Patent Publication Number: US-2019195032-A1

Title: Riser gas handling system and method of use

Description:
The present invention relates to a riser gas handling system and method of use, and in particular to riser gas handling systems for subsea applications. A particular aspect of the invention relates to riser gas handling systems that enable managed pressure drilling operations. 
     BACKGROUND TO THE INVENTION 
     Drilling operations typically use a rotating drill bit on the end of a drillstring. Mud is pumped down the drillstring from a rig mud pumping system and returned to the surface flowing in the annulus between the drillstring and the well. The returning mud exits the annulus above a blow-out preventer (BOP) into a mud return line where it freely flows into solids control equipment to allow sand and cuttings to be removed from the well. The mud is stored in holding tanks until it is pumped back down the well. 
     The mud which is pumped down the drillstring performs multiple functions, including providing hydraulic power to drilling tools at the end of the drillstring, stabilising the well, and cooling the drillbit. The mud provides pressure in the well which prevents an influx of pressurised gas or oil from any hydrocarbon bearing formations. The pressure is a function of the mud density, friction in the wellbore caused by the flowing mud, and the vertical depth of the well. The density of the mud must be controlled to provide a pressure at the bottom of the well which is above the pore pressure (the pressure at which the well may collapse or allow a hydrocarbon influx) but below the fracture pressure (the pressure where the well structure could fracture). 
     Managed Pressure Drilling (MPD) is a form of drilling where the pressure at the bottom of the well is more precisely controlled using various methods apart from controlling the mud density. MPD is used to drill wells in conditions where the local geology makes conventional drilling difficult or impossible. 
     For MCD operations the mud circulation system becomes a closed loop with returning mud from the wellbore flowing into an arrangement of valves or manifolds that can apply backpressure or route the flow to other processing systems. The annulus is capped above the BOP using a seal, typically a rotating control device (RCD). 
     Offshore drilling relies on the use of a tubular, known as a drilling riser, which allows the annulus to extend from the seabed to the surface. For floating drilling vessels, a riser section known as a slip joint or telescopic joint is used to allow the free movement of the drilling vessel caused by wave motion. 
     Below the telescopic joint, the riser is held in position using a device known as a tension ring, connected to an arrangement of cylinders via cable or directly, which provides a constant tension to the sections of riser below the tension ring. 
     During subsea drilling operations, whether drilling conventionally or by managed pressure drilling, well control issues may arise due to complex formation conditions. One example is the uncontrolled release of gas that can occur when a gas kick is not detected by conventional means and passes through the blow out preventer (BOP) into the marine riser. 
     Sudden uncontrolled expansion of gas in the marine riser may result in rapid gas ascend up the riser carrying a large volume of mud out of the riser at high pressure. This presents a serious risk to personnel on the rig. 
     Furthermore, such a rapid loss of mud may result in the riser becoming partially evacuated which may lead to riser damage or collapse due to hydrostatic pressure. 
     A riser gas handling (RGH) system is required to respond quickly to a gas influx to divert and release the gas in a controlled manner thereby avoiding potential dangers to rig personnel and mitigating damage to the riser and rig infrastructure. 
     Early riser gas handling and managed pressure drilling systems such as those disclosed in U.S. Pat. Nos. 7,866,399, 8,347,982, US 2013014991 and US 2001040052 utilise a riser arrangement known as Above the Tension Ring’ (ATR). In ATR configurations, the flowspool, riser isolation device, and rotating control device are installed above the tension ring. This equipment has a lower tension rating which allows the equipment to be positioned above the tension ring. 
     However, this configuration occupies space that would normally be used by the telescopic joint, reducing the possible stroke of the telescopic section. This reduces the possible geographic deployments of the drilling vessel and limits it to areas with a calmer range of sea states. It is not suitable for deep water applications with dynamic sea conditions. 
     To provide a full range of motion of the telescopic joint, an arrangement known as Below Tension Ring (BTR) was adopted in the industry. Examples of BTR arrangements are disclosed in U.S. Pat. Nos. 9,605,502, 4,626,135 and US20140209316. 
     In these BTR configurations, the flowspool, riser isolation device, and rotating control device are installed below the tension ring. In this arrangement, the telescopic joint can fully extend and contract to its full length, allowing a greater range of geographic deployments and more dynamic sea conditions. 
     However, the BTR configuration limits access to key components of the riser and requires time consuming and costly operations to install, replace and/or repair RGH and drilling components located beneath the tension ring. These operations involve closing the well, disconnecting the riser from the subsea BOP, and pulling the entire riser string and disassembling it section by section until the desired component housing is reached. Once the component has been replaced or repaired, the entire riser string must be reassembled in sections as the BOP is reattached to the wellhead. 
     SUMMARY OF THE INVENTION 
     It is an object of an aspect of the present invention to obviate or at least mitigate the foregoing disadvantages of prior art riser gas handling systems. 
     It is another object of an aspect of the present invention to provide a robust, reliable and compact RGH system suitable for deployment on riser assemblies used in a variety of drilling sites and areas which experience dynamic sea conditions. 
     It is a further object of an aspect of the present invention to provide marine risers with a riser gas handling system with improved reliability and accessibility and which is capable of supporting conventional and managed pressure drilling systems. 
     It is another object of an aspect of the present invention to provide a marine riser conversion system for RGH operations which enables managed pressure drilling operations. 
     Further aims of the invention will become apparent from the following description. 
     According to a first aspect of the invention there is provided a riser assembly comprising:
         a riser flow spool;   a riser isolation device and   an upper riser disconnect assembly;   wherein at least the riser flow spool is located on a riser below a riser tension ring and wherein the upper riser disconnect assembly is located above the riser tension ring.       

