~ ~?~
PRESSURE=CON'RQLLE~ AC~UMULATOR CH~ING VALV~ S~ST~M
FOR QT~ FI~L~ DQWNHO~_TOOLS
Backqround of the Invention
In quite a number of type~ of equipment used in analyzing
and operating oil wells, pressure accumulators are used ~o that
operations may be carried out by utilizing differential pressures
between the accumulator and pressure at other points within the
equipment. In some equipment, the accumulator is charged with
pressured fluid at the surface and remains constant during all
periods of use of the equipment. However it is desirable that
accumulator pressures be adjustable after the tool has been run
downhole and even at intervening times between different uses of
the equipment. with the tool down in a well hole several or many
thousands of feet below the earth's surface, it is not an easy
thing to do to change the accumulator pressure at such a remote
location. This invention seeks to provide apparatus and methods
for adjusting pressure entrapped in an accumulator so that the
accumulator may be used as a pressure reservoir and reference
pressure for performing certain functions. In U.S.P.
No. 4,415,027, an apparatus is disclosed for downhole recharging
of accumulators, but the apparatus requires the use of a blanking
off wire line tool and multiple valves. Other apparatuses are
known in the art for performing accumulator recharging functions,
but all suffer from serious defects limiting their utility.
~l29~f~
SummarY of the Invention
The invention provides apparatus for charging and recharg~
ing pressure accumulators oE a tool while the tool is downhole in
a well~ The apparatus performs in response to fluid pressure in
the drill string or production string in the well. The invention
will be useful in the operation of tools such as the surface
controlled blade stabilizer shown in U.S.P. No. 4,407,377, as
well as Eor other tools and apparatuses of somewhat similar
nature~ The subject apparatus provides a valve system for use in
introducing pressure fluid into an accumulator and a separate
valve system for use in discharging of pressured fluid from the
accumulator, wherehy the accumulator may be charged and dis-
charged repeatedly in a controlled fashion to obtain the pres-
sures required for tool operation.
The apparatus according to the invention is operated by
pressure within the tubing or other well pipe string passing
through a first valve system to the accumulator. Fluid may be
discharged from the accumulator through a parallel valve system
back into the tubing string. Plural embodiments of the apparatus
are disclosed. Use is made in all embodiments of a "fuse" which
permits introduction of fluids into the accumulator within cer-
tain pressure differential limits, but which shuts off when such
pressure limits are exceeded. Therefore, the apparatus may be
used with equipment utilizing tubing string pressures for opera-
tion of the tool or equipment, and at the same time lower tubing
string pressures may be used for accumulator charging and
recharging.
A principle object of the invention is to provide accumula-
tor charging and recharging apparatus for use downhole in a well.
3~
Another object of the invention is to provide such apparatus
which utilizes a pressure "fuse" for controlling accumulator
charging procedures. Yet another object of the invention is to
provide such apparatus which is reliable and dependable. A
further object of the invention is to provide such an apparatus
which may be used time and time again while a tool remains down-
hole in a well. Yet another object of the invention is to pro-
vide such an apparatus which i5 precharged with an inert gas such
as nitrogen prior to running into the well. Another object of
the invention i5 to provide such an apparatus which is easy to
use and which can be operated by relatively unskilled operators.
Yet another object of the invention is to provide such an appara-
tus which is not charged with excessively high pressures during
running thereof into the well and during withdrawal from the
well.
Other objects and advantages of the invention will appear
from the following detailed descriptions of preferred embodi-
ments, reference being made to the accompanying drawings.
BL` ef ~escriptions o~E the Drawinas
FIG. 1 is a transverse cross section taken at line 1 1 of
FIG. 5.
FIG. 2 iS a vertical cross section taken at arcuate line 2-
2 of FIG. 1.
FIG. 3 iS a schematic flow diagram showing one embodiment
of the valve system according to the invention.
FIG. 4 is a schematic flow diagram showing a modified form
of flow diagram according to the invention.
FIG. 5 is a partial quarter section showing the upper end
of the apparatus according to the invention.
FIG. 5A is an enlarged partial vertical cross section
showing a portion of the showing of FIG. S.
FIG. 6 is a partial quarter section showing a portion of
the apparatus below that shown in FIG. 5.
FIG. 7 is a partial vertical quarter section showing a
portion of the equipment below the portion shown in FIG. 6.
FIG~ 8 is a transverse cross section taken at line 8-8 of
FIG. 6.
FIG. 9 is a transverse cross section taken at line 9-9 of
FIG. 6.
