US20230250708A1

US20230250708A1 - Bell nipple with annular preventers and coolant injection

Info

Publication number: US20230250708A1
Application number: US17/650,476
Authority: US
Inventors: Ahmed Al-Mousa
Original assignee: Saudi Arabian Oil Co
Current assignee: Saudi Arabian Oil Co
Priority date: 2022-02-09
Filing date: 2022-02-09
Publication date: 2023-08-10

Abstract

A bell nipple assembly is attached to an upper end of a blowout preventer stack and has a central passageway fluidically connected to a central bore of the blowout preventer stack. The bell nipple assembly includes upper and lower nipple annular preventers. Closure of the nipple annular preventers forms a closed volume within the central passageway between the upper and lower nipple annular preventers. A coolant injection system selectively injects coolant through a coolant conduit positioned within the closed volume.

Description

TECHNICAL FIELD

This disclosure relates to wellbore operations, for example, operations performed while drilling a wellbore.

BACKGROUND

Hydrocarbons or other resources in subsurface reservoirs or locations below the Earth's surface can be produced to the surface by forming wellbores from the surface to the subsurface locations. A wellbore is drilled from a surface rig to the subsurface reservoir by a wellbore drilling assembly. During drilling, a drilling mud or other fluid is flowed from the surface into the wellbore through a drill string and is flowed to the surface out of the wellbore through an annulus formed between an outer surface of the drill string and the wellbore.
A well control event is an undesirable subsurface fluid or gas flow influx from the subsurface reservoirs into a wellbore. Well control events can happen during drilling, tripping, completion, or other well operations. The influx can be caused by pressure imbalances between formation fluids and wellbore fluids, such as drilling mud or cement. The likelihood of a well control event increases as the well gets deeper due to increased pressures in deep wells. Well control events can have severe environmental and financial ramifications. Various equipment, systems, and method have been developed for detecting and mitigating well control events.

SUMMARY

Certain aspects of the subject matter herein can be implemented as a system for drilling a wellbore into a subterranean zone. The system includes a drill string suspended from a drilling rig and a blow-out preventer stack comprising a central bore through which the drill string passes as the drill string is raised or lowered within the wellbore. The blow-out preventer stack further includes a plurality of preventers configured to selectively prevent a flow of fluids through the central bore. The system further includes a bell nipple assembly comprising a central passageway fluidically connected to the central bore and configured to receive the drill string. A a lower end of the bell nipple assembly is attached to an upper end of the blow-out preventer stack and an upper end of the bell nipple assembly is positioned below a rig floor of the drilling rig. The bell nipple assembly further includes a lower nipple annular preventer positioned above the lower end of the bell nipple assembly and configured to selectively prevent a flow of fluids from below the lower annular preventer through the central passageway, and an upper nipple annular preventer positioned above the lower nipple annular preventer and below the upper end of the bell nipple assembly and configured to selectively prevent a flow of fluid from above the lower annular preventer through the central passageway. Closure of the lower nipple annular preventer and of the upper nipple annular preventer forms a closed volume between the lower nipple annular preventer and the upper nipple annular preventer. The system further includes a coolant conduit positioned within the closed volume and a coolant injection system configured to selectively inject coolant into the coolant conduit within the closed volume.
An aspect combinable with any of the other aspects can include the following features. The closed volume can be an annular volume defined by a packing element of the upper nipple annular preventer, an exterior surface of the drill string, an inner wall of the central passageway, and a packing element of the lower nipple annular preventer.
An aspect combinable with any of the other aspects can include the following features. The coolant injection system can include a check valve for selectively allowing coolant to flow through the coolant conduit.
An aspect combinable with any of the other aspects can include the following features. The coolant tank can be external to the bell nipple assembly.
An aspect combinable with any of the other aspects can include the following features. The coolant tank can be a component of the bell nipple assembly.
An aspect combinable with any of the other aspects can include the following features. The system can be configured to close the upper nipple annular preventer and the lower nipple annular preventer simultaneously.
An aspect combinable with any of the other aspects can include the following features. The coolant injection system can be configured to inject the coolant into the closed volume after closure of the upper nipple annular preventer and of the lower nipple annular preventer.
An aspect combinable with any of the other aspects can include the following features. The system can be configured to close lower nipple annular preventer and upper nipple annular preventer in response to a detection of an indication of a partial or complete failure of one or more of the preventers of the blow-out preventer stack.
An aspect combinable with any of the other aspects can include the following features. The coolant conduit can be a helical coil.
An aspect combinable with any of the other aspects can include the following features. The inner diameter of the helical coil can be greater than the outside diameter of the drill string.
An aspect combinable with any of the other aspects can include the following features. The coolant can be liquid nitrogen.
An aspect combinable with any of the other aspects can include the following features. The coolant conduit can isolate the coolant from other fluids within the central passageway.
Certain aspects of the subject matter herein can be implemented as a method. The method includes drilling, with a drill string suspended from a drilling rig, a wellbore into a subterranean zone. The drilling rig can include a blow-out preventer stack comprising a central bore through which the drill string passes as the drill string is raised or lowered within the wellbore and a plurality of preventers configured to selectively prevent a flow of fluids through the central bore. The drilling rig can further include a bell nipple assembly including a central passageway fluidically connected to the central bore and configured to receive the drill string. A lower end of the bell nipple assembly is attached to an upper end of the blow-out preventer stack and an upper end of the bell nipple assembly is positioned below a rig floor of the drilling rig. The bell nipple assembly further includes a lower nipple annular preventer positioned above the lower end of the bell nipple assembly and configured to selectively prevent a flow of fluids from below the lower annular preventer through the central passageway and an upper nipple annular preventer positioned above the lower nipple annular preventer and below the upper end of the bell nipple assembly and configured to selectively prevent a flow of fluids from above the lower annular preventer through the central passageway. Closure of the lower nipple annular preventer and of the upper nipple annular preventer forms a closed volume between the lower nipple annular preventer and the upper nipple annular preventer. A coolant conduit is positioned within the closed volume. The method further includes closing the lower nipple annular preventer and the upper nipple annular preventer, and injecting, after the closing of the lower annular preventer and the upper annular preventer, coolant into the coolant conduit.
An aspect combinable with any of the other aspects can include the following features. The closed volume can be an annular volume defined by a packing element of the upper nipple annular preventer, an exterior surface of the drill string, an inner wall of the central passageway, and a packing element of the lower nipple annular preventer.
An aspect combinable with any of the other aspects can include the following features. The lower nipple annular preventer and the upper nipple annular preventer can be closed simultaneously.
An aspect combinable with any of the other aspects can include the following features. The closing the lower nipple annular preventer and the upper nipple annular preventer can be in response to a detection of an indication of a partial or complete failure of one or more of the preventers of the blow-out preventer stack.
An aspect combinable with any of the other aspects can include the following features. The coolant conduit can be a helical coil.
An aspect combinable with any of the other aspects can include the following features. The inner diameter of the helical coil can be greater than the outside diameter of the drill string.
An aspect combinable with any of the other aspects can include the following features. The coolant can be liquid nitrogen.
An aspect combinable with any of the other aspects can include the following features. The coolant conduit can isolates the coolant from other fluids within the central passageway.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustrations of a well system in accordance with an embodiment of the present disclosure.

FIGS. 2A, 2B, and 2C are schematic illustrations of a bell nipple assembly in operation in accordance with an embodiment of the present disclosure.

FIG. 3 is a schematic cross-section of a bell nipple assembly in accordance with an embodiment of the present disclosure.

FIG. 4 is a process flow diagram of a method of operating a well system in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

The details of one or more implementations of the subject matter of this specification are set forth in this detailed description, the accompanying drawings, and the claims. Other features, aspects, and advantages of the subject matter will become apparent from this detailed description, the claims, and the accompanying drawings.
In accordance with some embodiments of the present disclosure, a bell nipple assembly is attached to a blow-out preventer, configured with annular preventers that can act as backup preventers in the event of a full or partial failure of the preventers of the blow-out preventer. In addition, a coolant injection system is provide that can inject liquid nitrogen or other coolant into conduit positioned within a closed volume between the nipple annular preventers, thereby cooling the nipple assembly and its associated components. Such cooling can reduce the risk of fire or damage to the nipple assembly and its components. In some embodiments, the cooling can producing a frozen plug within the closed volume, thereby acting as a backup to further reduce fluid flow in the event of a well control event or other situations where such flow control is desirable.
FIG. 1 is an example of well system 100 in accordance with an embodiment of the present disclosure. As depicted, well system 100 includes a drilling rig 112 that is positioned on or above the earth's surface 104 (for example, a terranean surface or a sub-sea surface) and extends over and around a wellbore 102 that penetrates a subterranean formation 103 for the purpose of extracting hydrocarbons or other substances or for conducting other subsurface operations (such as fluid injection or geothermal heat recovery). The wellbore 102 may be drilled into the subterranean formation using any suitable drilling technique.
The illustrated wellbore 102 extends substantially vertically (that is, vertical as designed) away from the earth's surface 104. In alternative operating environments, all or portions of the wellbore 102 may be vertical, deviated at any suitable angle, horizontal, curved or both. The wellbore 102 may be a new wellbore, an existing wellbore, a straight wellbore, an extended reach wellbore, sidetracked wellbore, a multi-lateral wellbore, and other types of wellbores for drilling and completing one or more production zones. Casing 106 installed in wellbore 102 ensures integrity of the borehole and isolate formations adjacent to wellbore 102. Cement can fill the annulus between the casing 106 and wellbore 102. A drill string 108 or other wellbore tubular (such as a workover string or production string) can be lowered into the subterranean formation for a variety of purposes (for example, drilling, intervening, injecting or producing fluids from the wellbore, workover or treatment procedures, or otherwise) throughout the life of wellbore 102. In this illustrated example, the workover or drilling rig 112 comprises a derrick with the rig floor 120 through which the drill string 108 extends downward from the drilling rig into the wellbore 102.
Drill string 108 can comprise tubular pipe segments connected with tool joints and can include a drill bit 110 at its downhole end. The may comprise a motor driven winch and other associated equipment for extending the drill string 108 into the wellbore 102 to position the drill string at a selected depth. While the operating environment depicted in FIG. 1 refers to a drilling rig 112 for conveying the drill string 108 within a land-based wellbore 102, embodiments of the present invention can be used for drilling, workover, or completion rigs in onshore or offshore settings. For example, in some embodiments, workover rigs, wellbore servicing units (such as coiled tubing units), and the like may be used to lower a drill string or other wellbore tubular into the wellbore 102, in an on-shore or offshore setting.
As illustrated, drill string 108 extends through blowout preventer (BOP) stack 130, which can stop or reduce a flow of fluids from wellbore 102 during normal operations and/or in the event of a pressure kick, blowout, or other well control event or emergency. In the illustrated embodiment, BOP stack 130 has a central bore 132 in which an upper portion of drill string 108 is disposed. In the illustrated embodiment, BOP stack 130 includes two preventers 134 and 136, each of which can be, for example, a pipe ram preventer, a shear ram preventer, a blind ram preventer, or another suitable type of preventer. A pipe ram preventer can include, for example, a pair of horizontally opposed metal rams, each with a half-circle hole on the edge to mate with the other so as to form a hole, with the hole sized such that, when closed, the rams can fit around drill string 108, thereby closing BOP stack 130 and preventing further flow of fluids around drill string 108. A shear ram preventer can include, for example, a pair of rams with hardened tool steel blades designed to cut through a drill string segment. A blind ram preventer can include, for example, a pair of metal rams which can close to seal off the BOP stack if there is no drill string segment or other object within the stack (for example, if drill string 108 has been severed by a shear ram preventer). In some embodiments, BOP stack 130 can include additional or fewer preventers of one or more of the preceding types or other suitable types. In the illustrated embodiment, BOP stack 130 also includes an annular preventer 138 which can include, for example, a rubber packing element which can close around drill string 108, thus closing off the annulus between drill string 108 and the inner wall of central bore 132 (if drill string 108 is present in central bore 312), or close off central bore 132 if no drill string is present.
Well system 100 further includes a BOP control system 142 which can include sensors and other monitoring systems, processing, and input/output systems, and a pressure source configured to supply hydraulic pressure to the preventers 134, 136, and 138 both normal operational and emergency situations. BOP control system 142 can include a Koomey Unit with pumps and accumulator bottles to store hydraulic pressure. BOP stack 130 can also include various other preventers, spools, adapters, valves, and piping outlets (not shown) to permit, prevent, or regulate the circulation of wellbore fluids under pressure during normal operations and/or in the event of a well control incident or other situation or emergency.
In the illustrated embodiment, well system 100 further includes a bell nipple assembly 150 (which can also be referred to as a “flow nipple”). In the illustrated embodiment, a lower end 154 of bell nipple assembly 150 is attached to an upper end 140 of BOP stack 130 and an open upper end 156 of bell nipple assembly 150 is positioned below rig floor 120. A central passageway 152 of bell nipple assembly 150 is fluidically connected to central bore 132 of BOP stack 130. Central passageway 152 is configured to receive drill string 108 and, in operation, a drilling fluid is flowed down a central bore of drill string 108 and exits drill bit 110. The drilling fluid then flows upwards in the annulus between drill string 108 and casing 106. The drilling fluid flows upwards through BOP stack 130 and into bell nipple 150, and exits bell nipple 150 via flowline 170 into a fluid circulation system including a trip tank or other suitable container (not shown). A pump (not shown) can then return the drilling via return a Kelly hose or other suitable conveyance back to the central bore of drill string 108.
In the illustrated embodiment, bell nipple assembly 150 further includes a lower nipple annular preventer 160 and an upper nipple annular preventer 162. Lower nipple annular preventer 160 is positioned above the lower end 154 of the bell nipple assembly 150 and upper nipple annular preventer 162 is positioned above the lower nipple annular preventer 160 and below the upper end 156 of the bell nipple assembly 150. As shown in greater detail in FIGS. 2A and 2B, lower nipple annular preventer 160 and upper nipple annular preventer 162 can be configured to selectively prevent a flow of fluids through central passageway 152 or, if drill string 108 is present within central passageway 152, through the annular space between the exterior surface of drill string 108 and an inner wall of central passageway 152. Nipple annular preventers 160 and 162 can be selectively activated (closed) by hydraulic pressure from a nipple closure control system 164. In some embodiments, nipple closure control system 164 (which operates nipple annular preventers 160 and 162 of bell nipple assembly 150) is separate from BOP control system 142 (which operates preventers 134, 136, and 138 of BOP stack 130) and can have a separate control system, including in some embodiments separate sensors and other monitoring systems, processing, and input/output systems, and a separate pressure source or sources, such that a failure of BOP control system 142 and/or its associated monitoring and control systems will not affect operation of nipple closure control system 164. In some embodiments, nipple closure control system 164 can include a pressure tank with 1500 pounds per square inch (psi) or another suitable pressure.
As described in more detail in reference to FIGS. 2A and 2B, closure of the lower nipple annular preventer 160 and of the upper nipple annular preventer 162 forms a closed volume within the central passageway 152 between the lower nipple annular preventer 160 and the upper nipple annular preventer 162. If drill string 108 is present within central passageway 152, the closed volume formed by the closure is the annular volume between the exterior surface of drill string 108 and an inner wall of central passageway 152.
In some embodiments, in the event of a well control event, in addition to or instead of activating one or more of preventers 134, 136, and 138 of BOP stack 130, well system 100 can be configured to (automatically and/or upon command from an operator) activate (that is, to close) nipple annular preventers 160 and 162. Well system 100 can be configured to trigger such activation automatically (for example, by a computerize control system upon receipt by the control system of high pressure readings or other indications of a well control event) or manually by an operator. In some embodiments, activation by annular preventers 160 and 162 can be in response to an indication (received by a control system and/or an operator) that one or more of preventers 134, 136, and 138 of BOP stack 130 have failed or otherwise not operated properly or otherwise have not closed or sealed central bore 132 of BOP stack 130. Annular preventers 160 and 162 can thus act as back-up or additional protection from well control events. In some embodiments, system 100 is configured to close nipple annular preventers 160 and 162 simultaneously (that is, both preventers 160 and 162 are closed at the same time). Alternatively or in addition, in some embodiments, system 100 is configured to close nipple annular preventers 160 and 162 in sequence.
In the illustrated embodiment, well system 100 further includes a coolant injection system 180 configured to selectively flow liquid nitrogen or another suitable coolant into a coolant conduit positioned within the volume between nipple annular preventers 160 and 162. In the illustrated embodiment, injection system 180 includes an external coolant storage tank 182, compressor module 184, coolant flowline 186, check valve 188, and coolant conduit 190. In some embodiments, the coolant tank can be attached or be a component of bell nipple assembly 150. Compressor module 184 can include one or more compressors or pumps to maintain pressure within storage tank 182. In the event of a well control event, after closure of preventers 160 and 162 to form the closed volume between preventers 160 and 162, check valve 188 can be opened to allow pressurized coolant to flow from storage tank 182 into coolant conduit 190. The coolant conduit is positioned within central passage 152 above lower preventer 160 and below upper preventer 162 and can act as a heat exchanger, absorbing heat from fluids within the volume between nipple annular preventers 160 and 162. If the coolant is liquid nitrogen or another coolant with a sufficiently low temperature and having a sufficient heat absorption capacity, the absorption of heat can be sufficient to freeze a portion or all of the fluids in the closed volume, thereby forming a frozen plug to partially or completely block the flow of fluid. The plug can form an additional barrier to further partially or completely prevent the flow of fluids through bell nipple assembly 150, thus providing an additional barrier of protection from the well control event or other undesirable flow of fluids. In addition, by lowering the temperature of the bell nipple assembly, of the surrounding equipment, and of the fluids within, the cooling system can reduce the risk of fire or other undesirable conditions or effects.
FIGS. 2A, 2B, and 2C are schematic cross-sectional illustrations of a bell nipple assembly 150 of FIG. 1 in operation in accordance with an embodiment of the present disclosure. As shown in FIG. 2A, and described above in reference to FIG. 1 , bell nipple assembly 150 includes a central passageway 152 that is fluidically connected to a central bore of a BOP stack and that is configured to receive drill string 108. Drilling fluid can flow downhole through drill string 108 and then upwards into central passage 152 and exit bell nipple 150 via flowline 170. As also described in FIG. 1 , bell nipple assembly 150 further includes a lower nipple annular preventer 160 and an upper nipple annular preventer 162. Lower nipple annular preventer 160 includes lower packing element 202 and upper nipple annular preventer 160 includes upper packing element 204. Upon activation of the preventers, packing elements 202 and 204 are squeezed inwards due to hydraulic pressure from the pressure unit. Bell nipple assembly 150 further includes coolant injection system 180 to inject liquid nitrogen or another suitable coolant (selectively via check valve 188 from coolant flowline 186) into coolant conduit 190 positioned within central passage 152. Coolant conduit 190 in the illustrated embodiment is a hollow sealed tube through which coolant can flow, with the coolant being isolated from the other fluids in central passageway 152. That is, the coolant flowing through coolant injection system 180 and through coolant conduit 190 does not directly contact or mix with the drilling fluid (or other fluid within central passage 152 external to coolant conduit 190).
In the illustrated embodiment, coolant flowline 186 attaches to an opening that extends through the wall of nipple assembly 150 at a point between preventers 160 and 162 and is fluidically connected to coolant conduit 190 that is within central passage 152. In the illustrated embodiment, coolant conduit 190 is in the shape of a helical coil and is positioned within central passageway 152 between preventers 160 and 162. As shown in the cross section A-A′ illustrated schematically in FIG. 3 , the outer perimeter of the coil of coolant conduit 190 in the illustrated embodiment touches or is proximate to inner wall surface 232 of the wall of the nipple assembly and the inner diameter 302 (shown in FIG. 3 ) of the coil is greater than the outside diameter 304 (shown in FIG. 3 ) of drill string 108, such that drill string 108 can travel up and down within central passage 152 without contact with or friction from coolant conduit 190. In some embodiments, instead of as a separate component positioned within central passageway 152, the coolant conduit can be partially or completely enclosed within the wall of the nipple assembly. In the illustrated embodiment, the vertical extent of coolant conduit 190 (i.e., the vertical length of the coil) within central passage 152 is enclosed entirely within the space above lower preventer 160 and below upper preventer 162. (That is, within central passage 152, no segment or portion of coolant conduit 190 extends below lower preventer 160 or above upper preventer 162.) In some embodiments, coolant conduit 190 can have additional or different configurations.
FIG. 2B shows bell nipple assembly 150 wherein preventers 160 and 162 have been activated, thereby forming a closed volume 230. In the illustrated embodiment, drill string 108 is present within central passageway 152, and thus the closed volume 230 is the annular space defined by upper packing element 204, the exterior surface 234 of drill string 108, inner wall surface 232, and lower packing element 202. If drilling string 208 were not present, the closed volume would be defined by upper packing element 202, the inner wall surface 232, and lower packing element 202. So activated with the packing elements sealed or substantially sealed together or around drill string 108, a substantially stationary (non-flowing) volume of drilling or other fluid is held within closed volume 230.
As shown in FIG. 2C, check valve 188 has been opened to allow coolant 220 to flow into coolant conduit 190, thereby cooling the fluid within closed volume 230 outside of coolant conduit 190 via conductive heat transfer. Because as shown in FIG. 2C the preventers 160 and 162 are closed, the cooling is applied to the substantially stationary (non-flowing) volume of fluid captured within closed volume 230. In the illustrated embodiment, coolant 220 is liquid nitrogen and has been maintained within the closed volume for a sufficient time period to freeze the fluid within closed volume 230, thereby forming a frozen plug 250. Such plug can act to further block (partially or completely) flow of fluid (for example, caused by incomplete sealing of the packing elements 202 and 204 of preventers 160 and 162) through closed volume 230. In this way, coolant injection system 180 can act as backup or additional flow control system. If a drill string is present within closed volume 230, in addition to within the annular space between the drill string and the inner wall of the central passageway, such a plug can also form within the drill string itself.
FIG. 4 is a process flow diagram of a method 400 of operating a well system in accordance with an embodiment of the present disclosure. The method begins at step 402 in which a wellbore is drilled into a subterranean zone using a drill string suspended from a drilling rig. As described above in reference to FIG. 1 , the drilling rig can include a blow-out preventer stack with central bore and a plurality of preventers, and a bell nipple assembly that includes lower and upper nipple annular preventers. As further described above, the drilling rig also includes a cooling system with a coolant conduit to lower the temperature of fluids between the lower and upper nipple annular preventers.
Proceeding to step 404, a well control event is detected. In response to the well control event, one or more of the preventer blow-out preventer stack can be activated. Further in response to the well control event, and/or in response to an indication that the blow-out preventer stack preventers have partially or completely failed, then, at step 406, the lower nipple annular preventer and the upper nipple annular preventer of the bell nipple are closed, thereby forming a closed annular volume between the lower annular preventer and the upper annular preventer. Proceeding to step 408, coolant is injected into the coolant conduit, thereby cooling the fluid within the closed volume.
A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, example operations, methods, or processes described herein may include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims.

Claims

1. A system for drilling a wellbore into a subterranean zone, comprising:

a drill string suspended from a drilling rig;

a blow-out preventer stack comprising a central bore through which the drill string passes as the drill string is raised or lowered within the wellbore, and further comprising a plurality of preventers configured to selectively prevent a flow of fluids through the central bore;

a bell nipple assembly comprising a central passageway fluidically connected to the central bore and configured to receive the drill string, wherein a lower end of the bell nipple assembly is attached to an upper end of the blow-out preventer stack and an upper end of the bell nipple assembly is positioned below a rig floor of the drilling rig, and wherein the bell nipple assembly further comprises:

a lower nipple annular preventer positioned above the lower end of the bell nipple assembly and configured to selectively prevent a flow of fluids from below the lower nipple annular preventer through the central passageway; and

an upper nipple annular preventer positioned above the lower nipple annular preventer and below the upper end of the bell nipple assembly and configured to selectively prevent a flow of fluid from above the lower nipple annular preventer through the central passageway, wherein a closure of the lower nipple annular preventer and of the upper nipple annular preventer forms a closed volume between the lower nipple annular preventer and the upper nipple annular preventer;

a coolant conduit positioned within the closed volume; and

a coolant injection system configured to selectively inject coolant into the coolant conduit within the closed volume.

2. The system of claim 1, wherein the closed volume comprises an annular volume defined by a packing element of the upper nipple annular preventer, an exterior surface of the drill string, an inner wall of the central passageway, and a packing element of the lower nipple annular preventer.

3. The system of claim 1, wherein the coolant injection system comprises a check valve for selectively allowing coolant to flow through the coolant conduit.

4. The system of claim 1, further comprising a coolant tank that is external to the bell nipple assembly.

5. The system of claim 1, further comprising a coolant tank that is a component of the bell nipple assembly.

6. The system of claim 1, wherein the system is configured to close the upper nipple annular preventer and the lower nipple annular preventer simultaneously.

7. The system of claim 1, wherein the coolant injection system is configured to inject the coolant into the closed volume after closure of the upper nipple annular preventer and of the lower nipple annular preventer.

8. The system of claim 1, wherein the system is configured to close the lower nipple annular preventer and the upper nipple annular preventer in response to a detection of an indication of a partial or complete failure of one or more of the preventers of the blow-out preventer stack.

9. The system of claim 1, wherein the coolant conduit is a helical coil.

10. The system of claim 9, wherein an inner diameter of the helical coil is greater than an outside diameter of the drill string.

11. The system of claim 1, wherein the coolant is liquid nitrogen.

12. The system of claim 1, wherein the coolant conduit isolates the coolant from other fluids within the central passageway.

13. A method, comprising:

drilling, with a drill string suspended from a drilling rig, a wellbore into a subterranean zone, the drilling rig comprising:

a lower nipple annular preventer positioned above the lower end of the bell nipple assembly and configured to selectively prevent a flow of fluids from below the lower nipple annular preventer through the central passageway;

an upper nipple annular preventer positioned above the lower nipple annular preventer and below the upper end of the bell nipple assembly and configured to selectively prevent a flow of fluids from above the lower nipple annular preventer through the central passageway, wherein a closure of the lower nipple annular preventer and of the upper nipple annular preventer forms a closed volume between the lower nipple annular preventer and the upper nipple annular preventer; and

a coolant conduit positioned within the closed volume;

closing the lower nipple annular preventer and the upper nipple annular preventer; and

injecting, after the closing of the lower nipple annular preventer and the upper nipple annular preventer, coolant into the coolant conduit.

14. The method of claim 13, wherein the closed volume comprises an annular volume defined by a packing element of the upper nipple annular preventer, an exterior surface of the drill string, an inner wall of the central passageway, and a packing element of the lower nipple annular preventer.

15. The method of claim 13, wherein the lower nipple annular preventer and the upper nipple annular preventer are closed simultaneously.

16. The method of claim 13, the closing the lower nipple annular preventer and the upper nipple annular preventer is in response to a detection of an indication of a partial or complete failure of one or more of the preventers of the blow-out preventer stack.

17. The method of claim 13, wherein the coolant conduit is a helical coil.

18. The method of claim 13, wherein an inner diameter of the helical coil is greater than an outside diameter of the drill string.

19. The method of claim 13, wherein the coolant is liquid nitrogen.

20. The method of claim 13, wherein the coolant conduit isolates the coolant from other fluids within the central passageway.