Well pressure control and mud gas handling system and method for carbon dioxide bearing formations

Abstract

A carbon dioxide handling well pressure control system includes a well closure device arranged to close an annular space between a well conduit and a well construction and / or workover tool disposed in the well. The well closure device has a fluid outlet disposed below a closure element in the well closure device. A conduit connects the fluid outlet to at least one controllable orifice choke. A pump disposed in the sealed enclosure has an outlet connectable to be in fluid communication with mud solids removal devices disposed on or proximate a well construction and / or workover unit.

Description

PATENT APPLICATIONATTORNEY DOCKET NO. MD-24-02PCTWELL PRESSURE CONTROL AND MUD GAS HANDLING SYSTEM AND METHOD FOR CARBON DIOXIDE BEARING FORMATIONSBACKGROUND

[0001] This disclosure relates to the field of well pressure control apparatus and mud gas handling apparatus used in connection with drilling and workover (collectively, “construction and / or workover”) of subsurface wells. More particularly, the disclosure relates to such apparatus wherein carbon dioxide is present in subsurface formations being drilled or having been penetrated by a well.

[0002] Well pressure control apparatus known in the art used in connection with well construction and / or workover includes devices (“blowout preventers” - hereinafter BOPs) arranged to hydraulically close in a well in the event fluid pressure in formations penetrated by the well exceeds the hydrostatic and / or hydrodynamic fluid pressure in the well exerted by fluid in the well, wherein fluid entry (a “kick”) from such formations causes a well pressure control event that must be contained and remediated to avoid damage to the well and / or uncontrolled discharge of fluid from the well (a “blowout”).

[0003] A BOP is typically connected, directly or through a conduit called a “riser”, to the upper end of a well conduit or casing, the conduit or casing being cemented in place in the formations below the land surface or water bottom. The BOP includes one or more sets of closure elements, called “rams”, which can engage an exterior of a drill pipe or well construction and / or workover tool extending through the BOP (pipe rams); can completely close an internal bore in the BOP (blind rams); or can cut through any pipe or tool disposed in the bore (shear rams), wherein closure of the foregoing acts to hydraulically close the well. Upon closure, various valves, conduits, variable orifice devices (chokes) and other fluid circulation system components may be used to circulate out the fluid comprising the kick, whereupon construction and / or workover operations may resume.

[0004] In wells drilled through formations where carbon dioxide may be present, influx of such carbon dioxide into the well may complicate regular pressure control procedures.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCTFirst, carbon dioxide may be dissolved in the continuous phase of many well construction and / or workover fluids. The resulting solution can be corrosive; corrosion in the structure of well pressure control equipment may be hazardous in that the equipment maybe subject to sudden and unpredictable failure by reason of corrosion stress cracking. Elastomer sealing elements, such as may be used on pipe rams and blind rams, may be subject to failure by exposure to low temperature as a result of carbon dioxide in the gas phase expanding and cooling. Pressure and flow control devices such as chokes may be subject to ice formation and consequent clogging by reason of carbon dioxide gas expansion and consequent cooling. Finally, it is considered to be an environmental hazard and a hazard to well construction and / or workover unit personnel to release carbon dioxide gas to the atmosphere, which is the ordinary way known in the art to discharge gases released from well construction and / or workover fluid prior to reuse in the well.

[0005] Pressure control equipment known in the art could be refitted with suitable devices to address the foregoing known considerations when dealing with carbon dioxide. A limitation to such retrofit, among others, is the cost to retrofit all well pressure control and well construction and / or workover fluid circulation systems with components resistant to carbon dioxide, whereas in many cases it is known that carbon dioxide will not be a consideration during well construction and / or workover, thus making retrofit of equipment used in such circumstances unnecessarily costly.

[0006] What is needed is a system that can be assembled to existing well pressure control and fluid circulation equipment for the specific purpose of handling carbon dioxide, wherein such equipment may be removed and redeployed on a different well construction and / or workover unit when no longer needed.SUMMARY

[0007] One aspect of the present disclosure is a carbon dioxide handling well pressure control system. A system according to this aspect includes a well closure device arranged to close an annular space between a well conduit and a well construction and / or workover tool disposed in the well. The well closure device has a fluid outlet disposed below a closure element in the well closure device. A mud gas separator is disposed proximate thePATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT well closure device. A conduit connects the fluid outlet to at least one controllable orifice choke. An outlet of the choke is connected to the mud gas separator inlet at an elevation below a liquid level in the mud gas separator. A pump has an inlet in fluid communication with a liquid outlet of the mud gas separator and an outlet connectable to be in fluid communication with mud solids removal devices disposed on or proximate a well construction and / or workover unit.

[0008] In some implementations, an outlet of the mud gas separator is in fluid communication with a carbon dioxide capture device.

[0009] In some implementations, the carbon dioxide capture device comprises at least one of a chemical absorber, a physical absorber, an adsorber, or a membrane separator.

[0010] In some implementations, the chemical absorber comprises amine.

[0011] In some implementations, the physical absorber comprises a solvent.

