OA13057A - Annulus monitoring system. - Google Patents

Abstract

Apparatus and a system for accessing one or more of the annuli defined between casing strings in a subsea wellhead that are usually sealed for the production stage of the well. Access to an annulus (30) is made via the wall of the wellhead housing (12) at a location where is communicates with the annulus. The access is a passageway (31) having a first opening in communication with the annulus and a second opening either at the external surface of the wall or at a location on the inner surface of the wall above the casing hangar seal for the inner casing (14), which is not in communication with the annulus apart from the passageway. An isolation valve (32) communicates with the passageway and with apparatus for monitoring or controlling pressure of flow in the annulus. The passageway may be used with an open lower end to the annulus during drilling stages for material transfer and during production stage to monitor/control a sealed annulus.

Description

013057

ANNULUS MONITORING SYSTEM

This invention relates to subsea wellheads and to casings for such wellheads.

More particularly it concerns providing a way of accessing an annular passageway (orannulus) defîned between concentric casings, and to a pressure monitoring and/orcontrai System for the annulus The casings may be part of a sériés of casing strings. Thepressure control may include movement of materials and the access may be used at thedrilling or completion stage or during production.

Well casing emerging from subsea deposits of oil and/or gas is required to contain wéllfluids under high pressures. The well casing may typically be of 10 3/4" OD (approx273mm) pipe. The well casing is secured to a well casing hanger within the v^êllhead andcoaxial with the well bore. The well casing is surrounded by a further,^asing, whichforms an outer barrier of an annulus formed between the two casings. Tb'eTurther casingmay be of 13 3/4" (approx 356mm) OD pipe. This further casing may also besurrounded by other casings. During drilling the casings are open at the top and bottom,but they are generally sealed at various stages prior to production. Access to theinnermost annulus is maintained via the top and valves but there is not sufficient space toprovide such access to other annuli.

To prevent collapse under subsea pressure the annuli between the successive concentriccasings are fîlled with fluid, which may be for examplç gas, drilling mud or water. Thefluid is generally injected into the annulus via the open annulus access of the top duringthe completion phase of the well when the casings are sealed. For the avoidance ofdoubt, in this spécification the expression fluid covers any flowable substance whichmay be gas or liquid, or suspensions or slurry. If leakage from production occurs orthere is other ingress of fluid into an annulus there can be a build up of pressure.Presently, if this occurs the casings hâve to be pulled up, which requires the well to beshut down. It is being found that as drilling goes to deeper formations, the resultinghigher températures and pressures increases the instances of pressure build up.

There are also other circumstances where the balance of pressures on the casingschanges. On the inside there is high pressure from the réservoir and on the outside deep 013057 -2- sea pressure. During ihe course of production pressure may change, for examplereducing pressure due to natural déplétion of the réservoir, which may also beaccompanied by changing températures; in the example just mentioned, a températuredrop. Such pressure changes can resuit in a differential pressure increase, collapsing orbursting of casings or damage to the formation.

Thus it is désirable at the production stage to be able to monitor pressure within anannulus between concentric casings and/or to be able to bleed, circulate or inject fluids inorder to change or restore the annulus pressure to a particular level. It is also désirable tobe able to utilise the annuli for movement of material, either as part of drilling, afterdrilling or during production.

There are also instances where the ability to pressurize an annulus may enable designchanges to casing thickness. Also respective concentric annuli may be held at differentpressure levels.

According to the invention there is provided a weilhead housing assembly for a subseawellhead, the assembly comprising a weilhead housing that is adapted to receive aplurality of casing strings therewithin with an annular passage defined betweenrespective adjacent casing strings, and in which the wall of the weilhead housing has apénétration with a first opening on its inner surface in a location that will communicatewith one annular passageway formed by a pair of adjacent casing strings, the pénétrationextending to a second opening on a surface portion of the weilhead housing wall that willnot be in communication with any annular passageway between casing strings.