     Preferably the riser flow spool and the riser isolation device are configured to be connected to the riser below the tension ring. 
     By providing components of a RGH system including the Riser Flow Spool (RFS) and/or the Riser Isolation Device (RID) below the tension ring and an upper riser disconnect assembly above the tension ring the space available above the tension ring is maximized. This may reduce the impact on the stroke length of a slip joint and enables the riser to be utilised in a wide range of drilling sites and areas which experience dynamic sea conditions and significant heave movements. 
     The upper riser disconnect assembly may be configured to connect to a rotating control device (RCD). The rotating control device may be disposed above the upper riser disconnect assembly. The rotating control device may be disposed above the riser tension ring. 
     Preferably the RCD releasably connects above the upper riser disconnect assembly. Preferably the RCD releasably connects to the riser assembly above the upper riser disconnect assembly. 
     The RCD comprises one or more seals encased in a rotating bearing. The bearing sits in a housing that may provide lubrication for the movement of the bearing. The RCD may include latching elements that hold the bearing in a vertical position against a force possibly present in the wellbore. The RCD may require regular replacement of the seals, due to the axial movement of the drill pipe through the seals which cause wear. This wear can be aggravated by the surface finish of the drill pipe, the pressure in the wellbore, the vertical speed of the drill pipe, and the load on the seal caused by the connection points (known as tool joints). 
     In conventional riser configurations, the replacement of the seal involves sealing the well below the RCD (typically performed using one or more of the sealing elements in the BOP), then unlatching the bearing element which is then retrieved by pulling the drillstring out of the well. 
     By providing a RCD that can be releasably connected to the riser assembly by inclusion of an upper riser disconnect assembly disposed above the riser tension ring, the RCD may be installed, removed and/or temporarily disconnected for maintenance operations without having to remove components of the lower riser assembly below the tension ring or disconnect the riser string from the BOP or wellhead. This allows the RCD to be quickly and conveniently installed and/or removed from the riser assembly above the tension ring while minimising any impact on the stroke length of the slip joint. 
     A further benefit of an embodiment of the invention is that the RCD may be quickly and easily installed on the riser assembly only when managed pressure drilling is required. Conventional drilling with RGH functionality may be performed during routine drilling. However, in the event that the conditions of the wellbore change preventing conventional techniques, the drill system may be adapted for managed pressure drilling. By installing an RCD and/or other MPD equipment only when required may result in lower operation costs. 
     An additional benefit of an embodiment of the invention is improved hose management as the hoses and control lines connected to the RID and RFS may be vertically offset from the tensioning system, which includes the tension ring, tension cylinders and tension rods and/or lines. This may prevent the RGH hoses from being hindered by the tensioning cylinders or rods connected to the tensioning rings. 
     Preferably the RID is positioned above the RFS on the riser string. Preferably, the RID is closed during a riser gas handling event. 
     The upper riser disconnect assembly, riser flow spool and/or riser isolation device may be controlled remotely. Preferably the RID is controlled remotely. 
     The RID may comprise a packing element. Preferably the RID comprises at least one sensor to monitor actuation of the packing element and/or sealing of the RID. The RID may comprise pressure control for sealing the RID. The RID may be dimensioned to fit through a platform rig floor rotary table. 
     The RFS may have at least one flowline. The at least one flowline may be configured to be connected to a distribution assembly, choke assembly and/or a mud-gas separator. The at least one flowline may be connected to a safety valve. The safety valve may be configured to divert riser gas overboard. Preferably, the RFS has multiple flowlines. 
     The RFS may be configured to be connected to at least one hose. The at least one hose may be configured to be vertically offset from the tensioning system. 
     Preferably the RID and RFS are integrated in a single unit. The RID and RFS may be combined into an integrated riser joint. By providing the RID and RFS in a compact and lightweight integrated unit it may enable flexibility and easy handling of the RID and RFS during installation, removal and maintenance operations. The integrated riser joint may be dimensioned to pass through the rig floor rotary table. 
     Preferably the RFS has at least one valve assembly. The at least one valve assembly may be configured to open a pathway between the riser annulus and the distribution assembly, choke assembly and/or a mud-gas separator in the event of a riser gas influx. 
     The RFS assembly may be dimensioned to fit through a platform rig floor rotary table. Preferably the RFS is compact and lightweight to allow quick rig up/rig down time. 
     Preferably the tension ring is coupled to a tensioning system to allow relative vertical movement between the riser and the platform. 
     Preferably the tension ring is disposed between the tensioning system and the riser. The tension ring may be disposed circumferentially about a portion of the riser, a portion of the RID, a portion of slip joint, an outer barrel of a slip joint, a portion of the upper riser disconnect assembly and/or a tension joint. 
     The upper riser disconnect assembly may be connected to a RCD and/or other drilling operation components. The upper riser disconnect assembly may be configured to allow the RCD and/or other drilling operation components to be releasably latched to the riser assembly. 
     The upper riser disconnect assembly may comprise an upper connector and a lower connector. The upper and lower connectors may be configured to disconnect from one another. The separated upper and lower connectors may be configured to connect to one another. The upper and lower connectors may be configured to connect to or disconnect from one another on command. 
     The upper connector may be to an RCD or other drilling/riser components. The lower connector of the upper riser disconnect assembly may be connected to a tension ring, tension joint and/or an outer slip joint barrel. 
     Preferably the upper riser disconnect assembly is a slip joint disconnect assembly. 
     The upper riser disconnect assembly may comprise at least one sensor to monitor and/or indicate a latched and/or unlatched status. 
     Preferably the upper riser disconnect assembly is a quick disconnect assembly. The upper riser disconnect assembly may be controlled remotely. Preferably the upper riser disconnect assembly is configured for remote releasably latching/unlatching. 
     Preferably the upper riser disconnect assembly is configured for assembly to the slip joint above the tension ring. 
     The upper riser disconnect assembly may be disposed below the slip joint. 
     The slip joint may be a two-part slip joint. Alternatively, the slip joint may be a three or more part slip joint. The slip joint may comprise at least one sealing assembly. The slip joint may comprise two telescopic members. The slip joint may comprise more than two telescopic members. 
     The RCD may be installed onto the RGH system to allow a managed pressure drilling operation without requiring structural modifications to the RGH system. The RCD may be connected to the upper riser disconnect assembly located above the tension ring. 
     The RCD may be configured to seal off the riser annulus while a drill string is located in the RCD. 
     The system may comprise a choke. The choke may receive the drilling fluid from the annulus below the RCD, and may be an MPD choke. 
     According to a second aspect of the invention there is provided a system for handling gas in a riser comprising:
         a riser flow spool;   a riser isolation device and   an upper riser disconnect assembly;   wherein at least the riser flow spool is configured to be connected to the riser below a riser tension ring and wherein the upper riser disconnect assembly is configured to be connected to the riser above the tension ring.       