[0012] Some implementations further comprise an electrical resistance heating element disposed in an elastomer seal in the closure element.

[0013] In some implementations, the choke comprises a plurality of chokes connected in series.

[0014] In some implementations, the choke comprises a plurality of chokes connected in parallel.

[0015] In some implementations, a pressure drop in each of the plurality of chokes is a predetermined fraction of a total pressure drop across the plurality of chokes.

[0016] In some implementations, the predetermined fraction is chosen to limit a temperature drop across each of the plurality of chokes when carbon dioxide gas expands through each of the plurality of chokes.

[0017] In some implementations, the well closure device is disposed between an upper end of a well casing and a blowout preventer stack.

[0018] In some implementations, the well closure device is disposed at an upper end of a riser, the riser connected to an upper end of a well casing.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT

[0019] In some implementations, the well closure element is disposed at an upper end of a well casing, the well casing extending from above the bottom of a body of water downward into a sub-bottom well.

[0020] In some implementations, metal components thereof comprise carbon dioxide resistant metal.

[0021] In some implementations, the carbon dioxide resistant metal conforms to American Petroleum Institute grade CC.

[0022] In some implementations, elastomeric components thereof comprise carbon dioxide resistant material.

[0023] In some implementations, the carbon dioxide resistant material conforms to at least one of American Petroleum Institute grade FF or HH.

[0024] In some implementations, the mud gas separator and the mud pump are disposed in a sealed enclosure.

[0025] A method for circulating out a fluid influx containing carbon dioxide according to another aspect of the present disclosure includes detecting an influx of fluid into a well. A well closure device arranged to close an annular space between a well conduit and a well construction and / or workover tool disposed in the well is shut. The well closure device has a fluid outlet disposed below a closure element in the well closure device and a conduit connecting the fluid outlet to at least one controllable orifice choke. A bubble point pressure for carbon dioxide in a well construction and / or workover fluid in the well is calculated. A mud pump and the controllable orifice choke are operated to maintain a well construction and / or workover fluid pressure in the well above the bubble point pressure. The influx is bled through the controllable orifice choke into the sealed enclosure.

[0026] In some implementations, the sealed enclosure includes a gas vent line in fluid communication with a carbon capture unit arranged to remove carbon dioxide from gas leaving the sealed enclosure.

[0027] A method for controlling fluid pressure in a well during well construction and / or workover operations according to another aspect of the present disclosure includesPATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT coupling a carbon dioxide resistant well closure device in a well construction and / or workover apparatus between a well casing head and a well pressure control apparatus. The well closure device comprises a fluid outlet below a closure element in the well closure device. An inlet of a carbon dioxide resistant mud gas separator is fluidly connected to the fluid outlet. Well construction and / or workover operations are conducted using the carbon dioxide resistant well closure device and the carbon dioxide resistant mud gas separator. The carbon dioxide resistant well closure device and the carbon dioxide resistant mud gas separator are disconnected from the well construction and / or workover apparatus under predetermined conditions; and well construction and / or workover operations are resumed using the well construction and / or workover apparatus.

[0028] In some implementations, the carbon dioxide resistant mud gas separator and a mud transfer pump are disposed in a sealed enclosure.

[0029] Some implementations further comprise connecting a carbon dioxide resistant, controllable orifice choke between the fluid outlet and an inlet to the carbon dioxide resistant mud gas separator, and operating the carbon dioxide resistant, controllable orifice choke to limit a temperature drop to prevent ice formation.

[0030] In some implementations, the well pressure control apparatus comprises a blowout preventer stack.

[0031] Other aspects and possible advantages will be apparent from the description and claims that follow.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 shows schematically an example pressure control and well fluid gas handling system according to the present disclosure.

[0033] FIG. 1 A shows another example wherein a sealed enclosure as in FIG. 1 is not used.

[0034] FIG. 2 shows schematically the example pressure control and gas handling system according to FIG. 1 used in connection with a “riserless” well construction and / or workover system.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT

[0035] FIG. 3 shows a more detailed view of a mud gas separator (MGS) unit of the system in FIG 1 and FIG 2.

[0036] FIGS. 4A and 4B show example implementations of a choke valve used in connection with the MGS of FIG. 3 connected in series and parallel, respectively.

[0037] FIGS. 5 A - 5D show various components of an annular blowout preventer according to the present disclosure.

[0038] FIG. 6 shows an example implementation of a carbon capture unit disposed in a mud gas vent line to mitigate discharge of carbon dioxide to the atmosphere.

[0039] FIGS. 7A and 7B show an example of a switch that can be activated by presence of carbon dioxide in well construction and / or workover fluid.

[0040] FIGS. 8 A and 8B show an example of a pipe string valve that can be actuated by presence of carbon dioxide in well construction and / or workover fluid.