The invention also provides a pressure monitoring/control System for a subsea wellheadarrangement including an inner pipe surrounded by an outer pipe and defining an annularpassage therewith, the inner and outer pipes being adapted to withstand internai andextemal pressure and the annular passage being filled with fluid to prevent compression,characterized in that a pénétration communicates at one end with the annular passage andat its other end is connected via a pressure isolation valve to means for monitoring and/orcontrolling pressure or flow within the annular passage. 013057 -3-

The inner pipe may be a well casing and the outer pipe a barrier casing.

The pénétration may be radial with respect to the bore radius of the pipe, or it may beinclined upwardly and hâve a portion extending in the general axial direction intoanother annulus at the top of the wellhead assembly.

The pénétration may extend through the casing wall or run between two location on theinner surface of the wall on opposite sides of the seal for the casing defining the innerwall of the annular passageway.

Pressurizing the annulus may also be used to circulate fluids or to route material, forexample drill cuttings for reinjection back into the formation, or to route returns in mud-lift Systems.

The invention is now described by way of example with référencé to the accompanyingdrawings, in which:-

Figure 1 is a schematic cross section of a conventional well assembly at a drilling stage;Figure 2 is a schematic cross section of a subsea wellhead at seabed level showing accessto an annulus via a casing wall;

Figure 3 is a modification of the subsea wellhead of Figure 2 showing two valves;

Figure 4 is a further modification of the wellhead showing pénétrations to two annuli;Figure 5 is a schematic cross section of a wellhead showing an alternative pénétrationroute;

Figure 6 is a schematic diagram of the wellhead of Figure 5 showing a valve layout, andFigure 7 is a schematic diagram of a well assembly at a drilling stage showing use of apénétration according to the invention in a mud lift System

Figure 1 shows the schematic layout of a well. Extending from a platform 100 is amarine riser 101 within which is a drill pipe 102. When drilling is complété the drillpipe is recovered to the surface and the casings are left hanging ffom the subseawellhead. At this stage the casings will be sealed at the top but may be open at thebottom. 013057 -4-

At mudline or seabed level a sériés of casing strings extend down into the formation.

The more outward casing strings are suspended at the levei of a subsea welihead 10 on the seabed. Above the casing strings is a blowout preventer.

The invention generally relates to accessing one or more of the annuli defined betweencasing strings at the subsea welihead level that at présent are sealed for the productionstage of the well. Access provided in this way may also be used at earlier stages and toprovide additional fonctions. Access via the top of the casings is unavailable due tospace considérations and the technology established for providing casing hangars andsealing. Access in the invention involves a radial or laterally extending pénétration ofthe casing outside the annulus or more conveniently of the welihead housing where it isin communication with the annulus. The pénétration may go completely through thecasing or provide a bore through to an accessible location on the inner surface of thecasing that is above the hangar/seaî for the casing defining the inside of the annulus.

Referring now to Figure 2, the welihead arrangement 10 has a frame 11 installed on theseabed, The welihead arrangement 10 has a welihead housing 12, typically this housingmay be 18%" (approximately 476mm).

Extending down to the seabed strata from the welihead housing 12 are four coaxialcasings, termed herein as well casing 14, outer barrier pipe 15, casing 16 and conductor17. The casings are supported on casing hangars in the generally known manner. Thedrawing shows hangar packoff 21 engaging with welihead housing 12 to support wellcasing 14 and hangar packoff 22 engaging lower down welihead housing 12 to supportouter barrier pipe 15. A well bay insert 18 also coaxial and concentric with the weliheadhousing and casings locates the welihead and casings within the ffarne 11. It is usuallythe case that several casings are supported by the welihead housing, it may be more thanthe number illustrated in the drawings.

It will be appreciated that the sizes of the casings may be any of those appropriate, forexample conductor casing 17 may be 30 inches (approximately 762mm), casing 16 maythen be 20 inches (508mm), barrier pipe 15 being 14 inches (356mm) and the well 013057 -> casing being 103/4inches (273mm), with the wellhead housing 12 being 183/4inches(476mm).

