U.S. patent number 3,793,835 [Application Number 05/222,919] was granted by the patent office on 1974-02-26 for variable rate hydraulic-pneumatic weight control and compensating apparatus.
This patent grant is currently assigned to Vetco Offshore Industries, Inc.. Invention is credited to Edward Larralde.
United States Patent |
3,793,835 |
Larralde |
February 26, 1974 |
VARIABLE RATE HYDRAULIC-PNEUMATIC WEIGHT CONTROL AND COMPENSATING
APPARATUS
Abstract
Apparatus automatically compensating for relative vertical
movement between a hoisting or supporting mechanism and a load
carried thereby, which load, for example, may be a running string
connected to a drill bit used in drilling a subaqueous well bore,
the mechanism supporting the running string being mounted on a
floating vessel positioned over the well bore. The compensating
apparatus includes a cylinder and piston device containing a
hydraulic fluid exerting a lifting or tensioning force on the
running string, or other load, the pressure on the hydraulic fluid
being maintained generally constant by a gaseous medium, despite
relative axial movement between the cylinder and piston portions of
the device, that might result from heaving of the vessel due to
wind and wave action, or the lowering of the running or drilling
string as the bit drills the hole. The volume of the gaseous medium
for pressurizing the hydraulic fluid can be changed in order to
vary the spring-like rate of the gaseous medium.
Inventors: |
Larralde; Edward (Santa
Barbara, CA) |
Assignee: |
Vetco Offshore Industries, Inc.
(Ventura, CA)
|
Family
ID: |
22834268 |
Appl.
No.: |
05/222,919 |
Filed: |
February 2, 1972 |
Current U.S.
Class: |
60/413; 60/907;
175/5; 175/27; 254/270; 254/337; 254/900; 267/126 |
Current CPC
Class: |
E21B
19/09 (20130101); Y10S 254/90 (20130101); Y10S
60/907 (20130101) |
Current International
Class: |
E21B
19/00 (20060101); E21B 19/09 (20060101); F15b
001/02 () |
Field of
Search: |
;60/51,52PJ,413,414,415,464,469,907 ;91/390 ;175/5,27 ;267/125,126
;254/172 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Claims
I claim:
1. In apparatus for maintaining a predetermined stress in a running
string: cylinder means; piston means slidable in said cylinder
means; one of said means being adapted for operative connection to
the running string; the other of said means being adapted for
operative connection to a support; means for maintaining a liquid
medium under pressure in said cylinder means on one side of said
piston means as said piston means and cylinder means move
longitudinally relative to one another in both longitudinal
directions; said pressure maintaining means comprising container
means containing a gaseous medium, said container means being
separate from said cylinder means; and means for changing the
effective volume of said container means and of the gaseous medium
therein effective for operation upon said liquid medium at a given
unit pressure to vary the spring rate of said gaseous medium.
2. In apparatus for maintaining a predetermined stress in a running
string: cylinder means; piston means slidable in said cylinder
means; one of said means being adapted for operative connection to
the running string; the other of said means being adapted for
operative connection to a support; means for maintaining a liquid
medium under pressure in said cylinder means on one side of said
piston means as said piston means and cylinder means move
longitudinally relative to one another in both longitudinal
directions; said pressure maintaining means comprising a gaseous
medium under pressure exerting its pressure force on said liquid
medium; and means for varying the volume of said gaseous medium at
the same unit pressure effective for exerting its pressure force on
said liquid medium; said pressure maintaining means further
including an accumulator cylinder containing part of said liquid
medium in one portion thereof and said gaseous medium in another
portion thereof for transmitting its pressure to said liquid
medium; said volume varying means comprising a plurality of gaseous
medium containers connected to the gaseous medium portion of said
accumulator cylinder, and means for communicating said accumulator
cylinder with different numbers of said containers to selectively
determine the spring rate of said gaseous medium by permitting gas
to flow simultaneously and in both directions between the selected
number of containers and said accumulator cylinder.
3. In apparatus as defined in claim 2; said communicating means
including valve means for selectively permitting or preventing flow
of said gaseous medium between some of said containers and said
accumulator cylinder.