[0041] FIG. 9 shows a flow chart of an example method for circulating a well fluid influx (“kick”) containing carbon dioxide.DETAILED DESCRIPTION

[0042] An example implementation of a pressure control and well construction and / or workover (e.g., drilling) fluid (e.g., “mud”) gas handling system according to the present disclosure is shown generally at 10 in FIG. 1. The term “well construction and / or workover” as used in the present disclosure is intended to mean, without limitation, well drilling, well completion (together, well construction) and well rework or “workover” operations. The system 10 may comprise a carbon dioxide resistant well closure device, e.g., a pressure control device 14 such as an annular blowout preventer (hereinafter BOP for convenience). The BOP 14 may comprise a housing made from corrosion resistant, pressure resistant metal such as high chromium content steel. One or more well closure elements, e.g., rams or other sealing elements (see FIG. 5A; not shown in FIG. 1) may comprise elastomer seals made from carbon dioxide resistant composition and may comprise embedded heating elements (e.g., electrical resistance heating elements) toPATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT reduce the possibility of the elastomer being cooled below its glass transition temperature. The BOP 14 may be coupled to the top of a riser 16, or the BOP 14 may be coupled to a casing head flange (not shown) of a surface casing (not shown) in shallow water marine well construction and / or workover or in well construction and / or workover on the land surface. As will be appreciated by those skilled in the art, the casing (not shown) may extend upwardly from the bottom of a body of water or the land surface and extend below the water bottom or land surface into a subsurface or sub-bottom well. A conventional well pressure control BOP stack 12 may be coupled above the BOP 14 to provide both emergency well pressure control functions in the event of failure of the BOP 14, a pressure control event requiring severing a pipe string (not shown) extending into a well being drilled or reworked, or in the event well pressure exceeds the hydraulic pressure closure capacity of the BOP 14. The BOP stack 12 may be made from conventional materials and is not required to be resistant to carbon dioxide. The BOP stack 12 may be one that is associated with a particular well construction and / or workover unit and may remain therewith after the well construction and / or workover unit is moved to a different location. The BOP 14, being part of the system 10, may along with the rest of the system 10 be separated from the well construction and / or workover unit (not shown) and then be transported to a different well construction and / or workover unit for connection as shown in FIG. 1 (or as will be further explained, connected as shown in FIG. 2). In this way, it may be possible for a well construction and / or workover unit operator having multiple well construction and / or workover units to keep fewer systems according to the present disclosure than the total number of construction and / or workover units available, it being possible that not all well construction and / or workover units in the unit operator’s fleet are required to deal with or otherwise process carbon dioxide during well construction and / or workover operations.

[0043] The BOP 14 may comprise a fluid outlet 14A connected below the closure element(s) (not shown in FIG. 1) in the BOP 14 to provide hydraulic communication with the well (not shown in FIG. 1, see FIG. 2) after the BOP 14 is closed. Such outlet 14A may have one or more shut off valves 18 of types resistant to carbon dioxide connected in line to close the fluid outlet 14A as necessary. Fluid connection from the shut off valve(s)PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT18 may be directed by a conduit 17 to a mud handling unit and gas separator (MGS), shown generally at 20. Active components of the MGS 20 in some implementations may be disposed within a sealed, pressure resistant enclosure 22, both to exclude water in the case of marine drilling and to prevent escape to atmosphere of gases that exsolve from or otherwise separate from well fluid 19 as it returns from the well (not shown).

[0044] Such active components may comprise one or more carbon dioxide resistant, controllable orifice choke valves 24 (hereinafter choke valve(s) for convenience) hydraulically in line with the conduit 17. Example implementations of the choke valve(s) 24 will be explained in more detail with reference to FIG. 4. Outlet 24D from the choke valve(s) 24 may be into a volume of well construction and / or workover fluid 19 maintained in the enclosure 22. In some implementations, the outlet 24D is below the well construction and / or workover fluid 19 level. The fluid level may be controlled by a mud transfer pump 28 to be described further below. By placing the outlet 24D below the liquid 19 level, formation of carbon dioxide (dry) ice resulting from expansion of carbon dioxide gas is inhibited.

[0045] A degasser 26 may extract gas from solution in the well construction and / or workover fluid 19 and / or collect free gases that separate from the well construction and / or workover fluid 19, whereupon such gases may be transported to surface (or to other gas processing devices to be explained with reference to FIG. 6) along a gas vent line 32. Gas- free well construction and / or workover fluid 19 may be returned to a solids extractor (shale shaker) for cleaning and reuse, e.g., through a shaker line 30. It is preferred to locate the MGS 20 proximate the BOP 14, but in any event such that the choke valve(s) 24 outlet 24D is below the fluid level in the enclosure 22. A heat source such as a heating module 34 will be further explained with reference to FIG. 3 and may be disposed in the liquid 19 preferably proximate to or on the choke valve(s) 24. In FIG. 1A, a different example of the MGS 20 is shown wherein the sealed enclosure (22 in FIG. 1) is not used. In the example of FIG. 1 A, an inlet 20B of the MGS 20 (which performs the function of the degasser 26 in FIG. 1) is connected to the line 17 as in the previous example. A mud gas vent line 32 provides a discharge path for gas separated from the well fluid (19 in FIG. 2). A liquid outlet 20A of the MGS 20 is fluidly connected to the inlet of the mud transferPATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT pump 28. The mud transfer pump 28 may be operated to maintain the liquid level in the sealed enclosure 22 (or within the MGS 20 if arranged as shown in FIG. 1 A)

[0046] In a system according to the present disclosure, metals used to form certain of the components, such as the BOP 14 housing (ram block), flow line, choke valves, among other components, may conform to American Petroleum Institute (API) grade CC. Non- metallic materials, such as elastomers used in seal elements, may conform to API grades FF or HH.

