Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B33/00—Sealing or packing boreholes or wells
  • E21B33/02—Surface sealing or packing
  • E21B33/03—Well heads; Setting-up thereof
  • E21B33/035—Well heads; Setting-up thereof specially adapted for underwater installations
  • E21B33/0355—Control systems, e.g. hydraulic, pneumatic, electric, acoustic, for submerged well heads
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
  • E21B21/001—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor specially adapted for underwater drilling
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
  • E21B21/01—Arrangements for handling drilling fluids or cuttings outside the borehole, e.g. mud boxes
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
  • E21B21/08—Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B34/00—Valve arrangements for boreholes or wells
  • E21B34/02—Valve arrangements for boreholes or wells in well heads
  • E21B34/025—Chokes or valves in wellheads and sub-sea wellheads for variably regulating fluid flow
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B47/00—Survey of boreholes or wells
  • E21B47/04—Measuring depth or liquid level

Definitions

• the present invention relates to a method and apparatus for subsea well plug and abandonment operations, and in particular to a method and apparatus for controlling a fluid in a subsea wellbore system during a plug and abandonment procedure. Aspects and embodiments of the invention relate to a vessel-based riser-less method and apparatus for controlling a volume of fluid during a plugging and abandonment operation on a subsea hydrocarbon well. Background to the invention
• the drilling and construction of wells for example for the hydrocarbon exploration and production industry, includes many different operations which involve the pumping of fluids from surface through the wellbore and back to surface.
• a drilling operation typically
• Drilling fluid (referred to as drilling mud) is pumped from one or more pits on a drilling rig down through the drill string to the drill bit to fulfil a number of different functions, including providing hydrostatic pressure to control the entry of fluids from the formation into the wellbore, lubricating the drill bit, keeping the drill bit cool during drilling, and carrying particulate materials such as drill cuttings upwards and out of the well away from the drill bit.
• Drilling fluid and cuttings emanating from the wellbore are carried up the annular space between the wall of the bore being drilled and the drill pipe to the mudline.
• BOP blow-out preventer
• Drilling fluid and cuttings are returned to the drilling rig for processing, re-use, storage, removal and/or treatment through the annulus between the drill pipe and the riser.
• the drilling fluid system is a closed-loop system, which has a known well volume through which the drilling fluid is circulated, and one or more drilling fluid or "mud" pits on the drilling rig.
• the rig crew monitors the level of drilling fluid in the pit to detect unwanted influx of reservoir fluids (including gases) into the wellbore, referred to as a "kick".
• the rig crew responds to kicks by adding one or more barriers to control the influx and circulate the additional fluid out of the wellbore and prevent uncontrolled flow of fluids into the well.
• pit gain is the difference between the volume of fluid pumped into the well and the volume of fluid pumped out of the well. In a closed-loop system for a stable well, the two values should be equal, whereas a positive pit gain will indicate an influx of reservoir fluid and a pit loss will indicate a loss of drilling fluid into the formation. For a single pit drilling system, pit gain can be determined by monitoring the level of drilling fluid in the pit. Active pit systems are computer-controlled systems which enable several pits to be aggregated into one "active pit volume", which can be treated as a single pit for monitoring pit gain.
• Plug and abandonment methodologies are varied, but conventionally use a drilling rig (such as a jack-up rig installation) to install a blowout preventer (BOP) stack and marine riser on the well.
• BOP blowout preventer
• the production tubing is cut and pulled to surface to enable one or more cross- sectional barriers or plugs to be installed in the wellbore.
• the drilling fluid circulation system of the rig is used to provide drilling fluid from the pit, via the marine riser, to the wellbore to compensate for the loss of volume as the tubing is removed from the well.
• pit gain can be monitored at surface to determine whether there is an influx or outflow of fluid which is indicative of a problem with the seal or seals provided by the plugs.
• the BOP stack provides full control of wellbore fluids and enables any unwanted flow of reservoir fluids into the annulus to be mitigated against. Methods which rely on the use of drilling rigs are expensive and time-consuming to mobilise.
• a coiled tubing intervention in the absence of deployment through a marine riser, does not provide a return annulus for drilling fluids and does not enable volume control as the tubing is removed from the well. It is known to provide drilling fluid collection, handling and return equipment in subsea drilling operations which do not use conventional marine risers. For example, when drilling the uppermost section of the wellbore, which is referred to as the "tophole" is drilled, there is no riser pipe installed between the seabed and the drilling rig, and as there is no return path for drilling fluids from the wellbore back to the surface, the drilling mud and cuttings are conveyed to surface via a dedicated return line.