FIG. 10 is a cross section taken as FIG. 5A, showing a
larger portion of the apparatus.
FIG. 11 is a schematic graph showing pressure charges
versus time during operation of the apparatus according to the
invention.
FIG. 12 is a partial enlarged vertical cross section of a
portion of the apparatus.
Descri~tions of the Preferred Embodimçnts
Referring now to the drawings in detail, and first to FIGS.
5-7~ the apparatus 10 includes an outer housing body 11 which is
tubular in shape. Housing body 11 includes an upper internally
threaded socket or box 12, and a lower threaded pin 13. Housing
body 11 has a passageway 14 of varying diameters therethrough
from top to bottom. An inner mandrel 15 of elongated tubular
shape is fitted within passage 14 and has upper interior threads
16 into which inn2r mandrel cap 17 is screwed. Inner mandrel cap
17 is tubular in form, having upset upper portion 17a which fits
closely within pas~age 14 and has inner and outer O-ring seals,
19, 20 therearound. An upper mandrel element 21 has short out-
wardly faciny conical s~rface 22 which engages a cooperating
conical surface around the wall of passage 14. Mandrel 21 has
lower outwardly reduced portion 23 which its spacedly within
portion 17a of cap 17. Portion 23 of mandrel 21 has inner seal
24 and O-ring seal 25 to seal with thin walled port:ion 26 of a
tubular valve housing 27. The valve housing is tubular in form,
as i5 its upper thin walled portion 26. A piston tube 28 is
screwed at its outer threads 29 to corresponding threads at the
lower interior of valve housing 27. An annular accumulator space
30 is provided in the annulus formed between inner mandrel 15 and
piston tube 28. An annular floating isolator piston 31 is dis-
posed below valve housing 27 in accumulator space 30, and has
therearound inner and outer seals 32, 33 and O-ring seals 34, 35.
The seals 32-35 are preferably of a low friction type so that
piston 31 may be moved freely along the accumulator space under
low pressure differentials. Inner mandrel 15 has, at its lower
end, internal thread formation 38 to which is screwed a ball
~ ~t~ ;t~
housing 39. In inwardly ~hickened portion 39a of ball housing 39
there is pro~rided a gas char~ing valve 40 having lateral branch
40a (see also FIGS. 9 and 10) through which an inert gas such as
nitrogen may be introduced into accumulator space 30, the gas
passing through the annular space 41 between formation 39a and
piston tube 28. Valve housing 27 has around its interior an O-
ring seal 43. A valve body 44 is slidably disposed through a
cylindrical opening 45 partway through ~ody 27. At the left hand
end of passage 45, there is a short passage 46 of decreased
diameter and a cross passage 47 which intersects passage 46 at
its center. A conical shoulder 48 is provided between passage 45
and passage 46. A valve stem 50 is received at one end through a
piston 51 and fixed thereto by snap rings 52, 53. Valve body 44
is fixed in place in passage 45 by a shear pin 54. At its oppo-
site lower end, stem 50 has a second piston 56 fixed thereto by
snap rings ~7, 58. Stem 50 has an enlarged valve formation 59
(see FIGS. 5A and 10) having conical end 60 within a chamber 61
in body 44. Chamber 61 has conical seat end 62. Valve formation
59 seats at its surface 60 against surface 62, there being a
layer of sealing material 60a on surface 60. O-ring seal 63 is
provided around valve body 44. Stem 50 extends with clearance
through a passage 64 through body 44. Piston 56 has therearound
outer and inner O-ring ~eals 66, 66a.
A cylindrical screen 68 is disposed between the lower end
of housing portion 26 and the upper end of piston tube 28, as
shown, housing 27 having an interior recess 69 therearound at the
location of the screen. A helical compression spring 70 is
disposed between perforated washer 71 and the end of piston 56,
as shown~ washer 71 being supported by a snap ring 72.
-- 6 --
Passage 47 is plugged at 47a opposite recess 69, and pas-
sage 73 is plugged at its end 74. When pressured fluid from
passage 75 enters through screen 68 into passage 47, the pressure
acts on the lefthand (FIGS. 5, 5A, 10) side of piston 51.
Accumulator 30 pressure acts on the righthand side of piston 56.
Piston 51 is balanced because of fluid pressure from passage 75
entering to the righthand side of piston 51 through port 73.
Spring 70 urges the entire piston assembly toward the left.