     Preferably the riser flow spool and the riser isolation device are configured to be connected to the riser below the tension ring. 
     Preferably the upper riser disconnect assembly is configured to be connected to a slip joint above the tension ring. 
     A rotary control device may be configured to be connected to the upper riser disconnect assembly above the tension ring. Preferably the rotary control device and/or the upper riser disconnect assembly is configured to be releasably connected to the riser assembly above the tension ring. 
     Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa. 
     According to a third aspect of the invention there is provided a system for handling gas in a riser to enable managed pressure drilling operations comprising:
         a riser flow spool;   a riser isolation device;   an upper riser disconnect assembly and;   a rotary control device;   wherein at least the riser flow spool is configured to be connected to the riser below a riser tension ring and wherein the upper riser disconnect assembly and the rotary control device are configured to be connected to the riser above the tension ring.       

     Preferably the riser flow spool and the riser isolation device are configured to be connected to the riser below the tension ring. 
     Preferably the upper riser disconnect assembly is configured to be connected to a slip joint above the tension ring. 
     Preferably the rotary control device may be configured to be connected to the upper riser disconnect assembly above the tension ring. Preferably the rotary control device is configured to be releasably connected to the riser assembly above the tension ring via the upper riser disconnect assembly. 
     Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or its embodiments, or vice versa. 
     According to a fourth aspect of the invention there is provided a method of installing a riser gas handling system in a subsea riser comprising:
         installing a riser flow spool assembly on the riser below the tension ring; and   installing an upper riser disconnect assembly above the tension ring.       

     The method may comprise installing a riser isolation device below the tension ring. The method may comprise installing a riser isolation device on the riser string below the tension ring. 
     The method may comprise installing the riser flow spool assembly below the riser isolation device. 
     The method may comprise providing a distribution assembly and/or a choke manifold. The method may comprise making up a tension ring. The method may comprise connecting the tension ring to the riser, riser isolation device, slip joint and/or the upper riser disconnect assembly. 
     The method may comprise raising the RID and RFS to a position just below the tension ring. The method may comprise raising the RID and RFS to a position just below the tension ring by positioning a riser tension joint between the RID and the tension ring. 
     The method may comprise connecting a RCD and/or other drilling components to the upper riser disconnect assembly. 
     The method may comprise installing the upper riser disconnect assembly on the riser string above the tension ring. The method may comprise bolting, welding and/or clamping the rotary control device onto an upper connector of the upper riser disconnect assembly. The method may comprise connecting a lower connector of the upper riser disconnect assembly onto a tension ring, tension joint and/or an outer slip joint barrel. The method may comprise connecting the slip joint to the rotary control device 
     The method may comprise coupling the upper and lower connectors of the upper riser disconnect assembly. 
     Embodiments of the fourth aspect of the invention may include one or more features of the first, second or third aspects of the invention or their embodiments, or vice versa. 
     According to a fifth aspect of the invention there is provided a method of installing a riser gas handling system to enable managed pressure subsea drilling on a subsea riser comprising:
         installing a riser flow spool assembly on the riser below the tension ring; and   installing an upper riser disconnect assembly and a rotary control device above the tension ring.       

     The method may comprise installing a riser isolation device below the tension ring. The method may comprise installing a riser isolation device on the riser string below the tension ring. 
     The method may comprise providing a distribution assembly, a choke manifold and/or MPD choke manifold. 
     The method may comprise making up the tension ring. The method may comprise connecting the tension ring to the riser, RID, slip joint and/or the upper riser disconnect assembly. 
     The method may comprise installing the upper riser disconnect assembly on the riser string and then installing the rotary control device onto the upper riser disconnect assembly. The rotary control device may be installed on the upper riser disconnect assembly by releasably latching onto the upper riser disconnect assembly. 
     Embodiments of the fifth aspect of the invention may include one or more features of the first to fourth aspects of the invention or their embodiments, or vice versa. 
     According to a sixth aspect of the invention there is provided a method of converting a marine riser for RGH operations comprising:
         installing a riser flow spool assembly on the riser below the tension ring; and   installing an upper riser disconnect assembly above the tension ring.       