Between adjacent casings there is an annulus of free space which is filled with a fluidsuch as gas, sea water, methanol or drilling mud, or other such substance as conditionsdemand. The annulus between well casing 14 and outer barrier pipe 15 is shown shadedand with reference 30.

It is customary for the casings to be sealed to one another both at the top, where itprevents egress of gas or other substances that might otherwise escape front the annulus,and also at the end within the seabed strata. This sealing is done at the end of the drillingprocess.

In the embodiment shown a radial pénétration 31 is made in the wellhead housing 12,and it will be seen that at this point the annulus between casings 14 and 15 extendsupwards above the seal of hangar 22 to become an annulus between the wellheadhousing and the casing 14. An isolation valve 32 is provided intégral with the wellheadhousing 12 and this leads to an access port. The isolation valve 32 has a remotely ordirectly actuated valve operating arrangement outstanding fforn the body of the valve.These mechanisms may be of any appropriate type, for example the valve may be anhydraulic valve. The valve may be opérable by a ROV.

Figure 3 shows a second embodiment in which a second isolation valve 34 is connectedin sériés with the isolation valve 32. The second isolation valve 34 also has a remote ordirect operating arrangement with provision for ROV over ride. Hard piping may leaddown from the single or second isolation valve and loop round the wellhead housing 12to a connection point. Various monitoring/control features relating to the well outputmay be connected to the connection point.

As well as monitoring conditions in the annulus, excess pressure in the annulus can berelieved via the isolation valve or valves, or the annulus between the casings 14 and 15can be pressurised by pumping a fluid medium (e.g. methanol) through the valve orvalves, and via the pénétration 31, into the annulus. Pressurisation of the annulus 013057 -6- outside the well casing 14 may allow higher pressures to be contained within that casing.The invention provides ability to top up pressure to compensate for outward leakage,change of State or pressure réduction due to température variation, or to reduce pressurein the corresponding converse circumstances.

In order to position the pénétration and isolation valves with respect to the externallayout it may be necessary to provide an alignment mechanism. This is particularly thecase if the connections use rigid pipes. In the embodiments shown orientation betweenthe template 11 and the conductor housing 20 and also between the conductor housing20 and the wellhead housing 12 is achieved by alignment keys.

Alternatively a flexible conduit may lead off ffom the isolation valve 32 (or 34) topressure monitoring/control features elsewhere on the wellhead arrangement 10 or onassociated equipment. The wellhead housing 12 is installed complété with annulusmonitoring valve and flexible hose. A welded connection attaches the casing 16 to thebottom of the wellhead. Only rough orientation is required.

It is possible for pressure in different ones of the annuli between casings to be monitoredor adjusted, or for more than one annulus, possibly even ail, to be so monitored orcontrolled. Figure 4 shows an arrangement where the annulus between casings 15 and16 is monitored and/or adjusted via a second pénétration 41. At the level of pénétration41 through the wellhead housing 12, the wellhead housing forms an extension of theannulus between casings 15 and 16, it being above the suspension hangar for casing 16,but it is also below the seal for casing 15 and so isolated from the more inward annulusbetween casings 14 and 15. It will be appreciated that as the progressively more outwardcasing strings are hung at progressively lower levels, a pénétration to access them willalso be at a lower level, intermediate the casing hangars of the respective casings thatform the annulus.

When there are a plurality of pénétrations to different annuli they do not ail hâve to beprovided with the same facilities. For instance it may be required only to monitor one ormore while others may need to hâve pressure Controls. The provision of a pénétrationmay in some cases be used to pressurise only at the completion/sealing stage with lesser -7- 013057 monitoring only equipment being installed subsequently.

In the embodiments described above the pénétration is radial though it could be inclinedand an alignment framework is required. Also additional connections between thesubsea tree and the alignment framework are required. In an alternative embodimentshown in Figures 5 and 6 the additional connections can be avoided by extending thepénétration passageway to a void that is created between an isolation sleeve (reference40) and the wellhead housing.