Pressure from passage 75 also passes through port 73, chamber 61
and annulus 64 to act on the lefthand side of piston 56. When
the differential pressure of passage 75 is increased slowly, as
by slow operation of pumps 116 (FIG. 3)~ the pressure enters the
accumulator 30 through passages 78 without causing sufficient
differential pressure to develop across piston 56 to cause piston
formation 59 to be moved to the right to seat surface 60 at seat
620 ~owever, when the pressure in passage 75 is increased rapid-
ly, as by fast operation of pumps 116 (FIG. 3), then sufficient
differential pressure will be developed across piston 56 to
overcome the force of spring 70 and to cause surface 60 to seal
at seat 62 to shut off flow of the pressured fluid to the accumu-
lator 30.
For this reason, the valve assembly is termed a "fuse~,
because it will permit a flow under relatively lower pressure
differential conditions, but will close when the differential
pressure (between inlet and outlet) exceeds a certain pressure
level. The elevation of pressure at which the fuse closes is
controlled by the compression resistance of spring 70 and this
can be made of any desired value.
Fluid flowing past piston 59 through passage 64 outflows
-- 7 --
through passages 78. Flow through passages 78 is to check valve
assembly 79 having a ball valve 80, a spring 81, a seat 82 having
a sealing layer 83 and a seat opening 84. Flow through opening
84 depresses the ball valve against the bias of spring 81 and
permits flow through passage 85 into accumulator space 30. Flow
through passage 78 is blocked at plug 86. Fluid cannot flow in
the reverse direction from accumulator space 30 into passage 78
because of check valve 79.
As an alternative embodiment of the apparatus, check valve
79 may be replaced by a pressure relief type valve 44a. The
pressure relief type valve 44a would then act as a check valve
with a non-zero opening pressure. In addition, this alternative
arrangement permits building a bias between the tool bore and the
accumulator space 30. Such a bias can serve to overcome fric-
tional drag from piston seals and other non-ideal restraints. A
variable orifice (not shown) can be located on the charging
branch on the accumulator side of the fuse 44 and pressure relief
valve 44a, and this orifice can be adjusted to compensate for a
varying performance of pumps 116 (shown in FIG. 3).
Referring to FIGS. 1, 2, and 12, a pressure relief valve
119 is shown. Passages 125 of valve 119 are in communication
with the accumulator space 30 through end opening 125a. Spring
126 biases valve poppet 127 toward closed position against seat
ring 128 having seal ring 129 thereabove. The seat ring 128 is
held in place by a snap ring 130, as best shown in FIG. 12.
Spring 126 is disposed in a passage space 131 within the body 132
of valve 119. When the biasing pressure of spring 126 is over
come, valve 127 unseats from seat 128 and flow can pass upwardly
through valve 119 [as shown in FIG. 2.] A ball check valve 133
-- 8 --
J Jj~ -~
biased by compression sp~ing 134 pr~events backflow from passage
75 into the accumulator. By choosing the compression strength of
spring 126, ~low from the accumulator to passage 75 will not
occur unless a predetermined pressure differential exists.
Passage 135 communicates with passage 75, for flow of fluid from
the accumulator back into passage 75. Passage 125a, of course,
communicates with the interior of accumulator space 30.
Further down within passage 14 of the outer body 11, there
is provided the ball housing 39, which serves as a support for a
ball valve 94. Ball valve 94 has a flow passage 95 therethrough
which is of the same diameter as passage 75. ~all housing 39 has
therein a seat body 96 having a spherical seat 97 against which
the exterior of ball valve 94 is normally disposed in an open
condition. A seal 98 is provided at the seat surface. A pair of
O-ring seals 99, 100 are disposed inwardly and outwardly around
the upper end of member 96. A pair of O-ring seals 101, 102 are
disposed around the interior and exterior of lower member 103.
At the lower end of piston tube 28 where it contacts ball 94,
there are provided a plurality (usually four to eight) of the
rectangular notches 28a, allowing fluid in passage 75 to leak to
between ball valve 94 and seat body 96, so that when the ball
valve is closed, fluid will leak past the ball valve and the
fluid hammer described elsewhere is reduced. The ball valve 94
does not seat against the upper side of member 103 when closed so
the leak fluid can pass on down past the ball, the ball being
slightly displaced from seat member 96.
Referring now to FIG. 8 of the drawings, a pair of slide
elements 104, 105 are disposed one at each side of the ball, each
having an opening 107 to receive diametrically opposed pins
~ .J-~
108a, b at the sides of the ball and about which the ball
rotates. Each element 104, 105 has a pin 110 which operates in a
slot 111 in a face of the ball to cause rotation of the ball when
the ball supporting elements are moved upwardly and downwardly.
