The present invention concerns a device or an arrangement for cleaning a pipe separator in which the separator body consists of an extended, tubular body with an inlet at one end and an outlet at the other end. The inlet and the outlet have essentially the same diameter as the separator body and, at the outlet, there is a bend or a loop that is designed to maintain a fluid level in the separator, and, just ahead of the bend, an outlet for fluid, for example water, from the separator.

Separators of this kind are previously known from the prior art, including the applicant's own international patent application, PCT/NO 03/00265. However, the patent application in question contains no solutions for how the separator is to be cleaned. In particular in connection with the production of oil and gas, large or small quantities of sand and deposits will be produced, depending on the composition of the subterranean formation, which must be removed. In a separator of the above type that is used for the separation of water from the oil/gas produced, deposits may accumulate in places that a conventional reamer or pig cannot reach. This will apply, in particular, to the water outlet of the separator.

The present invention represents a solution for the cleaning of a separator of the above type that is simple and functional and that is inexpensive to produce and use.

The present invention is characterised in that sand particles or other particulate materials that are introduced into the outlet before the bend are designed to be returned to the separator after the bend by means of reversal with a valve via a return pipe, as specified in the attached independent claim 1. The dependent claims 2 - 5 define advantageous features of the present invention.

The present invention will be described in further detail in the following using examples and with reference to the attached drawings, where:

Fig. 1 shows a drawing of a separator with a flushing device in accordance with the present invention during reaming, a), and during operation, b),

Fig. 2 shows a) a drawing of a pig or reamer in accordance with the present invention and a drawing of part of the separator shown in Fig. 1 , over its outlet, with a reamer or pig (shown in Fig. 2 a)), which is designed to be used to clean the separator in accordance with the present invention.

Fig. 3 shows a drawing of part of a separator with a sleeve for covering the opening for the water outlet in the separator; Fig. 3 a) shows an axially displaceable sleeve and Fig. 3 b) shows a rotating sleeve.

Fig. 4 shows a) a drawing of a separator during operation and b) the same separator during cleaning.

Fig. 5 shows, in table form, the results of model calculations based on test results associated with particle transport (sand transport) in pipes, depending on the flow rate for different particle sizes.

Fig. 1 a) shows, as stated above, a drawing of a separator 1 for separation of a fluid, ideally oil/gas/water, in accordance with the present invention. It comprises a tubular body 2 (the entire length is not shown) with an inlet 4, an outlet 5, a bend 3 arranged in connection with the outlet and an outlet for water 6 arranged ahead of the bend 3. A pump 7 is arranged on the outlet pipe 9, downstream of the water outlet, to pump water that is separated from the separator on to a purification device (not shown) or for reinjection into an oil/gas reservoir, as shown in Fig. 1 b). To prevent sludge and particles from being deposited in the water outlet, the water outlet is equipped with a flushing system 10, which comprises a reversing valve 8 arranged on the outlet pipe 9 and a reversing pipe 11 in connection with it, plus a return pipe 12 with a return valve 13 connected to the outlet pipe 9 ahead of the reversing valve 8. As shown in Fig. 1 a), the solution involves the water phase from the water outlet 6 with accumulated sludge/sand being reversible using the reversing valve 8 arranged on the outlet pipe 9, being fully or partially pumped, using the pump 7, back to the outlet pipe 5 after the separator via a reversing pipe 11 , and being fully or partially returned, by opening the return valve, via the return pipe 12 to nozzles 14 in the water outlet 6, which are designed to flush sand and sludge located in the outlet chamber 15 downstream of the outlet towards the outlet pipe 9.

This flushing system can be in operation during the reaming operation, as shown and commented on in further detail in connection with Fig. 2 below, or, as required, in connection with the accumulation of sand or sludge at any time during the operation of the separator. An appropriate electronic/electric control system is used to control the flushing system, i.e. to open and close the valves, 8 and 13. This system will not be described here. Furthermore, to ensure that this water cannot cause a hydrate problem in the pipe downstream, hydrate inhibitor must be added to the pipe. This will not be described here either.

Fig. 2 a) shows a drawing of a pig or reamer 16, which is designed to be used to clean a separator in accordance with the present invention. It consists of an extended, flexible or articulated body, which will be able to pass through the water outlet part 6 (see Fig. 1) of a pipe separator without the outlet being covered and closed during the pigging operation. The reamer 16 consists of a standard reamer head 17 with a rear drive plate 18 connected to the reamer head via a flexible or articulated, extended body 19, which, in turn, may be fitted, along the central part, with support plates or centring plates 20. Normally, the reamer will be driven by the fluid pressure that acts on the rear drive plate 18. This pressure will be maintained until the rear drive plate reaches the beginning of the opening 21 in the water outlet, as shown in Fig. 2 b). When the drive plate is located over the opening of the water outlet, the water outlet ducts will short-circuit the rear drive plate so that it could have stopped moving. At this point, the pig head has passed the water outlet and has full fluid pressure on its rear. This will move the pig on until the rear drive plate reaches the end of the water outlet. This will then take over the propulsion of the pig again. The aim of this solution is to design the reamer with sufficient length and with sealing for the reamer head so that the reamer can pass the water outlet without stopping.

The extended body is, as stated above, either flexible or articulated, but has sufficient support against the pipe wall via the support plates 20 to allow the reamer to pass through the fluid seal and any bent parts of the pipe separator.

The above solution with a long reamer is customised so that the reamer can pass through the opening 21 of the water outlet.

Figs. 3 a) and b) respectively show two alternative systems for covering the opening in the water outlet 6 to allow conventional reamers (which are normally too short in length) to be used to clean the pipe separator. The outlet 21 is covered here when the reamer passes the outlet to prevent the bypass of drive fluid. To cover the opening, it is possible to use either a rotating (Fig. 3 a)) or longitudinally displaceable (Fig 3 b)) sleeve 22 that is driven by means of an actuator (not shown).

An alternative, simple method for cleaning a pipe separator is to increase the flow rate through the pipe separator for a short period at fixed intervals (for example 5 minutes every 24 hours). This method is shown in Figs. 4 a) and b) and is based on the same principle as that shown in Fig. 1. However, as shown in Fig. 4 b), there is also an alternative return pipe loop 23 from the reversing valve 8 and back to the inlet 4 of the separator. The water from the outlet passes, in this solution, from the pump 7 via the return pipe back to the separator inlet.

The flow rate must be increased to such an extent that the sand particles are redispersed and transported out of the pipe separator with the fluid phase (oil + water). It is important for hydrate inhibitor to be added to this water to prevent possible hydrate formation in the downstream outlet pipe from the separator.

Fig. 5 shows, in table form, the results of model calculations based on test results associated with particle transport (sand transport) in pipes, depending on the flow rate for different particle sizes. It is important for the flow rate (fluid speed) to reach the area in which the sand particles are dispersed in the fluid (i.e. E - entrained; see the middle column in Fig. 5).

If this method is used, the system must still be designed for reaming (pigging), but the intervals between pigging operations are considerably increased, for example to once a year.