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.

Description

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.

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.

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.

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.

The basic idea for all such methods is to drive more hydrocarbons out of reservoir.

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.

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.

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.

It is therefore an object of the present invention to minimize and possibly alleviate these problems.

It is further an object of the present invention to provide a device that eliminates or minimizes flow instability.

There is also an object of the present invention to provide a device with a low operating pressure difference.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

FIG. 1 shows a cross section of a first embodiment of the present invention.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.