Annulus monitoring system

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.

1 . A wellhead housing assembly for a subsea wellhead, the assembly comprising a wellhead housing that is adapted to receive a plurality of casing strings therewithin with an annular passage defined between respective adjacent casing strings, 
 and in which the wall of the wellhead housing has a penetration with a first opening on its inner surface in a location that will communicate with one annular passageway formed by a pair of adjacent casing strings, the penetration extending to a second opening on a surface portion of the wellhead housing wall that will not be in communication with any annular passageway between casing strings.    
     
     
         2 . A wellhead housing assembly according to  claim 1  in which the second opening of the penetration is on the exterior of the wellhead housing.  
     
     
         3 . A wellhead housing assembly according to  claim 2  in which the penetration extends through the wellhead housing wall substantially radially.  
     
     
         4 . A casing string assembly according to  claim 2  in which the penetration extends through the wellhead housing wall at an angle inclined longitudinally from radial.  
     
     
         5 . A casing string assembly according to any preceding claim in which the penetration is below a location for a casing hangar seal for the casing string defining the inner wall of the annular passageway.  
     
     
         6 . A wellhead housing assembly according to any preceding  claim 1  in which a plurality of penetrations are provided each with a first opening located to communicate with an annulus defined by respective different pairs of adjacent casing strings.  
     
     
         7 . A wellhead housing assembly according to  claim 1  in which the second opening of the penetration is on the interior of the wellhead housing above a location for a casing hangar seal for the casing string defining the inner wall of the annular passageway  
     
     
         8 . A wellhead housing assembly according to  claim 7  in which second end of the penetration communicates with a location where the wellhead housing defines an annulus with an isolation sleeve.  
     
     
         9 . A wellhead housing assembly according to  claim 7  or  claim 8  in which the penetration comprises a series of bores including one bore extending in the axial direction.  
     
     
         10 . A wellhead housing assembly according to any preceding claim further comprising an isolation valve in communication with the passageway.  
     
     
         11 . A wellhead housing assembly according to  claim 10  in which the isolation valve is integral with the wellhead housing.  
     
     
         12 . A pressure monitoring/control system for a subsea wellhead arrangement including a wellhead housing assembly according to any preceding claim and means for monitoring and/or controlling pressure or flow within the annular passage.  
     
     
         13 . A subsea wellhead arrangement having a plurality of casing strings disposed coaxially with respective adjacent casing strings defining an annular passage therebetween, and in which a respectively outward one of adjacent casings strings has a passageway in its wall with a first opening communicating with the annulus and a second opening connecting to apparatus for monitoring or controlling pressure or flow within the annular passage.  
     
     
         14 . A subsea wellhead arrangement according to  claim 12  in which the respectively outward one of the casings defining the annular passageway is open at its lower end and material is routed via the open end and passageway.  
     
     
         15 . A subsea wellhead arrangement according to  claim 14  in which the material is drill cuttings routed for reinjection to the formation.  
     
     
         16 . A subsea wellhead arrangement according to  claim 14  in which the material is mud in a mud-lift system.  
     
     
         17 . A subsea wellhead arrangement according to  claim 13  in which flow in the annulus is used to drive a pump.  
     
     
         18 . A subsea wellhead arrangement according to  claim 12  or  claim 13  in which there are a adjacent annular passageways defined between three concentrically disposed casings and an additional penetration to connect the annuli is made in the common casing.  
     
     
         19 . A subsea wellhead arrangement according to any preceding claim in which a bore in the wellhead housing interconnects two annular passageways between casing strings.  
     
     
         20 . A subsea wellhead arrangement according to  claim 18  in which the bore has a first opening between the seals for a first pair of casing strings and a second opening between seals for a second pair of casing strings.  
     
     
         21 . A pressure monitoring/control system for a subsea wellhead arrangement including an inner pipe surrounded by an outer pipe and defining an annular passage therewith, the inner and outer pipes being adapted to withstand internal and external pressure and the annular passage being filled with fluid to prevent compression, 
 characterized in that a penetration communicates at one end with the annular passage and at its other end is connected via a pressure isolation valve to means for monitoring and/or controlling pressure or flow within the annular passage.    
     
     
         22 . A system according to  claim 21  in which the penetration is in the wellhead housing with said one end at a level communicating with the annulus.  
     
     
         23 . A system according to  claim 21  in which the end of the penetration communicating with the annulus is below a casing seal for the inner pipe and above a casing seal for the outer pipe.  
     
     
         24 . A system according to  claim 21  in which the inner pipe is a well casing and the outer pipe is a barrier casing and the means for monitoring connects to a component at the subsea wellhead.  
     
     
         25 . A system as claimed in  claim 21  in which the penetration is radial with respect to the well bore.  
     
     
         26 . A system as claimed in any of  claims 21  to  25 , in which a second isolation valve is connected in series with said pressure isolation valve.  
     
     
         27 . A system as claimed in any one of  claims 21  to  26 , in which the isolation valve or valves are operable hydraulically, with provision for ROV override.  
     
     
         28 . A system as claimed in any one of  claims 21  to  27 , in which there is a rigid connection between the isolation valve and the monitoring/control feature.  
     
     
         29 . A system as claimed in  claim 28 , in which there is an alignment key between an outer housing and a system support structure to ensure aligned engagement of the rigid connection and the support structure.  
     
     
         30 . A system as claimed in any one of  claims 21  to  27 , in which there is a flexible connection between the isolation valve and the monitoring/control feature.  
     
     
         31 . A system as claimed in any one of  claims 21  to  30 , in combination with means to control/monitor fluid pressure within the annulus between the well casing and the outer barrier pipe, whereby to increase the allowable pressure within the well casing.  
     
     
         32 . A system as claimed in any one of  claims 21  to  31 , in which there is another pipe surrounding the outer barrier pipe, so forming a second annulus surrounding the annulus aforesaid, and in which there is a second penetration leading to another isolation valve by which the pressure in the second annulus may be monitored/controlled.  
     
     
         33 . A pressure monitoring/control system according to any of  claims 21  to  32  in which the isolation valve is integral with the wellhead housing.  
     
     
         34 . A pressure monitoring/control system according to  claim 21  in which the penetration has a portion that extends axially within the housing to a further annulus near to the top of the wellhead arrangement.  
     
     
         35 . A system as claimed in  claim 21  in which part of the penetration in the wellhead housing is directed radially upward and outward with respect to the well bore.  
     
     
         36 . A system as claimed in  claim 34  or  claim 35 , in which a second isolation valve is connected to an outflow from the further annulus in series with the isolation valve aforesaid.  
     
     
         37 . A system as claimed in any of  claims 21  to  36  in which the end of the penetration communicating with the annular passage is formed between the casing hangers for the well casing and the next outer casing.  
     
     
         38 . A system as claimed in  claim 34  in which the isolation valve in the wellhead housing is a small bore gate valve with metal to metal sealing.  
     
     
         39 . A system as claimed in  claim 34  in which the further annulus is between a tree isolation sleeve and a connector body.  
     
     
         40 . A system as claimed in  claim 39 , in which a port is formed in the connector body and the outlet includes the second isolation valve.  
     
     
         41 . A system as claimed in any of  claims 21  to  40 , in which the isolation valve or valves are operable hydraulically.  
     
     
         42 . A system as claimed in any of  claims 21  to  41 , in combination with means to control/monitor fluid pressure within the annulus between the well casing and the outer barrier pipe, whereby to increase the allowable pressure within the well casing.