FIELD OF THE INVENTION

The present invention relates generally to the treatment of fluids and more particularly to an integrated self-monitoring and self-cleaning system for removing solids from a feed stream comprising a hydrocarbon fluid and/or other fluids and a method thereof.

BACKGROUD OF THE INVENTION

The removal of solids such as sand, mercury particulate, carbonate solids or other suspended solids in a production of oil and gas industry is a challenge. Over a well’s production life, the amount of solids from a reservoir such as a sandstone reservoir and carbonate reservoir is expected to increase as water-cut increases and reservoir pressure depletes. Solids produced with hydrocarbon fluids pose various health, safety and integrity risks to the production operation, potentially causing injury/fatality to people, damage to the environment, assets and reputation.

Solids that include sand and/or or other particles size from a well production may range from lμm to 500 μm. Downhole sand control and separation using mechanical sand screen is typically expected to stop particles more than 45 μm from being produced to the surface facilities. However, with a downhole sand screen installation, crude oil transfer pump failures still happen as fines particles manage to pass through the screen and are carried over to the pumps of the surface facilities. This challenge requires a solution for a better surface sand management.

To manage sand production at the surface facility, a desander is typically installed at the wellhead to separate solids from the fluid stream. A desander typically comprises of hydrocyclonic liner, either built as a pressure vessel or housed in another pressure vessel with a sand accumulator either as an integrated or isolated system. A pressure vessel housing may include one or more liners or inserts depending on the requirement. For instance, a single liner system is suitable for a multiphase stream comprising of gas, liquids and solids compared to a multi-liner system. An ideal desander is expected to perform optimally under any flow conditions of the stream. However, the common issues of conventional desanders which prevent the desanders from operating efficiently include a tight design margin, low turndown ratio (approximately 1:2), low efficiency of separating solid particles of less than 45 μm and significant drop in efficiency under various multiphase flow regimes and conditions.

Conventional desanders usually separate solids suspended in a fluid via the centrifugal forces of a vortex that push the heavier and coarse particles of the solids toward the wall of the hydrocyclone liner where the said particles will eventually fall to a lower chamber of the desander. However, the centrifugal forces alone are not sufficient to effectively remove suspended solids comprising particles that are less than 45 μm in slug multiphase flow conditions. In conventional desanders, sand or particles of less than 45 microns generally do not separate and are carried over through the outflow line.

The US patent no. 80418181 discloses a filter apparatus for separating impurities from a fluid stream by using a filter element accommodated in a filter housing. The filter accommodated in said filter housing has to be designed to taper conically. The conically tapered as compared to cylindrical shape may subject filter element to higher plugging rate due to decreased flow area and caused accelerated pressure drop build up rate across the filter which is not suitable for use in various multiphase flow conditions of a stream comprising hydrocarbons and the heavy duty and long operation of a well production. The patent also does not specify the filter selection and design need to be accordance to specific sand properties for example sand size distribution and uniformity. It does emphasize only on separation but does not specify the requirement of the filter to provide screen permeability, which is important parameters in designing and selecting sand screen for this present invention for inflow capacity. The said US patent also does not claim self-monitoring mechanism to trigger backwash of the filter hence may require human intervention to monitor pressure drop build. The patent also does not claim special filter design to enhance fluid drainage and mechanical strength from collapse and burst.

The US patent no. 5478484 discloses a separator for separating solid particles from a liquid. The separator includes a filter element that is arranged in a separate chamber, it appears that the filter element allows the fluid to pass through/penetrate the filter wherein the fluid that has passed the filter is channelled downward. This is not desirable as the working of the separator will cause plugging of the screen and an effective separation process may not be attained.

In light of the above limitations, it is an object of the present invention to have an improved system and method that can effectively separate and remove solid particles from a stream to produce a treated stream with a reduced suspended solids content or a treated stream that is substantially free from solid particles when compared to the existing apparatuses and methods.

SUMMARY OF THE INVENTION

The present invention provides a system for treating a feed stream comprising a hydrocarbon fluid and/or other fluids and a method thereof. The system includes an apparatus for separating and removing suspended solids from the stream by way of a vortex and a screening process and a mean to monitor pressure drop across the system to initiate a backwash. The apparatus provides a chamber for removing coarse and fine particles of the suspended solids simultaneously.

According to the present invention, the apparatus comprises a vessel with an assembly of a screen that is arranged within the vessel to produce a treated stream with a reduced suspended solids content or a treated stream that is substantially free from solid particles. The screen assembly provides a contact surface for trapping fine particles of the solids and non-penetrable surface to induce a vortex at the area of tangential injection. During a vortex formation by the fluid, the fluid swirls and the centrifugal forces of the vortex will force the coarse or heavier particles of the solids towards the wall of the vessel while the finer particles will swirl towards and around the screen positioned at the centre to be trapped. The circling of fine particles around the screen will not significantly plug the screen. The provision of the screen according to the present invention allows the circling fluid motion near the screen to push away the approaching fines particles from the screen. In this invention, the particles do not directly hit the screen i.e. hitting in radial direction, which may cause a higher chance of plugging. The particles according to the present invention move in circular direction circling the screen. The particles may move substantially in tangent to the screen surface to contact the screen or when circling the screen. The particles that are in contact with the screen are to be captured by the screen surface and particles that continue to circle the screen are to scrape any build-up of particles on the screen or remove a top layer of particles trapped on the screen. This is one of the self-cleaning features of the system.

Over time, if fines particles started to build up on the screen, for example due to ramp-up and ramp-down of the fluid flow during well start up and shut in and causes reduction in screen effective flow area, the instrument installed at the feed/fluid inlet and outlet of the desander will indicate pressure drop as per set point and triggers isolation of the system for screen backwashing. The screen may include one or more layers of mechanical strainers. The screen design and selection typically starts with identification and understanding of reservoir sands/particles from samples taken from available sand/particle analysis which may include from manual spot sampling, cores and logs. These sand/particle samples will then be tested using sieving method or a laser particle size analysis (LPSA) to determine the particle size distribution, the range of grain sizes with indications of sorting, its uniformity, and grain consolidation. The screen selection in forms of type sizing, layering and material of construction is crucial to ensure that the screen is able to provide required strength, permeability for inflow capacity and adequate filtration for long-term and effective sand/particle separation. Example of screen that can be selected and chosen for this application may include basic screen, premium screens with multiple layers, wire-wrapped screen, slotted liner and prepacked screen. It is preferable to determine the screen opening size by testing a representative sand/particle or solids in a sand/particle retention laboratory or in numerical modeling simulation e.g. Computational Fluid Dynamic (CFD). Preferably, the screen is in a form of detachable screen. The screen is disposed inside the vessel by mean of existing connection type available in the market and the other end should be either be able to be closed with existing end cap available in the market or connected to another screen extension to increase the screen length and flow capacity.

The vessel that houses the screen comprises an inlet that is connectable to a feed stream. The vessel is in communication with a first outlet for evacuating a treated stream from the vessel. The vessel includes an outlet for evacuating particles which have been separated by the vortex. The vessel further comprises a backwash inlet for introducing a pressurized fluid into the vessel for cleaning the screen when required. A gauge for measuring pressure or differential pressure of the feed stream is provided to initiate backwashing and as a means to regulate the pressure within the vessel. This provides a self-monitoring and self-cleaning system and will ensure the screen and the separation process operable optimally.

According to an embodiment of the present invention, a chemical injection system is provided for introducing agglomeration chemicals such as polymers carrying cationic or anionic charges or non-ionic polymers or a combination thereof into the stream for increasing the size of the suspended solids so that the particles of the solids can be easily separated and removed during the separation process. The chemical may be injected into the feed line before the stream enters the vessel. The word ‘line’ in this context refers to piping for conveying a fluid.

According to another aspect of the present invention, a method for treating a feed stream comprising hydrocarbon fluids or other fluids is provided. The method comprises the steps of introducing a feed stream to a vessel with a screen that is centrally located within the vessel; and contacting the stream with the screen to produce a treated stream with a reduced suspended solid content; and the step of measuring pressure of the feed stream and/or vessel for initiating backwashing within the vessel. The method further comprising the step of injecting agglomeration chemicals into the stream for increasing the size of the solids, particularly the fine particles. The chemical may be injected into the feed line before the stream enters the vessel.

The method further comprises of a device to break the vortices near the vessel outlet stream where the particles of the solids are evacuated to the accumulator. For example, in operation, the device breaks the vortices between the vessel and the accumulator vessel.

Accordingly, the present invention includes a combination of a vortex effect for separating coarse and heavier particles and a screen for trapping finer particles from a fluid or fluids comprising hydrocarbon and non-hydrocarbon. The present invention also includes a combination of a vortex effect for separating coarse and heavier particles; a screen for trapping finer particles from a hydrocarbons fluid or other fluids; and chemical coagulation and agglomeration of particles of the solids.

The combination of the centrifugal forces of the vortex and the screen improves the separation of efficiency to result in a treated stream which is solids free or with a lower solid content when compared to a treated stream produced with only centrifugal forces alone. The centrifugal forces produces a filtering effect whereas the screen acts as a secondary filter wherein particles that are larger than 45 microns will be removed by the centrifugal forces and particles that are less than 45 microns that manage to escape the effect of the centrifugal forces will be trapped by the screen.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be described further by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagram showing a system for treating a feed stream according to an embodiment of the present invention.

Fig. 2 shows a side view of a vessel for treating a feed stream according to an embodiment of the present invention.

Fig. 3 shows a top view of a feed chamber of the apparatus shown in Fig. 3; and

Fig. 4 shows a side view of an apparatus for treating a feed stream according to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a system for treating a feed stream according to an embodiment of the present invention. The system includes an apparatus for treating the feed stream comprising a hydrocarbon fluid and/or other fluids from a wellhead (100) as shown in Fig. 1. The apparatus comprises a cyclone vessel (102) that is connectable to a tangential feed stream inlet for feeding a stream tangentially into the vessel (102) to form a vortex. As shown in Fig. 2, the vessel (102) comprises of a feed chamber (202a), a cylindrical section (202b) and a cone section (202c). Fig. 3 shows a top view of the feed chamber (202) where a feed stream inlet (303) in a tangential position. The said vessel can also be referred to as liner. The apparatus in accordance with the present invention includes an outer pressure vessel (105) that acts as a housing to enclose a single vessel/liner (102) or an outer pressure vessel with more than one vessel/liner (102) enclosed.

The vessel further comprises a screen (106) that is coaxially positioned within the vessel. The screen extends longitudinally inside the vessel to provide a contact surface for trapping particles that come into contact with the surface and to induce vortex formation in the vessel, thus improves the separation process of the solids from the stream. The screen is in the form of a tubing comprising one or more layers of filter media. Preferably, the screen is in the form of a cylindrical screen. The screen may include a wire cage as the base layer and a mesh. The mesh pattern includes, but is not limited to Dutch twill and perforated or wire wrapped shroud, with filtration of down to lμm particles.

The vessel includes a vortex finder (104) for guiding or channeling the treated stream or fluid that has undergone the separation process to exit the vessel (102). As shown in Fig. 4, the vortex finder (104) is in communication with an overflow chamber (407) located above the vessel (102). A first outlet (407a) is provided on the overflow chamber for evacuating the treated stream. The screen (106) is attached to the vortex finder (104) to channel the treated stream or fluid that has undergone the separation process out of the vessel. In Fig. 4, the screen is attached to the vortex finder. The screen (106) which is in the form of tubing may be attached to the vortex finder by using a thread connection or by welding or O-ring connection. A cap may be provided to close the lower end of the tubing. The lower end of the tubing may include a connection means to extend the length of the screen. The lower end of the tubing may include a connection thread or a threaded portion to receive a corresponding screen. For example, a standard thread connection such as National Pipe Thread (NPT) connection may be used to form the extension and the attachment between the vortex finder and the screen.

Preferably, the screen has a length that extends the length of the vortex finder. For example, the length of the screen is around or at least three times the length of the vortex finder. This is to prevent unreasonable pressure drop in the vessel (102) during the operation.

A second outlet (108) is provided at the spigot of the cone section (202c) of the vessel for evacuating solids that have been separated by the centrifugal forces of the vortex. A vortex breaker (201) is provided adjacent to the spigot of the vessel to disperse the flow outwardly and stop vortex precession downward, thus preventing particles or sand re-entrainment into the flow or vortex. The vortex breaker is a device that has a portion which is progressively narrowed with a tip or tapered section pointing upward. For example, the device may be in the form of a cone. This improves the efficiency of the separation process.

The system further includes a chemical injection system for introducing a chemical composition into the feed stream for increasing the size of the suspended solids so that the the solid particles can be easily separated and removed during the separation process in the vessel (102). The chemical may be injected into the feed line before the stream enters the vessel. For example, the composition can be introduced at point A shown in Fig. 1.

As shown in Fig. 1, the vessel (102) is integrated with a backwashing system (111) for removing or washing particles trapped on the screen. A gauge (203) is provided for measuring the pressure of the feed stream or differential pressure between the feed stream and the backwashing system to control and indicate the pressure of the feed stream or the differential pressure and to provide indication of specific range of pressure. The gauge is connected between the feed stream and the overflow/outlet of the vessel. As shown in Fig. 1, the gauge is connected to a connection point of the outlet and a connection point of the feed stream. In the event the pressure drops within a predetermined range, the backwashing process will be automatically or manually initiated. The backwashing system uses a medium with a higher pressure than the pressure in the vessel. The medium includes but is not limited to water or gas. For example, clean or filtered water or gas may be used for backwashing the screen.

Fig. 4 shows a side view of an example of the apparatus according to the present invention wherein the apparatus is enclosed within an outer pressure vessel (105) as a housing. In an integrated system, the apparatus is in communication with the accumulator vessel (108) via the second outlet (108) of the outer pressure vessel (105). The accumulator vessel is provided to collect separated solids prior to disposal.

According to another aspect of the present invention, a method of removing suspended solids from a fluid comprising hydrocarbon or non-hydrocarbon, wherein the method comprising feeding the fluid tangentially at sufficiently high velocity into a vessel (102) to create a vortex; separating particles from the fluid via centrifugal forces of the vortex and contacting the same with a screen that extends longitudinally inside the vessel; channelling a treated fluid or fluid from the separation/removing process to flow out of the vessel (102). whereby during the process the centrifugal forces push the particles against the vessel’s wall to allow the particles to settle: and the particles that are in contact with the screen be trapped by the screen; and the particles that continue to circle the screen to scrape any build-up of particles or remove a covering or top layer of the particles trapped on the screen. The method further comprising measuring the pressure or differential pressure between the feed stream and the overtflow/outlet of the vessel for initiating a backwashing process of the screen to remove particles trapped on the screen.

The method further comprising injecting a chemical to the feed stream for inducing the particles size of the suspended solids so that the particles can be easily separated and/or trapped.

The method further comprising a step of breaking the vortex at the lower section of the vessel by providing a device having a portion that is progressively narrowed with a tip pointing upward adjacent to a spigot of the vessel for breaking the vortex at its lower end and preventing particles from re-entering the vortex or re-entraining the flow.