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The present invention relates to a flow restrictor and particularly, but not exclusively, to a flow restrictor for a hydrocarbon well.

When a hydrocarbon or injection well is drilled it passes directly through or into a hydrocarbon reservoir from which hydrocarbons will be produced to the surface. A bore is drilled into the hydrocarbon reservoir and a production string is introduced into the bore to enable extraction of the hydrocarbon to the surface or to allow liquid to be injected into the reservoir to improve production. Production tubing string is made up of individual tubing sections approximately 9.1 metres (30 feet) long. Attached to the top end of each tubing section is a coupling with two female thread forms to allow corresponding male threads on the end of the tubing sections to be threaded together to create one continuous tubing string.

The rock which makes up the reservoir may vary in type and physical characteristics, but the main characteristic of interest is the permeability of the rock. The permeability determines the ease with which fluids can flow through the rock and to/from the well.

Certain rocks such as sandstone have a relatively even permeability and are called homogeneous. Oil/gas can flow through the homogeneous rock at a relatively even pace and will be produced evenly across the drilled section of reservoir. Other reservoir rocks such as limestone and chalk can be heavily, naturally fractured and vary greatly in permeability. These rocks are known as heterogeneous. Oil/gas from a heterogeneous reservoir will produce mainly from the areas of highest permeability where the fractures occur.

Even though the well may be drilled through a considerable length of the reservoir, the high permeability zones may account for only 10-15% of the length of the drilled reservoir section. If allowed to produce directly into the

drilled hole and production tubing string, the hydrocarbons will never be produced from the remaining 85-90% of the drilled section thus reducing the efficiency of the well.

A second problem is that directly beneath the reservoir there is typically a layer of naturally occurring water. When a well is drilled the aim is to produce as much hydrocarbon as possible and to limit the amount of natural water produced. Over time as the hydrocarbon is depleted, it is replaced by the natural water seeping up from the rock below it. In a homogeneous reservoir the water may rise slowly and evenly, prolonging the time before water eventually breaks through into the well bore. In a heterogeneous reservoir the mixed permeability of the reservoir and the natural faulting may allow water to be produced almost immediately at the expense of hydrocarbon production.

To overcome these two problems of producing hydrocarbons from a heterogeneous reservoir a number of mechanical components have been designed to control the flow of hydrocarbons into the production tubing string. Historically the hydrocarbon was allowed to pass from the hole drilled through the reservoir directly into the production tubing string via the open end of the tubing string or via holes drilled evenly along the length of the tubing string. This method of production made no difference to the permeability of the reservoir and resulted in production from a limited portion of the drilled section leading to early water break-through.

It was discovered that if the flow of hydrocarbon from the reservoir could be mechanically restricted as it passed into the tubing string, the resulting back pressure created would allow sections of the reservoir with lower permeabilities that would not normally get a chance to produce, due to the higher permeability zones, to contribute to the well's production, This effectively increased the hydrocarbon producing area of the reservoir and extended the time before eventual water break-through.

Devices which invoke this effect come in a variety of forms and have the common feature of restricting flow by creating a pressure drop as the hydrocarbon passes through them. The restriction can take the form of a series of orifices or a tortuous flow path. The devices are provided in the production tubing string and are spaced out at intervals across the reservoir section.

As the hydrocarbon produces it will pass out of the reservoir rock and fill the annular area between the bore hole drilled through the reservoir and the outside of the production tubing string. It will then flow towards the flow restriction devices and enter the production tubing string as described above.

Due to the expense of these flow restriction devices a limited number are placed in the well. For example, a production tubing string passing through a 1000 metre section of reservoir may only be provided with between 5 and 10 devices. This limits the efficiency of the process and may reduce the extent of hydrocarbon producing zones and thus reduce the time until water breakthrough.

Canadian Patent No. CA 2,132,458 discloses a flow restrictor device of this nature.

In some instances, the back pressure created by these restrictors is not sufficient and those sections of the reservoir with lower permeabilities still do not contribute to the well's production.

The present invention seeks to provide for a flow restrictor having advantages over known such flow restrictors.

In this regard, the present invention relates to a device capable of creating a greater flow restriction than in known restrictors to increase the yield of the well. The result offered by the present invention will be a more efficient

production from a greater proportion of the reservoir and an extension of the time until water break-through.

According to an aspect of the present invention, there is provided a hydrocarbon well flow restrictor comprising: a tubular member, where said tubular member is arranged to present at least one aperture through a wall thereof between first and second ends of said tubular member, the aperture having selectively variable dimensions for control of fluid flow therethrough; and a plurality of vanes located on an exterior surface of said tubular member which upstand from said surface, said vanes being arranged to space at least a portion of the surface from walls of a well and said vanes further being arranged to affect pressure of fluid in the region thereof.

An advantage of the present invention is that the vanes provide a pressure affect on the fluid in the region of the vanes towards the aperture which is in addition to that provided by the aperture itself.

If required, the vanes may be configured to decrease the pressure of fluid in the region thereof.

Conveniently, said vanes may be configured to employ a Venturi effect on fluid in the region thereof.

Preferably, fluid flow around the vanes of the flow restrictor may be influenced by the spacing between adjacent vanes.

Conveniently, fluid flow around the vanes of the flow restrictor may be influenced by the configuration of the vanes.

Further, fluid flow around the vanes of the flow restrictor may be influenced by the shape of the vanes.

If required, said vanes may be substantially parallel to each other.

In particular, said vanes may be formed as part of said tubular member.

Preferably, said vanes may be discrete elements secured to said tubular member with securing means.

Conveniently, said vanes may be located either at one end, or both ends of said tubular member and, in either case, extend toward a region between said first and second ends.

Further, said at least one aperture may be formed in said region.

If required, said vanes may extend across said region.

Also, said plurality of vanes may be proximate said at least one aperture.

In particular, said tubular member may comprise an internal thread arranged to engage with a corresponding thread on an exterior of a production tube, to secure the flow restrictor to the production tube, with the flow restrictor being secured such that said at least one aperture is aligned with a corresponding at least one aperture of the production tube.

Alternatively, said tubular member has at a first end thereof first means for engagement with an end of a first production tube and, at a second end thereof, second means for engagement with an end of a second production tube.

According to another aspect of the present invention, there is provided a pipeline system comprising a plurality of production tubes and at least one flow restrictor as described above.

The present invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which.

Fig. 1 illustrates a side view of a flow restrictor according to a first embodiment of the present invention;

Fig. 2 illustrates a cross-sectional view of the flow restrictor of Fig. 1 and a plan view of the flow restrictor;

Fig. 3a illustrates a perspective view of a flow restrictor in a second embodiment of the present invention;

Fig. 3b illustrates a perspective view of a production tube adapted to receive the flow restrictor of Fig. 3a;

Fig. 4 illustrates a side view of a flow restrictor according to a third embodiment of the present invention; and

Fig. 5 illustrates a schematic view of a conventional well, particularly an injection well, to indicate uneven distribution of an injected fluid.

As mentioned, Fig. 1 illustrates a flow restrictor 10, which comprises: a body section 12; at least one aperture 14 formed in the body section 12; and a plurality of centralising vanes 16.

Body section 12 comprises a tubular member (preferably a thin-walled steel cylinder) and the at least one aperture 14 is formed/provided in the wall of the body section 12 and extends between an exterior surface of the body section 12 to an interior surface of the body section 12 to allow fluid communication between the exterior and interior of the body section 12, The at least one aperture 14 is formed/provided preferably at the mid-point along the length of the body section 12.

Preferably, a plurality of apertures 14 are formed/provided in the wall of the body section 12 and are equally spaced around the perimeter of the body section 12.

In one arrangement, the apertures can themselves form the means by which fluid flows from the exterior of the body section 12 to a flow passage of the production tubing string in the interior of the body section 12, However, in a preferable embodiment, the apertures are each arranged to receive a corresponding nozzle (not shown) or blank nozzle (not shown).

The nozzles/blank nozzles may engage with the apertures formed in the body section 12 by any suitable means, but preferably the apertures are provided with a thread, with such a thread arranged to mate with a corresponding thread provided on the exterior of the nozzle or blank nozzle. Thus, the nozzle or blank nozzle can be threaded directly into the apertures of the body section 12.

Each nozzle has an internal orifice of given diameter to create a specific pressure drop for a specific flow rate of oil and water. By altering the number of nozzles installed in each flow _re strictor 10 _an d/or the size of the orifice selected, an operator can pre-set the desired pressure drop for a given flow rate.

In order to resist erosion from the produced fluid over time, the nozzles/blank nozzles are preferably manufactured from a very hard, wear-resistant, material such as tungsten carbide.

The blank nozzles have substantially the same external dimensions as nozzles so that they can be threaded into the apertures in body section 12.

However, the blank nozzles differ from nozzles in that they do not have an orifice and so do not allow fluid to pass between the exterior of the flow restrictor 10 and the flow passage of the production tubing string in the interior of the flow restrictor 10. Thus, the blank nozzles can be used to replace nozzϊes if the flow area through the combined nozzles/blank nozzles is to be limited further.

The centralising vanes 16 are located around the periphery of body section 12 and serve to hold the body section 12 and apertures/nozzles away from the faces of the well bore hole in the reservoir.

These vanes 16 are formed so that they upstand from a surface of the body section 12 and are formed at each end of the body section 12 and extend from the ends of the body section 12 toward the mid-point of the body section 12 between the ends.

In the illustrated arrangement, the vanes 16 are straight and substantially parallel, but this need not be so, and the vanes could be curved and/or not in parallel with each other.

Channels 18 are formed between adjacent vanes, and it is through these channels 18 that fluid will flow to reach the apertures 14 when the flow restrictor 10 is in-situ.

Typically, a well bore hole is drilled horizontally or at a very shallow angle with the result that a production tubing string within the bore hole will lie against one side of the bore hole. Thus, without the centralising vanes 16, the body section 12 might lie directly against the oil-well bore hole face and the entrance to the apertures/nozzles would be partially or fully blocked, thereby affecting the desired pressure restriction characteristics of the present invention.

A second purpose of the centralising vanes is to create a Venturi effect on the fluid flow prior to the flow reaching the apertures/nozzles.

The centralising vanes 16 are shaped and arranged with respect to each other to provide this Venturi effect, and the effect produced creates a pressure change, and particularly a pressure drop that can be combined with that provided by the apertures,

In the illustrated arrangement, the centralising vanes 16 are formed as part of the body section 12, but need not be integral with the body section 12 and could, for example, be discrete elements attached to the body section 12 by, for example, screws.

As illustrated, the centralising vanes 16 are provided at each end of the flow restrictor 10. However, in an alternative arrangement, the vanes may be provided at only one end of the flow restrictor 10.

Flow restrictors 10 are provided in the production tubing string across a reservoir zone. Produced hydrocarbons can only enter the production tubing string through the apertures 14 in the flow restrictors. Both the apertures 14 and the centralising vanes 16 restrict the flow of fluid into the production tubing string creating a pressure drop for any given flow rate which can be varied by altering the number of apertures 14, the diameter of the orifice in each nozzle (if such nozzles are provided), and the shape and configuration of the centralising vanes 16. The pressure drop created allows fluid to be produced from areas of the reservoir which would otherwise remain unproductive as the fluid would take the path of least resistance and flow only from the most permeable regions.

The features illustrated in Fig. 2 which correspond to features already described in the above embodiment are denoted by like reference numerals and will not be discussed further.

As stated above, Fig. 2 illustrates a cross-sectional side and plan view of the flow restrictor 10 of Fig. 1. In the illustrated plan view, the body section 12 is provided with six equally spaced apertures about its periphery, with each of the apertures each containing therein a nozzle 20.

Also, in the arrangement of Fig. 2, the apertures of the body section 12 for receiving the nozzles 20 are located at positions around the periphery of the body section 12 such that pairs of said apertures are diametricaiϊy opposite,

Fig. 3a illustrates another arrangement of the flow restrictor 10 of the present invention. Again, those features which correspond to features already described above are denoted by like reference numerals and will not be discussed further.

In the illustrated arrangement, the tubular member forming body section 12 has provided on its internal surface a thread 22. The purpose of this thread 22 will be explained further in the description relating to Fig. 3b below.

Fig. 3b illustrates a production tube 24 which can form part of a production tubing string in a well. The production tube has formed in its wall at least one aperture 26 which extends between an exterior surface of the tube and an interior surface of the tube to allow fluids to pass therethrough. In addition, the production tube 24 has a thread 28 formed on its exterior surface in the region of the at least one aperture 26.

The diameter of the bore of the body section 12 is slightly larger than the external diameter of the production tube 24 such that the production tube 24 can pass into the bore of body section 12. In this respect, the body section 12 is a sleeve about the production tube 24. As will be appreciated, when the production tube 24 is passed into the bore of the body section 12, the thread 28 of the production tube 24 can engage with the thread 22 of the flow restrictor 10 to enable the flow restrictor 10 to be secured to the production tube 24.

The arrangement of the at least one aperture 26 of the production tube 24 is such so that, when the flow restrictor 10 is secured in place, the apertures 14 of the flow restrictor 10 are coincident with the apertures 26 of the production tube 26. The alignment of the two sets of apertures in such a manner allows fluid which is external to both the production tube 24 and flow restrictor 10 to pass through the aligned sets of apertures into the interior of the production tube 24.

In the illustrated arrangement, the production tube 24 is arranged to secure the flow restrictor 10 at a mid-point of the production tube 24. However, the production tube 24 can be adapted to secure the flow restrictor 10 at any point along its length merely by altering the position at which the threads 28 are provided on the surface of the production tube

24.

As stated above, Fig. 4 illustrates a side view of a flow restrictor in yet another arrangement of the present invention.

The features illustrated in Fig. 4 which correspond to features already described above are denoted by like reference numerals and will not be discussed further.

In the illustrated arrangement, the flow restrictor 10 is provided at one end thereof with a male thread section 30 and, at another end thereof, with a female thread section 32. In this regard, the flow restrictor 10 can act as a spacing means between adjacent production tubes of a production tubing string.

As will be appreciated, if a production tube is provided with a female thread at one end thereof and a male thread at the other end thereof, these can engage with a corresponding male thread section 30 or female thread section 32 of the flow restrictor 10 respectively. By providing a flow restrictor 10 between adjacent production tubes, the production tubes can be linked together to form a production tubing string which benefits from the advantages of the present invention.

Fig. 5 illustrates a conventional injection type well where a conventional production tubing string 34 extends from surface 36 to a region of hydrocarbon bearing strata 38. An openhole section 40 extends from the end of the production tubing string 34 into the hydrocarbon bearing strata 38.

The figure illustrates the distribution of fluid 42 which has been injected into the well. This fluid may be injected to improve the production of hydrocarbons from the well or may be for cleaning purposes. As will be appreciated from the figure, the injected fluid 42 is unevenly distributed. However, by incorporating the flow restrictor of the present invention in the conventional production tubing string 34, this will provide an even pressure distribution across the well, and so injected fluid will be evenly distributed.

In chemical injection processes, extra equipment is required, such as coil tubing, to direct the injected chemicals to a certain zone within the well, since if the chemicals are injected at surface, the majority of injected fluid will flow into the heel of the well, and not be distributed evenly throughout the production region. However, in a well provided with flow restrictors according to the present invention, extra equipment is not required since the pressure distribution is evenly spaced along the well, with the result that the injected chemicals will follow this pressure distribution.