4. In apparatus as defined in claim 2; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means.
5. In apparatus as defined in claim 2; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said valve
means being operable to selectively effect increase or decrease in
pressure of said gaseous medium in said accumulator cylinder and
containers.
6. In apparatus as defined in claim 2; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said
conduit means including a first tubular line for conducting said
gaseous medium between said source and some of said containers and
a second tubular line for conducting said gaseous medium between
said source and other of said containers and said accumulator
cylinder; said valve means including valves in said first and
second tubular lines for individually controlling flow of said
gaseous medium in said tubular lines.
7. In apparatus as defined in claim 2; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said valve
means being operable to selectively effect increase or decrease in
pressure of said gaseous medium in said accumulator cylinder and
containers, said conduit means including a first tubular line for
conducting said gaseous medium between said source and some of said
containers and a second tubular line for conducting said gaseous
medium between said source and other of said containers and said
accumulator cylinder; said valve means including valves in said
first and second tubular lines for selectively effecting increase
or decrease in the pressure of the gaseous medium in said some of
said containers and said other of said containers and accumulator
cylinder.
8. In apparatus as defined in claim 2; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said
conduit means including a first tubular line for conducting said
gaseous medium between said source and some of said containers and
a second tubular line for conducting said gaseous medium between
said source and other of said containers and said accumulator
cylinder; said valve means including valves in said first and
second tubular lines for individually controlling flow of said
gaseous medium in said tubular lines; and means including an
isolation valve selectively preventing or permitting communication
between said some of said containers and said other of said
containers.
9. In apparatus as defined in claim 2; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said valve
means being operable to selectively effect increase or decrease in
pressure of said gaseous medium in said accumulator cylinder and
containers, said conduit means including a first tubular line for
conducting said gaseous medium between said source and some of said
containers and a second tubular line for conducting said gaseous
medium between said source and other of said containers and said
accumulator cylinder; said valve means including valves in said
first and second tubular lines for selectively effecting increase
or decrease in the pressure of the gaseous medium in said some of
said containers and said other of said containers and accumulator
cylinder; and means including an isolation valve selectively
preventing or permitting communication between said some of said
containers and said other of said containers.
10. In apparatus for maintaining a predetermined stress in a
running string disposed in a well bore and which is supported by a
rig: elongate cylinder means; piston means slidable in said
cylinder means; one of said means being adapted for operative
connection to the running string; the other of said means being
adapted for operative connection to the rig; means for maintaining
a liquid medium under pressure in said cylinder means on one side
of said piston means as said piston means and cylinder means move
longitudinally relative to one another in both longitudinal
directions; said pressure maintaining means comprising container
means containing a gaseous medium under pressure exerting its
pressure force on said liquid medium, said container means being
separate from said cylinder means; and means for changing the
effective volume of said container means and of the gaseous medium
therein effective for operation upon said liquid medium at a given
unit pressure to vary the spring rate of said gaseous medium.
11. In apparatus for maintaining a predetermined stress in a
running string disposed in a well bore and which is supported by a
rig: elongate cylinder means; piston means slidable in said
cylinder means; one of said means being adapted for operative
connection to the running string; the other of said means being
adapted for operative connection to the rig; means for maintaining
a liquid medium under pressure in said cylinder means on one side
of said piston means as said piston means and cylinder means move
longitudinally relative to one another in both longitudinal
directions; said pressure maintaining means comprising a gaseous
medium under pressure exerting its pressure force on said liquid
medium; and means for varying the volume of said gaseous medium at
the same unit pressure effective for exerting its pressure force on
said liquid medium; said pressure maintaining means further
including an accumulator cylinder containing part of said liquid
medium in one portion thereof and said gaseous medium in another
portion thereof for transmitting its pressure to said liquid
medium; said volume varying means comprising a plurality of gaseous
medium containers connected to the gaseous medium portion of said
accumulator cylinder, and means for connumicating said accumulator
cylinder with different numbers of said containers to selectively
determine the spring rate of said gaseous medium.
12. In apparatus as defined in claim 11; said communicating means
including valve means for selectively permitting or preventing flow
of said gaseous medium between some of said containers and said
accumulator cylinder.
