EP2726699B1

EP2726699B1 - Blowout preventer seal assembly and method of using same

Info

Publication number: EP2726699B1
Application number: EP12727727.5A
Authority: EP
Inventors: Perry Lee Mcclanahan; James Allen DOUTY; Richard M. Ward
Original assignee: National Oilwell Varco LP
Current assignee: National Oilwell Varco LP
Priority date: 2011-06-29
Filing date: 2012-06-06
Publication date: 2015-07-15
Anticipated expiration: 2032-06-06
Also published as: CA2840439A1; WO2013002971A3; US20140110611A1; EP2726699A2; WO2013002971A2

Description

BACKGROUND

This disclosure relates generally to techniques for performing wellsite operations. More specifically, this disclosure relates to techniques for preventing blowouts involving, for example, shearing a tubular and/or sealing a wellbore.
Oilfield operations may be performed to locate and gather valuable downhole fluids. Oil rigs are positionable at wellsites, and downhole tools, such as drilling tools, are deployed into the ground to reach subsurface reservoirs. Once the downhole tools form a wellbore to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Downhole tubular devices may be positioned in the wellbore to enable the passage of subsurface fluids to the surface.
Leakage of subsurface fluids may pose an environmental threat if released from the wellbore. Equipment, such as blowout preventers (BOPs), may be positioned about the wellbore to form a seal about a tubular therein to prevent leakage of fluid as the fluid is brought to the surface. BOPs may have selectively actuatable rams or ram bonnets, such as pipe rams or shear rams, that may be activated to sever a tubular in a wellbore. Some examples of BOPs for severing tubulars are provided in U.S. Patent/Application Nos. 20110000670 ; 7,814,979 ; and 7,367,396 . Seals may optionally be provided in BOPs. Examples of seals are provided in US Patent/Application Nos. 13/018217 , 2012/0012339 , 2012/0012340 , 2010/243926 , and 7967299 . Despite the development of techniques for addressing blowouts, there remains a need to provide techniques for shearing a tubular and/or sealing a wellbore.

