NO331727B1 - filter Events - Google Patents

Description

FILTER ARRANGEMENT

The present invention relates to a regenerable filter system, especially for the protection of pumps or the like, comprising a first filter for removing particles from a fluid stream which has an inlet and a first outlet for filtered fluid. More specifically, it also includes a power handling unit, e.g. pump or the like, connected to the outlet for filtered fluid flow, where the flow handling unit has an outlet connected to a downstream pipe, where the filter also has a second outlet for unfiltered fluid flow which is also connected to the above-mentioned downstream pipe system, where the above-mentioned first and second outlets have corresponding valves to control the current through the outputs of the first filter.

Seabed production systems

Over the past two decades, subsea production systems have been widely used for the production of oil and gas from deepwater areas where floating production units such as platforms and FPSOs are the most economically and technically feasible choice. Underwater Christmas trees (valve trees) and transport power lines are used to transport the gas and oil from the wellhead to the receiving platform. The production system is often optimized with respect to the plateau production rate, which often occurs in the early life of the field. In late field life, decreasing reservoir pressure and increasing fluid content, mostly due to water production, will limit hydrocarbon production. In addition, the production facilities may not be able to handle the produced water without costly modifications. When further production is not economical or possible, production will be suspended.

Underwater pumping

One way to extend the life of the field and to increase the accumulated production volume of gas and oil is to install multiphase pumps that boost the well flow. There are several reasons why boosting at the seabed is desirable. The most obvious reason is to compensate for the lowered reservoir pressure after a production period of plateau production. By boosting at the seabed, production can be accelerated or increased compared to just production with reservoir pressure. Another reason for using boosting is to compensate for the increased pressure drop in the production system due to increased water production.

At present, two different types of multiphase pumps for underwater installation have been used. One is of the positive displacement type which uses twin screw technology to generate current and pressure through the pump. Here, the fluid is confined in chambers which are then moved from the suction side to the pressure side of the pump. The other is of the roto-dynamic type and uses axial drive springs ("impellers") to generate current and pressure.

Standard centrifugal pumps are usually not very tolerant of gas content, and are therefore often used in combination with a separator where the separated gas either flows freely in a dedicated power line or is compressed by a compressor. The separated liquid (can) is pumped by the centrifugal pump to meet the required pressure for transport in the downstream stream line. If only water is separated from the well flow, it is often desirable to re-inject the water into a reservoir, either as pressure relief for the production reservoir or for waste.

Underwater processing

Subsea processing units can be used if it is possible to separate the flow, either with the intention of boosting the well flow or with the intention of splitting the phases to different receivers or to reinject a phase to the reservoir. Underwater compressors, centrifugal pumps or multiphase pumps can be part of the underwater processing station. In addition, separation centrifuges ("cyclones"), instrumentation, valves and piping can be included in the station

Solids

Solids in the well flow often originate from the reservoir where a lack of or defective sand filters allow sand particles from the formation to follow the flow into the well. Solids often posed challenges in subsea processing units due to the risk of wear on critical parts. Especially rotating equipment such as pumps are exposed to wear from solid particles. This is because of the low tolerance limits that often exist in the equipment and because of the high changes in torque as a result of the impact of solid particles on internal pump surfaces. In addition to pumps, equipment such as instruments, valves and swirling devices such as liquid-liquid oil separators are exposed to wear from sand.

Protection systems against solids

In both topside and subsea production systems, solids protection systems can be installed to protect the critical components from sand. Since the solids mostly follow the liquid phase, (is) a gas/liquid separator followed by centrifuge device designed to remove solids from the liquid stream. The solids are therefore often temporarily stored in a container before being transported in a diversion to a location downstream of the critical components. In this way, the critical components are not exposed to the sand.

Removal of sand from the produced water is mostly accomplished by allowing the solid particles to settle in the separator. The settled sand can later be removed by a batch operation and deposited into the hydrocarbon pipeline for transport to an overdraft receiving facility. However, the smallest sand particles will not settle in the separator, and the use of sand centrifuges may be necessary to remove these from the produced water. In the centrifuges, the higher density sand particles are drained through the centrifuge underflow and stored for later removal or reinjected directly into the hydrocarbon stream. The purified fluid will leave the centrifuge through the overflow outlet.