     The method may comprise installing a riser isolation device below the tension ring. The method may comprise installing a riser isolation device on the riser string below the tension ring. 
     The method may comprise removing an existing slip joint and/or an existing slip joint inner barrel on the subsea riser. 
     The method may comprise installing the RFS and RID onto an existing riser. The method may comprise installing the RFS and RID onto an existing riser above an existing riser termination joint. 
     The method may comprise installing a riser auxiliary line termination joint on the existing riser. The method may comprise installing the RFS and RID onto the termination joint. 
     The method may comprise making up the tension ring. The method may comprise connecting the tension ring to the riser, RID, slip joint and/or the upper riser disconnect assembly. 
     The method may comprise installing a slip joint outer barrel onto the RID. The tension ring may be made up and connected to the slip joint outer barrel. 
     The method may comprise installing the upper riser disconnect assembly above the tension ring. 
     The method may comprise reversibly latching a slip joint to the upper riser disconnect assembly. 
     Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth third aspects of the invention or their embodiments, or vice versa. 
     According to a seventh aspect of the invention there is provided a method of converting a marine riser for RGH operations which enables managed pressure subsea drilling operations comprising:
         installing a riser flow spool assembly on the riser below the tension ring; and   installing an upper riser disconnect assembly and a rotary control device above the tension ring.       

     The method may comprise installing a riser isolation device below the tension ring. The method may comprise installing a riser isolation device on the riser string below the tension ring. 
     The method may comprise providing a distribution assembly, a choke manifold and/or MPD choke manifold. 
     The method may comprise removing an existing slip joint and/or an existing slip joint inner barrel on the subsea riser. 
     The method may comprise installing the RFS and RID onto an existing riser. The method may comprise installing the RFS and RID onto an existing riser above an existing riser termination joint. 
     The method may comprise installing a riser auxiliary line termination joint on the existing riser. The method may comprise installing the RFS and RID onto the termination joint. 
     The method may comprise making up the tension ring. The method may comprise connecting the tension ring to the riser, RID, slip joint and/or the upper riser disconnect assembly. 
     The method may comprise installing a slip joint outer barrel onto the RID. The tension ring may be made up and connected to the slip joint outer barrel. 
     The method may comprise installing a lower connector of the upper riser disconnect assembly on the riser string above the tension ring. The method may comprise installing a rotary control device made up with a connector configured to releasably latch onto the lower connector of the upper riser disconnect assembly. 
     The method may comprise bolting, welding and/or clamping the rotary control device onto an upper connector of the upper riser disconnect assembly. The method may comprise connecting a lower connector of the upper riser disconnect assembly onto a tension ring, tension joint and/or an outer slip joint barrel. The method may comprise connecting the slip joint to the rotary control device. 
     The method may comprise coupling/decoupling the upper and lower connectors of the upper riser disconnect assembly to/from one another. 
     The method may comprise connecting a slip joint to the rotary control device. 
     Embodiments of the seventh aspect of the invention may include one or more features of any of the first to sixth aspects of the invention or their embodiments, or vice versa. 
     According to an eighth aspect of the invention there is provided a method of handling riser gas in a subsea riser comprising:
         providing a riser assembly comprising:   a riser flow spool;   a riser isolation device and   an upper riser disconnect assembly;   wherein the riser flow spool is located on a riser below a riser tension ring and wherein the upper riser disconnect assembly is located above the riser tension ring;   actuating the riser isolation device to close the riser above the riser flow spool and actuating the riser flow spool to divert gas trapped below the riser isolation device.       

     Preferably the riser flow spool and the riser isolation device are configured to be connected to the riser below the tension ring. 
     The method may comprise actuating a blowout preventer on the riser to close the riser below the flow spool. 
     The method may comprise actuating a distribution manifold and/or riser gas handling choke to control the diversion of gas trapped below the riser isolation device. 
     The method may comprise opening valves on the riser flow spool, distribution manifold and/or riser gas handling choke to enable the gas to flow to a mud gas separator. 
     Embodiments of the eighth aspect of the invention may include one or more features of any of the first to seventh aspects of the invention or their embodiments, or vice versa. 
     According to a ninth aspect of the invention there is provided a method of handling riser gas in a subsea riser during managed pressure subsea drilling operations comprising:
         providing a riser assembly comprising:   a riser flow spool;   a riser isolation device and   an upper riser disconnect assembly;   wherein the riser flow spool is located on a riser below a riser tension ring and wherein the upper riser disconnect assembly is located above the riser tension ring;   actuating the riser isolation device to close the riser above the riser flow spool and actuating the riser flow spool to divert gas trapped below the riser isolation device.       

     Preferably the riser flow spool and the riser isolation device are configured to be connected to the riser below the tension ring. 
     The method may comprise providing a rotary control device. The rotary control device may be releasably connected to the upper riser disconnect assembly. 
     The method may comprise actuating a blowout preventer on the riser to close the riser below the flow spool. 
     The method may comprise controlling the diversion of gas trapped below the riser isolation device. The method may comprise actuating a distribution manifold and/or riser gas handling choke to control the diversion of gas trapped below the riser isolation device. 
     The method may comprise opening valves on the riser flow spool, distribution manifold and/or riser gas handling choke to enable the gas to flow to a mud gas separator. 
     Embodiments of the ninth aspect of the invention may include one or more features of any of the first to eighth aspects of the invention or their embodiments, or vice versa. 
     According to a tenth aspect of the invention, there is provided a kit of parts for converting a riser for riser gas handling operations, the kit of parts including:
         a riser flow spool;   a riser isolation device and   an upper riser disconnect assembly;   wherein the riser flow spool and riser isolation device are mountable on a riser string below a riser tension ring; and   wherein the upper riser disconnect assembly is mountable on the riser string above the riser tension ring.       