[0047] In some example implementations, the system components shown in FIG. 1 may be transported to a well construction and / or workover unit and connected to the well construction and / or workover unit’s mud circulation and handling system when it is determined that formations to be drilled or having been penetrated by a well may have carbon dioxide. Connections may be made as shown in FIG. 1, the system 10 may be operated as needed, and after carbon dioxide well construction and / or workover operations are concluded, the system 10 may be removed and transported elsewhere. In this way, it is not necessary to have one such system 10 available at all times on any particular well construction and / or workover unit; if it is determined that on a particular well part of the well construction and / or workover operation is unlikely to encounter carbon dioxide in the well fluid or “mud.”

[0048] An example implementation of the system shown in FIG. 1 connected within a so- called “riserless” well drilling apparatus is shown schematically in FIG. 2. In the example in FIG. 2, the BOP 14 may be coupled to the flange 21A of a surface casing 21, which extends into a subsurface well (not shown) below the water bottom (not shown). A marine BOP stack 42 may be coupled to the BOP 14. In the absence of the system 10 in noncarbon dioxide well construction and / or workover, the marine BOP stack 42 would otherwise be connected to the flange 21 A. In the present example implementation, an annular control device 44 may be coupled to the top of the marine BOP stack 42. A rotating control device (RCD) 46 may be coupled to the annular control device 44 so that well construction and / or workover fluid (in the present example, drilling mud) leaving the well (not shown) is constrained to flow through a mud return hose 48, subsequently to bePATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT returned to surface (e.g., to the drilling unit on the water surface) by a mud lift pump 50. Drilling mud returned in such manner is discharged to a shale shaker line 43 for subsequent solids removal and cleaning for reuse. The apparatus shown in FIG. 2 is not limited to use in well drilling operations, but may be used in any other type of well construction and / or workover operations.

[0049] As will be appreciated by those skilled in the art, well construction and / or workover fluid (in this example, drilling mud) is moved from a storage tank or container (not shown) by one or more mud pumps 64 to be pumped through a top drive 40 and into a tool or pipe string 41, e.g., a drill string that extends into a well (not shown) below the water bottom (not shown) for various drilling operations. In some implementations, a shut off valve 61 may be interposed along the fluid connection between the top drive 40 and the tool or pipe string 41 to enable isolating the mud pumps 64 during certain operations to be explained in more detail below with reference to FIG. 8. In some implementations, a temperature sensor 58 and pressure sensor 56 may measure such properties of the mud as it enters the top drive 40. As necessary, a heater 60 or chiller 62 may be operated to adjust the temperature of the fluid or mud on its path to the top drive 40 such that temperature limitations on the mud in the well may be maintained.

[0050] Correspondingly, temperature and pressure of the well fluid (e.g., drilling mud) being returned to surface may be measured by corresponding sensors 52, 54. Signals from the foregoing sensors 52, 54, 58, 60 may be communicated to a controller 66, which may control operation of the heater 60, chiller 62, mud pump 64 and mud lift pump 50 to maintain the various measured parameters within prescribed limits or ranges. Operation of the controller 66 may be automatic, or manual through a human machine interface (not shown).

[0051] FIG. 3 shows an example implementation of the MGS 20. In the present example implementation, the heating module 34 may be associated with or disposed within the MGS enclosure 22 to heat the liquid 19 and thereby the choke valve(s) 24, or may heat the choke valve(s) 24 directly. In this way, gas expansion, in particular carbon dioxide expansion- induced cooling of the choke valve(s) 24 may be mitigated so as to reduce the possibilityPATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT of freezing or plugging due to freezing mud. In some example implementations, the heating module 34 may comprise electrical resistance heating element(s) and may be operated by the controller (66 in FIG. 2) in response to temperature measurements made by a temperature sensor 35 disposed in the enclosure 22 and in contact with the liquid 19 or the choke valve(s) 24.