SUMMARY

In at least one aspect, the disclosure relates to a shear sealing system of a blowout preventer of a wellbore. The wellbore has a tubular therein and the blowout preventer includes a housing having a bore and a guideway therethrough. The tubular is positionable in the bore. The shear sealing system includes at least one carriage slidably positionable in the guideway of the blowout preventer, at least one blade and at least one seal. The blade is carried by the carriage and movable thereby between a retracted position and an extended position. The blade is engageable with the tubular when in the extended position. The seal forming a seal about the tubular and with the blade when the blade is in the extended position
The blade may include an upper blade and a lower blade and the seal may include an upper seal and a lower seal. The upper blade, the lower blade, the upper seal and the lower seal may be placed in sealing engagement. The seal may be positionable in the housing. The seal may form a metal to metal seal with the blade. The seal may be a tubular member having an outer diameter positionable along an inner diameter of the bore. The seal may have a bottom surface positionable along an inner diameter of the guideway. The bottom surface may be engageable with a top surface of the blade when the blade moves to the extended position. The seal may include at least one seal collar, at least one coil spring, and/or at least one elastor seal.
The carriage may include a base having a blade pocket for receiving the blade. The base may have spars extending from a front end thereof defining a seal pocket for receiving the seal. The carriage may include a plurality of carriages and the blade may include a plurality of blades. Each of the carriages may have a blade pocket for receivingly supporting a corresponding one of the seals. The seal may include an elastomeric material disposable about each of the carriages. The carriages may include a base having a seal pocket shaped to receivingly and sealingly engage the blades carried by the carriages. The seal pocket may be defined along a top and side surfaces of the base.
In another aspect, the disclosure relates to a blowout preventer positionable about a wellbore. The wellbore has a tubular therein. The blowout preventer may include a housing having a bore and a guideway therethrough (with the tubular positionable in the bore), and a shear sealing system. The carriage may include upper and lower carriages, the blade may include upper and lower blades and the seal may include upper and lower seals. The upper seals may be positionable in the housing above the upper blades in sealing engagement therewith, and the lower seals may be positionable in the housing below the lower blades in sealing engagement therewith. The upper seals may be positionable about the upper blades of the upper carriage and the lower seals may be positionable about the lower blade of the lower carriage. The upper seals may be sealingly engageable with the lower blade and the lower seals sealingly engageable with the upper blades. The seal may form a metal to metal seal with the blade. The seal may include an elastomeric material carried by the carriage and sealable with the blade. The housing may have at least one receptacle for receiving the seal.
In another aspect, the disclosure relates to a method of forming a seal about a tubular of a wellbore. The method involves providing a blowout preventer including a housing having a bore and a guideway therethrough (the tubular positionable in the bore) and a shear sealing system including at least one carriage (at least one blade carried by the carriage and a seal). The method also involves engaging the tubular with the blade by slidably positioning the carriage in the guideway of the blowout preventer and moving the blade between a retracted position and an extended position, and forming a seal about the tubular and between the seal and the blade when the blade is in the extended position
The engaging may involve shearing the tubular, and the shearing may include piercing, cutting, raking, shaving, and/or severing. The blade may include an upper blade and a lower blade, and the seal an upper seal and a lower seal. The forming may involve forming a seal between the upper blade, the lower blade, the upper seal and the lower seal. The forming may involve sealingly engaging the upper blade with the lower seal and sealingly engaging the lower blade with the upper seal, and/or sealing engaging the upper blade with the lower seal and the lower blade with the upper seal.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features and advantages of the present disclosure can be understood in detail, a more particular description of the subject matter, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only example embodiments of the subject matter and are, therefore, not to be considered limiting of its scope. The figures are not necessarily to scale and certain features, and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

FIG. 1 shows a schematic view of an offshore wellsite provided with a blowout preventer (BOP) having a shear sealing system for shearing a tubular and sealing a wellbore.
FIGS. 2A-2B show schematic side and top views, respectively, partially in cross-section, of a BOP having a shear sealing system in a retracted position.
FIG. 2C is a schematic side view, partially in cross-section, of a BOP having a shear sealing system in an extended position.
FIGS. 3A-3B are horizontal and vertical cross-sectional views, respectively, of a BOP having a shear sealing system therein.
FIG. 3C is a schematic view depicting an end view, partially in cross-section, of the BOP of FIG. 3B.
FIGS. 4A-4C show perspective views of the shear sealing system of Figures 3A-3C having a pair of carriages in a retracted, partially extended, and fully extended position about a seal assembly.
FIGS. 5A-5C depict side, top and perspective views, respectively, of an alternate seal assembly.
FIG. 5D depicts a perspective view of a portion of the alternate seal assembly of Figure 5B.
FIG. 6 is a flow chart depicting a method of forming a sealing about a tubular of a wellbore.