13. In apparatus as defined in claim 11; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means.
14. In apparatus as defined in claim 11; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said
conduit means including a first tubular line for conducting said
gaseous medium between said source and some of said containers and
a second tubular line for conducting said gaseous medium between
said source and other of said containers and said accumulator
cylinder; said valve means including valves in said first and
second tubular lines for individually controlling flow of said
gaseous medium in said tubular lines.
15. In apparatus as defined in claim 11; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; and valve means in said conduit means for controlling
flow of said gaseous medium through said conduit means, said
conduit means including a first tubular line for conducting said
gaseous medium between said source and some of said containers and
a second tubular line for conducting said gaseous medium between
said source and other of said containers and said accumulator
cylinder; said valve means including valves in said first and
second tubular lines for individually controlling flow of said
gaseous medium in said tubular lines; and means including an
isolation valve selectively preventing or permitting communication
between said some of said containers and said other of said
containers.
16. In apparatus for maintaining a predetermined stress in a
running string disposed in a well bore and which is supported by a
rig including a suspension mechanism: elongate cylinder means;
piston means slidable in said cylinder means; one of said means
having a device thereon for operative connection to the running
string; the other of said means having a device thereon for
operative connection to the suspension mechanism, whereby said
cylinder means and piston means are disposed between the suspension
mechanism and running string; means for maintaining a liquid medium
under pressure in said cylinder means on one side of said piston
means as said piston means and cylinder means move longitudinally
relative to one another in both longitudinal directions, whereby
the stress of the running string and of said one means is
transmitted through the liquid to said other means and suspension
mechanism; said pressure maintaining means comprising container
means containing a gaseous medium under pressure exerting its
pressure force on said liquid medium; said pressure maintaining
means further including an accumulator cylinder communicating with
said container means and containing part of said liquid medium in
one portion thereof and said gaseous medium in another portion
thereof for transmitting its pressure to said liquid medium; said
container means being separate from said accumulator cylinder; and
means for changing the effective volume of said container means and
of the gaseous medium therein effective for operation upon said
liquid medium at a given unit pressure to vary the spring rate of
said gaseous medium.
17. In apparatus for maintaining a predetermined stress in a
running string disposed in a well bore and which is supported by a
rig including a suspension mechanism: elongate cylinder means;
piston means slidable in said cylinder menas; one of said means
having a device thereon for operative connection to the running
string; the other of said means having a device thereon for
operative connection to the suspension mechanism, whereby said
cylinder means and piston means are disposed between the suspension
mechanism and running string: means for maintaining a liquid medium
under pressure in said cylinder means on one side of said piston
means as said piston means and cylinder means move longitudinally
relative to one another in both longitudinal directions, whereby
the stress of the running string and of said one means is
transmitted through the liquid to said other means and suspension
mechanism; said pressure maintaining means comprising a gaseous
medium under pressure exerting its pressure force on said liquid
medium; said pressure maintaining means further including an
accumulator cylinder containing part of said liquid medium in one
portion thereof and said gaseous medium in another portion thereof
for transmitting its pressure to said liquid means; and means for
varying the volume of said gaseous medium at the same unit pressure
effective for exerting its pressure force on said liquid medium;
said volume varying means comprising a plurality of gaseous medium
containers connected to the gaseous medium portion of said
accumulator cylinder, and means for communicating said accumulator
cylinder with different numbers of said containers to selectively
determine the spring rate of said gaseous medium by permitting gas
to flow simultaneously and in both directions between the selected
number of containers and said accumulator cylinder.
18. In apparatus as defined in claim 17; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; valve means in said conduit means for controlling flow
of said gaseous medium through said conduit means; said conduit
means including a first tubular line for conducting said gaseous
medium between said source and some of said containers and a second
tubular line for conducting said gaseous medium between said source
and other of said containers and said accumulator cylinder; said
valve means including valves in said first and second tubular lines
for individually controlling flow of said gaseous medium in said
tubular lines.
19. In apparatus as defined in claim 17; a source of said gaseous
medium under pressure; conduit means for conducting said gaseous
medium from said source to said accumulator cylinder and said
containers; valve means in said conduit means for controlling flow
of said gaseous medium through said conduit means; said conduit
means including a first tubular line for conducting said gaseous
medium between said source and some of said containers and a second
tubular line for conducting said gaseous medium between said source
and other of said containers and said accumulator cylinder; said
valve means including valves in said first and second tubular lines
for individually controlling flow of said gaseous medium in said
tubular lines; and means including an isolation valve selectively
preventing or permitting communication between said some of said
containers and said other of said containers.