     Preferably, the riser flow spool has connections configured to engage and connect to a riser below a riser tension ring. 
     The riser flow spool may be engageable with the riser isolation device. Preferably, the riser flow spool and riser isolation device form an integrated unit. 
     The kit of parts may comprise a slip joint. 
     Preferably, the upper riser disconnect assembly has connections configured to engage and mount a slip joint above a riser tension ring. 
     The kit of parts may comprise a choke manifold and/or distribution manifold. 
     The kit of parts may comprise a rotary control device for converting a riser for riser gas handling operations which enables managed pressure subsea drilling operations. The rotary control device may be mountable on the riser string above the riser tension ring. 
     Preferably the rotary control device may be releasably mountable on the upper riser disconnect assembly. 
     Embodiments of the tenth aspect of the invention may include one or more features of any of the first to ninth aspects of the invention or their embodiments, or vice versa. 
     According to an eleventh aspect of the invention there is provided a method of installing a rotary control device in a riser with riser gas handling comprising:
         providing a riser assembly comprising   a riser flow spool;   a riser isolation device; and   an upper riser disconnect assembly;   wherein at least the riser flow spool is connected to the riser below a riser tension ring and   wherein the upper riser disconnect assembly is connected to the riser above the tension ring and   connecting a rotary control device to the upper riser disconnect assembly.       

     Preferably the riser flow spool and the riser isolation device are configured to be connected to the riser below the tension ring. 
     The method may comprise closing a blowout preventer on the riser prior to connecting the rotary control device to the upper riser disconnect assembly. 
     Embodiments of the eleventh aspect of the invention may include one or more features of any of the first to tenth aspects of the invention or their embodiments, or vice versa. 
     According to a twelfth aspect of the invention there is provided a method of recovering a rotary control device from a riser comprising:
         providing a riser assembly comprising   a riser flow spool;   a riser isolation device;   an upper riser disconnect assembly and   a rotary control device;   wherein at least the riser flow spool is connected to the riser below a riser tension ring and wherein the upper riser disconnect assembly and the rotary control device are connected to the riser above the tension ring and   disconnecting the rotary control device from the riser above the tension ring.       

     The method may comprise actuating the upper riser disconnect assembly to disconnect the rotary control device from the riser assembly. 
     The method may comprise closing a blowout preventer on the riser prior to disconnect the rotary control device. 
     Embodiments of the twelfth aspect of the invention may include one or more features of any of the first to eleventh aspects of the invention or their embodiments, or vice versa. 
     According to a thirteenth aspect of the invention there is provided a method of replacing a rotary control device on a riser comprising:
         providing a riser assembly comprising   a riser flow spool;   a riser isolation device;   an upper riser disconnect assembly and   a rotary control device;   wherein at least the riser flow spool is connected to the riser below a riser tension ring and wherein the upper riser disconnect assembly and the rotary control device are connected to the riser above the tension ring;   disconnecting the rotary control device; and   connecting a replacement rotary control device to the riser above the tension ring.       

