WO2010142612A1

WO2010142612A1 - Filter arrangement

Info

Publication number: WO2010142612A1
Application number: PCT/EP2010/057837
Authority: WO
Inventors: Steinar ØYULVSTAD
Original assignee: Aker Subsea As
Priority date: 2009-06-08
Filing date: 2010-06-04
Publication date: 2010-12-16
Also published as: NO20092182A1; NO331727B1

Abstract

This invention relates to a cleanable filter system comprising a first filter (2) for removing particles from a fluid flow having an inlet and a first outlet for filtered fluid, and a flow handling unit(l), e.g. pump, coupled to the outlet for filtered fluid flow, the flow handling unit having an outlet coupled to a downstream pipe, the filter also having a second outlet for unfiltered fluid flow also being coupled to said downstream pipe system (4), said first and second outlets having corresponding valves (5, 7) for controlling the flow, a second filter (8) having an inlet for a fluid flow and a first outlet for filtered fluids coupled to said flow handling unit and a second outlet for unfiltered fluids coupled to said downstream pipe (4), the outlets of said second filter (8) also having corresponding valves ( 5,9) for controlling the flow, and a control unit for controlling said outlet valves so as to selectively providing filtered fluid from at least one of said filtered outlets of said filters to the flow handling unit.

Description

FILTER ARRANGEMENT

This invention relates to a cleanable filter system, especially for protecting pumps or the like, comprising a first filter for removing particles from a fluid flow having an inlet and a first outlet for filtered fluid. More specifically it also includes a flow handling unit, e.g. pump or similar, coupled to the outlet for filtered fluid flow, where the flow handling unit having an outlet coupled to a downstream pipe, the filter also having a second outlet for unfiltered fluid flow also being coupled to said downstream pipe system, said first and second outlets having corresponding valves for controlling the flow through the outlets of the first filter.

Subsea production systems

The last two decades subsea production systems have been widely applied for producing oil and gas from deepwater fields where floating production units like platforms and FPSO's are the most economical and technically feasible option. Subsea Xmas-trees (valve trees) and transport flow lines are applied to transport the gas and oil from the wellhead and to the receiving platform. The production system is often optimized with regard to the plateau production rate, which often takes place in the field's early lifetime. In late field lifetime decreasing reservoir pressure and increasing liquid content, mostly due to water production, will restrict production of hydrocarbons. In addition the production facilities may not be able to handle the produced water without costly modifications. When further production is not economical or feasible the production will be discontinued.

Subsea pumping

One way to prolong the field lifetime 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 to why a boosting at the seabed is desirable. The most obvious reason is to compensate for the lowered reservoir pressure after a production period with plateau production. By boosting at seabed the production can be accelerated or increased compared to production with reservoir pressure only. Another reason to apply boosting is to compensate for the increased pressure drop in the production system due to increased water production.

Currently two different types of multiphase pumps for subsea installation have been applied. One is of positive displacement type that applies twin screw technology to generate flow and pressure across the pump. Here, the fluid is enclosed in champers which is then moved from the suction side to the pressure side of the pump. The other is of roto-dynamic type and utilizes axial impellers to generate flow and pressure.

Standard centrifugal pumps are generally not very tolerant with respect to gas content and is therefore often be used in combination with a separator where the separated gas either flows freely in a dedicated flowline 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 flowline. If water only is separated from the wellstream it is often desirable to re-inject the water into a reservoir, either as pressure support for the production reservoir or for disposal.

Subsea processing

Subsea processing units can be applied if it is feasible to separate the flow, either with the intention to boost the well flow or with the intention to split the phases to different hosts or to re-inject one phase to the reservoir. Subsea compressors, centrifugal pumps or multiphase pumps may be part of the subsea processing station. In addition separation cyclones, instrumentation, valves and piping be included in the station

Solids

Solids in the wells stream often origins from the reservoir where lack of or defect sand screens allow sand particles from the formation to follow the flow into the well. Solids often imposed challenges in subsea processing units due to risk of wear on critical parts. Especially rotating equipment like pumps is exposed to wear from solids particles. This is due to the small tolerances that often exist in the equipment and due to the high changes in momentum as a result of impact of solids particles on pump internal surfaces. In addition to pumps, equipment like instruments, valves and cyclonic devices like liquid-liquid de-oilers are exposed to wear from sand.

Solids protection systems Both in topside and subsea production systems solids protection systems may be installed to protect the critical components from sand. Since the solids mostly follows the liquid phase, a gas/liquid separator followed by cyclonic device designed to remove solids from the liquid stream. The solids are then often temporary stored in a vessel before it is transported in bypass to a location downstream of the critical components. In this way the critical components is not exposed for the sand.

Removal of sand from the produced water is mostly done by letting the solid particles settle in the separator. The settled sand can later be removed by a batch- wise operation and disposed into the hydrocarbon pipeline for transport to a topside receiving facility. However, the smallest sand particles will not settle in the separator, and application of sand cyclones may be required to remove these from the produced water. In the cyclones the higher density sand particles are drained through the cyclone underflow and stored for later disposal or re-injected directly into the hydrocarbon flow. The cleaned fluid will leave the cyclone through the overflow outlet.

Another method for removal of solids from the well stream is to apply filters. Filters, or sand screens, are widely used in wells to prevent sand from the reservoir to enter the well. These screens often consist of a triangular shaped wire (wedge wire) wrapped and welded onto a circular and hollow structure with same diameter as the well. The structure may actually be a pipe section with holes that allow for fluid entrance from the outside to the inside of the pipe. The carefully wrapped wires are spaced according to the size of the solids particles that are allowed to enter. The spacing distance is often called the slot opening. Due to a bridging effect created by particles stopped by the filter, the largest particle slipping through the filter may be of considerable less size than the slot opening. Thus the solids particles outside the screen will actually perform as part of the active filter. No cleaning of the filter will be possible for units applied in a well and the slot size is often selected large enough to avoid risk of plugging. Thus quite large particles may slip through the filter during production.

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

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

In many cases it is desirable to be able to clean the filter regularly to avoid plugging, but usually this would imply that the operation is stopped, which in turn results in cooling of the system and risk of hydrate formation. The invention describes a system for cleaning of the filter that makes it possible for solids to bypass the critical component(s) while are still protected against solids and with small or no impact on the process.

Thus the invention relates to a system where particles will bypass a pump, cyclone or similar using filters, and which also allows for cleaning the filter while maintaining the operation and thus also keeping the filters warm so as to avoid hydrate formation. These objects are obtained as described above and being characterized as stated in the accompanying claims.

The invention will be described below with reference to the accompanying drawings, illustrating the invention by way of examples. Figure la,b illustrates the known art including a pump protected by a filter, as well as a filter which may be used in the invention. Figure 2 illustrates the principle of the invention with two filters and including means for cleaning the filters.

Figure 3a-c illustrates the operation of the system in figure 2. Figure 4a,b illustrates an embodiment using external flushing fluids.

Figure 5 illustrates the embodiment in figures 4a,4b including means for high pressure backflushing. Figure 6a,b illustrates an embodiment of the invention using parallel filters. Figure 7a,b illustrates an embodiment using parallel filters and two pumps allowing two flow lines.

In figure Ia a system is shown with a pump 1 being protected by a filter 2 thus being adapted to pump fluids in a pipe 3 from a well and onwards e.g. to topside or other parts of the processing system. The filter may be of the type shown in figure Ib having a coaxial filtering means 2a and a first outlet in the radial direction where the fluids have to pass through the filter thus removing particles from the flow. The first outlet 5 is leading to the pump. A second outlet 4 is positioned in the axial direction where fluids may pass without filtering in which process the passing fluids may flush and thus clean the filter. The second flushing outlet 4 may be closed by a valve to direct the filtered fluids to the pump or opened for flushing, but this will require that the pump is stopped or disconnected from the pipe. As is well known in the art the pump 1 has a circulation system Ib for protecting the pump and maintaining pump operation even if the valve at the first outlet 5 is closed.

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

For illustration purposes the suction pressure SP and discharge pressure, as well as the moderated discharge pressure DP-, e.g. after passing an orifice 10, is shown in the drawings with different patterns. Thus the flow conditions in the system is illustrated. Also open valves and closed valves are illustrated so as to clarify the operation of the system.

The systems according to the invention also incorporates a control unit for controlling the valves so as to obtain the wanted effect such as maintaining the fluid input to the pump and directing the fluids through the chosen pipes so as to obtain the required cleaning effect without letting unfiltered fluids through the pump. The specific valve control as such is evident from required flow patterns through the filters and pump(s).

In a similar manner by opening the outlet flush valve 7 of the first filter 2 and closing the flush outlet valve 9 of the second filter 8 the first filter may be flushed while the pump is supplied with filtered fluid from the second filter 8. As the second filter is subject to a fairly large amount of solids in the flow, but already present in the flow and resulting from the flushing of the first filter, the second filter should preferably have larger capacity than the first, which in the illustrated example is indicated by a longer filter. Thus the second filter is 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 preventing overpressure.

In figure 3b and 3c non-return valves 7a,9a are used at the direct second outlets of the filters 2,8 so as to balance the flow throughput and filtering in the two filters and a directional valve 6a distributes the pressure partially through the second filter 8 (figure 3 c) for cleaning it and/or partially passed the second filter

In figures 4a and 4b illustrates a situation where there is flushing fluid 11 available from outside the system, e.g. stabilization oil. In this case both axial flushing and backflushing may be applied. In this case large volumes are needed so flushing by using methanol injection through ordinary lines is giving too low rate.

Figure 5 illustrate systems where the pumped fluid from the outlet 4 is directed back to the filter for providing backflushing. The backflushing will be performed in short periods, in the range of seconds, or pulses so that the pressure pulses will release solids stuck on the surface. The valves 12 may be opened individually so as only to clean one of the filters, and the pressure may be limited by an orifice 10.

In figure 6a and 6b a parallel filter 2a,2b configuration is shown where the pump is supplied with fluids from one filter 2a while backflushing through the other filter 2b. Outlet valves 15 a, 15b are provided for controlling the fluid pumped from the first outlet 5 of each filter and backflush valves 16a, 16b are provided for allowing backflush fluids in through a downstream first filter outlet, and output valves 9a,9b are provided at the axial second outlet of the filters, the control system thus being able to control rout of the fluid flow through the system. The system comprises an orifice 10 at the pump output to help preventing extreme high pressure through all closed valves downstream of the pump. The orifice is, however, only required when the pump is a positive displacement pump.

Figure 7a and 7b illustrates a dual system incorporating two well flow lines 3a,3b,4a,4b and two pumps 13,14, e.g. in a pigging loop 18a, 18b, 18c, where one filter 2a,2b is position in each flowline. Figure 7a illustrates the normal operation where the filtered fluids are sucked into one or both pumps 13,14 and back into the individual flow lines 4a,4b or into a common flowline. This is controlled by setting the system valves

15a, 15b, 16a, 16b, 17a, 17b so as to rout the flow through the system. In figure 7b one of the filters 2a is cleaned by backflushing by directing the flow in through the downhole first filter outlet. For this operation, before flushing, suction pressure in the two flowlines must be aligned. This can be done by opening for the pigging loop valve 18a or a similar dedicated valve. Both pumps suck from the same filter 2b while the other filter 2a is "moved" to the pressure side, and the pump speed for one pump is reduced to give lower differential pressure than the other. To start flushing, fluid from the "high pressure pump" 14 is used to backflush the filter resting 2a on the pressure from the "low pressure pump" 13. The system requires that it is possible to operate the two flowlines at similar pressures, and that they do not need to operated independently, and preferably should also incorporate pig bypass lines 18b, 18c.

Claims

C l a i m s

1. Cleanable filter system, especially for protecting pumps or the like, comprising a first filter for removing particles from a fluid flow having an inlet and a first outlet for filtered fluid, and a flow handling unit, e.g. pump or similar, coupled to the outlet for filtered fluid flow, the flow handling unit having an outlet coupled to a downstream pipe, the filter also having a second outlet for unfiltered fluid flow also being coupled to said downstream pipe system, said first and second outlets having corresponding valves for controlling the flow through the outlets of the first filter, the system also comprising a second filter having an inlet for a fluid flow and a first outlet for filtered fluids coupled to said flow handling unit and a second outlet for unfiltered fluids coupled to said downstream pipe, the outlets of said second filter also having corresponding valves for controlling the flow through the outlets of the second filter, and a control unit for controlling said outlet valves so as to selectively providing filtered fluid from at least one of said filtered outlets of said filters to the flow handling unit, wherein the unfiltered outlet of the first filter being coupled to the inlet of the second filter, the output of the flow handling unit being coupled to the input of the second filter through a valve, the control unit being adapted to selectively opening of 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 allow flushing of the first filter while feeding the flow 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 said flow handling unit to the input of the second filter, the filtered outlet valve of the second filter being closed and the unfiltered outlet valve of the second filter being open so as to flush the second filter.

2. Filter system according to claim 1, wherein the first and second filters are positioned in a series.

3. Filter system according to claim 1, wherein at least one of said filters is provided with a second inlet with a corresponding valve on the filtered side of the filter, allowing for pressurized backflushing the filter.

4. Filter system according to claim 3, wherein said second inlet is coupled to the outlet of said flow handling unit, the flow handling unit being a pump.

5. Filter system according to claim 1 wherein said flow handling unit includes at least one pump.

6. Filter system according to claim 5, wherein the pump is a displacement pump.

7. Filter system according to claim 1, wherein the filters are parallel, the first inlets being coupled to at least one fluid flow and the first filtered outlets being coupled to said fluid flow handling unit and the second unfiltered outlet being coupled to at least one outlet pipe.

8. Filter system according to claim 7, wherein filters are provided with an second inlet with a corresponding valve on the filtered side of the filter, allowing for pressurized backflushing the filter from said fluid flow handling unit.

9. Filter system according to claim 1, wherein the filters are based on a hollow filter element adapted for filtering fluids flowing from inside to the outside of said filter element.

10. Filter system according to claim 1 comprising said first and second filter each including a filter element and a filter housing constituting a filter unit, the filtering element inside the filter unit being shaped such that filtering is performed from inside to the outside and assembled in said filters so that the filter unit housing collects the filtered fluid on the outer side, filter units having an inlet (3) and an outlet (4) of the centre channel of the filter unit and a third connection (5) to the filter unit housing for the filtered fluid, the filter units being arranged with valves at the first and second outlets, the filter units and their valves being connected together with pipes so that filtered fluid can be fed from the second outlet of either of the two filter units by proper operation of the valves to the inlet of a pressure creating device thereby protecting the pressure creating device from particles in the incoming flow, the pressure creating device having two valves at the outlet, the filter system also comprising a proper valve operation unit being able to route cleaned fluid to the pressure creating device while simultaneously allowing a sequential cleaning of the two serially arranged filters.

11. Method for sequential cleaning the filter system according to claim 10 comprising the steps of allowing in the first sequence step cleaning of the second filter unit by routing the outlet flow from the pressure creating device to the first connection of the second filter unit while taking cleaned fluid from the first filter unit and in the second sequence step cleaning the first filter unit by allowing the incoming, un-cleaned fluid to pass through the second connection of first filter unit into the first connection of the second filter unit and routing the pressurised fluid downstream of the second outlet of second filter unit.