[0052] An example implementation of the choke valve(s) 24 that may be used in some implementations is shown schematically in FIG. 4A. In the present example implementation, the choke valve (24 in FIG. 2) may comprise a plurality of, e.g., three choke valves 24A, 24B, 24C connected in series between the conduit 17 and the outlet 24D within the enclosure (22 in FIG. 3). The choke valves 24A, 24B, 24C may be individually controllable as to the orifice size or any related flow control parameter so that for each choke valve 24A, 24B, 24C, a pressure drop, flow rate or temperature may be maintained so as to reduce the possibility of freezing by reason of carbon dioxide gas expansion as mud from the well (not shown; see FIG. 2) flows through the choke valves 24A, 24B, 24C. In some implementations, the choke valves 24A, 24B, 24C may each comprise an associated actuator 24A1, 24B1, 24C1 such as an electrically or hydraulically operated actuator, wherein each choke valve may have its opening individually controlled. In some implementations, the actuators 24A1, 24B1, 24C1 may be operated by the controller 66, either manually through a human / machine interface (not shown) and / or automatically in response to pressure and / or temperature measurements made by respective transducers 25A, 25B, 25C associated with each choke valve 24A1, 24B1, 24C1 and in signal communication with the controller 66. In some implementations, the controller 66 may automatically operate the choke valves 24A, 24B, 24C to maintain a selected pressure drop and / or temperature during well construction and / or workover operations such that choke valve(s) and / or well fluid freezing is avoided. In some embodiments, only one pressure / temperature transducer, e.g., at 25C may be used to enable the controller 66 to operate the choke valves 24A, 24B, 24C to maintain a selected total pressure drop or temperature drop, while operating the choke valves 24A, 24B, 24C to maintain a corresponding fraction, e.g., equal, of the total pressure drop across each choke valve, 24A, 24B, 24C.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT

[0053] In some implementations, and referring to FIG. 4B, the choke valves 124 A, 124B, 124C may be connected in parallel, and operated as explained with reference to FIG. 4A, using, for example, a respective electrical or hydraulic actuator 124A1, 124B1, 124C1. It will be appreciated that the flow range capacity of the choke valves 124 A, 124B, 124C shown in FIG. 4B will be different than those of the implementation shown in FIG. 4A because of the parallel connection. In some implementations, each of the choke valves 124A, 124B, 124C may comprise choke valves connected in series as shown in FIG. 4A, wherein choke valve 124A performs the primary flow control function, and choke valves 124B and 124C are provided for redundancy.

[0054] FIGS. 5A through 5D show various parts of the BOP (14 in FIG. 1) in which elastomer sealing element(s) may comprise heating elements, for example, electrical resistance heating elements, to prevent the elastomer from being cooled to below its glass transition temperature by reason of expansion of carbon dioxide. A cross section of a ram block 14D portion of the BOP 14 is shown in FIG. 5 A. A retainer 14C is disposed above the ram (not shown in FIG. 5 A) to retain it within the ram block 14D. An upper seal 14A may hydraulically close space between the ram block 14D and the retainer 14C. Such seal 14A is shown in plan view in FIG. 5C. A face seal 14B, such as an elastomer seal, may be disposed on the exterior surface of the ram (not shown) to engage any well construction and / or workover tool extending though the BOP so as to hydraulically close the well. Referring to FIG. 5D, the face seal 14C may comprise an electrical resistance heating element 14B2 disposed on an elastomer substrate 14B1, wherein the elastomer substate 14B1 may sealingly engage the exterior of the well construction and / or workover tool (see, e.g., 41 in FIG. 2), while the heating element 14B2 may be operated to keep the elastomer substrate 14B1 above the glass transition temperature as may be necessary.

[0055] In some implementations, the mud gas vent line (see 30 in FIG. 2) may have its ultimate outlet to the atmosphere. In order to minimize discharge of carbon dioxide to the atmosphere, and referring to FIG. 6, in some implementations, the vent line 32 (which originates at the degasser 26 in FIG. 1) may have fluidly coupled at its end a carbon capture unit 70 to extract carbon dioxide from the vented gas for handling, e.g., by pumping into a subsurface formation. Carbon dioxide scrubbed gas may be discharged to the atmospherePATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT or, e.g., to a flare though a mud gas vent line 72. As will be appreciated by those skilled in the art, combustible gas such as methane present in the carbon dioxide scrubbed gas may be burned at the end of a flare boom (not shown) or the like to avoid creating hazardous conditions by accumulation of combustible gas proximate the well construction and / or workover unit (not shown). Some possible technologies that could be used for the carbon capture unit are chemical absorbers such as amines, physical absorbers such as physical solvents, adsorption, or membrane separation. It may not be necessary to regenerate the carbon dioxide from the capturing material as part of the wellsite system (10 in FIG. 1) depending on the expected volume of carbon dioxide to be captured. The carbon capture unit 70 may include a carbon dioxide gas outlet 71, wherein carbon dioxide may be moved from the carbon capture unit 70 for disposal, e.g., without release to the atmosphere.