DETAILED DESCRIPTION

The description that follows includes exemplary apparatus, methods, techniques, and/or instruction sequences that embody techniques of the subject matter. However, it is understood that the described embodiments may be practiced without these specific details.
Blowout preventers (BOPs) may be positioned about a tubular and provided with devices for shearing a tubular and/or sealing a wellbore. Shearing may involve piercing, cutting, raking, shaving, severing or otherwise penetrating at least a portion of the tubular. In some cases, such shearing involves advancing blades of the BOP into the tubular to break the tubular into two pieces. In some cases, such sealing may involve creating a seal about the severed tubular to prevent fluid from passing from the tubular. Such seal may be positioned about the blades used to shear the tubular. Tubulars may be, for example, pipes, certain downhole tools, casings, drill pipe, liner, coiled tubing, production tubing, wireline, slickline, or other tubular members positioned in the wellbore and associated components, such as drill collars, tool joints, drill bits, logging tools, packers, and the like.
Such shearing and/or sealing devices may provide a metal-to-metal and/or bi-directional differential pressure barrier against, for example, extreme conditions, such as low/high pressure hydrostatic and gas media with an effect temperature range of from about -30 F (-34.40 C) through about 400 F (204.44 C) or more. These devices may be intended to provide one or more of the following, among others: reduced operational force, reduced failure, reduced wear, efficient part replacement, modular components, enhanced sealing, efficient shearing, metal-to-metal sealing, incorporation into (or use with) existing equipment and less maintenance time for part replacement, operability at extreme conditions (e.g., extreme temperatures and pressures), etc.
Figure 1 depicts an offshore wellsite 100 having a subsea system 104 and a surface system 102. The surface system 102 may be used to facilitate the oilfield operations at the offshore wellsite 100. The surface system 102 may include a rig 105, a platform 106 (or vessel) and a controller 108.
The subsea system 104 includes a conduit 110 extending from the platform 106 to a sea floor 112. The subsea system further includes a wellhead 114 with a tubular 116 extending into a wellbore 118, a BOP 120 and a controller 108. The BOP 120 has a shear sealing system 124 for shearing the tubular 116 and sealing the wellbore, as will be described further herein.
The surface system 102 and subsea system 104 may be provided with one or more controllers 108 located at various locations to control the surface system 102 and/or the subsea system 104. Communication links 126 may be provided for communication between the controllers 108 and various parts of the wellsite 100.
Although the BOP 120 is described herein as being used in subsea operations, it will be appreciated that the wellsite 100 may be land or water based, and the BOP 120 and/or shear sealing system 124 may be used in any wellsite environment.
Figures 2A-2C depict the BOP 120 in greater detail. Figures 2A and 2B show the BOP 120 in the retracted position before actuation. Figure 2C shows the BOP 120 in the extended position after actuation. The BOP 120 may be similar to, for example, the BOP described in U.S. Patent/Application Nos. 20110000670 ; 7,814,979 ; and 7,367,396 .
As shown in FIGS. 2A-2C, the BOP 120 may have a body 212 with a bore 214 extending therethrough. The tubular 116 may pass through the bore 214. The body 212 may have a lower flange 216 and an upper flange 218 for connecting the BOP 120 to other equipment about the wellsite, such as the wellhead 114 (Fig. 1). The BOP 120 may have the one or more actuators 228 for actuating the shear sealing system 124 therein, for example, in order to shear the tubular 116 and sealing the wellbore.
Each of the actuators 228 may move a piston 230 within a cylinder 232 in order to move a rod 234. Each rod 234 may couple to a carriage 240a,b of the shear sealing system 124. Each of the carriages 240a,b carries a blade 242a,b. Thus, the actuators 228 may move the blades 242a,b toward and away from the bore 214 in order to shear the tubular 116 within the bore 214. The actuators 228 may actuate the blades 242a,b in response to direct control from the controller(s) 108 (Fig. 1), an operator, and/or a condition, such as a pressure surge, in the wellbore 118 (as shown in Figure 1). As shown in Figures 2A-2C, the actuators 228 may be hydraulically operated and driven by a hydraulic system (not shown), although any suitable means for actuating the shear sealing system 124 may be used, such as pneumatic, electric, and the like.
