U.S. patent application number 12/670860 was filed with the patent office on 2010-08-26 for stealth orifice.
This patent application is currently assigned to PETROLEUM TECHNOLOGY COMPANY AS. Invention is credited to Ole Sevheim, Oyvind Stokka.
Application Number | 20100212908 12/670860 |
Document ID | / |
Family ID | 40040039 |
Filed Date | 2010-08-26 |
United States Patent
Application |
20100212908 |
Kind Code |
A1 |
Stokka; Oyvind ; et
al. |
August 26, 2010 |
Stealth Orifice
Abstract
The present invention regards a surface controlled device
designed for injection of fluids in a well bore, typically Man
offshore well bore for petroleum production and gas injection/gas
lift system for fluid injection. The device comprises a outer
hollow housing (1) with at least one inlet and outlet and an
internal body (2) moveable in a longitudinal direction within the
outer N housing (1). An inlet, in form of a variable orifice, is
connected, through a mainly longitudinal bore of the internal body,
with at least one slot. The present invention will give a fluid
exiting the device with a minimal amount of energy or pressure loss
over the device.
Inventors: |
Stokka; Oyvind; (Sandnes,
NO) ; Sevheim; Ole; (Stavanger, NO) |
Correspondence
Address: |
CHRISTIAN D. ABEL
ONSAGERS AS, POSTBOKS 6963 ST. OLAVS PLASS
OSLO
N-0130
NO
|
Assignee: |
PETROLEUM TECHNOLOGY COMPANY
AS
Stavanger
NO
|
Family ID: |
40040039 |
Appl. No.: |
12/670860 |
Filed: |
August 6, 2008 |
PCT Filed: |
August 6, 2008 |
PCT NO: |
PCT/NO2008/000284 |
371 Date: |
February 22, 2010 |
Current U.S.
Class: |
166/319 |
Current CPC
Class: |
E21B 43/123
20130101 |
Class at
Publication: |
166/319 |
International
Class: |
E21B 34/06 20060101
E21B034/06; E21B 43/12 20060101 E21B043/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2007 |
NO |
20074105 |
Claims
1. Device for injection of fluids in a process fluid for use in a
well bore, comprising an outer hollow housing with at least one
inlet and one outlet and an internal body movable in a longitudinal
direction within the outer hollow housing and hereby forming a
closed and open state of the device, where the movement of the
internal body is operated by pressure differential across the
device, wherein the internal body further comprises a mainly
longitudinal bore with an outlet in the form of at least one slot
from the bore to an outside of the internal body and that the
internal bore at an inlet comprises an orifice with a variable
cross section along the longitudinal axis of the bore.
2. Device according to claim 1, wherein the orifice is a separate
unit, mounted to the internal body by a threaded connection.
3. Device according to claim 1, wherein the orifice is divided into
an inlet section, a middle section and an outlet section, where the
inlet and outlet sections have a form of a truncated cone.
4. Device according to claim 3, wherein the sides in the truncated
cone are rectilinear.
5. Device according to claim 3, wherein the sides in the truncated
cone are curvilinear.
6. Device according to claim 3, wherein the inlet section has a
wider opening angle than the outlet section.
7. Device according to claim 3, wherein the middle section has an
inner uniform surface which is mainly parallel with the
longitudinal bore of the internal body, and where a cross section
of the middle section is smaller than a cross section of the
longitudinal bore.
8. Device according to claim 3, wherein an end termination of the
outlet section is extended a length into the longitudinal bore.
9. Device according to claim 3, wherein the center axis of the
middle section is misaligned according to a center axis of the
internal bore.
Description
[0001] The present invention regards a device for injection of
fluids in a well bore, typically a well bore for petroleum
production, and in particular for a gas lift valve, which is used
to inject high pressure gas into a tubing string disposed in a well
bore for the purpose of aerating and/or displacing the liquid in
the tubing string, thereby lifting the liquid to the surface or top
of the well bore.
[0002] In producing hydrocarbons, including water, oil, oil with
entrained gas and gas, from a geological formation, natural
pressure in the formation is employed to lift the hydrocarbons
upwards to the ground surface. This pressure can decrease over the
life time of the well and will require assist to improve lift,
where this can be done by artificial supplying of energy to the
liquid or medium in the production tubing. One known method to
increase lift is to inject a medium into the production tubing.
This injection is usually done by forcing the medium down the
annulus between the production tubing, which tubing conducts
hydrocarbons to the surface, and the (steel) casing of the well,
further through a device for injection and into the production
tubing. Here the medium will mix with the hydrocarbons, thus
reducing the overall density of the mixture, which will lead to
that lift in the well bore is improved. The medium that is to be
injected into the production tubing is usually gas or water,
although other constituents such as well stimulation fluids etc.
also can be used.
[0003] The properties and/or flow of the injected gas or water have
however to be controlled, as parameters like pressure, speed,
density etc are critical in order to obtain most favourable
conditions in the production tubing. The two most common types of
gas or water control devices that are employed to control the
injected medium into the production tubing are gas lift valves and
orifices.
[0004] Other production enhancement method exists through
installation of sub sea or sub surface electrically driven pumps or
other elements to assist the production flow out of the production
tubing.
[0005] The basic idea for all such methods is to drive more
hydrocarbons out of reservoir.
[0006] Several different principles of operating a gas injection
valve are known, one of these is based on the venturi principles,
for instance as described in WO 2004/092537 A1. One another
approach is to have a central stem with outer sealing surface and a
through going flow between an outer housing and the central stem
across the sealing surfaces, for instance as described in CA
02461485 A1.
[0007] A common problem that arises in connection with gas lift is
flow instability where this is characterized by large flow rate and
pressure fluctuations that can cause severe separation and gas
injection distribution problems. These gas lift instabilities are
associated with low productivity wells that have a large annulus
and/or produce at low gas injection rates. In addition, gas lift
instability can also occur if the flow through a gas flow control
device is in the sub critical flow range. In the critical or sonic
flow range, the production pressure does not affect the gas flow
rate through the device and flow instability cannot occur. The gas
flow control device may be preferred to be in critical or sonic
flow range with the least possible pressure differential across the
device.
[0008] In order to prevent flow instabilities, one can increase the
gas injection rate and or choke the production of the hydrocarbons
at the wellhead. This will however result in that the gas injection
is to be performed above the most economical rate and the choking
reduces rate of production. Thus, there are economical objections
to the usual measures for managing with gas lift instability.
[0009] It is therefore an object of the present invention to
minimize and possibly alleviate these problems.
[0010] It is further an object of the present invention to provide
a device that eliminates or minimizes flow instability.
[0011] There is also an object of the present invention to provide
a device with a low operating pressure difference.
[0012] These aims are achieved with a device for injection of fluid
according to the invention as defined in the enclosed independent
claim, where embodiments of the invention are given in independent
claims.
[0013] The present invention is intended to provide a device for
altering flow characteristics that eliminates or minimizes flow
instability, where the device comprises an outer hollow housing
with an internal body (a so-called dart). The internal body is
movable in the longitudinal direction of the outer housing and
comprises an internal bore. In order to permit the fluid to flow
through the device, both outer housing and internal body is formed
with at least one inlet and outlet, where the internal body
restrain the passage through the device in a closed position. When
a pressure differential over the device at a given value is large
enough, the internal body will be forced to move to an open
position. In this position the outlets of the internal body and the
outer hollow housing correspond to each other, thereby letting the
fluid which is to be injected in the production tubing,
through.
[0014] This pressure differential may be a fluid pressure operating
on surfaces of the internal body, which surfaces may be exposed to
different fluids. These fluids may be well fluids on one or more
surfaces for operating the device or injections fluid on one
surface and well fluid on another surface or combinations.
According to an aspect the pressure differential across the
internal body may be assisted by at least one predetermined
pressure balanced elastic element to open and close the device.
[0015] The inlet of the internal body is connected to the outlet of
the internal body through the internal bore, where the inlet is in
form of a variable orifice. With variable orifice it should be
understood in this application that the orifice is changing in form
over its length when seen in the longitudinal direction of the
device. The orifice is further a separate unit which can be mounted
to the internal body through a threaded connection thereby
following the movement of the internal body, or the orifice could
be fastened to the internal body by different adhesives, locking
ring(s), set screw(s) etc.
[0016] According to an other embodiment the orifice can be mounted
or fastened to the inner surface of the outer hollow housing by for
instance adhesives, threaded connections etc.
[0017] In order to achieve a critical flow through the device, the
orifice has a variable design over its length. In a first
embodiment the orifice is divided into an inlet section, a middle
section and an outlet section, where the inlet and outlet sections
have form of a rectilinear truncated cone. The length of each
section, when seen in the longitudinal direction of the device, can
be different, where this will depend on the medium to be used in
the device etc. The medium used will also affect the shaping of the
different sections, where this for instance can give that the inlet
section has a wider opening angle than the outlet section. The
inner surface (walls) of the inlet and outlet sections form an
angle to a horizontal line, where this line is an imagined
extension of the inner surface of the middle section.
[0018] The inner surfaces of the orifice will give minimal
resistance to the flow of medium as the medium run through the
orifice. This may be achieved by machine the inner surfaces of each
section or by coating the inner surface with a coating.
[0019] The truncated cone can in alternative embodiments of the
present invention have sides that are curvilinear, for instance
convex or concave or any other form, where both the inlet and
outlet section can be shaped in same form. It can also be imagined
that the inlet and outlet section can be combinations of the above
described forms, for instance can the inlet section have a concave
form while the outlet section can have a convex or rectilinear
inner surface.
[0020] The middle section of the orifice can in a first embodiment
of the invention have an inner uniform and rectilinear surface,
which is parallel with the surface of the longitudinal bore of the
internal body. The cross section of the middle section can further
be smaller than the cross section of the longitudinal bore. The
inner surface of the middle section can also have other forms, for
instance an expanding or increasing form, curvilinear etc.
[0021] It is also possible that a center axis of the middle section
is displaced compared with a center axis of the longitudinal bore,
where this will give that the inner surface of the middle section
that is misaligned, but parallel, with the inner surface of the
internal bore.
[0022] In yet another embodiment an end termination of the outlet
section can be extended a length into the longitudinal bore. This
can result in, as described above, that the orifice do not have to
be mounted to the internal body, but can in appropriate ways be
connected to the inner surface of the outer housing. The end
termination may for instance be a sleeve that is mounted to the
outlet section where the sleeve has a diameter that is slightly
smaller than the inner diameter of the internal bore. This will
cause that only the internal body is moved when the pressure is
large enough to move it to an open position.
[0023] The orifice unit can be manufactured from any suitable
material, for instance in a metallic or other casted/moulded or
ductile material. A skilled person will know how this can be
done.
[0024] Even though the device above is referred to as a gas
injection device, it is to be understood that the principles of the
device may also be used for other kind of injection valves. This
may for instance be when the device is used for injection of other
constituents such as well stimulation fluids, cutting injection,
water injection etc.
[0025] These features of the present invention will provide a
device where the flow path of the injection fluid is substantially
less tortuous than other known gas injection valves due to more
direct flow through the bore in the internal body and directly out
through the slots.
[0026] This also gives less pressure losses across the valve. By
designing the inlets, orifice, outlets and the slots of the device,
one could achieve the desired effect with regard to flow pattern
and cavitations. The present invention is also a simplified device
with few elements, compared with the majority of other known
injection valves. This gives a more reliable device as well. The
present invention also has a relatively large flow area through the
device, compared with the majority of other known injection valves
of similar size.
[0027] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred non-limiting embodiments of the invention,
as illustrated in the accompanying drawing, where
[0028] FIG. 1 shows a cross section of a first embodiment of the
present invention.
[0029] In FIG. 1 is shown a first embodiment of a device according
to the invention, where the device is used as a gas lift valve
which is to be positioned in a well stream. A skilled person will
understand how this is done and this is therefore not described in
this application.
[0030] In the FIG. 1 the device, normally used as a gas lift valve,
comprises an outer hollow housing 100 with an internal body 2
movable within the outer hollow housing 100. The internal body 2 is
movable between a closed and an open position of the device, and is
in this embodiment shown in an open position. The outer hollow
housing 100 in this embodiment is manufactured of a main part 1 and
a nose 11. The nose 11 is connected to the main part 1 with
suitable means, for instance by a threaded connection. In the outer
hollow housing 100 are arranged one or more inlets 14 for injection
fluid, where these inlets 14 are arranged around the circumference
of the outer housing 100. In the shown embodiment the outer hollow
housing 100 is arranged with four slots, two and two placed above
each other. The inlets 14 are in contact with an injection fluid
source (not shown). On the opposite end of the outer housing 100,
that is in the nose 11, there are arranged one or more outlets 5,
these outlets 5 also being placed around the circumference of the
nose 11.
[0031] From the inlets 14 the injection fluid is flowing into an
internal void 15 of the outer hollow housing 100 through an orifice
4 and into an internal bore 3 of the internal body 2. The orifice 4
in this embodiment is a separate unit, but is mounted by a threaded
connection 7 on an outside of one end of the internal body 2, and
forms therefore part of the internal bore 3. The bore 3 stretches
in the longitudinal direction of the internal body 2 from an end of
the internal body 2 and nearly to the other end of the internal
body 2. The injection fluid will thereafter in an open position of
the valve flow trough one or more slots 6 leading from the internal
bore 3 to the outside of the internal body 2. In the shown example
four slots 6 are arranged around the circumference of the internal
body 2, but there may of course be less or more slots 6 arranged
around the circumference of the internal body 2. In an open
position of the valve the slots 6 of the internal body are aligned
with outlets 5 in the outer hollow housing 100, thereby leading the
injection fluid out into the process fluid flow. The injection
fluid will in this open position of the device therefore have a
flow pattern with a minimum amount of bends and or other
obstructions, where this will result in minimal pressure losses
across the valve.
[0032] As can be seen in the figure, the internal body 2 comprises
an annular, valve sealing surface 19, with a mainly conical shaped
surface. This surface 19 is arranged close to an end of the
internal body 2 with the end of the conical shaped surface 19 with
the larger diameter, furthest away from the slots 6 of the internal
body 2. The slots 6 are arranged close to an end of the internal
body 2, and the surface 19 closer to the same end of the internal
body 2. The sealing surface 19 of the internal body cooperates with
a valve seat 20 arranged in the outer hollow housing 100. The valve
seat 20 in the outer hollow housing 100 is arranged on the relative
speaking other side of the slots 6 and outlets 5, where these are
aligned in an open position of the valve, compared with the sealing
surface 19 of the internal body, seen in the longitudinal direction
of the device. In a closed position, the internal body 2 is moved
relative the outer hollow housing 100 so that the sealing surface
19 is abutting the valve seat 20, giving a sealed, metal to metal
seal for the valve. In this closed position the slots 6 of the
internal body 2 will be positioned within the valve and the outlets
5 of the outer hollow housing on the other side of the interaction
between the sealing surface 19 and the valve seat 20. The sealing
surface on the internal body 2 and the valve seat 20 in the outer
hollow housing 100 will in an open position of the device be at
least partly covered by the other element of the device, outer
hollow house 100 and internal body 2 respectively.
[0033] The orifice 4 have an important purpose in the device and
that is to gain a critical flow for the injection medium, where
this is obtained by separating the orifice 4 in three different
sections, namely an inlet section 8, a middle section 9 and a
outlet section 10, leading the injection medium into the internal
bore 3. Although it in the figure is shown that the orifice 4 is
consisted of three sections it should be understood that the
orifice 4 also could be divided into more sections. The sections 8,
9, 10 are connected with each other and can be made by machining
the orifice 4 unit or by moulding. A skilled person will know how
this could be done.
[0034] In this embodiment the length of the different sections 8,
9, 10 in the orifice 4, when seen in the longitudinal direction of
the device, are different, but they can also be of equal lengths.
The inlet section 8 and the outlet section 10 have a form of a
truncated and rectilinear cone Inner surfaces or walls of the inlet
section 8 and outlet section 10 form an angle 13 with a horizontal
line 12, where this horizontal line 12 is an imaginary prolongation
of the inner surface of the middle section 9. This angle 13
(opening angle) may for instance be up to eighty degrees, and in
the shown embodiment the opening angle of the inlet section 8 is
larger than the opening angle of the outlet section 10. The inlet
section 8 will further narrow in to the same form or cross section
as the middle section 9 has.
[0035] The middle section 9, that connects the inlet section 8 and
the outlet section 10, is shaped as a bore, where the inner surface
is uniform and rectilinear. A centre axis 21 of the middle section
9 coincides with a centre axis 21 of the internal bore 3, and the
inner surface of the middle section 9 is therefore parallel with
the inner surface of the internal bore 3. The middle section 9 has
further a smaller diameter than the internal bore 3.
[0036] The outlet section 10 will have its smallest cross section
where it is connected to the middle section 9, and will thereafter
widen out when seen in the longitudinal direction of the device,
until it connects with the internal bore 3.
[0037] Cross sections taken along planes perpendicular to the
centre axis 21 of the orifice 4 have a circular form. Other
geometries can however be possible.
[0038] In one other embodiment of the present invention, the
orifice 4 still is formed as a truncated cone, but the inner
surfaces or walls of the inlet section 8 and outlet section 10 are
concavely shaped.
[0039] When the device is used as a gas lift valve, pressurized gas
at injection pressure enters device through inlets 16 and into the
internal void 15 of the outer hollow housing 100, and flows
thereafter through the orifice 4. The pressurized gas will gain an
increase in flow velocity and reduction in pressure through the
inlet section 8 of the orifice 4, where these parameters are
"stabilized" in the middle section 9 of the orifice 4; over the
outlet section 10 the flow velocity for the pressurized gas will
decrease while the pressure will increase until the pressurized gas
enters the internal bore 3, through which the parameters again are
"stabilized". The gas is then discharged through slots 6 and
outlets 5 at production pressure, and passes into the production
tubing.
[0040] Only elements related to the invention is described and a
skilled person will understand that an outer hollow housing or
internal body may be formed in one unit or be comprised of several
connected elements, and that the inlets have to be connected to a
source of fluid to be injected, that there should be appropriate
attachment devices for attaching the valve within a process fluid
stream, and that there of course will be arranged for instance
sealing element between several elements as a standard. The skilled
person will also understand that one may make several alterations
and modifications to the described and shown embodiments that are
within the scope of the invention as defined in the following
claims.
* * * * *