[0056] FIGS. 7A and 7B show an example implementation of a carbon dioxide soluble restraint in connection with a switch 74, whereby presence of carbon dioxide in the well fluid serves to close the switch 74. Closing the switch 74 may cause generation of a signal by the controller 66, whereupon an indication may be provided to the well construction and / or workover unit operator to actuate the system (10 in FIG. 1) to contain and circulate out carbon dioxide from the well fluid. In FIG. 7A, the switch 74 is open and is in tension toward the closed position by a spring 73 or other biasing device. The switch 74 is held open by a carbon dioxide soluble link 75. The switch 74 and the link 75 may be disposed proximate the bottom of the drill string 41 such that the link 75 may be exposed to well construction and / or workover fluid, e.g., drilling mud (19 in FIG. 1) returning to surface. In the event the returning well fluid includes any carbon dioxide, the link 75 will dissolve, causing the spring 73 to close the switch 74. The switch 74 may be connected to any form of communication circuitry, e.g., and without limitation measurement while drilling technology, wherein a signal of the switch 74 being closed may be communicated to the controller 66. In such event, the controller 66 may send a warning or other indication to the well construction and / or workover unit operator, or may actuate components of the system (10 in FIG. 1) to close the well hydraulically and circulate out the carbon dioxide without discharge to atmosphere.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT

[0057] FIGS. 8 A and 8B show another example implementation of a tool string conveyed device that can provide prompt indication of presence of carbon dioxide in the returning well fluid. In FIG. 8A, a shuttle valve 43 may be disposed on the exterior of the tool string 41 so as to cover flow ports 45 in hydraulic communication with the interior of the tool string 41 (wherein mud from the mud pump 64 in FIG. 2 moves under pressure). The shuttle valve 43 is in tension toward the open position by a spring or biasing device 47, but is held closed against the biasing force by a carbon dioxide soluble link 49. In the event carbon dioxide enters the returning well fluid, the link 49 will dissolve, enabling the spring 47 to open the shuttle valve 43. In such event, the flow ports become open to the well and measured pressure (using, e.g., transducer 56 in FIG. 1) will decrease rapidly. In such event, the controller (66 in FIG. 2) may cause the system (10 in FIG. 1) to operate automatically to contain and safely circulate out the carbon dioxide, or may provide the well construction and / or workover unit operator indication of the carbon dioxide influx so that the well construction and / or workover unit operator may control the system (10 in FIG. 1) manually for the same purpose.

[0058] For the various implementations shown in FIGS. 7A, 7B, 8A and 8B, examples of materials that may be used in accordance with the present disclosure, materials that my dissolve or disintegrate on contact with carbon dioxide for the switch or shuttle valve may include materials sold by Sentinel Subsea Limited, Unit 9 Greenrole Trading Estate, Howe Moss Drive, Dyce, Aberdeen | AB21 0GL United Kingdom that only react in the presence of a carbon dioxide. Additional, non-limiting examples of substances that can be used in accordance with the present disclosure include:Waxes and LipidsPharmaceutical Compounds: Certain pharmaceutical compounds can be dissolved in supercritical carbon dioxide for purposes of purification or formulation.Polymers: Some polymers can be processed or modified using supercritical carbon dioxide. Supercritical carbon dioxide, is known to be used, for example, to create porous materials or for blending additives into polymers.ChloridesPATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT

[0059] In some implementations, the carbon dioxide soluble sensing elements disclosed may be substituted by a carbon dioxide sensor (not shown). An example of such a sensor may be one sold under model number 17155304-Q Ventis PRO 4 / 5 by Industrial Scientific, 1 Life Way, Pittsburgh, PA 15205-7500. Such sensor may in signal communication with the controller (66 in FIG. 2), wherein the controller (66 in FIG. 2) may send a suitable indication or alarm signal to the drilling or workover unit operator as to the presence of carbon dioxide gas in the well.

[0060] Referring to FIG. 9, an example procedure for detecting and circulating out of a well an influx (“kick”) of fluid from open or hydraulically connected formations into the well will be explained. A kick may be detected using any known method. If a kick is detected, for purposes of the procedures described below, it may be assumed that the kick comprises carbon dioxide and conventional kick detection and circulation methods may be modified to address the presence of carbon dioxide. Upon kick detection, the well may be “shut in”, that is, hydraulically closed, and the influx removed from the well by suitable procedures as explained below.

[0061] First, stop pipe string rotation, e.g., stop operating the top drive (40 in FIG. 2) and place the uppermost tool joint in the pipe string at the “space out position.” Next, stop operating the mud pumps (64 in FIG. 2). Next, conduct a well fluid flow check. If there is indication of flow, shut in the well by closing the BOP (14 in FIG. 2) and adjust the BOP closing pressure if and as necessary. Next, open the choke line valve (e.g., 18 in FIG. 1), against a closed surface valve in the choke line. Close the (standpipe) valve, e.g., shown at 61 in FIG. 2 to isolate the mud pumps (64 in FIG. 2). If necessary, close pipe rams in the BOP stack (42 in FIG. 2) and equalize pressure prior to opening the BOP (14 in FIG. 2).

[0062] Circulating the kick out of the well using a supercritical circulation method according to the present disclosure comprises some or all of the following. When a suspected supercritical carbon dioxide kick is detected, a trapped supercritical method can be used to keep the carbon dioxide in its supercritical phase during circulation through the wellbore until a designated flow location is reached, in this case at the choke (24 in FIG. 2). The principle of such method is based on the fact that carbon dioxide is highly solublePATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT in drilling fluid, especially oil based well construction and / or workover fluid. The carbon dioxide influx will be dissolved in, and thereby “trapped’ in the well construction and / or workover fluid if the circulating pressure (CP) is greater than the bubble point pressure (BPP) for carbon dioxide. BPP is defined as the pressure at which dissolved carbon dioxide will boil out or bubble out as free gas from a solvent. The value of BPP is dependent on temperature of the drilling fluid as it moves through the well, concentration and size of the carbon dioxide kick, and the composition of the well construction and / or workover fluid. A procedural change in a method according to the present disclosure is the calculation of the BPP during operations and using a comparison of CP to BPP to drive well circulation actions.

[0063] An example procedure according to the present disclosure to maintain a supercritical phase of carbon dioxide until the influx or kick reaches the choke is described below.

[0064] After the well is shut in as explained above, record the shut in drill pipe pressure (SIDPP) and the shut in casing pressure (SICP). This is shown at 90 in FIG. 9.

[0065] Reset the stroke counters for the mud pumps (64 in FIG. 2). This is shown at 91 in FIG. 9.

[0066] Calculate the BPP for the specific kick, considering composition of the well construction and / or workover fluid being used, temperature of the well at the suspected kick depth and an estimated size of the kick from the various sensors, e.g., as shown in FIG. 2. This is shown at 92 in FIG. 2.

[0067] Begin to open the choke (24 in FIG. 2) slowly while starting the mud pumps (64 in FIG. 2) at the previously recorded rate. The method includes at this point monitoring shut in pressures and any gain in circulation system mud volume (“pit gain”) This is shown at 93 in FIG. 2.

[0068] Keep the mud pump operating rate constant throughout the present circulation process.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT

[0069] Adjust the choke (24 in FIG. 2) to maintain the CP greater than the BPP while maintaining constant bottom hole pressure. This is shown at 94 in FIG. 9.

[0070] If the circulating pressure is nearing the bubble point pressure, close, e.g., reduce the flow area of the choke (24 in FIG. 2). Then increase the mud pump rate to increase the drilling fluid pressure throughout the wellbore. Then open the choke (24 in FIG. 2), e.g., increase the flow area, once a suitable differential pressure between the CP and BPP is established, and continue circulation. This is shown at 95 in FIG. 9.

[0071] Once the carbon dioxide kick has been circulated in its supercritical phase through the wellbore, it will change phase once it reaches the choke (24 in FIG. 2). Bleed the supercritical carbon dioxide through the choke (24 in FIG. 2) to remove it from the well. This is shown at 96 in FIG. 9.

[0072] Once the kick is circulated out, stop the mud pumps (64 in FIG. 2) and ensure the shut in drill pipe pressure (SIDPP) and shut in casing pressure (SICP) are the same. This is shown at 97 in FIG. 2. Once such verification is completed, the BOP (14 in FIG. 2) may be opened, and well construction and / or workover operations may be resumed, as shown at 98 in FIG. 2. In a practical implementation, a trip tank may be lined up and circulation may be performed across the BOP prior to opening to check for any system leaks.

[0073] A system and kick detection / circulation method according to the present disclosure may safely, environmentally responsibly and efficiently enable well construction and / or workover operations to continue in the presence of subsurface formation fluids containing carbon dioxide.

[0074] In light of the principles and example implementations described and illustrated herein, it will be recognized that the example implementations can be modified in arrangement and detail without departing from such principles. The foregoing discussion has focused on specific implementations, but other configurations are also contemplated. In particular, even though expressions such as in “an implementation," or the like are used herein, these phrases are meant to generally reference implementation possibilities, and are not intended to limit the disclosure to particular implementation configurations. As used herein, these terms may reference the same or different implementations that arePATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT combinable into other implementations. As a rule, any implementation referenced herein is freely combinable with any one or more of the other implementations referenced herein, and any number of features of different implementations are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCTCLAIMSWhat is claimed is:

1. A carbon dioxide handling well pressure control system, comprising: a well closure device arranged to close an annular space between a conduit disposed in a well and a well construction and / or workover tool disposed in the well, the well closure device having a fluid outlet disposed below a closure element in the well closure device; a mud gas separator; a conduit connecting the fluid outlet to at least one controllable orifice choke, an outlet of the at least one controllable orifice choke fluidly connected to the mud gas separator; and a pump having an inlet in fluid communication with a liquid outlet of the mud gas separator, the pump having an outlet in fluid communication with mud solids removal devices disposed on or proximate a well construction and / or workover unit.

2. The system of claim 1 wherein a gas outlet of the mud gas separator is in fluid communication with a carbon dioxide capture device.

3. The system of claim 2 wherein the carbon dioxide capture device comprises at least one of a chemical absorber, a physical absorber, an adsorber, or a membrane separator.

4. The system of claim 3 wherein the chemical absorber comprises amine.

5. The system of claim 3 wherein the physical absorber comprises a solvent.

6. The system of claim 1 further comprising an electrical resistance heating element disposed in an elastomer seal in the closure element.

7. The system of claim 1 wherein the controllable orifice choke comprises a plurality of controllable orifice chokes connected in series or parallel.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT8. The system of claim 7 wherein a pressure drop in each of the plurality of controllable orifice chokes is a predetermined fraction of a total pressure drop across the plurality of chokes.

9. The system of claim 7 wherein the predetermined fraction is chosen to limit a temperature drop across each of the plurality of chokes when carbon dioxide gas expands through each of the plurality of chokes.

10. The system of claim 1 wherein the well closure device is disposed between an upper end of a well casing and a blowout preventer stack.

11. The system of claim 10 wherein the well closure device is disposed at an upper end of a riser, the riser connected to an upper end of a well casing.

12. The system of claim 10 wherein the well closure element is disposed at an upper end of a well casing, the well casing extending upwardly above the bottom of a body of water and downwardly into a sub-bottom well.

13. The system of claim 1 wherein metal components of the system comprise carbon dioxide resistant metal.

14. The system of claim 13 wherein the carbon dioxide resistant metal conforms to American Petroleum Institute grade CC.

15. The system of claim 1 wherein elastomeric components of the system comprise carbon dioxide resistant material.

16. The system of claim 15 wherein the carbon dioxide resistant material conforms to at least one of American Petroleum Institute grade FF or HH.

17. The system of claim 1 wherein the mud gas separator and the mud pump are disposed in a sealed enclosure.

18. The system of claim 17 wherein the controllable orifice choke is submerged in liquid within the sealed enclosure.PATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT19. The system of claim 18 further comprising a heat source proximate the controllable orifice choke within the sealed enclosure.

20. The system of claim 20 wherein the heat source comprises an electrical resistance heating element.

21. The system of claim 1 wherein the controllable orifice choke is submerged in liquid in a container associated with the mud gas separator.

22. The system of claim 1 further comprising a heat source proximate the variable orifice choke.

23. The system of claim 19 wherein the heat source comprises an electrical resistance heating element.

24. The system of claim 1 wherein the variable orifice choke is disposed at an elevation below an elevation of the fluid outlet.

25. A method for circulating out a fluid influx containing carbon dioxide, comprising: detecting an influx of fluid into a well’ shutting a well closure device arranged to close an annular space between a well conduit and a well construction and / or workover tool disposed in the well, the well closure device having a fluid outlet disposed below a closure element in the well closure device and a conduit connecting the fluid outlet to at least one controllable orifice choke; calculating a bubble point pressure for carbon dioxide in a well construction and / or workover fluid in the well; operating a pump and the controllable orifice choke to maintain a well construction and / or workover fluid pressure in the well above the bubble point pressure; and bleeding the influx through the controllable orifice choke into a mud gas separator.

26. The method of claim 25 wherein an outlet of the controllable orifice choke is disposed in a sealed enclosure, the sealed enclosure comprising a gas vent line in fluid communicationPATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT with a carbon capture unit arranged to remove carbon dioxide from gas leaving the sealed enclosure.

27. The method of claim 25 wherein an outlet of the controllable orifice choke is in fluid communication with a mud gas separator, a gas outlet of the mud gas separator in fluid communication with a carbon capture unit arranged to remove carbon dioxide from gas leaving the mud gas separator.

28. A method for controlling fluid pressure in a well during well construction and / or workover operations, comprising: coupling a carbon dioxide resistant well closure device in a well construction and / or workover apparatus between a well casing head and a well pressure control apparatus, the well closure device comprising a fluid outlet below a closure element in the well closure device; fluidly connecting an inlet of a carbon dioxide resistant mud gas separator to the fluid outlet; conducting well construction and / or workover operations using the carbon dioxide resistant well closure device and the carbon dioxide resistant mud gas separator; removing the carbon dioxide resistant well closure device and the carbon dioxide resistant mud gas separator from the well construction and / or workover apparatus under predetermined conditions; and resuming well construction and / or workover operations using the well construction and / or workover apparatus.

29. The method of claim 28 wherein the well pressure control apparatus comprises a blowout preventer stack.

30. The method of claim 28 wherein the carbon dioxide resistant mud gas separator and a mud transfer pump are disposed in a sealed enclosure.

31. The method of claim 28 further comprising connecting a carbon dioxide resistant, controllable orifice choke between the fluid outlet and an inlet to the carbon dioxidePATENT APPLICATIONATTY DOCKET NO. MD-24-02PCT resistant mud gas separator, and operating the carbon dioxide resistant, controllable orifice choke to limit a temperature drop to prevent ice formation.

32. The method of claim 28 further comprising operating a controllable orifice choke disposed between the fluid outlet and the carbon dioxide resistant mud gas separator to maintain a selected fluid pressure in the well.

33. The method of claim 32 further comprising operating the controllable orifice choke to maintain a temperature thereof above a predetermined temperature limit.

34. The method of claim 33 wherein the predetermined temperature limit is a freezing temperature of the fluid.

35. The method of claim 27 further comprising heating the controllable orifice choke to maintain a temperature thereof above a predetermined temperature.

36. The method of claim 34 wherein the heating comprises operating an electrical resistance heating element.

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