Bidirectional sealing blowout preventer

Details Bidirectional sealing blowout preventer Bidirectional sealing blowout preventer

2001-08-06

2004-04-13

Bastianelli, John (Department: 3754)

Valves and valve actuation

Blow-out preventers

Radial reciprocating ram

C166S085400

Reexamination Certificate

active

06719262

ABSTRACT:

TECHNICAL FIELD
The invention relates to ram-type blowout preventers used in well operations, such as in the recovery of hydrocarbons, for well control including preventing a well blowout. More particularly, the present invention pertains to the construction and operation of sealing devices included in the blowout preventers, and finds particular application in the operation and testing of subsea blowout preventers and other apparatus in a blowout preventer stack.
BACKGROUND OF THE INVENTION
Blowout preventers are typically included in the assembly at a wellhead when drilling or completing a well to close off the well to prevent a blowout. Such a blowout might occur, for example, when the well suddenly intersects a pocket of fluid under high pressure, which then blows up the well bore. A blowout preventer seals the well against the fluid pressure from below. A blowout preventer can also be used to seal off the well around a well pipe in normal drilling operations involving positive downhole pressure. In practice, multiple blowout preventers are arrayed in a vertical stack, which is positioned over the well, with the well piping extending up through the center of the blowout preventer stack.
FIGS. 1 and 2
provide two views of an underwater blowout preventer stack shown generally at
10
. Various hydraulic lines, framework and control apparatus for operating the blowout preventer stack
10
are not shown for purposes of clarity. The stack
10
includes four ram-type blowout preventers
12
,
14
,
16
and
18
. An annular blowout preventer
20
, a connector
22
, a second annular blowout preventer
24
and a flex joint
26
are arrayed above the ram-type blowout preventers
12
-
18
. A riser adapter
28
is positioned at the top of the stack
10
for connection to a marine riser above (not shown). A wellhead connector
30
is located at the bottom of the stack
10
for connection to a wellhead below (not shown). In general, the number and kind of blowout preventers in a stack, as well as the order in which they are arrayed in the stack, may vary.
A ram-type blowout preventer includes a pair of linear drive devices, or linear actuators, located on opposite sides of a central housing to provide movement along a straight line, perpendicular to the vertical, toward and away from the housing. For example, a ram-type blowout preventer such as shown at
12
provides a pair of piston and cylinder assemblies
32
and
34
with the cylinders fixed on opposite sides of a central housing
36
positioned over the well so that the pistons are movable along a line perpendicular to the vertical, that is, perpendicular to the well bore at the surface of the well. As shown, the bottom two blowout preventers
12
and
14
have a common, extended central housing
36
. A central vertical bore through the housing
36
is aligned with the well bore so that well pipe extending from the well passes upwardly through the housing along its central bore. The pistons are hydraulically operated to simultaneously move toward each other, or away from each other. Each piston carries a ram at the piston end toward the well, so that the two rams meet in a closed configuration at the housing central bore when the pistons are driven together, and are pulled apart by the pistons to an open configuration. The central vertical bores through housings of the ram-type blowout preventers
12
-
18
form part of a central vertical passageway extending from the wellhead and the well bore below, up through all of the elements in the blowout preventer stack
10
and on through the marine riser.
A cavity is provided within the central housing for each ram-type blowout preventer
12
-
18
, that is, for each pair of piston and cylinder combinations
32
/
34
. Each cavity intersects the vertical bore of the housing
36
and extends radially outwardly toward the piston and cylinder structures
32
and
34
in two guideways
38
and
40
, with each guideway interposed between the central housing and a corresponding piston and cylinder assembly. The ram carried by a piston resides and moves within the corresponding guideway.
The rams in a multiple blowout preventer stack may operate in different ways in closing off the well. Pipe rams seal around a tubular pipe extending from the well, closing off the annulus between the well pipe and the well bore surface. Blind rams seal across the well with no pipe at the location of the blind ram. Shear, or cutting, rams shear the well pipe, but do not seal off the annulus around the pipe. Blind shear rams shear the well pipe and close and seal the well. A blowout preventer with blind shear rams is typically at the top of a ram-type blowout preventer stack, with various pipe rams in blowout preventers located below. In a typical application, the top ram-type blowout preventer
18
would be fitted with blind shear rams, and the lower preventers
12
-
16
would contain pipe rams.
FIG. 3
shows a matched pair of pipe rams generally at
42
and
44
, and is used herein to illustrate various features of rams. To the extent that the rams
42
and
44
are alike, the same number label is used to identify their like parts and features. Each of the rams
42
and
44
includes a ram body
46
having a groove
48
in its front, or leading, end. A packer
50
is carried in the groove
48
. A groove
52
extends across the top surface of the ram body
46
. A top seal
54
is received within the top groove
52
such that the ends of the top seal extend to the ends of the packer
50
. A T-slot
56
is cut into the back of each ram body
46
to receive a button at the end of a linear drive device (not shown), such as are included in the piston and cylinder assemblies
32
and
34
(FIGS.
1
and
2
), used to operate the rams
42
and
44
.
The ram bodies
46
are generally curved, oblong cylinders as shown. The guideways (not shown) are also curved, oblong cylindrical inner surfaces that receive the rams
42
and
44
, and along which the rams are driven by the corresponding pistons. In general, blowout preventer ram bodies and corresponding guideways may also have other cross-sectional shapes, such as circular or rectangular. When the rams
42
and
44
are driven together, they meet at the well pipe (not shown) within the central vertical passageway within the blowout preventer stack
10
. The pipe ram packers
50
feature a vertical, cylindrical groove
58
that receives the well pipe, and the front ends of the ram bodies
46
are cut to fit together with each other. Thus, in the closed configuration, the pipe rams
42
and
46
fit together and around the well pipe to enclose the well pipe in annular sealing engagement. To complete the sealing of the well with the rams
42
and
44
in the closed configuration, the rams must be sealed to their respective guideways against well fluid under pressure from moving around the rams and up into the housing above the level of the ram packers. This sealing is provided by the top seals
54
that engage the interior guideway surfaces in a sliding seal. Consequently, the combination of the top seal
54
and the packer
50
of a ram
42
or
44
completes the seal between the well pipe and the corresponding guideway, and the pair of rams
42
and
44
in the closed configuration completes the sealing of the annulus of the well bore surrounding the well pipe.
Each ram
42
and
44
is provided with a pressure equalization path in the form of a groove, or mud slot,
60
machined longitudinally into the bottom surface of the ram to communicate fluid pressure between the vertical bore of the central housing below the ram packer
50
and the respective guideway behind the ram seals. Thus, each ram
42
and
44
may be driven back and forth along its guideway without having to work against fluid pressure differentials between the area behind the ram and the central vertical passageway through the stack
10
below the packers
50
.
Each of the ram-type blowout preventers
12
-
18
has an access port
62
(
FIGS. 1 and 2
) toward the bottom of each side of the corresponding cen

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