Another method for removing solids from the well stream is to use filters. Filters, or sand filters, are widely used in wells to prevent sand from the reservoir from entering the well. These altars often consist of a triangular wire (wedge-shaped wire) wound around and welded onto a circular and hollow structure with the same diameter as the well. The structure can actually be a pipe part with holes that enable fluid entry from the outside to the inside of the pipe. The thoroughly wrapped wires are spaced according to the size of the solid particles allowed to enter. The gap distance is often called the slot opening ("the slot opening"). Due to a bridging effect created by particles stopped by the filter, the largest particle passing through the filter may be significantly smaller in size than the slot opening. The solid particles outside the filter will therefore actually act as part of the active filter.

No cleaning of the filter will be possible for units used in a well, and the slot size is often chosen large enough to avoid the risk of plugging. Fairly large particles can therefore escape through the filter during production.

Wedge wire filters are also used in other applications, especially in industrial applications where filtering of fluid is necessary.

In the present invention, it is intended to use wedge wire type filters. However, filters of any other type may be used if found appropriate.

In many cases it is desirable to be able to clean the filter regularly to avoid plugging, but this would usually involve stopping the operation, which in turn results in cooling the system and the risk of hydrate formation. Such a solution is described in Norwegian patent application no. 20042196, which shows a filter solution based on wedge-shaped wires, which can be cleaned by being flushed loose. Another solution showing partial backwashing as a cleaning method is shown in German patent application DE 102997009419. The present invention describes a system for cleaning the filter which enables solids to bypass the critical component(s) while still being protected against solids and with little or no impact on the process.

The present invention therefore relates to a system where particles will bypass a pump, centrifuge or the like by using filters, and which also takes into account the cleaning of the filter while the operation is being maintained and therefore also keeps the filters warm in order to avoid hydrate formation. These purposes are achieved as described above and are presented as set forth in the accompanying claims.

The present invention will be described below with reference to the accompanying drawings, which illustrate the present invention as examples.

Figures la,b illustrate the prior art including a pump protected by a filter, as well

as a filter that can be used in the present invention.

Figure 2 illustrates the principle of the present invention with two filters and

including aids for cleaning the filters.

Figure 3a-c illustrates the operation of the system in Figure 2.

Figure 4a,b illustrates an embodiment that uses external flushing fluids.

Figure 5 illustrates the embodiment in figures 4a, 4b including aids for

high pressure backwash.

Figure 6a,b illustrates an embodiment of the present invention which uses

parallel filters.

Figure 7a,b illustrates an embodiment that uses parallel filters and two pumps

which enables two connection lines ("flow lines").

Figure la shows a system with a pump 1 which is protected by a filter 2 which is therefore adapted to pump fluids in a pipe 3 from a well onwards e.g. to the superstructure) or other parts of the processing system. The filter can be of the type shown in figure 1b which has a coaxial filtering aid 2a and a first exit in the radial direction where the fluids must pass through the filter which therefore removes particles from the flow. The first output 5 leads to the pump. A second outlet 4 is arranged in the axial direction where fluids can pass without filtration in which process the passing fluids can flush and therefore clean the filter. The second flushing outlet 4 can be closed by a valve to direct the filtered fluids to the pumps or be opened for flushing, but this will require the pumps to be stopped or disconnected from the pipe. As is well known in the art, the pumps 1 have a circulation system lb for protecting the pumps and maintaining pump operation even if the valve at the first outlet 5 is closed.

As mentioned above, there is a need to clean the filters, but in some applications this is not possible without stopping the pump. In Figure 2, the principle according to the present invention is illustrated where it has two filters 2,8, each with a valve 7,9 at the flushing outlet 4 and the pump outlet 5 connected to the pump 1. If the flushing outlet 7 of the first filter 2 is closed, the flow is directed to the pump that pumps the flow towards the rest of the main pipe 4 as illustrated in Figure 3 a. As illustrated, the fluid flow after the pump 1 can also be directed into the entrance of the second filter 8, and by opening the flush outlet valve 6, the second filter can be cleaned in the same process of the fluid flowing through it. Since both filters are active, both remain warm during operation and hydrate formation is avoided.