Description
The present invention relates to apparatus for controlling the
stress in a running string, and more particularly to apparatus used
on or in connection with a floating vessel for maintaining the
strain in a running string, such as a pipe string, substantially
constant while being used in the performance of diverse functions
in a sub-aqueous well bore, such as drilling and completion
operations therein, despite vertical movement of the vessel while
such operations are performed. One specific form of such apparatus
is disclosed in U.S. Pat. application Ser. No. 69,758, filed Sept.
4, 1970 for "Hydraulic-Pneumatic Weight Control and Compensating
Apparatus", now U.S. Pat. No. 3,718,316.
In the normal operation of drilling a well bore on land, or from a
drilling platform supported in a fixed position from the ocean
floor, the weight imposed on the drill bit is equal to the total
weight of the drilling string less the weight of the drill pipe
carried by the drawworks. Usually, the weight imposed on the bit is
equal to the weight of the drill collar sections connected to the
lower end of the drill pipe. In drilling a sub-aqueous well bore
from a floating vessel, problems of compensating for the weight on
the bit arise due to the heaving of the vessel under conditions of
tide, wind and waves. In the above-identified U.S. patent, an
apparatus is illustrated in which the drilling string is supported
hydraulically by interposing a compensating apparatus between the
travelling block and hook of the usual drilling apparatus employed
in drilling the well bore. The apparatus relies upon the
maintenance of a required pressure in the hydraulic fluid disposed
within a cylinder and piston device of the apparatus by subjecting
the hydraulic fluid to the pressure of a gaseous medium, such
pressure being maintained in the absence or presence of
longitudinal movement of the cylinder and piston portions of the
device with respect to each other, the hydraulic fluid exerting a
continuous and substantially constant stress on a running string,
such as a drilling string. When the apparatus is used in the
drilling of a sub-aqueous well bore from a floating vessel, the
stress exerted is a substantially constant lifting force on the
drilling string despite heaving of the drilling vessel in the
water, thereby insuring the maintenance of the desired drilling
weight on the drill bit secured to the lower end of the drilling
string. The pressure of the gaseous medium can be varied to vary
the lifting force on the drilling string, and thereby determine the
drilling weight on the drill bit.
In the apparatus or system illustrated in U.S. Pat. application
Ser. No. 69,758, filed Sept. 4, 1970, now U.S. Pat. No. 3,718,316
the desired pressure on the hydraulic fluid is maintained through
use of an accumulator hydraulically connected to the compensator
cylinder and containing gas at a desired pressure acting on the
hydraulic fluid, the gas expanding and contracting as the
compensator piston moves relatively longitudinally in the
compensator cylinders to maintain a generally constant pressure on
the hydraulic fluid. The effective gas volume of the accumulator
portion of the apparatus remains substantially constant, thereby
providing a "gas spring" having a substantially constant spring
rate for a particular gas pressure, regardless of the range of
relative movement of the compensating piston in the compensator
cylinder.
By virtue of the present invention, the rate of the gas spring for
a given pressure can be changed at any time. More particularly,
such change is effected by changing the effective gas volume of the
accumulator, an increase or decrease of the volume correspondingly
decreasing or increasing the spring rate. If the relative
longitudinal movement of the compensator piston in its cylinder is
large, due to a large vertical reciprocation of the drilling ship
in the water, it would be desirable to provide a large effective
accumulator gas volume to hold variations in the gas pressure to a
low value. On the other hand, if the relative movement of the
compensator piston in its cylinder is small, due to a small
vertical reciprocation of the ship in the water, a lesser effective
accumulator gas volume can be provided, variations in gas pressure
still being held to a low value.