One or more ram guideways (or guides) 220 and 222 may guide each of the carriages 240a,b within the BOP 120 as the actuator 228 moves the blades 242a,b. The ram guideways 220 and 222 may extend outwardly from opposite sides of the bore 214. Figure 2B shows a top view of the BOP 120. The carriages 240a,b are shown holding the blades 242a,b in an unactuated (or retracted) position within the ram guideways 220 and 222.
The blades 242a,b of carriages 240a,b may be positioned to pass one another within the bore 214 while shearing the tubular 116. As shown, the pair of blades 242a,b includes an upper cutting blade 242a on the carriage 240a and a lower cutting blade 242b on the carriage 240b. The blades 242a,b may be movably positioned so that the upper blade 242a passes some distance above the blade 242b when shearing the tubular 116.
As shown in Figure 2C, the shearing action of cutting blades 242a,b may pierce, rake, cut, shave, sever, and/or shear the tubular 116 such that the tubular is compressed or separated into upper portion 116a and lower portion 116b. After the tubular 116 is severed, the lower portion of the tubular 116b may drop into the wellbore 118 (as shown in Figure 1) below the BOP 120. In the closed position, a seal assembly 243 of the shear sealing system 124 positioned in the BOP 120 may form a seal with the blades 242a,b.
Figures 3A-3C depict various views of a BOP 320 having a shear sealing system 324 usable for shearing the tubular 116 and/or sealing the wellbore (see, e.g., Figure 1). Figures 3A and 3B are cross-sectional views of the BOP 320 having a bore 314 therethrough for receiving the tubular 116 (see, e.g., Figure 1). The shear sealing system 324 includes a carriage assembly 325 movably positionable in a guideway 321, and a seal assembly 330 positioned in receptacles 331a,b in the BOP 320.
The guideway 321 extends into the bore 314 to enable movement of the carriage assembly 325 therein for sealing engagement with seal assembly 330 and the tubular 116. As shown in Figure 3A, the carriage assembly 325 is in a retracted (or disengaged) position. As shown in Figure 3B, the carriage assembly 325 is advanced to an extended (or engaged) position. The shear sealing system 324 includes a pair of carriages 326a,b, and a pair of blades (or blade inserts) 328a,b. Each of the carriages 326a,b carries a blade 328a,b such that the blades 328a,b may be advanced to pass through the tubular 116.
The guideway 321 of the BOP 320 may be shaped to slidingly receive the carriages 326a,b for back and forth movement therein. The carriages 326a,b may be selectively extended and retracted in the guideway 321 such that the blades 328a,b carried by the carriages 326a,b may selectively engage the tubular 116 in the bore 314. The carriages 326a,b may be provided with rails 337 for slidable movement within the guideway 321. The rails 337 (and other components of the shear seal assembly 324) may be replaceable.
The components of the shear seal assembly 324 may be modular. For example, each blade 328a,b may be inserted into its corresponding carriage 326a,b and secured therein by conventional means, such as bolts 329. Each blade 328a,b may be positioned in the carriage 326a,b at an end near the bore 314 for engagement with the tubular 116. The blades 328a,b may be the same or different blades, such as those described in U.S. Patent/Application Nos. 20110000670 ; 7,814,979 ; and 7,367,396 . The blades 328a,b may have protrusions (or points) 333 to first pierce and then shear the tubular 116 during a shearing operation.
During operation, the carriages 326a,b may be positioned in the BOP 320 and advanced such that the blade 328a passes a distance below the blade 328b to provide shearing engagement with the tubular 116 as shown in the extended position of Figure 3B. An actuator (not shown) may be used to activate the shear sealing system 324 to move the carriages and the blades in a similar manner as shown in Figures 2A-2C. As the carriages 326a,b move to the extended position of Figure 3B, the blades 328a,b may also engage and form a seal with the seal assembly 330.
The seal assembly 330 may be positioned in the receptacles 331a,b along the bore 314 and the guideway 321. The seal assembly 330 includes seal collars 332a,b, coil springs 334a,b, and elastor seals 336a,b as shown in Figure 3C. In Figure 3C, an end view of the carriage assembly 325 is depicted adjacent a cross-sectional view of the seal assembly 330 and BOP 320. The seal assembly 330 (and/or its components) may be made of metal or non-elastomeric material to prevent deterioration over time and/or under harsh conditions.
The upper receptacle 331a has the corresponding upper seal collar 332a, coil spring 334a and elastor seal 336a therein. The lower receptacle 331b has the corresponding lower seal collar 332b, coil spring 334b and elastor seal 336b therein. The coil springs 334a,b may be used to support the seal collar 332a,b against the carriages 326a,b (see, e.g., FIG. 3B), particularly in high pressure conditions. Additional seals, such as the elastor seals 336a,b, may be provided for additional sealing support about the seal collar 332. Additional seals may also be positioned about the shear sealing system to further prevent leakage.
The upper and lower seal collars 332a,b, coil springs 334a,b, and elastor seals 336a,b may be used to cooperatively seal with the blades 328a,b to provide a seal about the bore 314. Once the carriages 326a,b are advanced and the blades 328a,b engage the seal collars 332a,b as shown in Figure 3B, a metal-to-metal seal is formed therebetween. In this position, the seal collars 332a,b are perpendicular to and in sealing engagement with a seal surface 338a,b of the blades 328a,b. The coil springs 334a,b may be used to provide compressive forces to maintain a constant interface between the seal collars 332a,b and seal surfaces 338a,b, for example, to provide low pressure differential seal performance.
Figures 4A-4C depict the shear sealing system 324 in greater detail and in a retracted, partially extended and extended position, respectively. For descriptive purposes, the shear sealing system 324 is depicted outside of the BOP 320 in Figures 4A-4C. As shown Figure 4A, the carriage 326b is in an inverted and opposing position relative to the carriage 326a. The upper seal collar 332a, coil spring 334a and elastor seal 336a are also inverted from the lower seal collar 332b, coil spring 334b and elastor seal 336b therein.
As further depicted in Figures 4A and 4B, each of the carriages 326a,b includes a base 440a,b and a rod 442a,b. The rods 442a,b may be coupled to an actuator (not shown), such as the actuator 228 depicted in Figure 2. The rods 442a,b are also coupled to the bases 440a,b for selective extension and retraction thereof.
The bases 440a,b are shaped for sliding engagement within the guideway 321 of BOP 320 (see, e.g., Figures 3A-3C). The bases 440a,b are also shaped such that they may pass adjacent to each other as shown in Figures 4B-4C and to facilitate sealing with the seal assembly 330. The base 440 includes a pair of side portions 444 with a rear portion 446 therebetween. The base 440 also defines a blade pocket 447 for receiving and supporting a blade 328a,b. The blade pocket 447 may be configured to support the blades 328a,b such that loads are applied to the base 440 to support the blades during operation. The rear portion 446 may be connected to the rod 442a,b and provide a platform for receiving the blades 328a,b.
The pair of side portions 444 may extend a distance beyond the rear portion 446 and/or the blades 328a,b to define spars (or supports) 445 on an end of the side portions 444 that form a seal pocket 448 therebetween for receiving the seal collars 332a,b (see, e.g., Figures 3A-3C). The seal collars 332a,b are nestled into a staging position by the spars 445 to position the seal collar 332 in a readied state of use. The side portions 444 may also have a shoulder 450 for engagement with the seal collar 332.
The seal collar 332 has a series of ribbed convolutions 452 circumferentially positioned on an outer surface thereof for facilitating sealing therewith. These convolutions 452 may be used, for example, to help form the metal-to-metal seal profile against the mating blade seal surface in the event of interference, such as misalignment or trapped debris.
One or more redundant or secondary elastomeric seals, such as elastor 336a,b, may be provided to further reinforce and/or prevent leakage of the seal collar 332a,b. Such redundant seals may be used to further bias the seal collar 332a,b towards the seal surface 338a,b. The metal-to-metal interface of the seal assembly 330 may be self energizing to provide support during operation. Secondary elastomer seals, such as elastors 336a,b, may be reactive to wellbore pressure to enhance seal characteristics as wellbore pressures increase. Positioning the components of the seal assembly 330 both above and below the carriage assembly 325 may be used to create a bidirectional seal arrangement.
The shear sealing system as provided herein may be provided with various features, such as modular independent components that may be replaced independently regarding service life or wear condition. The shear sealing system may also provide a metal-to-metal primary sealing interface between components, such as seal assembly 330 and carriage assembly 325. Additional sealing components, such as elastors 336a,b and/or other seals (of elastomeric or other materials) may optionally be provided.