     The method may comprise actuating the upper riser disconnect assembly to disconnect the rotary control device from the riser assembly. The method may comprise actuating the upper riser disconnect assembly to disconnect the upper riser disconnect assembly and rotary control device from the riser assembly. 
     The method may comprise actuating the upper riser disconnect assembly to connect the replacement rotary control device to the riser assembly. The method may comprise actuating the upper riser disconnect assembly to connect the upper riser disconnect assembly and replacement rotary control device to the riser assembly. 
     The method may comprise closing a blowout preventer on the riser prior to disconnect the rotary control device. The method may comprise closing a blowout preventer on the riser prior to connecting the replacement rotary control device. 
     Embodiments of the thirteenth aspect of the invention may include one or more features of any of the first to twelfth aspects of the invention or their embodiments, or vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: 
         FIGS. 1A and 1B  are representations of riser assemblies according to the prior art; 
         FIG. 2  is a schematic representation of a riser assembly with a RGH system for conventional drilling according to a first embodiment of the invention; 
         FIG. 3  is a schematic representation of a riser assembly with a RGH system for managed pressure drilling according to a second embodiment of the invention; 
         FIGS. 4A, 4B and 4C  are schematic representations of conventional riser assemblies shown in  FIGS. 1A and 1B  converted for RGH operations; 
         FIGS. 5A and 5B  are schematic representations of the riser assemblies with RGH systems of  FIGS. 4A and 4B  for managed pressure drilling according to an embodiment of the invention; 
         FIG. 6  is a block diagram of a RGH system for a conventional drilling operation according to an embodiment of the invention; and 
         FIG. 7  is a block diagram of a RGH system for a managed pressure drilling operation according to a further embodiment of the invention. 
         FIG. 8  is schematic drawings of a riser assembly with an integrated RGH system according to an embodiment of the invention. 
         FIGS. 9A and 9B  are schematic drawings of different configurations of riser assembly with an integrated RGH system for managed pressure drilling according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1A and 1B  show features of conventional drilling riser assemblies for extracting oil and natural gas from a subsea reservoir known in the prior art. 
     The riser assembly  10  comprises a riser  12  located between a rig platform  16  and a blowout preventer (BOP) assembly (not shown) secured to the top of the wellhead. The riser  12  is connected to a slip joint  14 . The slip joint  14  is configured to respond to heave movement of the platform  16  during dynamic sea conditions. 
     A portion of platform  16  is shown, which may be a floating rig or drillship. The platform supports the riser assembly  10  and comprises a moon pool opening  18 . A plurality of tensioning cylinders  20  are secured to the platform and exert an upward force on rods or cables  22 . The lower end of each rod or cable  22  is connected to a riser tensioning ring  24  which is connected to maintain the stability of the riser  12  in the offshore environment. 
     External auxiliary lines  26  are connected to the BOP (not shown) and circulate fluids and provide control lines to the BOP. A termination ring  28  is disposed circumferentially about a portion of the riser  12 . The auxiliary lines  26  terminate at the termination ring. Flexible hoses  30  are connected to the termination ring  28  and extend upward coupling to the platform. The hoses  30  have been truncated in these drawings for clarity. The termination joint  28  provides fluid communication between the auxiliary lines  26  and the flexible hoses  30 . 
       FIG. 2  schematically shows features of the riser assembly with RGH according to a first embodiment of the present invention. It will be appreciated that the RGH system can adopt different configurations depending on the type of riser system on which it is being installed and the type of drilling operation.  FIG. 2  represents one possible configuration that the RGH system may adopt. 
     The riser assembly  100  with RGH system comprises a riser  112  located between a platform  116  and a blowout preventer (BOP) assembly (not shown) secured to the top of the wellhead. 
     The RGH system comprises a riser flow spool (RFS)  134  connected to the riser  112  and a riser isolation device (RID)  136  mounted above the RFS  134 . The RFS and RID are disposed on the riser string below the tension ring  124 . 
     The RFS comprises two flexible hoses  140  which have been truncated in  FIG. 2  for clarity. The hoses  140  are connected to a choke manifold or distribution manifold (not shown) to divert return flow to the choke manifold and/or distribution manifold for handling as discussed in  FIG. 6  below. 
     The tension ring  124  is disposed circumferentially about a tension joint  125  located between the RID  136  and the quick disconnect assembly  150 . Although in this example the tension ring  124  is connected to tension joint  125 , it may alternatively be connected to an existing rig outer barrel located between the RID  136  and the quick disconnect assembly  150 . The RID  136  and RFS  134  are disposed below the tension ring  124  and the quick disconnect assembly  150  is disposed above the tension ring  124 . 
     Tensioning cylinders  120  are secured to the platform  116  and exert an upward force on rods or cables  122 . The lower end of each rod or cable  122  is connected to a riser tensioning ring  124  which is connected to maintain the stability of the riser string. The quick disconnect assembly  150  is connected to a slip joint  114 . The slip joint  114  is configured to respond to heave movement of the platform  116  during dynamic sea conditions. The platform  116  supports the riser  112  and RGH system  100 . The slip joint is a telescopic three-part slip joint. However, it is appreciated that other types of slip joint may be used. The slip joint enables the riser system to adjust in length as the platform heaves in response to motion of the waves. 
     It will be appreciated that this is an example configuration of an RGH system and that other components may be included in an RGH system depending on the type of drilling operation. In some embodiments, the riser gas handling system may include additional assemblies such as a rotating control device and/or diverter systems capable of releasably coupling to the RGH system for different drilling operations. 
       FIG. 3  schematically shows features of the riser assembly  200  with RGH system enabled for Managed Pressure Drilling (MPD) operations according to an embodiment of the present invention. The RGH system  200  is similar to the system  100  described in  FIG. 2  and will be understood from the description of  FIG. 2 . However, the system  200  described in  FIG. 3  includes a rotating control device (RCD)  260  connected above the quick disconnect assembly  250  and below the slip joint  214 . 
     In this configuration the RCD  260  is disposed above the tension ring  224  and may be easily installed on the riser assembly when managed pressure drilling is required. 
     The RCD  260  is a drill through device with a rotating internal sealing element that seals against the drill string to create a pressure-tight barrier. The RCD  260  is installed between the disconnect assembly  250  and the slip joint  214  above the tension ring  224 . 
     A MPD choke manifold is also provided (not shown). The choke manifold is connected to the distribution manifold and is configured to receive drilling fluid from the annulus and restricts the flow of the drilling fluid to adjust the pressure in the annulus. 