For a complete description of the operation of ball valve 94,
reference is made to U.S.P. No. 4,415,027, which contains such
description. Valve 94 is shown in FIG. 6 in open condition. The
valve 94 is moved to closed condition by downward movement
thereof. When tool bore pressure in passage 75 exceeds accumu-
lator pressurel the annular piston comprising the differential
area of valve housing upper portion 26 and piston tube 28 is
stroked downwardly. This stroke will cause ball 94 to rotate and
partially close so that it serves as further flow restriction to
passage 75, thereby amplifying the force on the inner mandrel 15
and transmitting a detectable water hammer pulse to the surface
to indicate tool function. Maintaining the resulting force on
inner mandrel 15 permits performing work, as exemplified in my
pending U. S. patent application serial no. 06/368,993, filed
April 16, 1982 and entitled Surface Controlled Bent Sub for
Direction Drilling of Petroleum Wells and now U.S. Patent
4,596,294, issued June 24, 1986.
Referring now to schematic FIG. 3 of the drawings, a supply
of drilling mud at the well surface is represented by symbolic
element 115. Drilling mud is pumped by one or more rig pumps 116
through the drill string 117, a portion of which is formed by
passage 75. The lower drill string 102 continues on down to a
drill bit, the bit nozzles of which are indicated symbolically by
reference number 118~ Portions of the drill string, of course,
are connected to the apparatus herein disclosed at internally
-- 10 --
threaded box 12 and at threaded pin 13~ The valve 44 shown in
FIG. 5 is indicated by its reference numeral in ~IG. 3, same
being described as a fuse for the reasons given. Check valve 79
is shown in FIG. 3, with suitable flow lines connecting filter
68, fuse 44, and check valve 79 and a flow line to the accumu-
lator 30. The return flow from the accumulator to passage 75 is
indicated by flow lines leading to a pressure relief valve 119
and a check valve 120. Flow therefrom passes through flow pas-
sage 121 back through filter 68 i~to passageway 75~
Referring to FIG. 4 of the drawings, a portion of the same
flow assembly as shown in FIG. 3 is shown, except that a relief
valve, mentioned earlier and referred to by reference numeral
44a, is substituted for check valve 79, as earlier described.
Referring to the system shown in FIG. 3l and also referring
to FIG. 11~ and noting Prr ~POPr P, and PO indicated thereon,
the operational sequence of adjusting the accumulator charge and
operating the tool will be described. The downhole hydrostatic
pressure at the least depth of desired tool actuation is known to
be approximately PO. The accumulator 30 is precharged at the
surface with nitrogen (through valve 40, shown in FIG. 9) to an
initial pressure Pl, less than Po~ Thus Pl<Po. As the tool is
lowered into the hole, the void areas in the valving and flow
passages will be filled with drilling fluid moving from drill-
string flow passage 75 through cylindrical ~creen 68. The float-
ing isolator piston 15 is not displaced until the pressure in the
flow passage 75r Pf, exceeds Pl. Normally the pressure Pf in the
flow passage builds smoothly and relatively slowly as the drill-
string is lowered. Typically some amount of fluid enters the
control valving 44 and 79 to displace the isolator piston 15 and
-- 11 --
substantially balance the accumulat:or pressure, Pa~ with the
external pressure Pf before reaching the least operating depth
(lowest required trigger pressure)
When the rig pump 116 is started slowly, the hydraulic fuse
44 does not experience sufficient differential pressure between
Pf and Pa to cause it -to close. Thus, there is one-way communi-
cation into the accumulator 30 through the fuse 44 and check
valve 79. In the meantime, check valve 120 remains seated,
against the contrary pressure gradient, blocking flow through the
accumulator exhaust passage 121. Therefore, when the pump starts
slowly, the accumulator pressure Pa will substantially equalize
to Pf, i.e., Pa~Pfo If the pump 116 i8 stopped, or slowed,
pressure Pf will reduce. Pump stoppage causes P~ to be equal to
the hydrostatic head at the tool depth. In the event that
Pa-~Pr>Pf, where ~Pr is the pressure differential that causes
relief valve 119 and check valve 120 to openr the accumulator
will exhaust fluid through return passage 121 into the main flow
passage 75 until Pa-~Pr=Pf. Henceforth, if the hydrostatic
pressure is unchanged and the pump 116 pressure does not exceed
~Pr~ the pump may be started rapidly without risk of triggeriny
closure of fuse 44.
