type) (23) ― which acts on the production tube (22) of the lower portion of the completion string (2) installed inside the well, characterized in that the body (9) of said valve block is provided with a vertical through-bore (10) wherein the upper end of said lower portion of the completion string is connected with a sub surface tubing hanger (25) which is fastened, with a tight sealing, inside the bottom end of said vertical through-bore (10) by means of gaskets (27) and a mechanical hooking means (26) disengageable by means of a hydraulic-controlled action, and which is provided with a through-channel (28) which connects the production tube (22) of said lower portion of said completion string with the central region of said through-bore (10), which can be closed by means of one (17) of said hydraulic-driven gate valves, as well as with branched channels (31, 33) provided in order to respectively connect the service tube and the hydraulic control line (24) for the hydraulic drive of the SSSV safety valve (23) of said lower portion of said completion string (21) with a corresponding service channel (34) and a corresponding control channel (32) provided inside said body (9) of the valve block (8), with a further one of said hydraulic-driven gate valves (16) making it possible for said service channel (34) inside said valve block body (9) to be closed, and with the lower end of the upper portion (38) of said completion string installed inside said riser is connected with a packer (42), which in its turn is fastened under tight sealing conditions inside the upper end of said vertical through-bore (10) by means of gaskets (44) and a mechanical hooking means (45) disengageable by means of a hydraulic-controlled action, and is provided as well with a through-channel (47) which connects the production tube (39) of said upper portion of said completion string with said central region of said through-bore (10), as well as with two branched channels (48, 49) in order to respectively connect the service tube (40) and the hydraulic control line (41) for the hydraulic drive of the SSSV safety valve (23) of said upper portion (38) of the completion string with said corresponding service channel (34) and control channel (32) provided inside said body (9) of the valve block (8), with said branched channel (48) provided inside said packer (42), which corresponds to the service tube (40), being equipped with a nonreturn valve (52). 2. Sub surface safety valve block (8) according to claim 1, characterized in that said bottom end of said upper portion (38) of said completion string is connected with said packer (42) by means of housing flares (43) provided in the top portion of said packer (42), inside which the lower ends of the production tube (39) and of the service tube (40), as well as of said SSSV safety valve control line (41), which constitute the upper portion (38) of said completion string, enter under tight-sealing conditions accomplished by means of gaskets (44), with said flares (43) being in correspondence with said channels (47, 40, 49) provided in said packer. 3. Sub surface safety valve block (8) according to claim 1, characterized in that said branched channels (31, 33, 48, 49), provided in both said packer (42) and said tubing hanger (25), are caused to open into corresponding annular chambers (50, 51, 53, 54) provided on the peripheral surface of said packer (42) and of said tubing hanger (25), opposite to said corresponding service channel (34) and control channel (32) provided in said body (9) of said valve block (8). 4. Sub surface safety valve block valve according to claim 1, characterized in that said tubing hanger (25) is provided on its bottom side with a protruding part (35) which enters, under tight-seal conditions accomplished by means of a gasket (36), the collar of the borehole string, which bounds said well.

Inventors: AMENDOLA, GIANCARLO, DONATI, FRANCESCO, FRANCESCHINI, GIULIANO, GALLETTI DI CADILHAC , ARTHUR ROBIN
Applicants: AGIP S.P.A.
Application year: 1989
Main classification: E21B33
IPC codes: E21B34, E21B33