For illustration purposes, the suction pressure (suction pressure) SP and the outlet pressure, as well as the moderated outlet pressure (discharge pressure) DP-, e.g. after passing through an orifice 10, shown in the drawings with different patterns. The current conditions in the system are therefore illustrated. Also open valves and closed valves are illustrated in order to clarify the operation of the system.

The systems according to the present invention also incorporate a control unit to control the valves in order to achieve the desired effect such as maintaining the fluid supply to the pumps and directing the fluids through the selected pipes in order to achieve the required cleaning effect without allowing unfiltered fluids through the pump. The specific valve control as such is evident from required flow patterns through the filters and pump(s).

Similarly, by opening the outlet flush valve 7 of the first filter 2 and closing the outlet flush valve 9 of the second filter 8, the first filter can be flushed while the pumps are supplied with filtered fluid from the second filter 8. Since the second filter is exposed for a fairly large amount of solids in the stream, but already present in the stream and resulting from the flushing of the first filter, the second filter should preferably have a larger capacity than the first, as indicated in the illustrated example by a longer filter. The second filter is therefore flushed by axial flow through the filter.

An orifice 10 may also be used in this embodiment to distribute most of the flow through the second filter 8 but prevent overpressure.

In Figures 3b and 3c, non-return valves 7a, 9a are used at the direct second outputs of the filters 2,8 in order to balance the flow and filtration in the two filters, and a directional valve 6a distributes the pressure partially through the second filter 8 (Figure 3c) for to clean it and/or partially pass the second filter Figures 4a and 4b illustrate a situation where there is flushing fluid 11 available from the outside of the system, e.g. stabilization oil. In this case, both axial flushing and back flushing can be used. In this case large volumes are required so flushing using methanol injection through normal lines gives too low a rate. Figure 5 illustrates systems where pumped fluid from outlet 4 is led back to the filter to provide backwashing. The backwashing will be carried out for short periods, in the range of seconds, or pulses so that the pressure pulses will release solids stuck to the surface. The valves 12 can be opened individually so as to clean only one of the filters, and the pressure can be limited by a mouth 10.

Figures 6a and 6b show a parallel filter configuration 2a, 2b where the pumps are supplied with fluid from one filter 2a, while it is flushed back through the other filter 2b. Outlet valves 15a, 15b are provided to control the fluid pumped from the first outlet 5 to each filter and backwash valves 16a, 16b are provided to allow backwash fluid to enter through a downstream first filter outlet, and outlet valves 9a, 9b are provided at the axial second outlet to the filters, where the control system is thus able to control the route of fluid flow through the system. The system includes a nozzle 10 at the pump outlet to assist and prevent extremely high pressure through all closed valves downstream of the pump. The orifice is, however, only necessary when the pump is a positive displacement pump.

Figures 7a and 7b illustrate a two-part system incorporating two

well connection lines 3a,3b,4a,4b and two pumps 13,14, e.g. in a plug driving loop 18a, 18b, 18c, where one filter 2a, 2b is positioned in each connecting line. Figure 7a illustrates the normal operation where the filtered fluids are sucked into one or both pumps 13,14 and back into the individual connection lines 4a,4b or into a common connection line. This is controlled by setting the system valves 15 a, 15b, 16a, 16b, 17a, 17b so as to send the current through the system. In Figure 7b, one of the filters 2a is cleaned by backwashing by directing the flow in through the borehole's first filter outlet. For this operation, before flushing, the suction pressure in the two connecting lines must be adjusted. This can be done by opening the plug driving loop valve 18a or a similar dedicated valve. Both pumps draw from the same filter 2b, while the other filter 2a is "moved" to the pressure side, and the pumping speed of one pump is reduced to give a lower differential pressure than the other. To start flushing, fluid from the "high-pressure pump" 14 is used to backwash the filter, which rests 2a on the pressure from the "low-pressure pump" 13. The system requires that it is possible to operate the two connecting lines at similar pressures, and that it does not need to be operated independently, and should preferably also incorporate pig bypass lines 18b, 18c.

Claims (11)

1. Cleanable filter system, particularly for the protection of pumps or the like, comprising a first filter for removing particles from a fluid stream having an inlet and a first outlet for filtered fluid, and a stream handling unit, e.g. pump or the like, connected to the outlet for filtered fluid flow, wherein the flow handling unit has an outlet connected to a downstream pipe, where the filter also has a second outlet for unfiltered fluid flow which is also connected to the above-mentioned downstream pipe system, where the above-mentioned first and second outlets have corresponding valves to control the current through the outputs of the first filter, wherein the system also comprises a second filter having an inlet for a fluid stream and a first outlet for filtered fluids connected to the above-mentioned flow handling unit and a second outlet for unfiltered fluids connected to the above-mentioned downstream pipe, where the outlets of the above-mentioned second filter also have corresponding valves to check the current through the outputs of the second filter, and a control unit for controlling the above outlet valves so as to selectively provide filtered fluid from at least one of the above filtered outlets from the above filters to the flow handling unit, characterized in that the unfiltered output of the first filter is connected to the input of the second filter, where the output of the current handling unit is connected to the input of the second filter through a valve, where the control unit is adapted to selectively: opening the unfiltered outlet valve of the first filter and the filtered outlet valve of the second, while closing the unfiltered outlet valve of the second filter, thereby enabling flushing of the first filter while feeding the power handling unit from the second filter, or closing the unfiltered outlet valve of the first filter and opening the filtered outlet valve of the first filter while directing filtered fluid flow through the above flow handling unit to the inlet of the second filter, where the filtered outlet valve of the second filter is closed and the unfiltered outlet valve of the second filter is opened so as to flush the second filter. 2. Filter system according to claim 1, where the first and second filters are arranged in series. 3. Filter system according to claim 1, in which at least one of the above-mentioned filters is provided with a second inlet with a corresponding valve on the filtered side of the filter, which enables pressurized backwashing of the filter. 4. Filter system according to claim 3, in which the above-mentioned second input is connected to the output of the above-mentioned current handling unit, where the current handling unit is a pump. 5. Filter system according to claim 1, wherein the above-mentioned current handling unit includes at least one pump. 6. Filter system according to claim 5, in which the pump is a displacement pump. 7. Filter system according to claim 1, in which the filters are parallel, where the first inputs are connected to at least one fluid flow and the first filtered outputs are connected to the above-mentioned fluid flow handling unit and the second unfiltered output is connected to at least one output pipe. 8. Filter system according to claim 7, in which filters are provided with a second inlet with a corresponding valve on the filtered side of the filter, which enables pressurized backwashing of the filter from the above-mentioned fluid flow handling unit. 9. Filter system according to claim 1, in which the filters are based on a hollow filter element adapted for filtering fluids that flow from the inside to the outside of the above-mentioned filter element. 10. Filter system according to claim 1, in which it comprises the above-mentioned first and second filters which each include a filter element and a filter housing which constitutes a filter unit, where the filtering element inside the filter unit is shaped so that filtering is carried out from the inside to the outside and mounted in the above-mentioned filters as follows that the filter unit housing collects the filtered fluid on the outside, where the filter units have an inlet (3) and an outlet (4) from the central channel of the filter unit and a third connection (5) to the filter unit housing for the filtered fluid, where the filter units are arranged with valves at the first and the second outlets, where the filter units and their valves are connected by pipes so that filtered fluid can be fed from the second outlet to both of the two filter units by proper operation of the valves to the inlet of a pressurizing device thereby protecting the pressurizing device from particles in the incoming flow, where the pressure-generating device has two valves is at the exit, wherein the filter system also comprises a suitable valve operating unit capable of sending purified fluid to the pressurizing device while at the same time allowing a sequential cleaning of the two series-arranged filters. 11. Method for sequential cleaning of the filter system according to claim 10, wherein it comprises the steps of enabling, in the first sequence step, purification of the second filter unit by sending the output stream from the pressurizing device to the first connection of the second filter unit while taking purified fluid from the first filter unit and in the second sequence step purifying the first filter unit by allowing the incoming uncleaned fluid to pass through the second connection of the first filter unit into the first connection of the second filter unit and sending the pressurized fluid downstream to the second outlet of the second filter unit.