• the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore, a subsea flow control package, a fluid conduit extending between the subsea flow control package and surface, and a system control module, wherein the subsea flow control package defines a first flow path between wellhead interface module and the fluid conduit via a pump and defines a second flow path between the wellhead interface module and the fluid conduit via a flow control valve;
• a method of performing a plug and abandonment operation on a subsea hydrocarbon well comprising: providing an apparatus having a wellhead interface module located on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore; and a system control module;
• the method may comprise providing wellbore fluid from a wellbore fluid source to the wellbore system consisting of the apparatus and the wellbore, in response to the derived volume data.
• the method comprises characterising the change in wellbore conditions according to the group comprising: a steady state; a fluid influx state; a fluid loss state; a tubing run-in state; or a tubing pull-out state.
• the method may comprise displaying a characterised change to an operator.
• the method may comprise removing a second length of tubing or casing from the wellbore and monitoring at least one parameter of the wellbore fluid in the chamber and outputting a measurement signal to the system control module in dependence on the at least one parameter.
• the method may comprise providing additional wellbore fluid from a wellbore fluid source to the chamber in response to the derived volume data.
• the wellbore fluid source may provide a head of wellbore fluid pressure.
• the method may comprise repeating the steps of removing the tubing or casing and providing wellbore fluid from a wellbore fluid source to the chamber in response to the measurement signal.
• the method comprises providing wellbore fluid from a wellbore fluid source to the wellbore system while the tubing or casing is stationary (or between successive steps of removing tubing from the wellbore).
• the method comprises measuring, using a level sensor of the wellhead interface module, the level of wellbore fluid in the chamber and outputting a measurement signal to the system control module.
• the method may comprise cutting a length of tubing or casing, which step may be performed during refill of the chamber.
• the method may comprise analysing the measurement signal to identify a condition of the wellbore, which may be classified as one or more of a steady state; a fluid influx state; a fluid loss state; a tubing run-in state; or a tubing pull-out state.
• the method may comprise providing wellbore fluid from a wellbore fluid source to the chamber, and may comprise pumping wellbore fluid from the wellbore fluid source.
• the method may comprise pumping wellbore fluid from the wellbore fluid source using a feed pump.
• the method may comprise controlling the flow of wellbore fluid to the chamber using a subsea flow control valve, which may comprise a choke.
• the flow of wellbore fluid may be directed through the second flow path defined by the subsea flow control package.
• the method may comprise pumping wellbore fluid from the chamber to a remote location, which may be at surface.
• the method may comprise deploying the apparatus from a vessel.
• the vessel may comprise a support vessel, and/or may comprise a lightweight intervention vessel (LWIV).
• LWIV lightweight intervention vessel
• 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.
• a third aspect of the invention there is provided apparatus for monitoring and/or controlling the volume of a fluid in a subsea wellbore system during a plug and abandonment operation, the apparatus comprising:
• a wellhead interface module configured to be disposed on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore;
• subsea flow control package defines a first flow path between wellhead interface module and the fluid conduit via a pump, and defines a second flow path between the wellhead interface module and the fluid conduit via a flow control valve;
• the wellhead interface module comprises a sensor for monitoring at least one parameter of the wellbore fluid in the chamber and outputting a measurement signal to the system control module;
• system control module is configured to derive volume data relating to a change in volume of wellbore fluid in the chamber and compare the derived volume data with a volume change expected due to the removal of tubing or casing from the wellbore; and wherein the subsea flow control package is configured to control the flow of fluid from the fluid conduit to the wellhead interface module.
• Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or their embodiments, or vice versa.
• a wellhead interface module configured to be disposed on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore;
• the wellhead interface module comprises a sensor for monitoring at least one parameter of the wellbore fluid in the chamber and outputting a measurement signal to the system control module;
• system control module is configured to derive volume data relating to a change in volume of wellbore fluid in the chamber and compare the derived volume data with a volume change expected due to the removal of tubing or casing from the wellbore.
• the system control module is configured to characterise the change in wellbore conditions according to the group comprising: a steady state; a fluid influx state; a fluid loss state; a tubing run-in state; or a tubing pull-out state.
• the system control module may be configured to display a characterised change to an operator.
• the apparatus preferably comprises at least one flow control package, and at least one fluid conduit connecting the chamber with the at least one flow control package.
• the apparatus may comprise a subsea flow control package, and may further comprise a surface flow control package.
• a fluid return line may connect a subsea flow control package with a surface flow control package.
• the apparatus preferably comprises at least one fluid conduit connecting the chamber with the at least one flow control package.
• the at least one flow control package may be configured to control the flow of wellbore fluid into the chamber from a wellbore fluid source.
• the wellbore fluid source may comprise a tank, and/or may be disposed at surface.
• the at least one flow control package may be configured to control the flow of wellbore fluid from the chamber to a remote location.
• the remote location may be at surface, and a may be a tank.
• the at least one flow control package may comprise a pump, and/or may comprise at least one valve.
• the at least one flow control package comprises a pump for pumping wellbore fluid to surface.
• the subsea flow control package comprises a subsea flow control valve (which comprises a choke mechanism).
• the subsea flow control valve is preferably configured to choke the flow from a wellbore fluid source to wellhead interface module.
• the subsea flow control package may comprise a pump, which may be a variable speed pump.
• the wellbore fluid may be drilling fluid or "mud".
• the wellhead interface module may be open to a subsea environment in use, and may comprise an upper opening.
• the body may define a throughbore from an upper opening to the wellhead.
• the wellhead interface module may comprise a safety valve, and may comprise an annular blowout preventer.
• the wellhead interface module may comprise a shear and seal device.
• the apparatus may comprise an optical inspection system, which may comprise a camera and may comprise an illumination source.
• the optical inspection system may be in two- way communication with the system control module.
• the subsea flow control package a may be mounted on a seabed skid.
• the subsea flow control package may define a first flow path for a fluid passing from a wellbore fluid source and the wellhead interface module, and may define a second flow path for a fluid passing from the wellhead interface module to a remote location.
• the first and/or second flow paths may comprise one or more shut-off valves.
• the surface flow control package may comprise a wellbore fluid source, and may comprise a feed pump.
• the feed pump may be disposed between the wellbore fluid source and the fluid return line.
• a bypass flow line may be provided for the feed pump.
• the wellbore fluid source may comprise a tank, and/or may further comprise a level sensor for measuring a volume of wellbore fluid in the wellbore fluid source and outputting a measurement signal to the system control module.
• the apparatus is configured to be used in a plug and abandonment operation. More preferably, the apparatus is configured to be used in a rig-less plug and
• Embodiments of the fourth aspect of the invention may include one or more features of the first to third aspects of the invention or their embodiments, or vice versa.
• a system comprising the apparatus according to the second aspect of the invention, a vessel, and the wellbore on which the wellhead interface module is disposed.
• 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.
• a method of performing a plug and abandonment operation on a subsea hydrocarbon well comprising: providing an apparatus having a wellhead interface module located on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore; and a system control module;
• the method may comprise removing a second length of tubing or casing from the wellbore; measuring the level of wellbore fluid in the chamber and outputting a
• the method may comprise repeating the steps of removing the tubing or casing and providing wellbore fluid from a wellbore fluid source to the chamber in response to the measurement signal.
• the method may comprise cutting a length of tubing or casing, which step may be performed during refill of the chamber.
• the method may comprise analysing the measurement signal to identify a condition of the wellbore, which may be classified as one or more of a steady state; a fluid influx state; a fluid loss state; a tubing run-in state; or a tubing pull-out state.
• Embodiments of the sixth aspect of the invention may include one or more features of the first to fifth aspects of the invention or their embodiments, or vice versa.
• a seventh aspect of the invention there is provided a method of performing a plug and abandonment operation, the method comprising:
• the wellhead interface module located on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore; and a system control module;
• determining a condition of the wellbore independence on the measurement signal selected from a fluid loss condition, a fluid influx condition, or a steady state condition of the wellbore may comprise removing wellbore fluid to the chamber in a fluid influx condition of the wellbore.
• the method may comprise providing wellbore fluid to the chamber in a fluid loss condition of the wellbore.
• Embodiments of the seventh aspect of the invention may include one or more features of the first to sixth aspects of the invention or their embodiments, or vice versa.
• the wellhead interface module located on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore; and a system control module;
• Embodiments of the eighth aspect of the invention may include one or more features of the first to seventh aspects of the invention or their embodiments, or vice versa.
• an apparatus for monitoring or controlling the volume of a fluid in a subsea wellbore system during a plug and abandonment operation comprising: a wellhead interface module configured to be disposed on a wellhead, the wellhead interface module comprising a body defining a chamber which accommodates a volume of wellbore fluid in fluid communication with the wellbore;
• the wellhead interface module comprises a sensor for measuring a volume of wellbore fluid in the chamber and outputting a measurement signal to the system control module;
• Embodiments of the ninth aspect of the invention may include one or more features of the first to eighth aspects of the invention or their embodiments, or vice versa.
• Figure 1 is a schematic representation of a volume control system according to a first embodiment of the invention, consisting of a volume control apparatus and a vessel;
• Figure 2 is a schematic representation of a detail of subsea components of the volume control apparatus shown in Figure 1 ;
• Figure 3 is a representative screenshot of a control module used in conjunction with the volume control system of Figure 1 ;
• Figure 4 is a schematic representation of a detail of subsea components of the volume control apparatus shown in Figure 1 during a filling operation;
• Figure 5 is a graph showing plots of the length of casing pulled from a wellbore and a measured drilling fluid column height over time during a tubing pulling operation;
• Figure 6 is a graph showing plots of the length of casing pulled from a wellbore and a measured drilling fluid column height over time during a pulling and refilling operation;
• Figure 7 is a schematic representation of a detail of subsea components of the volume
• FIG. 1 there is shown schematically a volume control system according to a first embodiment of the invention, generally depicted at 10, applied to a plug and abandonment operation in a subsea wellbore 1 1.
• the system 100 comprises a subsea wellhead interface module 20, a subsea flow control package 40, and a surface control package 60 on a vessel 12.
• the subsea wellhead interface module 20 is coupled to the subsea wellhead 13 of the wellbore 1 1 via a connector 14.
• the subsea flow control package 40 is located subsea, and in this example is a skid package resting on the seabed 15.
• the subsea wellhead interface module 20 and subsea flow control package 40 are connected by a seabed umbilical system 21 comprising electrical, hydraulic, and fluid lines.
• An upper umbilical 41 contains electrical, hydraulic, and fluid lines running between the subsea flow control package 40 and the surface control package 60 on the vessel.
• a system control module 80 which provides control and communication between the various components of the system, and which receives and processes, transmits and/or displays measurement data to an operator of the system.
• the system control module 80 is implemented in software running on a computer on the vessel, which receives input data acquired from the system and processes the data for recording, display, and/or onward transmission.
• the wellhead interface module 20 comprises a body 22 which defines a chamber in the form of a longitudinal throughbore 23, an upper end of which is open to the subsea environment. A second, lower end of the module 20 is in fluid communication with the wellbore 1 1 , and is able to receive flow from the production bore or the annulus via wellhead valves.
• the wellhead interface module 20 is also provided with an annular BOP 24a and a shear-and-seal device 24b.
• the wellhead interface module 20 also comprises a pressure sensor 27 which functions to detect and measure the level of drilling fluid in the body 22 and provide a signal to the control module 80.
• a subsea camera system 28 comprising an illumination source 29 and a camera 30 is mounted to the module 20 to enable visual monitoring of the levels of fluid in the body 22, providing back-up to the pressure sensor 27.
• the camera system 28 also enables visual detection of gas bubbles in the wellbore fluid in the event of gas in flux.
• Located between the first and second ends of the body is an outlet 25 which connects the throughbore 23 with a conduit which forms part of the seabed umbilical 21 and is connected to the subsea flow control package 40.
• the package 40 is mounted in a skid 50 which rests on the seabed 15.
• the package 40 comprises a flow control valve 46 communicating with a conduit portion 26a of the umbilical 21 , and a variable speed subsea pump 42 coupled to a conduit portion 26b of the umbilical 21.
• the umbilical enables two- way communication between the various components of the wellhead interface module 20 and the system control module 80 and flow control package 40.
• a pair of subsea shut-off valves 44a and 44b enable selective isolation of the conduit portions 26a, 26b from a hose portion of the umbilical 41 , which joins the subsea flow control package 40 to the surface control package 60.
• the subsea flow control package 40 also comprises pressure, depth and temperature sensors (not shown) and is in data communication with the control module 80 via the umbilical 21.
• Conduit portions 26a and 26b define parallel flow paths, and the conduit portion 26a therefore provides a bypass flow path to the conduit portion 26b which comprises the pump 42.
• the surface control package 60 is mounted on the vessel 12, which is preferably a lightweight intervention vessel (LWIV).
• LWIV lightweight intervention vessel
• the invention facilitates the provision of full volume control for the wellbore in a manner that is suitable for deployment from a LWIV, without relying on a drilling rig deployment process. This makes the systems of embodiments of the invention more cost-effective and time-efficient compared with traditional rig-deployed methods, and renders embodiments of the invention suitable for a wide range of applications.
• the surface control package 60 comprises a drilling fluid tank 62, a feed pump 66, and a power supply for surface package and the subsea components 20 and 40.
• a launch and recovery system (not shown) is also provided for deployment and recovery of the subsea package 40 and optionally the wellhead interface module 20.
• the drilling fluid tank 62 is joined to the feed pump 66 via conduit 68, and also comprises pressure sensors which detect and measure the level of drilling fluid in the tank 62 and provide a signal to the control module 80.
• An external transceiver 64 enables two-way communication between the package 60 and the system control module 80.
• FIG. 3 there is shown a representative screenshot for the subsea control module 80 in a plug and abandonment application.
• the system control module 80 is implemented in software running on a computer on the vessel, which receives input data acquired from the system and enables transmission of control signals for operation of the surface and subsea components.
• Data pertaining to the operation is displayed at 302, which in this case is a graph which includes plots of changing fluid levels over time.
• Screen area 304 displays a representation of the conduits and hoses of the system including pressure data from a number of pressure sensors distributed around the system.
• Screen area 306 displays an image captured from the cameras 29, enabling an operator to view the activity at the body 22.
• a number of graphical user interface icons are provided at 308 and 310 to provide an operator with the ability to control the system and/or elements of the display.
• the system control module 80 is therefore able to display data from the system, which may be in real-time, and issue control instructions to begin, cease or modify operations from a single interface.
• Use of the system of this embodiment will now be described in the context of a plug and abandonment operation.
• the wellhead interface module 20 is deployed from the LWIV 12 to the seabed, assisted by remotely operated vehicles (ROVS) or divers as is known in the art.
• the module 20 is connected to the wellhead 13 via a connector 14.
• the subsea flow control package skid 50 is deployed to the seabed from a launch and recovery system on the vessel, again with the assistance of ROVs or divers.
• the skid 50 is deployed with the hose 41 connected to the package 40, to avoid making up a wet mate connection subsea, although it will be appreciated that subsea connection is also possible.
• the subsea shut-off valves 44a, 44b are closed, and the subsea package 40 is preferably deployed along with the seabed umbilical 21 and conduit portions 26a, 26b already connected to the subsea package, only requiring make up of the seabed umbilical 21 with the outlet 25 of the wellhead interface module 20.
• the subsea flow control valve 46 and subsea shut-off valve 44b are closed, and the subsea shut-off valve 44a is opened by a signal from the system control module 80.
• the feed pump 66 is activated to create a differential pressure sufficient to initiate flow of drilling fluid from the tank 62 to the subsea flow control module, and the flow control valve 46 is gradually opened to allow controlled flow of drilling fluid to the chamber of the wellhead interface module 20.
• the flow control valve 46 enables flow due to the hydrostatic head of fluid to be controlled, and prevents unwanted filling of the wellhead interface module 20.
• the sensors 27 and camera system 30 monitor the level in the throughbore 23.
• FIG. 5 is a graph 500 which plots a tubing retrieval length and a corresponding measured change in the fluid level in the throughbore 23 of the wellhead interface module 20, both against a time axis.
• the fluid level measurement corresponds to a volume of wellbore fluid in the combined wellbore system consisting of the wellhead interface module 20 and wellbore itself, and monitoring the fluid level in the chamber of the wellhead interface module 20 enables data relating to a volume change in the wellbore system to be derived.
• a preliminary phase referred to as a flow check operation
• Plot B shows at arrow 501 the response during steady state (i.e. flow check) conditions, i.e. where the pumps are not operational and drilling fluid is not circulated, and there is no movement of the tubing or casing. The volume of fluid is verified as being constant during the flow check phase of the operation.
• Plot B of Figure 5 shows a drop in fluid levels in the throughbore 23 as tubing is pulled out of hole, resulting from additional fluid from the chamber defined by the throughbore 23 entering the wellbore into the volume previously occupied by the tubing material.
• the removal of the tubing from the wellbore results in a reduction in fluid volume of tubing within the wellbore itself, as the upper end of the tubing is pulled out of the well into the subsea environment.
• the specification of the well tubing being known, it is possible to compute the expected volume change in the wellbore as the tubing is removed. As the tubing is removed, wellbore fluid passes from the chamber and into the wellbore itself, displacing the volume previously occupied by the material of the tubing.
• the reduction in fluid volume the chamber is derived from the measurement of fluid levels, and compared with the expected volume change due to the removal of well tubing.
• This comparison of a measured or derived volume change with the expected volume change enables conditions in the wellbore to be characterised, for example as a steady state; a fluid influx state; or a fluid loss state, as described below.
• Figure 5 also shows that when the removal of the tubing ceases (indicated at 503 on the graph), the fluid level in the chamber remains static (shown at 502). This is verified as part of a flow check operation prior to subsequent operational steps.
• Figure 6 is a graph 600 which plots a tubing retrieval length and a corresponding measured change in the fluid levels in the throughbore 23 of the wellhead interface module 20 during tubing pulling and re-filling.
• the data shows the fluid level response as a length of tubing, in this case about 15m, is pulled under conditions when the pumps are not operational and drilling fluid is not circulated over the time period 601.
• Plot B shows a drop in fluid levels in the throughbore 23 as tubing is pulled out of hole in period 601 , as fluid from the chamber displaces the volume of tubing material removed from the well (the response in period 601 corresponds to plot B of Figure 5).
• FIG. 4 depicts the system being operated in a re-fill mode.
• the subsea flow control valve 46 and subsea shut-off valve 44b are closed, and the subsea shut-off valve 44a is opened by a signal from the system control module 80.
• the feed pump 66 is activated and the flow control valve 46 is gradually opened to allow controlled flow of drilling fluid to the chamber of the wellhead interface module 20.
• the sensors 27 and camera system 30 monitor the level in the throughbore 23.
• the valve 46 is closed and the feed pump 62 is switched off.
• the re-filling of the chamber takes place during the time period 602, in which plot B shows (at 604) an increase in the fluid level in the chamber. Pulling of the tubing or casing recommences in the period 603, in which plot B shows a corresponding reduction in drilling fluid level.
• the process is repeated as successive lengths of tubing or casing are removed from the wellbore, with the re-filling of the chamber of the subsea module taking place between successive pulling phases. It may be preferable for the replenishment or re-filling of the chamber to take place during a period in which the tubing is not being pulled, as this may facilitate accurate monitoring of the fluid volume and control of the fluid replenishment step.
• the uppermost joints of the drill string may be disassembled at surface at the same time as fluid replenishment.
• the fluid replenishment periods may be determined by disassembly of drill string sections, or by depletion of the fluid volume in the chamber, depending on the configuration of the system. Either way, it is convenient for the operations to be performed simultaneously for the efficiency of the plug and abandonment operation.
• Use of a lifting cable as will be the case in certain embodiments of the invention, enables continuous lifting. However, it is possible even in this configuration for the pulling operation to be performed in discrete steps to allow controlled re-filling under steady state conditions. When the tubing or casing reaches the surface, it becomes necessary to cut the upper portions of the tubing or casing at regular intervals.
• the re-filling of the wellbore system takes place during cutting of the tubing or casing, to improve the efficiency of the plug and abandonment operation.
• the chamber of the module 20 may be re-filled during pulling of the tubing or casing out of hole, with the level of drilling fluid constantly monitored by the system control module 80.
• the system control module 80 uses data from the sensors 27 and 64, and controls the operation of the valves and pumps in the surface and subsea flow control modules to manage the fluid volume in the wellbore at a suitable value.
• the above-described embodiment of the invention provides a volume buffer which accommodates the change in fluid volume in the wellbore system during each pull and cut stage as material is removed from the well.
• the system provides full volume monitoring and control without reliance on a marine riser: the drilling fluid which is displacing the pulled tubing is provided directly from a subsea chamber forming a part of the wellhead interface module.
• the system provides sufficient drilling fluid in the tank 62 to provide fluid displacement for the volume of tubing material being removed.
• additional auxiliary drilling fluid volumes may be provided from additional tanks or pits.
• the wellbore fluid is replenished via a conduit from the flow control package. It will be appreciated that other mechanisms for delivering wellbore fluid to the wellbore system may be used in alternative embodiments. This includes (but is not limited to) a dedicated flow conduit from the surface or a remote subsea location to the chamber.
• a further alternative is to provide wellbore fluid from the surface via the drill string, through the casing or tubing being pulled, and out of the lower end of the casing or tubing to replenish the fluid volume from the wellbore (from which fluid is displaced upwards into the chamber).
• Figure 7 schematically shows the system 100 used during an operational phase in which fluid influx occurs from the wellbore.
• Figure 8 is a graph 800 which plots a tubing retrieval length and a corresponding measured change in the fluid levels in the throughbore 23 of the wellhead interface module 20 during pulling of tubing from the wellbore. As a length of tubing or casing is pulled, as shown at plot A, the sensors of the module 20 detect a drop in drilling fluid level. This measured data is shown at plot C.
• a comparison with the expected volume change (shown at plot B), reveals a discrepancy between the measured change in volume and that expected for the length of tubing removed, indicated at 802.
• the discrepancy shows that there is additional fluid in the chamber of the module 20, which is indicative of fluid influx into the wellbore.
• a problem with the seals provided by the plugs can be inferred from the presence of fluid influx, which allows the operator (via the control module 80) to activate the pump 42 to pump excess fluid to the vessel 12 via the return line.
• the subsea shut-off valve 44a is closed, and the valve 44b is open. Drilling fluid is pumped from the chamber of the module 20 via conduit portion 26b to the skid 50, and upwards to the vessel 12.
• a bypass conduit (not shown) may be provided for the feed pump 66.
• the influx may result in the well being identified as being unsuccessfully plugged, and can be shut-in temporarily, pending attendance by a drilling rig closed-loop plug and abandonment system (this may be necessary where the fluid influx is identified as severe and beyond the handling capabilities of the system 100).
• the excess fluid may be contained at the seabed in an auxiliary tank or discharged to the subsea environment.
• the subsea pump may be omitted from the subsea flow control package 40.
• inclusion of a subsea pump is preferred as it avoids undesirable discharge of drilling fluids into the sea.
• the system 100 may also be used in the configuration shown in Figure 7 to flush the return line with seawater at the end of the operation.
• drilling fluid present in the chamber may be pumped through the conduit portion 26b and upwards through the return line 41.
• seawater from the surrounding seawater will enter the upper opening of the chamber and will be pumped through the seabed umbilical 21 , through the subsea flow control package 40 via the pump 42 and the shut-off valve 44b, and up through the return line.
• Valve arrangements may also allow complete flushing of the conduit portion 26a, flow control valve 46 and shut-off valve 44b. It will be apparent that the system 100 may also be used to identify a drilling fluid loss.
• Figure 9 is a graph 900 which plots a tubing retrieval length and a corresponding measured change in the fluid levels in the throughbore 23 of the wellhead interface module 20 during pulling of tubing from the wellbore.
• the sensors of the module 20 detect a drop in drilling fluid level, shown at plot C.
• a comparison with the expected volume change shows a discrepancy between the measured change in volume and that expected for the length of tubing removed (indicated at 902), which shows that there is less fluid in the chamber of the module 20. This is indicative of fluid losses to the formation.
• the invention provides a method of and apparatus for performing a plug and abandonment operation on a subsea hydrocarbon well.
• the method comprises providing an apparatus having a wellhead interface module located on a wellhead, which accommodates a volume of wellbore fluid in fluid communication with the wellbore.
• a system control module receives a measurement signal from a sensor for monitoring at least one parameter of the wellbore fluid in the chamber.
• the system control module is configured to derive volume data relating to a change in volume of wellbore fluid in the chamber and compares the derived volume data with a volume change expected due to the removal of tubing or casing from the wellbore. This enables a change in wellbore conditions to be
• the method comprises providing additional wellbore fluid to the chamber to replace fluid which enters the wellbore to occupy the volume vacated by the removed tubing, and/or removing or adding fluid in fluid influx/loss situations respectively.
• the invention addresses one or more of the problems associated with conventional plugging and abandonment techniques when used from vessels.
• the invention provides a method and apparatus for controlled re-filling of a subsea
• hydrocarbon well from a dedicated well fluid conduit during a plugging and abandonment operation.
• the operation may be performed from a LWIV and without relying on a drilling rig and/or marine riser system.
• Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein.

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• 2013
  • 2013-03-27 NO NO20130438A patent/NO20130438A1/no not_active Application Discontinuation
• 2014
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