As in previous embodiments, the wellhead assembly 10 has a wellhead housing 12, wellcasing 14 and outer barrier pipe 15.

As can be seen in Figure 5, as the wellhead body 12 extends upwardly beyond the casinghangar 22 there is an upper annulus defined between the wellhead body 12 and anisolation sleeve 40. In this embodiment a passage is created through the wellhead bodyfrom the annulus between casings 14 and 15 and into the upper annulus. This enablesthe monitoring and pressure adjustment mechanism to be located higher up and avoidextra connections to the tree.

In Figure 5, the first part of the passageway from the annulus between casings 14 and 15has an opening in the same location on the inside of the wellhead housing as previousembodiments. This time bore 31 is upwardly inclined and communicates with an accessport additionally provided on the wellhead housing. A valve 43, such as a small boregâte valve is provided within bore 31 to isolate the pressure of the annulus. The port andthis location for the valve are option. Pénétration through the wall of the wellhead is notneeded but blocking a through bore with a port may be a more convenient way ofproviding the passageway.

The passageway then continues through further communicating bores 44, 45 and 46 tothe upper annulus and then via bore 48 to valves and connections at the top of thewellhead assembly. The arrangement shown is a convenient way to drill the bores,however ail that is required is to provide a looped passage from the inner surface of the 013057 wellhead housing below packoff 21 to the inner surface of the wellhead housing abovepackoff 21. Thus the configuration, number and inclination of the bores may vary.

Figure 6 shows schematically the bores and valves of the assembly. Hydrocarbon fluidsemerge from the well bore to an outlet 50 via a primary master valve 51 and primarywing valve 52. When isolation valve 43 is open the monitoring and control of theannulus pressure is via valve 53 and, optionally, other valves shown generally at 54.

Valves controlling full flow of hydrocarbon fluids and access to the annulus betweencasings 14 and 15 can be applied both to Side Valve Trees (also known as HorizontalTrees or Spool Trees) and conventional trees.

The spécifie example of the invention described above with reference to Figures 5 and 6has the advantages that it éliminâtes the use of additional connections and isolationvalves between the wellhead System and the subsea tree system. It does not add any extraoperations to the conventional running/installation procedures for the tree or wellhead asit is usual to hâve test ports in this annulus, for example to test the connection betweenthe Subsea Xmas Tree and the Subsea wellhead. Thus this communication will in thisembodiment additionally hâve the application of monitoring the annulus, once theclosure/isolation mechanism is left open in the wellhead.

The embodiment of Figures 5 and 6 may also be used in combination with lower levelpénétrations to one or more annulus at lower Ievels as described in respect of theembodiment of Figure 4. Likewise a looped passageway from between other pairs ofpackoffs to above packoff 21 may also be provided. Isolating valves and onwardseparate routing would be required if more than one annulus is connected to the annulusbetween the wellhead housing and isolation sleeve.

It will be appreciated that the embodiments described are ali situated below the Blowoutpreventor and therefore do not interfère with the construction of that part of theassembly. 013057 -9-

The invention has been described so far generally within the context of coaxial casingsthat hâve, or will be, sealed at their top and at the base of the more outward casing so asto form an enclosed, sealed annulus. While it is most probable that top seals will alwaysbe in place, there need not always be a lower seal. This then offers the possibility ofmonitoring pressure that is in communication with seabed strata or of applying pressureor introducing fluid or material to the formation via the open end of the annulus. Theopen lower end of the casing may hâve modified structure or openings for spécifiepurposes.

Figure 7 shows a so called 'mud lift' system employing a modification of the inventionused during drilling.