The present invention also contemplates apparatus capable of
readily reducing the effective gas volume of the accumulator to
provide a relatively rapid change in the gas pressure in the
system, either its increase or decrease. Moreover, while the
compensator is in operation with a reduced effective accumulator
gas volume, due to a portion of the available gas value being held
ineffective, the pressure in said ineffective portion can be
changed so as to be available to change the accumulator gas
pressure promptly when rendered effective. Such pressure in the
ineffective portion of the system can be changed to the same
pressure as exists in the effective portion to permit prompt
reduction of the gas spring rate of the system to a relatively low
value.
This invention possesses many other advantages, and has other
purposes which may be made more clearly apparent from a
consideration of a form in which it may be embodied. This form is
shown in the drawings accompanying and forming part of the present
specification. It will now be described in detail, for the purpose
of illustrating the general principles of the invention; but it is
to be understood that such detailed description is not to be taken
in a limiting sense.
Referring to the drawings:
FIG. 1 is a diagrammatic view of a drilling rig mounted on a
floating vessel for drilling a sub-aqueous bore hole;
FIG. 2 is a front elevational view, with parts in longitudinal
section, of the compensator portion of the apparatus disclosed in
FIG. 1; and
FIG. 3 is a diagrammatic view of the compensator system.
Apparatus is disclosed in FIGS. 1 to 3 in connection with the
drilling of a vertical well bore W from a sub-aqueous floor F above
which a floating vessel V, such as a drilling barge, is located,
the barge being suitably anchored against lateral displacement for
the purpose of holding a tubular drilling string S in centered
relation with respect to the well bore. A drill bit B is secured to
the lower end of the drill string, such as a string of drill pipe
or drill casing, the upper kelly portion K of the drill string
passing through the usual rotary table T rotated by a suitable
drive mechanism (not shown). The upper end of the kelly is secured
to a swivel R suspended from a hook C pivotally connected to the
lower end of a compensating apparatus D, the upper end of which is
pivotally connected to the travelling block E associated with the
usual lines H passing over the crown block J at the upper end of
the derrick L secured in place on the floating drilling vessel, the
cables or lines being connected to a suitable drawworks N mounted
on the floating barge.
A suitable mud line P is connected to the swivel for the purpose of
delivering drilling mud to the drill string for discharge from the
drill bit B, to remove the cuttings produced by the latter while
appropriate drilling weight is imposed thereon, with the drilling
string being rotated by the table T at the desired speed. Usually,
the drilling weight is provided by a suitable length of drill
collars disposed in the lower portion of the drill string
immediately above the drill bit, the drill string above the drill
collars being maintained in tension by the drawworks N and lines H,
the drawworks permitting the drill string to lower as the hole W is
being produced.
The compensating apparatus D permits the floating vessel V, and the
mechanism carried thereby, to shift vertically relative to the well
bore W and drilling string S without appreciably modifying the
drilling weight imposed on the drill bit B. This compensating
apparatus includes a lower supporting structure 10 connected to the
hook C, and an upper supporting structure 11 connected to the lower
end of the travelling block E. In the specific form of compensating
apparatus illustrated, the lower supporting structure 10 is secured
to the lower ends of a pair of piston rods 12 extending upwardly
into a pair of cylinders 13 affixed to the upper supporting
structure 11. The upper ends of the piston rods are secured to
pistons 14 having appropriate seal rings (not shown) thereon for
slidably sealing against the cylinder walls, the rod ends of the
cylinders carrying appropriate packings 12a for slidably sealing
against the periphery of the piston rods 12. The cylinders 13 are
disposed on opposite sides of the travelling block E and extend
thereabove, to reduce the overall length of the compensating unit D
while permitting the pistons 14 and rods 12 to shift longitudinally
within the cylinders to a substantial extent, the pistons, when
disposed at the upper, head ends of the cylinders, still permitting
the drawworks to elevate the travelling block and compensating unit
to an extent at which the usual length of drill pipe can be
connected to, or removed from, the drilling string. The arrangement
of the compensating apparatus D with respect to the travelling
block E and hook C forms the subject matter of the application of
Edward Larralde and James W. E. Hanes, for "Motion Compensating
Apparatus," U.S. Pat. Ser. No. 69,759, Filed Sept. 4, 1970 now U.S.
Pat. No. 3,714,995.