Figures 5A-5D depict an alternate shear sealing system 524 usable, for example, as the shear sealing system 124 of Figure 1. The shear sealing system 524 is similar to the shear sealing system 324, except that the shear sealing system 524 includes a pair of carriages 526a,b, and a pair of blades (or blade inserts) 528a,b with seals 530a,b on the carriages 526a,b. Each of the carriages 526a,b carries a blade 528a,b such that the blades 528a,b may be advanced to pass through the tubular 116.
In this version, each of the carriages 526a,b has a top surface 552a,b, a bottom surface 554a,b and a side surface 556a. A blade pocket 558a,b is formed about the top surface 552a,b for receiving the blade 538a,b. A seal pocket 560a,b is formed about the bottom surface 554a,b to receive the blade 538b,a of the other carriage 526b,a. Each of the seal pockets 560a,b has a receiving edge 562a,b that conforms to the profile of the blade 538a,b it is receiving to form a seal therewith.
The side surfaces 556a,b extend a distance from the receiving edge 562a,b to receivingly engage sides of the blades 538a,b to extend the seal thereabout. The side surfaces 556a,b may extend sufficiently to engage the seal 530b,a of the other carriage 526b,a. As shown, the seals 530a,b may extend over at least a portion of each carriage 526a,b sufficient to provide a seal about the blades 538a,b and/or carriage 526a,b. When the blades 538a,b are moved to the extended position (see, e.g., Figures 2C and 3B), a seal is formed about the blades (e.g., along the cutting profile and along the sides of the blades). The seals 530a,b may be made of an elastomeric material (e.g., rubber) to form a seal with the blades 528a,b.
Additional coverage may also optionally be provided about the BOP. For example, one or more of the seals 330 can be used alone, separately or in combination with one or more of the seals 530a,b. Various combinations of the shear sealing system 324 and the shear sealing system 524 may be provided.
In operation, as shown in Figure 6, the shear sealing systems may be used in a method 670 of forming a seal about a tubular of a wellbore. The method involves providing 672 a blowout preventer including a housing and a shear sealing system. The housing has a bore and a guideway therethrough. The tubular is positionable in the bore. The shear sealing system may include at least one carriage, at least one blade carried by the carriage and at least one seal. The method may also involve engaging 674 the tubular with the blade by slidably positioning the carriage in the guideway of the blowout preventer and moving 676 the blade between a retracted position and an extended position, and forming a seal about the tubular with the seal.
The engaging may involve shearing the tubular. The shearing may involve piercing, cutting, raking, shaving, and/or severing the tubular. The forming may involve sealingly engaging the upper blade with the upper seal and sealingly engaging the lower blade with the lower seal, sealingly engaging the upper blade with the lower seal and the lower blade with the upper seal, and/or forming a seal between the housing and the blade.
The method may be performed in any order, and repeated as desired.
It will be appreciated by those skilled in the art that the techniques disclosed herein can be implemented for automated/autonomous applications via software configured with algorithms to perform the desired functions. These aspects can be implemented by programming one or more suitable general-purpose computers having appropriate hardware. The programming may be accomplished through the use of one or more program storage devices readable by the processor(s) and encoding one or more programs of instructions executable by the computer for performing the operations described herein. The program storage device may take the form of, e.g., one or more floppy disks; a CD ROM or other optical disk; a read-only memory chip (ROM); and other forms of the kind well known in the art or subsequently developed. The program of instructions may be "object code," i.e., in binary form that is executable more-or-less directly by the computer; in "source code" that requires compilation or interpretation before execution; or in some intermediate form such as partially compiled code. The precise forms of the program storage device and of the encoding of instructions are immaterial here. Aspects of the subject matter may also be configured to perform the described functions (via appropriate hardware/software) solely on site and/or remotely controlled via an extended communication (e.g., wireless, internet, satellite, etc.) network.
While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. For example, one or more shear sealing systems may be used in a BOP to shear a tubular and/or seal a wellbore, and one or more carriages and blades may be used in a shear sealing system.
Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.

Claims

A shear sealing system (124, 324) of a blowout preventer (120) of a wellbore (118), the wellbore having a tubular (116) therein, the blowout preventer comprising a housing (212) having a bore (214) and a guideway (321) therethrough, the tubular positionable in the bore, the shear sealing system comprising:
at least one carriage (326a,b) slidably positionable in the guideway of the blowout preventer;

at least one blade (328a,b) carried by the at least one carriage and movable thereby between a retracted position and an extended position, the at least one blade engageable with the tubular when in the extended position;

characterised in that the shear sealing system comprises at least one seal (330) forming a seal about the tubular and with the at least one blade when the at least one blade is in the extended position, the at least one seal comprising at least one seal collar (332a,b) positionable in the housing of the blowout preventer;

wherein the at least one carriage comprises a base (440) and side portions (444) having spars (445) extending from a front end of the base, the spars defining a seal pocket (448) therebetween to receive the tubular and engage the seal collars.
The shear sealing system of Claim 1, wherein the at least one blade comprises an upper blade (328a) and a lower blade (328b) and the at least one seal comprises an upper seal (332a) and a lower seal (332b), and wherein the upper blade, the lower blade, the upper seal and the lower seal are positionable in sealing engagement.
The shear sealing system of any preceding Claim, wherein the at least one seal forms a metal to metal seal with the at least one blade.
The shear sealing system of any preceding Claim, wherein the at least one seal is positionable in the housing.
The shear sealing system of any preceding Claim, wherein the at least one seal is a tubular member having an outer diameter positionable along an inner diameter () of the bore.
The shear sealing system of Claim 5, wherein the at least one seal has a bottom surface positionable along an inner diameter of the guideway, the bottom surface engageable with a top surface of the at least one blade when the at least one blade moves to the extended position.
The shear sealing system of any preceding Claim, wherein the at least one seal collar has convolutions (452) on an outer surface thereof
The shear sealing system of any preceding Claim, wherein the at least one seal comprises at least one coil spring and/or
at least one elastor seal (336a,b).
The shear sealing system of any preceding Claim, wherein the base has a blade pocket (447) for receiving the at least one blade.
The shear sealing system of any preceding Claim, wherein the at least one seal comprises an elastomeric material (530a,b) disposable about each of the at least one carriages.
A method of forming a seal about a tubular (116) of a wellbore (118), the method comprising:
providing a blowout preventer (120), comprising:
a housing (212) having a bore (214) and a guideway (321) therethrough, the tubular positionable in the bore; and

a shear sealing system (330) comprising at least one carriage (326a,b) and at least one blade (328a,b) carried by the at least one carriage and at least one seal (330);

characterised in that the at least one seal comprises at least one seal collar (332a,b) positionable in the housing of the blowout preventer, the at least one carriage comprises a base (440) and side portions (444) having spars (445) extending from a front end of the base, the spars defining a seal pocket (448) therebetween to receive the tubular and engage the seal collars; and

engaging the tubular with the at least one blade by slidably positioning the at least one carriage in the guideway of the blowout preventer and moving the at least one blade between a retracted position and an extended position; and

forming a seal about the tubular and between the at least one seal and the at least one blade when the blade is in the extended position.
The method of Claim 11, wherein the at least one blade comprises an upper blade (328a) and a lower blade (328b) and the at least one seal comprises an upper seal (332a) and a lower seal (332b), and wherein the forming comprises forming a seal between the upper blade, the lower blade, the upper seal and the lower seal.