     When managed pressure drilling operations are not required the RCD  260  may be removed by decoupling and/or unlatching the quick disconnect assembly  250 . The RGH system will then adopt the configuration described in  FIG. 2 . By facilitating the easy installation and/or removal of the RCD it may only be installed when MPD operation are required. This may extend the working lifespan of the RCD and reduce operating costs. 
     By locating the RCD  260  above the tension ring  224  the RCD  260  may be quickly and easily removed without removing components of the RGH system  200  below the tension ring  224  or disconnecting the BOP. The compact size of the RCD  260  and the quick disconnect assembly  250  above the tension ring  224  reduces or minimises loss of stroke length of the slip joint, without adjustment of the vertical position of the tension ring from its preferred location. This facilitates marine riser assemblies to be located in areas which experience dynamic sea conditions to be converted for RGH systems. 
       FIGS. 4A, 4B and 4C  show schematic representation of conventional drill systems shown in  FIGS. 1A and 1B  converted for RGH operations. 
     In  FIG. 1A  the auxiliary lines  26  terminate below the slip joint. As shown in  FIG. 4A , to convert this riser for RGH operations the existing slip joint shown as  14  in  FIG. 1A  is removed. The RFS  334  and RID  336  are installed onto the existing riser  312  above the existing riser termination ring  328 . The tension ring  324  is made up and connected above the RID  336  on the tension joint  325 . The lower connector  350   a  of the disconnect assembly  350  is then installed on the tension joint  325  above the tension ring  324 . The telescopic slip joint  314  is made up with an upper connector  350   b  and is run in and releasably latched to the lower connector of the disconnect assembly  350 . 
     To convert the conventional drill systems shown in  FIG. 1B  for RGH operations there are two options for terminating the auxiliary lines. The first example provides a riser assembly RGH system  400  with the auxiliary lines terminating below the RFS and RID as described below and shown in  FIG. 4B . An alternative is to provide a riser assembly RGH system  500  with the auxiliary lines terminating above the RFS and RID as described below and shown in  FIG. 4C . 
     To install the RGH system  400  with the auxiliary lines terminating below the RFS and RID as shown in  FIG. 4B , the existing slip joint shown as  14  in  FIG. 1B  is removed. 
     A new riser auxiliary line termination joint  462  is installed on the existing riser  412 . The RFS  434  and RID  436  are installed above the termination joint  462 . The tension ring  424  is made up and connected to a tension joint  425  positioned above the RID  436 . The lower connector  450   a  of disconnect assembly  450  is installed above the tension ring  424 . The telescopic slip joint  414  is made up with upper connector  450   b  and run in and releasably latched to the lower connector  450   a  of disconnect assembly  450 . 
       FIG. 4C  shows a conventional drill system shown in  FIG. 1B  converted to include a RGH system. In  FIG. 1B  the auxiliary lines  26  terminate on the slip joint outer barrel. The example shown in  FIG. 4C  provides a riser assembly  500  with the auxiliary lines  526  terminating above the RFS  534  and RID  536 . 
     To install the RGH system in this type riser assembly the existing slip joint inner barrel is removed. The RFS  534  and RID  536  are installed onto the existing riser  512 . The slip joint outer barrel  515  is installed onto the RID  536 . The tension ring is made up and connected to an upper end of the slip joint outer barrel  515 . The lower connector  550   a  of quick disconnect assembly  550  is then installed on the slip joint outer barrel  515  above the tension ring  524 . The telescopic joint  514  is made up with an upper connector  550   b  and is run in and releasably latched to the lower connector  550   a  of quick disconnect assembly  550 . 
       FIGS. 5A and 5B  show schematic representations of the RGH systems of  FIGS. 4A and 4B  setup for managed pressure drilling according to an embodiment of the invention. 
     The system  600  is similar to the configuration of the systems  300 ,  500  described in  FIGS. 4A and 4C  and will be understood from the descriptions of  FIG. 4A and 4C  above. However, the system  600  described in  FIGS. 5A and 5B  includes a rotating control device (RCD)  660  connected above the quick disconnect assembly and below the slip joint  614 . 
     A MPD choke manifold is also provided (not shown). The choke manifold is connected to the distribution manifold and receives drilling fluid from the riser annulus. The RCD  660  and choke manifold control are configured to maintain the desired pressure in the annulus to allow managed pressure drilling operations. 
     By locating the RCD  660  above the tension ring  624  the RCD  660  may be quickly and easily removed without removing components of the RGH system below the tension ring or requiring the BOP to be disconnected. The compact size of the RCD and the quick disconnect assembly above the tension ring maximizes the space available above the tension ring  624  and minimizes the loss of the slip joint stroke length. 
       FIG. 6  shows a flow diagram of a method of operating the RGH system during a conventional drilling operation. 
     The RGH system  700  is similar to the configuration of the system  200  described in  FIG. 2  and will be understood from the description of  FIG. 2  above. 
     The RGH system  700  comprises a RFS  734  with two return flowlines  730  and  731 . The RFS is also provided with a riser protection line  732 . In this example the flowlines are six inch flexible hoses. However, it should be appreciated that a different number and configuration of flowlines may be used. 
     The RGH system  700  also comprises a RID  736  and quick disconnect assembly  750 . The RID  736  comprises a packing element (not shown). A tension ring (not shown) is configured to be connected to the riser assembly between the RID  736  and quick disconnect assembly  750 . 
     During conventional drilling operations, the RID is open. In the event of a gas kick, formation gas may go into solution in the mud and may get past the subsea BOP resulting in release of gas into the riser which may endanger personnel and damage the riser and platform. 
     An annular BOP (not shown) located on the lower riser is closed to seal around the drill string. The RID  736  is closed around the drill string to isolate the upper riser system and allow any gas in the riser to be contained. 
     After the RID  736  has been closed a volume of gas is trapped below the RID. The function of the RFS  734  is to divert the isolated gas. The options for venting the gas are either to a Mud-Gas Separator  780  (MGS) via the RGH choke or can be diverted overboard via valve  776   e.    
     A riser over pressure protection system will vent the gas overboard via the riser protection line  732  on the RFS in the event of a control system failure. 
     In order to circulate the gas to the MGS  780 , isolation valves  730   a  and  731   a  on the RFS are opened to allow trapped gas to be safely circulated along at least one of the flowlines  730  and  731  to the distribution manifold  770  and choke manifold  772  for gas handling. Valves  774   a,    774   b,    774   c  and  774   d  in the distribution manifold  770  and valves  776   a,    776   c  on the choke manifold  772  are opened to open a pathway to the RGH chokes  776   b  and  776   d  used to maintain a back pressure in the riser allowing the gas to be circulated out in a controlled manor to the MGS to capture and separate large volume of free gas from the mud. The gas once separated from the mud is then safely vented via pathway  782 . 
       FIG. 7  shows a flow diagram of a method of operating the RGH system during conventional drilling operations. 
     The method of operating the RGH system described in system  800  is similar to the method of operating the RGH system described in system  700  and  FIG. 6  and will be understood from the description of  FIG. 6  above. However, the system  800  includes operation of a rotating control device (RCD)  860  connected above the quick disconnect assembly  850  and below the slip joint  814 . 
     During managed pressure drilling operations, the RCD  860  provides a rotating internal sealing element that seals against the drill string to create a pressure-tight barrier for the purpose of controlling the pressure or fluid flow to surface. A MPD Choke Manifold  868  is connected to the distribution manifold  870  and enables control of the annular pressure by increasing or decreasing the annual flow. 
     In the event of a gas kick the annular BOP (not shown) located on the lower riser is closed to seal around the drill string. The RID  836  is closed around the drill string to isolate the upper riser system and allow any gas in the riser to be contained. The gas handling method as described in  FIG. 6  above is followed while valve  874   e  on the distribution manifold  870  is isolated. 
       FIG. 8  shows a schematic drawing of a riser assembly with an integrated RGH. The riser assembly  900  comprises a riser  912  located between a rig platform  916  and a blowout preventer (BOP) assembly (not shown) secured to the top of the wellhead. The riser  912  is connected to a slip joint  914 . A rig diverter  913   a  and flex joint  913   b  are located at the top of the riser assembly. The slip joint  914  is configured to respond to heave movement of the platform  916  during dynamic sea conditions. 
     A portion of platform  916  is shown, which may be a floating rig or drillship. The platform supports the riser assembly  900  and comprises a moon pool opening  918 . A plurality of tensioning cylinders  920  are secured to the platform and exert an upward force on rods or cables  922 . The lower end of each rod or cable  922  is connected to a riser tensioning ring  924  which is connected to maintain the stability of the riser  912  in the offshore environment. 
     The RGH system integrated on the riser assembly comprises a riser flow spool (RFS)  934  connected to the riser  912  and a riser isolation device (RID)  936  mounted above the RFS  934 . The RFS and RID are disposed on the riser string below the tension ring  924 . The RFS comprises two flexible hoses  940 . 
     The tension ring  924  is connected to a tension joint  925  which is positioned between the RID  936  and the quick disconnect assembly  950 . Although in this example the tension ring is shown connected an interface between the RID  936  and the quick disconnect assembly  950 , the tension ring may be connected to other components of the riser assembly. The RID  936  and RFS  934  are disposed below the tension ring  924  and the quick disconnect assembly  950  is disposed above the tension ring  924 . 
     The quick disconnect assembly  950  is connected to the slip joint  914 . The slip joint  914  is configured to respond to heave movement of the platform  916  during dynamic sea conditions. The platform  916  supports the riser  912 . The slip joint  914  is a telescopic three-part slip joint. However, it is appreciated that other types of slip joint may be used. The slip joint enables the riser system to adjust in length as the platform heaves in response to motion of the waves. 
       FIGS. 9A and 9B  are schematic drawings of different configurations of riser assembly with an integrated RGH system for managed pressure drilling. 
     The riser assembly described in  FIGS. 9A and 9B  is similar to the configuration of the assembly in  FIG. 8  and will be understood from the description of  FIG. 8  above. However, riser assemblies described in  FIGS. 9A and 9B  includes a rotating control device (RCD)  1060  connected above the quick disconnect assembly and below the slip joint  1014 . 
     By locating the RCD  1060  above the tension ring  1024  the RCD  1060  may be quickly and easily removed from the riser assembly without requiring the removal of components of the riser assembly  1000  below the tension ring  1024  or disconnecting the BOP. The compact size of the RCD  1060  and the quick disconnect assembly  1050  above the tension ring  1024  enable the riser assembly to maximise the space available above the tension ring and minimise the loss of the slip joint stroke length. This facilitates marine riser assemblies to be located in areas which experience dynamic sea conditions to be converted for RGH systems. 
     The quick disconnect assembly  1050  is releasably connected to a RCD  1060 . The slip joint  1014  is connected to the RCD  1060 . The slip joint  1014  is configured to respond to heave movement of the platform  1016  during dynamic sea conditions. The platform  1016  supports the riser  1012 . The slip joint  1014  is a telescopic three-part slip joint. However, it is appreciated that other types of slip joint may be used. The slip joint enables the riser system to adjust in length as the platform heaves in response to motion of the waves. 
     The riser assembly described in  FIG. 9B  is similar to the configuration of the assembly in  FIG. 9A . However, in  FIG. 9B  the tension joint  1025  ( FIG. 9A ) is not present. The tension ring interface is a rig telescopic joint outer barrel  1027 . 
     The RID  1036  and RFS  1034  are mounted on the riser  1012 . The rig telescopic joint outer barrel  1027  is connected above the RID  1036 . The tension ring  1024  is connected to rig telescopic joint outer barrel  1027 . 
     The quick disconnect assembly  1050 , RCD  1060  and slip joint  1014  are connected as described in  FIG. 9A  above. 
     Throughout the specification, unless the context demands otherwise, the terms ‘comprise’ or ‘include’, or variations such as ‘comprises’ or ‘comprising’, ‘includes’ or ‘including’ will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. 
     Furthermore, relative terms such as”, “lower” , “upper, “up”, “down”, above, below and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations. 
     The RGH systems described above may be provided with a plurality of pressure sensors and/or flow meters disposes throughout the RGH system to monitor pressure and/or flow rate at various stages of the RGH system. 
     The invention provides a system for handling gas in a riser. The system comprises a riser flow spool, a riser isolation device and an upper riser disconnect assembly wherein at least the riser flow spool is connected to the riser below a riser tension ring and the upper riser disconnect assembly is located above the riser tension ring. 
     The present invention provides a riser gas handling system with improved reliability and accessibility and which is capable of supporting conventional and managed pressure drilling systems. 
     The invention may facilitate the conversion of marine riser assemblies for RGH operations which enable conventional and/or managed pressure drilling operations. 
     By providing an upper riser disconnect assembly above the tension ring, components of the drilling or RGH operation may quickly, safely and easily installed and/or removed from the riser assembly without requiring the BOP to be disconnected and the riser string pulled to surface. This configuration may allow components of a riser assembly, drilling system or RGH system to be installed only when they are required. 
     By providing at least the RFS below the tension ring and the upper riser disconnect assembly above the tension ring, the invention facilitates the easy and efficient installation and/or recovery of drilling operation components such as a RCD from the upper riser assembly while reducing and/or minimising a loss of stroke length in a slip joint provided above the tension ring. This improves the ability of the riser assembly to withstand dynamic heave conditions. 
     Embodiments of the invention may provide improved hose management as the hoses and control lines connected to at least the RFS may be vertically offset from the tensioning system by being located below the tension ring. By positioning the RFS hoses under the tension ring they are not hindered by the tensioning cylinders or rods connected to the tension ring. 
     The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended.