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
  • 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
  • E21B21/082—Dual gradient systems, i.e. using two hydrostatic gradients or drilling fluid densities
• • 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
  • 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
  • E21B21/10—Valve arrangements in drilling-fluid circulation systems
• • 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
  • E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
  • E21B41/0007—Equipment or details not covered by groups E21B15/00 - E21B40/00 for underwater installations
• • 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
  • E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
  • E21B41/0078—Nozzles used in boreholes
• • 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
  • E21B7/00—Special methods or apparatus for drilling
  • E21B7/12—Underwater drilling

Definitions

• the invention relates to a system and a method of circulating drilling-fluid with drillcuttings from a subsea well to the surface, as part of an open water drilling system for oil and gas drilling, typically from a floating mobile offshore drilling unit (MODU).
• MODU floating mobile offshore drilling unit
• one main aspect of the invention relates to a reduction of ancillary fluid conduits to be integrated as part of a fluid return riser, facilitated through the implementation of a new drilling/well control solution with subsea chokes and circulation of possible hydrocarbon influx from the well via the fluid return riser, with kill-fluid supply via the drillstring as the primary pathway. Secondary pathways for supply of kill-fluid are provided in case the drill-string is sheared.
• Another aspect of the invention is a fluid lift assistance feature, based on arrangements of riser mounted eductors, to reduce the dependence on a subsea pump to provide fluid lift.
• the marine drilling riser conduit extends from the top of the subsea BOP to the underside of the drill-floor of the vessel.
• the marine drilling riser has several functions; - to serve as a return conduit for cuttings laden drilling-fluid from the well, to be used for attachment and support of ancillary lines between the subsea BOP and the MODU for well control and to bring the subsea BOP to/from the subsea wellhead.
• the lower end of the drilling riser is attached, via a flexible element, to the top of the Lower Marine Riser Package (LMRP), which is connected on top of the lower BOP.
• LMRP Lower Marine Riser Package
• a riser tensioning system keeps the riser stable, while, at the same time, compensating passively for vertical motion of the vessel.
• the riser can be disconnected from the lower BOP with a LMRP high-angle release connector.
• Many mature fields with existing production infrastructure that could be utilized for new production are "undrillable" with conventional drilling techniques.
• the challenge is narrow margins between pore-pressures and fracture-gradients in the reservoir, because of depleted and/or pressurised reservoir zones. This limits options for new infill wells and increased recovery. Narrow drilling windows is also a major challenge and limitation for the development of many ultra-deep-water assets.
• MPD Managed Pressure Drilling
• Open water drilling also known as Dual-Gradient Drilling, (DGD) will provide a large range of cost and labour savings related to the drilling vessel and equipment. The benefits will increase with the water depth. Casing set points in wells drilled in deep and ultra-deep water are kick tolerance dependent and pressure control must be maintained within the pore/fracture gradient window.
• the solution will open the "drilling window" by increasing margins so that the Bottom Hole Pressure (BHP) can be more easily contained between the formation pore pressure and the formation fracture pressure during drilling. This will provide improved well bore pressure management, longer sections can be drilled with the same casing diameter, and wellbore instability can be avoided.
• the open water drilling solution will eliminate the conventional marine riser and diverter system and will enable full simultaneous drilling capabilities for the well construction.
• the fluid return riser system will be based on existing riser and riser tensioner technology, but should be optimised to minimize the weight, complexity, and cost. This is particularly important for operations in deep and ultra-deep water.
• BOP subsea blowout preventer
• the BOP provides safety-critical functions to prevent uncontrolled release of reservoir fluids and gasses during well construction.
• Subsea BOP's and their associated control systems have evolved through many decades of use with conventional offshore riser drilling. For open water drilling operations, the BOP must be fitted with a subsea ROD at the top. Another BOP adaptation to be implemented is an interface with the drilling-fluid return system.
• the BOP control system must also be adapted to the open water drilling mode of operation.
• the BOP may either be hydraulically or electro-mechanically operated.
• Fluid-lift systems and combinations thereof can be:
• a major challenge is to develop a subsea fluid return pump that will have sufficient differential pressure capacity at required flowrate, to operate in deep and ultra-deep water. Economic benefits of open water drilling increase with the water depth. A goal should be to enable open water drilling at water depths of 12-13,000 ft. (3,660m - 3,960m), which will for the most part satisfy current and future demands.
• a solution could in principle be to put several pumps in series, connected to, and supported by the fluid return riser, but the mass and physical dimensions of a subsea fluid-pump will be a major obstacle.
• Another challenging aspect is the considerable electrical power supply requirement, depending on the capacity of the installed pump, which will require at least one power and signal cable to be clamped to the riser.
• liquid lift based on an arrangement of subsea eductors in the upper part of the riser, to boost the flow of drilling-fluid, up through the fluid return riser system, for treatment and re-circulation at the drilling vessel.
• Eductors which is known in the art, require a propellant to initiate lift and boost of the well fluid.
• the propellant fluid will be provided from a surface pump and will typically be a lighter drilling fluid.
• the solution can be used to overcome the possible differential pressure limitations of a fluid return pump at the seabed, as a supplementary solution. It may also be an alternative to the fluid-pump.
• Document WO 2016/134442 A1 equivalent to LIS2018073314 A1, presents a Controlled Fluid Level, (CML) system, with a side outlet from a marine drilling riser, connected to a fluid return conduit that extends to the surface.
• CML Controlled Fluid Level
• Such systems have been in use for some years. They facilitate bottom hole pressure regulation during offshore drilling through level control of the liquid column inside the drilling riser.
• a subsea pump module mounted onto the marine drilling riser, is used for fluid-lift and level control in the riser.
• the referenced document describes an alternative fluid-lift/-level control solution, where an eductor replaces the fluid return pump.
• a single eductor insert is shown, close to the side outlet of the marine drilling riser, inside the fluid return line. It is intended to be retrievable to the surface by means of a wireline tool or a similar intervention method.
• a separate conduit for supply of eductor "propellant fluid" from the surface is included in the solution.
• US2012067590 A1 describes an arrangement and a method for regulating bottom hole pressures when drilling deep-water offshore wells.
• the arrangement comprises both a surface and a subsea pressure containment, i.e. BOPs, a high pressure riser and a high pressure drilling pipe.
• the high-pressure riser and high-pressure drilling pipe may be so arranged between the subsea blowout preventer and the surface blowout preventer that they can be used as separate high-pressure lines as a substitute for choke line and kill line.
• the subsea BOP has an equalizing loop/bypass that gives the ability to circulate out a large influx past the closed subsea BOP into the high-pressure riser.
• the arrangement also includes a low riser return system that involves two drilling fluid return pumps.
• US2012168171 A1 describes a subsea pressure control system with subsea chokes.
• the system comprises a blowout preventer stack, a subsea annular sealing device, and a choke manifold that variably restricts the flow of the drilling fluid and thereby adjust pressure applied to the annulus at the subsea location.
• the system also comprises a pressure control system involving several sensors, which can detect well control problems such as an influx in the well.
• LIS2014048331 A1 describes a managed pressure drilling system having a well control mode.
• the system includes a fluid transport system that comprises a booster line coupled to a booster pump, which may be used to compensate for any size discrepancy between the riser annulus and the casing/wellbore annulus.
• the drilling fluid pumped down through the booster line may be used to displace any contaminated returns present in the lower marine riser package.
• Drilling in shallow formations prior to the installation of a subsea blowout preventer, is done in open water. This is known as “top-hole” drilling. Drill-cuttings have been deposited at the seabed with conventional top-hole drilling. The release of drilling fluid to the environment in this manner is undesirable, both from a cost and environmental perspective. Solutions for top-hole drilling with fluid return for treatment and re-circulation at the surface have been successfully employed since the turn of the century, initially for shallow water, and later also for deep water.
• a subsea pump typically conveys drilling-fluid returns from a suction module through a flexible hose to the drilling vessel. The return line is anchored at one end by the pump, while the upper end is connected to equipment on the vessel.
• Document US 7,938,190 B2 describes a fluid return system for top-hole drilling in open water, with a mono-bore, rigid riser, typically made up of drill pipe.
• a subsea BOP is installed, for safe drilling into the oil and gas reservoir.
• the blowout preventer is hydraulically controlled and actuated, the number of ancillary lines to the BOP will be five: 2 hydraulic conduits, 1 kill line, 1 choke line and 1 fluid boost line.
• the lines are supported by the marine drilling riser for conventional riser drilling. They would contribute significantly to the weight and cost of a fluid return riser for open water drilling. This is especially true for drilling in deep and ultra-deep water.
• the object of the invention is to simplify the drilling-fluid return riser configuration for the open water drilling solution, as well as overcoming operational depth constraints, resulting from limited drilling-fluid lifting capacity of current art subsea fluid pumps and the use of hydraulic BOP.
• a first aspect of the invention relates to elimination of a choke line in the drilling fluidreturn riser, facilitated through the integration of at least one drilling choke as part of an electrical subsea BOP.
• Subsea drilling chokes are known in the patent literature from patent application CA 1054932 A.
• Document US 9,222,320 B2 describes a subsea pressure control system with subsea chokes.
• BHP bottom hole pressure
• the well is shut-in by the activation of pipe-rams on the BOP stack to seal against the drill-string.
• well-fluids are then circulated out via the choke line of a marine drilling riser, and through the choke and kill manifold at the surface.
• the topsides drilling choke will in this case be adjusted to control and vary the drill pipe pressure, casing pressure and BHP during the circulation of hydrocarbons from the well.
• a possible advantage, if the kick tolerance is limited, is that eliminated choke line pressure drop may allow for a larger bore well casing design programme than would otherwise be employed. This could improve drilling cost-efficiency and may even provide increased production value from better well design.
• a second aspect of the invention relates to the elimination of the kill line.
• circulation for influx recovery will primarily be via the drill-string, which will act as a bull-head line.
• a drill-string will have better flow capacity than a riser mounted kill line.
• a third aspect of the invention is to use an Electrical BOP, thus removing the need for hydraulic supply lines. Advantages will increase with the operational water depth.
• Benefits of using an electrical BOP are:
• Hydraulic accumulators are less efficient at high ambient pressure, experienced at deep and ultra-deep water.
• a full hydro-acoustic system will have secondary control over all remotely operated valving, as well as all safety-critical functionality of the electrically controlled and actuated drilling BOP.
• a fourth aspect of the invention is a fluid lift assistance feature, based on arrangements of riser mounted eductors, to reduce the reliance on a subsea pump to provide the fluid lift.
• An advantage with the use of eductors is that fluid-lift can be generated without moving parts subsea.
• the invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.
• the invention relates more particularly to a circulation system for circulating drilling fluid contaminated with hydrocarbons to a surface system via a drilling fluid return riser connected to a subsea wellhead in connection with drilling in open water, the circulation system comprising: a blowout preventer locked on the wellhead; a drill-string extending from the surface down through open water and further to the bottom of a subsea well in an oil and gas reservoir; sealing devices connected on top of the blowout preventer, arranged to seal around the drill-string in connection with the drilling operation; a control system connected to the blowout preventer and arranged for detection of hydrocarbon influx from the well formation during the drilling operation; inlet ports of drilling chokes connected to a vertical centre-bore of the blowout preventer and with outlets ports connected to the drilling fluid return riser; a drilling fluid return line spool provided between well barriers of the blowout preventer and the sealing devices forming alternative flow outlet connections to the drilling fluid return riser via a pipe system; a return line arranged for flowing returned drilling
• the invention relates more particularly to a method for circulating drilling fluid contaminated with hydrocarbons to a surface system from a subsea well via a circulation system according to the first aspect of the invention in connection with a need for well control and circulation of drilling fluid after unintentional influx of hydrocarbons into the well, wherein the method comprising the steps of: a) detecting any influx of hydrocarbons by the control system connected to the blowout preventer; b) closing pipe-rams in the blowout preventer to seal around the drill string; c) opening fourth isolation valves on the line connecting the vertical centre-bore of the blowout preventer to the inlet of the drilling chokes; d) opening one of the drilling chokes, while drilling fluid is pumped down through the drill string; e) circulating out hydrocarbon-containing well fluid via a well annulus through one of the a drilling chokes on the blowout preventer and further to the surface system via the fluid-lift pump and the drilling fluid return riser; f) regulating the flowrate of
• the method may comprise the further steps of: h) connecting a supply line, in open water, from the surface system to the connection point on the blowout preventer; i) opening the fifth isolation valves; and j) pumping heavy drilling fluid from the surface system via the open water supply line, the BOP mounted well kill-line and openings in the lower part of the blowout preventer to the annulus of the well.
• the method may comprise the further steps of: k) disconnecting anyone of the one or more eductors by closing sixth isolation valves; l) opening any throttling devices at anyone of the one or more of the eductors of the fluid-boost line; m) opening seventh isolation valves on the blowout preventer; and n) pumping the heavy drilling fluid from the surface system to the well annulus through the fluid-boost line, a second flexible hose, a connector, and further through the pipe arrangement and a first flexible hose, and through openings in the lower part of the blowout preventer.
• Fig. 1 shows a subsea BOP fitted with drilling chokes.
• An annular preventer and an ROD are connected on top of the BOP.
• An offset fluid return system with a seabed pump and optional eductors in the upper part of the riser is connected to the BOP.
• the figure also includes a separate emergency kill, stab-in connection and kill valves on the BOP.
• An extension of a common eductor drive fluid line has a possible, secondary function as a kill-line.
• Fig. 2 illustrates the eductor principle and arrangement.
• Figure 1 shows an open water drilling system after completed top-hole drilling, and with a subsea wellhead 1 installed.
• BOP preferably fitted with electromechanical actuators and "all-electric” subsea controls (not shown) is locked onto the subsea wellhead 1 with a wellhead connector 3.
• One end of a flexible fluid return flowline 4 is connected to an outlet of a spool piece 5 on the BOP 2.
• the other end of the flexible fluid return flowline 4 is connected to an offset fluid return line base assembly frame 6, anchored on the seabed.
• the fluid return system may be connected to a direct connection spool piece 7 on the BOP 2.
• a first isolation valve 8 on the spool piece 7 will be kept closed and an outlet of the spool piece 7 will be blanked-off.
• the first isolation valve may also be denoted spool piece isolation valve 8.
• the subsea BOP 2 is equipped with well barrier devices, known in the industry, and which can be arranged with different configurations for cutting and sealing around a drill-string 9.
• the BOP 2 arrangement shown on figure 1 is different from a conventional subsea BOP, in that there is no marine drilling riser and Lower Marine Riser Package (LMRP) connected to the BOP 2. Instead, an assembly of a rotating control device (ROD) housing 10 and an annular preventer 11 is locked to a connector on top of the BOP 2 by means of a connector 12.
• the spool pieces 5, 7 are connected to outlets of a fluid return line spool 13 of the BOP 2 above the well barrier elements and below the connector 12.
• a drill-string 9 is deployed in open water from a drilling vessel (not shown).
• a bottom-hole assembly (not shown) of the drill-string 9 is entered into the subsea well via the ROD housing 10, the annular preventer 11 , the BOP 2 and the well-head 1.
• An internal ROD sealing arrangement (not shown) is deployed with the drill-string 9 and is oriented and locked inside the ROD housing 10 prior to the drilling operation.
• the flow exits the flowline 4 it enters a right-angled spool piece 15, where the flow changes direction and is brought to flow up through a fluid return conduit.
• An electrically driven, subsea fluid-lift pump 16 at the base of a rigid fluid return riser 17 boosts the drilling fluid returns towards the surface.
• the fluid-lift pump 16 is controlled with a variable speed drive, which will adjust the pump speed according to output signals from the drilling control system (not shown). Depending on the water depth and the capacity of the fluid-lift pump 16 further boosting of the drilling fluid flow to the surface may be required.
• One or more eductors 18 (only one depicted in figure 1) is integrated in the fluid return riser 17 to provide additional fluid-lift along the upper part of the fluid return riser 17.
• Special eductor riser joints (not shown) will be provided, as required.
• the placement and numbers of eductors 19 in the fluid return riser 17 will depend on the differential pressure capacity of the seabed located pump 16, the efficiency of each eductor 18 and the total operational water depth of the open water drilling system.
• FIG 2 illustrates the principle and arrangement of the eductor 18.
• An eductor is a simple type of pump, which utilize the so-called "venturi effect”.
• the eductor 18 requires a propellant fluid for its operation, which will be provided from a designated rig pump, (not shown) via a riser mounted fluid-boost line 19.
• the propellant fluid will typically be a treated, lighter fluid-mix of a similar type as that which will be pumped into the well via the drill-string 9 during drilling.
• the eductor 18 is shown with an array of propellant fluid nozzles 18A, which are connected to a ring-manifold 18B.
• the individual nozzles 18A and the ring-manifold 18B are shown fixed onto a support ring 18C.
• the nozzles 18A penetrate fluid a pipe wall of the fluid return riser 17 and extend towards a suction side of a so-called diffuser 18D, which provides a reduced diameter flow-section inside the drilling fluid return riser 17.
• a so-called diffuser 18D which provides a reduced diameter flow-section inside the drilling fluid return riser 17.
• control system design must balance the volumetric flow rates of the propellant fluid at multiple elevations throughout the water column. This will be facilitated with remotely adjustable orifices and associated flowmeters (not shown) at output ports of the fluid-boost line 19 of each eductor 18.
• the drilling fluid return riser 17 is preferably provided with an emergency disconnect system arranged to unlatch a riser connector 20 and closure of a drilling fluid retention valve 21 when required.
• a flexible joint 22 is arranged above the drilling fluid retention valve 21. The drill-string 9 will, in case of the drilling fluid return riser 17 being disconnected, be pulled out of the BOP 2, with no need of unlatching connector 12.
• the configuration of the open water drilling system with a drilling fluid return riser 17 without choke & kill lines and with subsea chokes will enable efficient and safe handling of a possible hydrocarbon influx during drilling.
• Early kick detection functionality will be included on the BOP 2.
• the subsea BOP 2 is provided with at least one remotely adjustable drilling choke.
• the BOP system shown in figure 1 is provided with an upper drilling choke 23 and a lower drilling choke 24. Both drilling chokes 23, 24 are shown with discharge into the drilling fluid return line spool-piece 7 upstream of closed first isolation valve 8.
• the upper and lower subsea chokes 23, 24 discharge will thus always have a flow path to the drilling fluid-return system, independent of how it is connected to the BOP 2 (direct or offset alternatives).
• An upstream side of the drilling chokes 23, 24 is shown connected to a main bore of the BOP 2, with one connection above a lower pipe ram 25 of the BOP 2, and one connection below shear rams 26, 27 the BOP 2.
• the choke connections to the main bore of the BOP 2 is provided with third isolation valves 28A, 28B and fourth isolation valves 29A, 29B, respectively.
• the third isolation valves may also be denoted upstream of choke upper isolation valves 28A, 28B, and the fourth isolation valves may be denoted upstream of choke lower isolation valves 29A, 29B.
• the surface arrangement (not shown) for the drilling fluid returns is a directional flow head with an interconnecting flowline to fluid system shale shakers.
• provision for gas cut fluid disposal is accommodated by a surface arrangement, featuring flow diverters and an in-line degasser unit, complete with a gas vent line.
• control system comprising flowmeters, pressure sensors, temperature sensors and level sensors (not shown).
• the control system is provided with early kick detection capability built-in, arranged to register well influx with a best possible sensitivity.
• the control system incorporates statistical modelling to define the control limits to main- tain exact and continuous control of the well pressures during drilling and when drill pipe connections are made.
• the open water drilling system arrangement offers three ways of delivering heavy kill fluid to the well to re-gain control and circulate hydrocarbons out of the wellbore and drilling fluid return system.
• the primary method is to pump drilling fluid down into the bottom-hole with the installed drill-string 9. Two other pathways for the distribution of kill-fluid to the well are shown in figure 1.
• Kill fluid can also be pumped down through a stand-alone deployed emergency kill line (not shown) connectable to a mating connecting point 30 that can be mounted on a top plate 31 of the BOP 2.
• a connector 30 is connected to the main bore of the BOP 2 below the lower pipe-rams 25 via a BOP mounted kill-line 32, with two fifth isolation valves 33A, 33B. The use of this pathway would apply if the drill-string 9 is sheared.
• the fifth isolation valves may also be denoted kill-line isolation valves 33A, 33B.
• the fluid-boost-line 19 may be utilized as a kill-fluid conduit. This possible pathway will be available as long that the drilling fluid return riser 17 remains connected.
• Figure 1 shows the common fluid-boost line 19 extended and connected to the main bore of the BOP 2 below the lower pipe-rams 25.
• the eductor(s) 18 will in this case be shut-off with sixth isolation valves 34.
• the sixth isolation valve may also be denoted fluid-boost line isolation valves 34.
• Adjustable orifices (not shown) in the fluid boost-line 19 will be kept open, if used.
• An associated line 35 on the BOP 2 is fitted with two seventh isolation valves 36A, 36B.
• the seventh isolation valves may also be denoted blowout preventer isolation valves 36A, 36B.
• a first flexible hose 37 is laid out on the seabed to connect the fluid-boost line 19 from the drilling fluid return riser system to the BOP 2 via a second flexible hose 38 connecting the base of the drilling fluid return riser 17 and a connector 39 to allow line separation if the riser connector 20 is unlatched.
• fluid-boost-line 19 of the fluid-lift eductor 18 as a secondary conduit for kill fluid supply in a well control event could apply if the drill-string is sheared but will not be available if the drilling fluid return riser 17 is disconnected. If the fluid-boost line 19 is used for kill-fluid supply, the eductor control system (not shown) will be changed from "autocontrol" to manual control.

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• Environmental & Geological Engineering (AREA)
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• General Life Sciences & Earth Sciences (AREA)
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• Earth Drilling (AREA)

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Citations (5)

• 2021
  • 2021-01-12 NO NO20210037A patent/NO346362B1/no unknown
  • 2021-12-22 WO PCT/NO2021/050279 patent/WO2022154666A1/en active Application Filing
  • 2021-12-22 GB GB2309678.7A patent/GB2616787A/en active Pending

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