It is evident that the travelling block E is secured to the
cylinders 13 so that the latter move vertically therewith, while
the pistons 14 and piston rods 12 are secured to the hook C, and
through the swivel R to the upper end of the drill string S. The
weight of the drill string is transmitted through the hook C to the
piston rods 12 and pistons 14, and then to liquid 15 filling the
cylinder spaces below the pistons 14, from where it is transmitted
to the lower cylinder heads 13a and to the cylinders 13 themselves,
from where the load is transferred to the travelling block E and
the lines H to the crown block J. As noted above, elevation and
descent of the travelling block, and, therefore, of the
compensating unit D, and the entire load S suspended therefrom, is
determined by the operation of the drawworks N.
A substantially constant predetermined pressure is maintained on
the liquid medium 15 disposed in the cylinders. Such liquid under
pressure acts in an upward direction on the pistons 14 and,
therefore, on the hook C, swivel R and drill string S connected
thereto. Since the weight of the entire drill string is known, the
unit pressure of the liquid medium is selected such that all of
such weight, with the exception of the drilling weight to be
imposed on the drill bit B, which is usually the weight of the
drill collars, is supported by the liquid pressure acting in an
upward direction over the areas of the pistons. This pressure is
derived from a gaseous medium 16, such as dry compressed air, or
any other suitable gas, disposed in one or a bank of accumulators
17 supported on the vessel V. The rod ends of the cylinders 13 are
connected to liquid lines 18 extending to a control valve 19, from
where fluid lines 20 run to the liquid ends 21 of the cylindrical
accumulator member or members 22. The lower portions of the
accumulators are filled with the liquid 15, and the upper ends 23
are filled with the gas 16 under pressure, the gas and liquid in
each cylindrical accumulator being separated by a floating piston
24 that makes a suitable slidable seal against the cylindrical wall
of the accumulator housing 22. Accordingly, the gas pressure of the
gas 16 is transmitted through the floating piston 24 to the liquid
15, the same liquid pressure being present in the compensator
cylinders 13. Movement of the pistons 14 in the cylinders 13 is
permitted, the floating pistons 24 correspondingly shifting while
transmitting the pressure of the gaseous medium 16 to the liquid 15
in the accumulators, and thence through the lines 20, 18 to the
liquid 15 in the compensator cylinders 13.
The ability of the liquid to pass between the compensator cylinders
and the accumulators is controlled by the valve 19 of any suitable
type, which may be remotely opened or closed by the operator
manipulating a manually operated control valve 26. Normally, during
the operation of the compensator apparatus, the valve 19 is in its
open position to permit the free transfer of liquid between the
compensator cylinders 13 and the accumulator cylinders 22.
An accumulator gas supply at a desired pressure is contained in a
bank of accumulator back-up containers 30, 30a of a suitable
number, which are connected to the gas side of the accumulator
cylinder 22 through a suitable manifold 31, there being a shut-off
valve 32, 32a between each back-up container and the manifold. One
of the containers 30 can be isolated from the other containers 30a
by an isolation valve 33 in the manifold, and this isolation valve
can be opened or closed from a remote point by a suitable isolator
valve 34 appropriately connected thereto. The number of back-up gas
containers 30, 30a placed in communication with the accumulator
cylinder or cylinders 22 can be varied to thereby vary the
effective volume of the gas operating upon the liquid 15 in the
accumulator, thereby effecting a change in the spring rate of such
gas, as described more in detail hereinbelow.
The liquid medium 15 is derived from a reservoir 40, a suction line
41 from the reservoir running to one or more pumps 42, which can
force the liquid through a discharge line 43 through a valve 44
into a branch line 45 communicating with the line 20 and the
compensator and accumulator cylinders 13, 22. An exhaust or return
line 46 extends between the liquid reservoir 40 and the branch line
45, permitting a reduction in the volume of liquid in the system
through opening of a suitable valve 47 in the return line.
As specifically illustrated in the drawings, the gas used in the
system is air. Air compressors 50 are the primary source of the
energy for the system, the compressed air passing through one or
more air dryers 51 to one or more high-pressure air storage
containers 52 which supply air at a pressure substantially higher
than the maximum pressure of the air in the accumulator cylinders
22 and back-up containers 30, 30a. Such higher pressure is desired
to reduce the time required to increase the operating pressure of
the gas in the accumulator cylinders 22 and back-up containers 30,
30a.