Mud lift Systems hâve been proposed for deep drilling where the weight of mud in themarine riser as shown in Figure 1 is too great to be supported by the formation. Toovercome this there hâve been proposais to seal the marine riser at the subsea wellheadlevel and only hâve seawater in the riser above that level. It is then proposed to pumpthe mud via a mud return to the surface. However such Systems hâve not yet evoiveddue to the complexity of routing the mud from the riser. Proposais for this routing hâvebeen located within the biowout preventer (BOP) which is both complex and requiresredesign of the BOP.

The présent invention proposes providing a pénétration 31 as previously described andconnecting the pénétration to the mud lift system. In a further modification (not shown),a pénétration may be provided to route the mud into a casing outside the marine riser, oreven back into the marine riser if the load is supported at the level of the seal.

The arrangements described in respect of Figure 7 may also be used to transfer materialin the reverse direction. For example after drilling, drill cuttings may be reinjected backinto the formation. This reinjection may alternativeiy be performed between othercasings, with open lower ends providing access to the formation.

After use for mud lift and/or reinjection as the case may be, the same pénétration may beused at the production stage for monitoring, controi or other functions. 013057 -10- A further embodiment of the invention may establish multiple pénétrations into anannulus so as to provide a flow path. Such a flow path may be used to drive a pumplocated in the annulus. Adjacent annuli may be interconnected by a pénétration in theircommon casing (at a lower level) and then pénétrations as described above to each of theannuli used as respective inward and outward flow paths.

Interconnection of casing annuli via a looped pénétration in the wellhead housing is alsopossible in a manner similar to the connection shown between the casing 14 and 15annulus and the upper annulus in Figure 5.

Claims (14)

013057 -11 - CLAIMS

1. Λ wellhead assembly for a subsea wellhead. the assembly comprising awcllhead housing having a wall and adaptcd to receivc a plurality of casing stringstherewithin with an annular passage defined between respective adjacent casingstrings, and in which the wall of the wellhead housing has a passageway with a first openingon its inner surface in a location that will communicate wilh an annular passagewaydefined between an inner casing string and an outer casing string, the pénétrationextending in an axial direction in the wall of the wellhead housing to a secondopening on an inner surface portion ofthe wellhead housing wall above a location fora casing hangar scal of the inner casing string.

2. Λ wellhead assembly according to claim ) in which a plural ïty ofpassageways are provided in the wellhead housing wall, each wilh a first openinglocated to communicate with an annulus defined by respective dïfifercnt pairs of innerand outer adjacent casing strings.

3. Λ wellhead housing assembly according to claim 1 in which the secondopening ofthe passageway communicates with a location where the wellhead housingdefines an annulus with an isolation sleeve,

4. A wellhead housing assembly according to claim 1 in which the passagewaycomprises a sériés of bores including one bore extending in tbe axial direction.

5 A wellhead housing assembly according to claim I fùrther comprising anisolation valve in communication with the passageway.

6. A wellhead housing assembly according to claim S in which the isolationvalve is intégral with the wellhead housing,

7. A wcllhead assembly according to claim 1 further comprising means for 013057 - 12- monîtoring and/or controlling pressure or flow within the annuiar passage.

8. Λ wellhead asscmbly according to daim 1 in which the outer casing string isopen at its Iower end and matcrial is routed via the open end and passageway. 5

9. A wellhead assembly according to daim 8 in which the material is drillcuttings routed for reinjection to the formation.

10. A wellhead assembly according to daim 8 in which the matcrial is mud in a 1Û mud-liû System,

11. Λ wellhead asscmbly according to daim 1 in which flow jn the annuiarpassageway is used to drive a pump. 15

12. A wellhead asscmbly according to daim 1 in which there are adjacent annuiar passageways defined between three concentrically disposed casîngs and an additionalpénétration to conncct the adjacent annuiar passageways is made in the commoncasing. 20

13, A wellhead assembly according to daim 5 in which a second isolation valve is conncctcd in sériés with the isolation valve.

14. A wellhead asscmbly according to daim 13 in which the isolation valve orvalves are opérable hydraulically, with provision for ROV override. 25