GB2308995A

GB2308995A - Downhole separation apparatus

Info

Publication number: GB2308995A
Application number: GB9600600A
Authority: GB
Inventors: Bill E Bowers; John Gunnar Hole
Original assignee: Vortoil Separation Systems Ltd
Current assignee: Vortoil Separation Systems Ltd
Priority date: 1996-01-12
Filing date: 1996-01-12
Publication date: 1997-07-16
Anticipated expiration: 2016-01-12
Also published as: GB2308995B; GB9600600D0

Abstract

Fluid separation apparatus suitable for use in a borehole (ie: narrow, elongate and cylindrical) comprises a body 1 containing one or several cyclones 4, 5 operating in parallel. The cavity C of the body 1 acts as the conduit for the fluid feedstock (oil and water) which arrives under pressure from a well or from a pump. The fluid enters each cyclone tangentially through a hole 6 in the wall of the wide portion of each cyclone. The overflow output streams of the cyclones are combined in one pipe 9 and 10 and the underflow output streams in another pipe 7 and 8. The cyclones are staggered and vertically stacked, with their output pipes of non-circular cross-section 7A so as to optimise the limited amount of space available.

Description

DOWNHOLE SEPARATION APPARATUS The present invention relates to a downhole separation apparatus. Such an apparatus is particularly useful for making a preliminary separation of oil from water in a production fluid down an oil well prior to the production fluid being transported to the surface.

Both W0 94/13930 and US-A-5296153 disclose such a separation apparatus in which one or more cyclonic separators are contained within an axially elongate tubular housing with the inlet of the or each separator extending to the wall of the housing, and having an opening externally of the housing. The separated streams from the or each separator are transported from the housing by a system of pipes. With these apparatus there must be sufficient clearance between the housing and the adjacent well casing to provide a flow annulus for the production fluid to the separator inlets. This reduces the maximum diameter of the housing for a given casing size, and hence reduces the separation capacity.Further, the internal space within the housing and outside of the separators and pipework is dry, so that there is a pressure differential across the wall of the housing, and the housing must also be sealed against the full well bore pressure.

According to the present invention, there is provided a downhole separation apparatus comprising an axially elongate tubular housing defining an internal chamber, and having at least one inlet which, in use, is arranged to allow production fluid to flood the chamber, at least one cyclonic separator contained in the chamber and having an inlet open to the chamber so that, in use, the production fluid in the chamber enters the or each separator, wherein an overflow outlet and an underflow outlet of the or each separator are connected to pipes which lead out of the chamber.

By flooding the chamber containing the separator(s) in this way, it is unnecessary to provide a flow annulus to the separator inlet(s) between the housing and the well casing, so that the gap between the housing and the well casing can be reduced to that which is necessary to provide adequate clearance for running the housing into the casing.

It is even possible, if a cheap apparatus is required, to use the well casing as the housing, in which case, the chamber is defined between the well casing, and a pair of axially spaced packers. The present invention also allows the maximum diameter of the housing for a given casing size can be increased so that the capacity of the separation apparatus is increased. Further, as there is a reduced or no pressure differential across the housing wall it is unnecessary to provide the heavy duty seals required by the prior art, nor is the same structural integrity required of the housing.

If the pressure in the well bore is low enough that pumping of the production fluid prior to separation is required, the separation apparatus preferably comprises a pump unit which discharges into the chamber. If, on the other hand, the pressure in the well bore is sufficiently high that no upstream pumping is required, the housing can be provided with a plurality of apertures so that the production fluid can enter the housing at a plurality of locations along the length of the tubular housing. In this case, the apertures can be sized to be smaller than the smallest critical size of the separator(s), to prevent blockage of the separator(s).

Preferably a plurality of axially spaced separators are contained in the chamber. In order to provide increased capacity, it may be desirable, in some cases, for adjacent separators to face in opposite directions, with some axial overlap between the tailpipes of adjacent separators.

In order to reduce the complexity of the pipework and seals required, it is desirable for the pipes leading from the overflow outlets of the separators to be connected within the chamber to a common overflow outlet manifold, and for the pipes which lead from the underflow outlets of the separators to be connected within the chamber to a common underflow outlet manifold.

For most applications the overflow outlet manifold will leave the chamber at one end of the housing for the transportation of an oil enriched stream to the surface, while the underflow outlet manifold will leave the chamber at the opposite end of the housing for the transportation of an oil depleted stream for downhole disposal.

If all of the overflow outlet pipes discharge through one end of the housing and/or all of the underflow outlet pipes discharge through the opposite end, it will be necessary for a pipe leading from the overflow outlet of a separator to pass the separator or separators positioned above it in the chamber, and/or for a pipe leading from the underflow outlet of a separator to pass the separator or separators positioned below it in the chamber. In this case, the space available for a pipe will be limited adjacent to the head of each cyclonic separator, which by its nature is the widest part of a cyclonic separator. At such locations, it is preferable for the pipe to be formed with a non-circular cross section having substantially the same area as adjacent portions of the pipe. Preferably, the non-circular cross section is substantially kidney shape.

An example of a separation apparatus constructed in accordance with the present invention will now be described with reference to the accompanying drawing which shows a broken axial section of a separation apparatus constructed in accordance with the present invention.

The separation apparatus comprises a housing 1 defining a internal chamber C which is sealed at an upper end by a first sealing block 2 and at lower end by a second sealing block 3. A production fluid inlet is not illustrated in the drawings but can be provided in one of two ways. If a production fluid pump is provided above the first sealing block 2 or below the second sealing block 3, an inlet into the chamber C is provided through the appropriate sealing block. On the other hand, if no pump is required, the housing can be provided with a plurality of apertures, such as slots, which allow direct access for the production fluid into the chamber C.

Within the housing are an upper cyclonic separator 4 and a lower cyclonic separator 5 arranged in parallel. The cyclonic separators have a well known de-oiling configuration for example as described in GB-A-2248198.

Both separators have one or more tangential inlets 6 which are open to the interior of the housing 1. Although the inlets are illustrated as being in the plane of the section, this is only for clarity and, in practice, the inlets will generally be out of this plane where more space is available.

An underflow pipe 7 is connected to the underflow outlet of the upper cyclonic separator 4 and leads down the chamber C past the lower separator 5. In the region adjacent to the head of the lower separator 5 the first underflow outlet pipe is provided with a squashed portion 7A which, in plan, has a substantially kidney shape cross section. This ensures that the cross sectional area of the pipe remains substantially unchanged despite the limited space available adjacent to the head of the second separator 5. The underflow outlet pipe 7 leads to a manifold 8 which is a part of the second sealing block 3.

The underflow outlet of the lower separator 5 is also connected to the manifold 8 so that the underflow stream from the two separators 4, 5 is combined prior to leaving the housing through second sealing block 3.

Similarly, an overflow outlet pipe 9 leads from the lower separator 5 past the upper separator 4, and combines with the overflow outlet 10 from the upper separator 4 in a manifold (not shown) which leads out of the housing 1 through first sealing block 2.

The structure of the separator is very simple consisting mainly of standard pipe sections and cyclonic separators. The only specially required parts are the first 2 and second 3 sealing blocks, the squashed pipe section 7A, and an adapter portion 11 provided between the two separators for connecting separator outlets to corresponding pipes.

In use, the separator is run into a well bore with minimal clearance between the housing 1 and the well casing. Production fluid floods the cavity C through the alternative production fluid inlets described above. The production fluid in the cavity, which has either been pressurized by a pump or is naturally under pressure, enters the two separators 4, 5 through separator inlets 6 and is caused to swirl. In the separators 4, 5 the production fluid is separated into an oil depleted stream which reports to the underflow and an oil rich stream which reports to the overflow. The underflow from the two separators flows through the second sealing block 3 for downhole disposal. The oil rich stream from the overflow flows up through the first sealing block 2 and to the surface for further treatment.

Although the illustrated example has only two cyclonic separators, further separators can be used if required. In this case, a common underflow outlet pipe generally gets progressively bigger down the chamber as the underflow outlet streams from further separators join the common underflow outlet pipe. Similarly, a common overflow outlet pipe generally gets progressively bigger up the chamber as overflow outlet streams from further separators join the common overflow outlet pipe.

A modular system can be created, so that, for example, two of the apparatus illustrated in Figure 1 could be used with appropriate manifold connections.

Claims

1. A downhole separation apparatus comprising an axially elongate tubular housing (1) defining an internal chamber (C), and having at least one inlet which, in use, is arranged to allow production fluid to flood the chamber, at least one cyclonic separator (4,5) contained in the chamber and having an inlet (6) open to the chamber so that, in use, the production fluid in the chamber enters the or each separator, wherein an overflow outlet and an underflow outlet of the or each separator are connected to pipes (7,9) which lead out of the chamber.

2. An apparatus according to claim 1, wherein the separation apparatus comprises a pump unit which discharges into the chamber (C).

3. An apparatus according to claim 1, wherein the housing (1) is provided with a plurality of apertures so that the production fluid can enter the housing at a plurality of locations along the length of the housing.

4. An apparatus according to any one of the preceding claims, wherein a plurality of axially spaced separators (4,5) are contained in the chamber (C).

5. An apparatus according to claim 4, wherein adjacent separators (4,5) face in opposite directions, with some axial overlap between the tailpipes of adjacent separators.

6. An apparatus according to claim 4 or claim 5, wherein the pipes (9) leading from the overflow outlets of the separators are connected within the chamber to a common overflow outlet manifold, and the pipes (7) which lead from the underflow outlets of the separators are connected within the chamber to a common underflow outlet manifold.

7. An apparatus according to any one of the preceding claims, wherein adjacent to the inlet end of each cyclonic separator (4,5) the pipe (7) is formed with a non-circular cross section (7A) having substantially the same area as adjacent portions of the pipe.

8. An apparatus according to claim 7, wherein the noncircular cross section (7A) is substantially kidney shape.