The compressed air in the storage container 52 can flow through a
suitable line 53 to a valve 54 connected through a line 55 to the
manifold 31. The connection of such line 55 to the manifold is
located between the back-up container 30 and the isolation valve
33. The high pressure air can also pass through the line 53 and
another valve 56 connected through a line 57 to the manifold 31 on
the other side of the isolation valve 33. The valves 54, 56 are
manually operable and are of a known type, each of them being
capable of occupying a closed position and open position, to permit
air to pass from the high pressure storage container 52 to the
manifold 31, or to an exhaust condition, to allow air to bleed from
the manifold 31, and the back-up containers 30, 30a and cylinders
22 connected thereto through an exhaust line 58 and through a
muffler 59 to the atmosphere, whenever a reduction in the gas or
air pressure in the system is desired. Suitable pressure gauges 60,
61 indicate the pressures of the compressed air in the back-up
containers 30a connected to the manifold 31 on one side of the
isolation valve 33 and accumulators 17 and back-up container 30 on
the other side of the isolation valve.
In the operation of the apparatus illustrated in the drawings, the
accumulators 17 and back-up containers 30, 30a are charged with dry
compressed air at a desired pressure through suitable manipulation
of the valves 54, 56, there being sufficient liquid 15 in the
system such that the same pressure is imposed on the liquid in the
compensator cylinders 13 which exerts an upper force on the pistons
14 and on the drill string S, the supported load being carried from
the cylinders 13 to the travelling block E and from the lines H to
the crown block J. Drilling proceeds through appropriate rotation
of the rotary table T, with drilling mud being pumped down the
drilling string, returning in a normal manner to the floating
vessel V through a marine conductor pipe (not shown in the interest
of clarity of the illustration) extending from the drilling vessel
V to the well bore W. In the event the floating vessel were to
shift vertically, for example, rise, the cylinders 13 would move
upwardly along the piston rods 12 and pistons 14, the liquid 15
therein remaining at substantially the same pressure and being
forced through the lines 18, 19 into the lower portions 21 of the
accumulators 17, forcing the floating pistons 24 upwardly to
further compress the air to a small extent, which will reflect some
increase in the pressure of the liquid 15, but, as a practical
matter, to too small an extent as to have any material effect on
the drilling weight imposed on the drill bit B. Similarly, should
the vessel V move downwardly, the cylinder 13 will move downwardly
therewith, the cylinder volume below the pistons 14 increasing, the
compressed air 16 under pressure forcing the liquid 15 from the
accumulators 17 back into the compensator cylinders 13 while
maintaining the required pressure on the liquid 15.
Thus, within the operative scope of the compensator apparatus, the
drilling vessel V can heave upwardly and downwardly relative to the
drill string S without materially altering the drilling weight on
the drill bit B. The number of accumulators 17 and their effective
gas or compressed air volume, which is made variable by the number
of back-up containers 30, 30a connected thereto, is preferably many
times the annular areas of the pistons 14, so that a large liquid
volume change in the cylinders 13 produces a much smaller combined
volume change in each accumulator or expansion space 21 and 23 and
the back-up containers 30, 30a operatively connected thereto,
thereby effecting only a relatively small change in the pressure of
the compressed air in the upper portion 23 of the accumulators.
The compressed air in the accumulators 17 and back-up containers
30, 30a functions as a gas spring. By virtue of the system
illustrated and described, the rate of this gas spring can be
varied, depending upon the operating conditions of the compensator
system. Such change or variation in spring rate is effected for
each air pressure desired in the system, such air pressure
depending upon the drilling weight to be supported by the liquid 15
in the compensator cylinders 13. Thus, the greater the weight to be
supported, the higher must be the liquid pressure, and, conversely,
the less the weight to be supported the lower must be the liquid
pressure. The change of the liquid pressure to the desired value is
secured by changing the pressure of the air 16 in the accumulators
17 and in the back-up containers 30, 30a connected therewith.
Increasing air pressure is effected, as noted above, by
manipulating the valve 54 to permit flow of air from the high
pressure storage container 52 to the accumulators 17 and back-up
containers 30, 30a communicating therewith. If some of the back-up
containers, such as 30a, are isolated from the accumulators through
closing of the isolation valve 33, the air pressure in such
ineffective back-up containers 30a can still be increased by
appropriate manipulation of the other valve 56 to permit high
pressure air to flow through the line 57 and into the ineffective
back-up containers.
On the other hand, should it be desired to decrease the air
pressure in the accumulators 17 and back-up containers 30, 30a
normally communicating therewith, the manual valve 54 is
appropriately manipulated to permit some of the compressed air to
exhaust through the line 58 and muffler 59 to the atmosphere.
Similarly, the air pressure in the back-up containers 30a, if
isolated from the container 30, can also be reduced by suitably
manipulating the other valve 56 to an exhaust condition, permitting
air to exhaust through the line 58 and muffler 59 to atmosphere. If
the isolation valve 33 is open and the shut-off valves 32, 32a are
open, then the air pressure in the accumulators 17 and the back-up
containers 30, 30a will be the same, manipulation of the single
valve 54 or 56 effecting an increase or decrease in the air
pressure in all accumulators 17 and back-up containers.
The back-up containers 30, 30a are actually extensions of the
accumulators 17 when operatively connected thereto. By changing the
number of back-up containers 30, 30a operatively connected to the
accumulators, the effective gas volume is changed, as well as the
spring rate of the compressed air 16 operating in the system. If,
for example, the relative longitudinal movement of the compensator
pistons 14 and their associated cylinders 13 is relatively large,
because of relatively large vertical reciprocation of the drilling
ship V in the water, a low spring rate is desirable to hold
variations in the gas pressure to a low value. This condition can
be provided by having the isolation valve 33 open, so that all of
the back-up containers 30, 30a communicate with the accumulators
17, such containers and accumulators having air at the same
pressure. If the vertical reciprocation of the drilling ship V in
the water is relatively small, then the isolation valve 33 can be
closed, and only the single back-up container 30 illustrated in the
drawings will be in communication with the accumulators 17, the
spring rate for a given pressure of the compressed air then being
relatively high. Intermediate spring rates can be provided by a
determination of the number of back-up containers 30, 30a
operatively connectable to the accumulators, by closing one or more
of the shut-off valves 32a between the back-up containers 30a and
the manifold 31. The number of such back-up containers 30a can be
greater than specifically illustrated, thereby giving a wider
potential variation that can be secured in the spring rate of the
compressed air operating in the system.
Assuming the system is operating at a relatively high air spring
rate, that is, with the isolation valve 33 closed, the air pressure
can be rapidly increased in the system by charging the ineffective
back-up containers 30a with compressed air at a higher desired
pressure through manipulation of the valve 56, to allow compressed
air to flow from the high pressure storage container 52 to the
ineffective back-up containers, until the desired pressure is
achieved in such containers, as noted on the pressure gauge 60. At
any time the pressure in the accumulators 17 is to be increased,
the isolation valve 33 is opened through suitable manipulation of
the remotely located valve 34, a very rapid increase in the air
pressure in the system being achieved, since the higher air
pressure flows from the initially ineffective containers 30a into
the other back-up container 30 and the accumulator cylinders
22.
Conversely, a reduction in air pressure can be achieved. The
isolation valve 33 is closed, and the valve 56 then manipulated to
bleed air from the ineffective back-up containers 30a into the
atmosphere, until the pressure in the containers 30a is at a
desired value, as noted on the gauge 60. Thereafter, upon opening
of the isolation valve 33, a fairly rapid decrease in air pressure
in the accumulator system will be achieved.
If the system is operating at a relatively high spring rate, the
effective air pressure in the accumulators 17 can be changed
rapidly. If it is to be increased, the valve 54 is suitably
manipulated to permit high pressure air from the storage container
52 to flow to the accumulators 17 and the single back-up container
30 (the isolation valve 33 being closed), increase in pressure
being achieved rapidly in view of the relatively small gas volume
of the system. Similarly, if the air pressure in the system is to
be decreased, within the system operating at a high spring rate,
the valve 54 is suitably manipulated to exhaust some of the air to
atmosphere, there being a relatively rapid decrease in the air
pressure in the system.
* * * * *