If the tool is raised in the well so that the pressure Pf
is reduced, the accumulator will tend to relieve pressure by flow
through the relief valve 119 and check valve 120 as long as
Pa-~Pr>Pf. If the tool is lowered in the well or the pump pres-
sure is slowly raised so Pf-Pa<PFUSe, where PFUse is the closure
pressure differential for the fuse 44, then the accumulator will
tend to balance to pressure Pf by admitting flow through fuse 44
and check valve 79.
- 12 -
~2~ 7~-~
In order to operate the tool 10~ it is necessary to build
sufficient bias between Pf and Pa ,~POP is the pressure differen-
tial required to cause the piston tube 28 and coacting components
26 and 27 to stroke downwardly to operate the ball 94. Tool
operation will occur if P~~Pa~P~p~ Such a pressure differential
can be obtained by speeding up pump 116 sufficiently or using
other techniques in order to rapidly raise pressure Pf without
permitting equalization of accumulator pressure Pa to Pf. Rapid
building of Pf in excess of Pa causes 44 to close, thus fully
isolatiny the accumulator. ~fter sufficient time has been
allowed for performing "work~ of the type described in my pending
U.S. Patent Application Serial No. 06/368,993, and now U.S.
Patent 4,596,294, the excess pressure Pf may be reduced, permit-
ting return of piston tube 28. While a pressure differential
Pf~Pa>~Pop could be obtained by replacing fuse 44 with a
restrictive orifice~ such a system would lead to eventual reduc-
tion of the differential pressure below aPop~
This system readily permits adjustment of accumulator pres-
sures for increasing hydrostatic pressures, even with large
ratios of maximum P~/PO, by simple, straightforward pump manipu-
lations.
Referring to FIG. 4, the two systems (FIG. 3 and FIG. 4)
are structurally similar except for substitution of relief valve
44a for check valve 79. Such a system behaves identically to the
system of FIG. 3 except that an additional bias pressure equal to
the opening (relief) pressure of valve 44a, ~Px~ must be overcome
to admit flow into the accumulator 30. In this case~ Pa~ is the
accumulator pressure. Then Pa4=Pa-~PX, where Pa is the accum-
ulator pressure of the system of FIG. 3, may be substituted in
- 13 -
the pressure relationship described for the other case. Such a
bias has a variety of uses. For instance, the bias may be used
to overcome high seal frictions or help compensate for low pump
performances.
It should be noted that this method of accumulator charging
could be adapted to respond to annular pressures or other
sources. Further, the accumulator pressure charging circuit need
not be the same source of the pump side component of the differ-
ential pressure between the pump side and the accumulator side of
the control piston.
A snap ring 122 retains element 21 against upward movement
in passage 14.
Below the ball valve 94 assembly, passage 75 has an
upwardly facing conical shoulder 143 which limits downward move-
ment of the ball valve assembly. A spring-engaging element 144
at the lower end of the ball valve assembly has a slot 145, the
slot engaging a pin 146 screwed into a tapped opening through the
outer body and sealed therearound by an O-ring seal 147. Member
144 has a lower conical shoulder 148. Member 144 has lower
interior threads 150 to which is screwed a tubing 151 which con
tinues on down to lower level operator assemblies, adapted to
perform ~work" attached below tool 10. A helical compression
spring 152 engages between a shoulder 153 in the outer housing
and the lower end of member 144. A lubrication port 155 closable
by plug 156 permits lubrication of the lower interior elements of
the assembly. The outer body has an interior upwardly facing
shoulder 157 which may be engaged by surface 148. Restrictive
annular flow passages between the bore 14 of body 11 and the
outer surfaces of elements 144, 39, 1~ provides damping to
- 14 -
cushio~l downward motion of the mandrel, etc.
It will be understood that the accumulator 30 pressure may
be used for operation of other apparatuses than the ball valve
94. It will additionally be clear that an apparatus for accumu-
lator pressure control has been disclosed which may be operated
over a definite pressure range within the drill string to control
the accumulator pressure to any desired level, and that addi-
tional apparatus may be operated by drill string pressure outside
of the accumulator actuating range to do other operations in the
well. It will be realized that the apparatus herein disclosed is
simple in operation, safe, and readily understood by operators of
the well.
While preferred embodiments of the apparatus according to
the invention have been described and shown in the drawings, many
modification~ thereof may be made by a person skilled in the art
without departing from the spirit of the invention, and it is
intended to protect by Letter Patent all forms of the invention
falling within the scope of the following claims.
I claim:
