Field of invention

The present invention relates to an injectable fluid control valve to provide a change in a flow characteristic of a fluid passing through a conduit and in particular, although not exclusively, to a valve to regulate and stabilise fluid flow suitable to mitigate multiphase slugging in oil and gas extraction systems.

Background art

Multiphase slugging flow is typically problematic within offshore oil and gas production systems and is typically characterised by substantial oscillations in fluid pressure and flow rate. In the extreme, liquid slugs may extend to one or several lengths of a 'riser' that provides the vertical (or height) transport of the oil and gas from the subterranean reservoir to a desired delivery location (i.e. settlement tank) at the surface. Slugging significantly decreases oil and gas recovery rates and efficiency. Conventional solutions to reduce or eliminate severe slugging include 'choking' at or near the surface or 'gas liff at or near the base of the riser. Choking typically involves introducing a localised pressure drop (head loss) due to a construction in the flow at the top of the riser. This provides a stabilisation of the fluid and accordingly a reduced risk of slugging. In particular, the counter pressure imposed by the choke at the surface is effective to stabilise the flow. However, it is not always possible to successfully prevent slugging in that the restriction of flow may be undesirably excessive which in turn imposes a stabilisation at an average pressure which is much greater than the pressure arising due to severe slugging.

Gas lift is an attempt to reduce the hydrostatic pressure of the column of liquid in the riser in an attempt reduce the pressure in the line and keep the liquid moving up the riser.

However, such solutions tend to be complex to install and require sophisticated

arrangements for the supply of compressed gas which are not always available.

Accordingly, what is required is method and apparatus to regulate, stabilise and/or control multiphase fluid flow suitable for specific application in reducing slugging within oil and gas production systems.

Summary of the Invention It is an objective of the present invention to provide fluid flow regulation apparatus and in particular a flow regulator device to achieve active slug control within oil and/or gas production systems. It is a specific objective to provide a flow regulator and/or stabiliser that is effective to control and regulate the pressure within a conduit network to specifically reduce the risk of undesirable pressure changes (in particular pressure rises) within the system.

It is a specific objective to provide a venturi valve that is adapted specifically to control and reduce flow oscillations within a multiphase fluid flow. The objectives are achieved by providing a flow control valve having an injector port configured to provide a secondary fluid flow injectable into a main flow within the primary flow conduit to selectively adjust and control a chocking effect provided by the valve. Preferably, the valve is a venturi valve or tube having an internal construction or narrow section between a respective inlet and outlet, with the restriction or narrow section acting to provide a choke of the fluid flow passing through a conduit within which the valve is installed or is coupled in fluid communication. By injecting a secondary fluid flow (being a gas, liquid or gas-liquid multiphase) into the primary flow, a chocking effect provided by the venturi is controllable. This control may be supplemented for example by adjustment of the secondary fluid injection flow rate, pressure, velocity, volume etc. Accordingly, the present apparatus and method provide a flow regulation device to selectively adjust a choking affect within a conduit network so as to reduce and potentially eliminate (gas- liquid) multiphase slugging in offshore oil and/or gas production systems.

Preferably, the present valve is installable within an oil and/or gas production conduit network (pipeline). Preferably, the valve is positioned at the top and downstream (in the primary flow direction) of the riser. Accordingly, the present valve provides selective adjustment of a counter pressure imposed by the device at the surface being selectively proportional to a velocity of fluid flow through this valve.

According to a first aspect of the present invention there is provided a valve to effect at least one characteristic of a flow of fluid through a conduit, the valve comprising: a main body having an internal bore provided with a bore inlet and outlet at respective axial ends of the bore to allow a primary fluid flow through the bore; an injector port having a port outlet in fluid communication with the bore and positioned at the main body to allow injection of a secondary fluid flow into the bore between the bore inlet and outlet; wherein at least the port outlet is arranged so as to create a second fluid flow resultant from the injector port orientated generally transverse to the longitudinal axis of the bore and aligned counter to the primary fluid flow.

Reference within this specification to a 'characteristic of a flow of fluid' encompasses control, stabilisation or regulation of fluid flow, controlling turbulence, effecting fluid flow rate, fluid flow behaviour, fluid pressure and multiphase fluid flow mixing within a flow conduit or conduit network. Preferably, the port outlet is positioned within an upper half of the throat and preferably at a roof of the throat corresponding to a position between eleven o'clock and one o'clock at a cross section of the valve (in a plane perpendicular to the longitudinal axis). Optionally, the port outlet is positioned at twelve o'clock in the perpendicular plane. Due to the counter and transverse alignment of the injector port, the secondary fluid flow is configured to be injected into the bore against the oncoming primary fluid flow within at least the upper half of the bore. This upper half may typically be occupied by a gas phase with a bottom half being occupied by a liquid phase. With the transverse alignment of the injector port, relative to the longitudinal axis of the bore, the port outlet, injector passageway and/or main length of the injector passageway may be configured to direct the secondary fluid flow in an axial direction within the bore towards the bore inlet relative to the bore outlet. Such an arrangement is advantageous to control or smoothen the pressure differential as the fluid flows through the valve particularly where the valve is a venturi configuration having a throat (alternatively termed a constriction). The injected secondary flow, being aligned transverse to the longitudinal axis, stabilises turbulence to facilitate a smooth flow of a multiphase fluid through the throat that, in turn, regulates pressure of the primary fluid flow both upstream and downstream of the valve.

Preferably, the injector port has an internal passageway terminating at the port outlet, a longitudinal axis of the passageway aligned transverse to the longitudinal axis of the bore. The full length of the passageway, or a portion of the length of the passageway may be aligned transverse to the longitudinal axis of the bore. Such aligned is provided to be sufficient to provide the desired orientation of the secondary fluid flow into the oncoming primary flow. Optionally, a longitudinal axis of the passageway at or towards the port outlet is aligned at an angle in a range 10 to 70°, 20 to 60°, 40 to 50° or 42 to 48° relative to the longitudinal axis of the bore. This alignment provides the desired stabilising or regulating effect to the primary flow so as to counter turbulence that would otherwise be created within the valve. Preferably, a diameter of the passageway is less than a diameter of the bore. More preferably, the diameter of the passageway is less than 70%, less than 60%, less than 50%, less than 40%, less than 30% or less than 20% of the diameter of the bore, where a passageway diameter that is approximately 70% of the diameter of the bore represents a corresponding cross sectional area that is around 50% of the cross sectional area of the main bore of the valve. The present valve is configured to control, stabilise or regulate the fluid flow and is not intended or configured as a mixer valve. The relative difference in the bore sizes of the primary bore of the valve and the bore of the injector port ensures a minimum volume quantity of the secondary fluid flow is delivered into the primary fluid flow. The secondary fluid flow may comprise a gas, a liquid or a multiphase gas-liquid medium. Optionally, the injected fluid is air or water.

Preferably, the valve is a venturi valve in which the bore comprises a constriction representing a throat or narrow section. Preferably, the constriction comprises a multi section arrangement in which a first section comprises a reducing diameter, a central section of generally uniform diameter and a third section having an increasing diameter. Preferably, the main bore comprises an inlet and outlet having the same diameter. The constriction is advantageous to induce a pressure differential upstream and downstream of the valve that has been found to be beneficial for reducing slugging. The subject invention is further advantageous to provide regulation of the pressure differential either side of the valve so as to firstly further reduce or eliminate the likelihood of slugging and to improve efficiency and recovery rates in oil or gas extraction and production pipelines.

Preferably, the port outlet is positioned in a lengthwise direction of the bore at the construction. More preferably, the port outlet is positioned at a smallest diameter region of the construction. This arrangement maximises the stabilising and regulating effect of the injector port.

According to a second aspect of the present invention there is provided a valve to effect at least one flow characteristic of a flow of a fluid through a conduit, the valve comprising: a main body having an internal bore provided with a bore inlet and outlet at respective axial ends of the bore to allow a primary fluid flow through the bore; an injector port having a port outlet in fluid communication with the bore and positioned at the main body to allow injection of a secondary fluid flow into the bore between the bore inlet and outlet; wherein at least the port outlet is arranged, in a plane perpendicular to a longitudinal axis of the bore, off-centre relative an axial centre of the bore to create a second fluid flow resultant from the injector port that is directed to a region between the axial centre and an internal surface of the main body that defines the bore so as to induce a rotational flow path of the primary fluid flow around the longitudinal axis of the bore downstream of the valve.

Optionally, in the plane perpendicular to the longitudinal axis of the bore, at least the port outlet is arranged such that at least a majority of the second fluid flow is orientated to be off-centre from the axial centre of the bore. More preferably, the majority of the second fluid flow is directed into the bore primarily towards the internal surface of the main body that defines the bore. This maximises the effect of inducing the primary fluid flow to adopt a helical flow path downstream of the valve which is beneficial for manipulating the fluid flow through bent, curved, angled or otherwise transverse (non-axially parallel) sections of conduit.

Optionally, the valve may comprise a single injector port or a plurality of injector ports, each port configured to provide a respective said second fluid flow and positioned at different regions of the bore. Preferably, the plurality of injector ports may be positioned in the same plane aligned perpendicular to the longitudinal axis of the bore. Optionally, the injector port or ports each comprise an internal passageway terminating at the port outlet, a longitudinal axis of the passageway(s), in a plane perpendicular to the longitudinal axis of the bore, being aligned tangential or at a secant to the internal surface that defines the bore.

According to a third aspect of the present invention there is provided fluid flow apparatus to provide transport of a fluid comprising: a conduit network connecting a fluid source to a fluid delivery location, the network capable of providing at least a primary fluid flow from the source to the delivery location; a valve as claimed herein located within the network at a position of the primary fluid flow between the source and the delivery location.

Optionally, the network may comprise a riser to provide transport of the fluid against gravity in the upward direction from the source at a first height position to the delivery location at a second height position separated from the source. As will be appreciated, the riser may be positioned downstream of a subterranean flow line and upstream of a head line (with respect to the flow direction of the primary fluid flow from the source to the delivery location). Optionally, the source may comprise a subterranean reservoir containing oil or gas. Optionally, the delivery location may comprise a reservoir, separation tank, settlement tank or the like positioned at a raised or elevated position relative to the source. Preferably, the valve is positioned in the direction of the primary fluid flow downstream of the riser and preferably at the head line of the pipeline system in the flow direction between the riser and the delivery location. In particular and preferably, the valve is positioned in a height direction closer to the delivery location than the source. Preferably, the apparatus further comprises a choke valve component positioned downstream of the valve. The choke valve may comprise a conventional choke valve configured to restrict fluid flow through the network. Optionally or in addition, the present valve may be configured with a choke component that may be selectively narrowed with regard to the diameter of the conduit so as to choke or restrict selectively the flow of the primary fluid through the valve. Such an adjustable restriction may be supplementary and additional to the constriction (or throat) of the venturi valve at which the injector port is positioned. Accordingly, the present valve may comprise two throats or constrictions with at least one of the constrictions being adjustable so as to change the diameter or cross section of the conduit in a plane perpendicular to the longitudinal axis of the bore.

Preferably, the apparatus further comprises a control system having a plurality of sensors positioned at the conduit network, the control system configured to control at least one of a flow rate, a volume of fluid, a velocity of fluid, a pressure of the secondary fluid flow delivered by the injector port into the bore. The control system is advantageous to provide regulation of the primary fluid flow dynamically in response to gradual or changes in the internal status of the pipeline network including for example flow rate, pressure, flow velocity and in particular the extent of slugging including the axial length of liquid slugs within a multiphase system. Such control is provided by adjustment of at least one characteristic of the secondary fluid flow injected into the primary flow as described. Brief description of drawings

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 is a longitudinal cross section and schematic view of a fluid flow control venturi valve assembly according to a specific implementation configured to stabilise a flow of fluid through a conduit according to a specific implementation of the present invention;

Figure 2 is a schematic illustration of an oil pipeline system configured for the extraction of oil and/or gas from a subterranean reservoir incorporating a fluid control venture valve of figure 1 ; Figure 3 is a graph of slug flow transitional boundaries with respect to liquid and gas flow rates for three different systems with and without the venturi valve of figure 1 ;

Figure 4a is three-dimensional computational fluid dynamics image of a gas-liquid multiphase flow through the valve of figure 1 without injection of a secondary fluid flow into the valve;

Figure 4b is three-dimensional computational fluid dynamic image of a gas-liquid multiphase flow through the valve of figure 1 with injection of a secondary fluid flow into the valve;

Figure 5 is a cross sectional view through an elongate fluid flow conduit provided with two secondary fluid flow injection ports arranged to induce a rotational flow about a longitudinal axis of the conduit according to further specific implementations of the present invention. Detailed description of preferred embodiment of the invention

Referring to figure 1, a fluid flow control valve 10 comprises a main body 1 1 provided with a through-bore 12 centred on a longitudinal axis 16 that extends through main body 1 1. Bore 12 comprises a fluid flow inlet 15 and a fluid flow outlet 14 provided at each respective end of bore 12 and main body 1 1. Valve 10 comprises a venturi configuration in which bore 12 includes a construction 13 (alternatively termed a throat) within the bore diameter. Accordingly, a diameter D of the bore 12 at a position upstream and

downstream of the throat 13 is greater than a corresponding diameter d of bore 12 within the region of the throat 13. In particular, the constricted throat region 13 may be considered to comprise three axial throat portions including a first frusto-conical section 25 (positioned axially closest to inlet 15), an intermediate or central cylindrical section 26 and second frusto-conical section 27 positioned axially closest to outlet 14 and being a mirror image of the first section 25. Accordingly, the diameter d of bore 12 at the cylindrical section 26 is approximately half of the diameter D of the bore 12 at and towards inlet and outlet 15, 14. According to the specific implementation, an axial length H of constriction 13 (encompassing axial sections 25, 26 and 27) is in a range 20 to 40% of the total axial length L of the main body 1 1. Additionally, an axial length E of central cylindrical section 26 is in a range 10 to 30% if the total axial length H of the constriction 13.

According to the specific implementation, valve 10 comprises an injector port 18 extending through a portion of the main body 1 1 at the region constriction 13. Injector port 18 comprises an internal passageway 18b having a passageway axial end 18a in fluid communication with central section 26 of constriction 13. Injector port 18 and in particular passageway 18b is orientated relative to the longitudinal axis 16 of bore 12 so as to be transverse to the bore 12 and in particular bore longitudinal axis 16. Injector port 18 comprises or is coupled in fluid communication with a fluid storage tank 19. A pump or the flow driving component (not shown) is connected to or provided at injector port 18 so as to drive a secondary flow of fluid 22 from tank 19 through passageway 18b and into bore 12 (at the region of central section 26) via passageway outlet 18a. A flow regulator valve 40 provides control of the flow of fluid 22 from tank 19 though the injector port 18. Valve 40 may be additional to or integral with the injector port such that the injector port 18 and the component 40 may be regarded as a single valve. Alternatively, component 40 may be considered a secondary control valve in addition to the primary control valve 10.

According to the specific implementation, the transverse alignment of passageway 18b relative to bore axis 16 is such that secondary fluid flow 22 is delivered into the throat region 13 of the bore 12 counter to a primary flow of fluid 23 through the bore 12 from bore inlet 15 to bore outlet 14. Such an arrangement, as will be described in detail below, is advantageous to stabilise and regulate the fluid flow 23 through the valve 10 particularly when a multiphase (gas-liquid) fluid is flowing through a conduit network within which the valve 10 is installed.

According to the specific implementation, a longitudinal axis of passageway 18b (and accordingly the secondary fluid flow 22) is aligned at a transverse angle a relative to bore longitudinal axis 16. That is, at a cross section along the longitudinal axis of the main body 1 1 and bore 12, the angle a is less than 90°. Preferably, a is in a range 30 to 60° and more preferably 40 to 50°. It is an objective of the present valve 10 to provide a regulatory or stabilising effect to a multiphase fluid flowing through valve 10 and not to provide mixing of a primary fluid flow 23 and a secondary fluid flow 22. Accordingly, a diameter of passageway 18b is much less than the diameter D of the majority of the length of bore 12 and the diameter d of the central throat section 26. Preferably, a diameter of the injector port passageway 18b is in a range 5 to 30% or more preferably 10 to 25 or 15 to 20% of the diameter D of the central bore 12 at an axial position at or close to the bore inlet and/or outlet 15, 14. According to the specific implementation, valve 10 comprises a single injector port 18 having a single internal passageway 18b. According to further

implementations, valve 10 may comprise a plurality of injector ports 18 each comprising an internal passageway 18b capable of supporting delivery of a secondary fluid flow 22 into the region of the constriction 13 so as to effect the flow of characteristics of the primary fluid flow 23 axially between the inlet 15 and the outlet 14. A plurality of the injector ports 18 may be positioned approximately at the same plane perpendicular to axis 16 and may be spaced apart relative to each other in a circumferential direction around axis 16. Optionally, the valve 10 may comprise 2, 3, 4, 5 or 6 injector ports 18 positioned at the same or different axial positions along the axial length of bore 12 at the region of constriction 13.

Figures 4a and 4b are images generated using computational fluid dynamics of fluid flow through valve 10. Figure 4a illustrates a highly disturbed multiphase fluid flow 23 at the downstream side of the constriction 13 where component 33 represents the liquid phase and component 34 represents the gas phase. This is to be contrasted with the image of figure 4b in which a gas phase secondary fluid flow 22 is delivered into central throat section 26. As will be noted, the multiphase flow appears smoother and is effectively stabilised by the delivery of the secondary fluid flow 22 orientated counter and transverse to the oncoming primary fluid flow 23. Accordingly, the present valve arrangement is advantageous to stabilise the flow and hence selectively control and adjust the pressure loss of a multiphase fluid within a conduit network within which the valve is positioned. Accordingly, when installed within an oil production or recovery pipeline network, the present valve is advantageous to significantly reduce or eliminate slugging by selective regulation of at least one flow characteristic of the secondary fluid flow 22 within injector port 18. For example, the secondary fluid flow 22 may be regulated by adjustment of the flow rate, pressure, flow velocity, flow volume so as to selectively control and effect the flow characteristics of a primary fluid flow through the conduit network both upstream and downstream of the value 10.

Referring again to figure 1, control of the second fluid flow characteristics may be achieved via a control system illustrated schematically by reference 20. Control system 20 may be implemented via electronic components including for example: a series of sensors, wired or wireless communication means, electronic circuitry and boards such as PCB's, microprocessors, data storage, a user interface, network communication components and the like as will be appreciated. According to the specific implementation, valve 10 comprises a first sensor 17a mounted at bore 12 axially close to bore outlet 14; a second sensor 17c positioned at bore 12 and mounted axially towards inlet 15; a third sensor 17b positioned at bore 12 at central throat section 26 and a fourth sensor 17d provided at injector port 18 in fluid communication with passageway 18b. Sensors 17a to 17d are coupled in electronic communication to a central hub. According to the specific implementation, further components represented illustratively by reference 21 may be coupled to the central hub with the components 21 positioned at different regions of an oil recovery or production pipeline. The control system 20 is then provided optionally in coupled relationship with tank 19 and the pump or other means to create and controllably drive the secondary fluid flow 22 including for example valve 40. Accordingly, the control system 20 is capable of receiving information from sensors 17a to 17d and then to selectively regulate a flow characteristic of the secondary fluid flow 22 in response to the status of the fluid flowing within the primary conduit and in particular bore 12. Sensors 17a to 17d may be configured to provide sensing of flow rate, flow velocity, fluid pressure, phase status (gas-liquid), temperature and the like as will be appreciated.

Referring to figure 2, valve 10 is illustrated installed within an oil recovery/production system in which a fluid source 32 is coupled in fluid communication with a desired fluid delivery location 35 via conduits 30, 29 and 31. As will be appreciated, within commercial oil production, an offshore oil recovery system typically comprises a pipeline network in which a well (oil source reservoir 32) is connected to an underwater flow line 30. The underwater flow line 30 is then connected at a central point to an ascending riser 29 to provide vertical transport of the recovered oil. A head line 31 is coupled downstream to the top of the riser 29 and in fluid communication with a separating chamber representing the delivery location 35. The present venturi valve 10 is positioned at the head line 31 downstream of the riser 29. An additional choke valve 28 is positioned downstream of the venturi valve 10 and upstream of the separation chamber (in the primary flow direction). As illustrated, control system 20 comprises sensors 17a to 17d in addition to at least one further sensor 21 positioned at the base of riser 29. Other components typically associated with offshore oil or petroleum field are not shown within figure 2 for brevity. The pipeline system is configured to provide a primary fluid flow 23 that includes a multiphase flow having a liquid component 33 and a gas component 34. As indicated, control system 22 is configured to regulate at least one characteristic of the secondary fluid flow 22 so as to regulate and stabilise the multiphase fluid flow 23 through the venturi valve 10. In particular, by specifically regulating the pressure and in particular pressure rises and pressure drops both upstream and downstream of riser 29, the occurrence and risk of slugging within the riser 29 is reduced and preferably eliminated. Figure 3 illustrates the effect of providing a counter secondary fluid flow 22 into the venturi valve 10 and the occurrence of slugging. The liquid flow rate (y axis) and gas flow rate (x axis) were varied for a system of figure 2 and the occurrence of slugging observed of the different flow rate conditions. Slugging (represented by the points on the graph) occurred only within the smaller boundary 38 with introduction of the secondary gas flow 22 into a bore 12 via injector port 18. With no secondary fluid flow 22, the occurrence of slugging extended over a greater range of liquid and gas flow rates as represented by boundary 37. Boundary 36 defines a system similar to figure 2 but without a venturi valve 10 within the conduit network. As will be evident from figure 3, injecting a counter flow 22 into the path of the oncoming primary fluid flow 23 is beneficial to reduce the multiphase flow rates over which slugging occurs. Accordingly, the present valve is advantageous to allow enhanced oil and gas recovery rate from subterranean and offshore wells.

The present valve 10 is further advantageous to be implemented as a measurement device comprising the array of sensors 17a to 17b. By stabilising the fluid flow through the bore 12, the valve 10 may be operated in a measurement mode that would otherwise not be possible due to the high turbulence and instability of the fluid phase downstream of the constriction 13 as illustrated in figure 4a.

According to further aspects of the present invention one or a plurality of injector ports 18 may be provided at main body 1 1 so as to induce a rotational motion to the primary fluid flow 23. Such an arrangement is advantageous to facilitate transport of a single or multiphase fluid through angled, curved or bent regions conduit (pipeline) for example when transitioning upstream and downstream of the riser 29 and at various other regions of the pipeline. According to the further implementation, valve 10 comprises a pair of generally opposed injector ports 18 having respective internal passageways 18b terminating at the passageway outlet 18a in fluid communication with central bore 12. A longitudinal axis of each passageway 18b is off-centre relative to the axial centre

(longitudinal axis 16) of bore 12 so as to deliver the secondary fluid flow 22 into a region between an internal facing surface 24 that defines bore 12 and the bore axis 16. That is, the passageway outlets 18b are positioned close to and facing and internal surface 24 (relative to axis 16) such that an axis of each passageway 18b is approximately tangential to internal surface 24 (in a plane perpendicular to longitudinal axis 16). Accordingly, each passageway 18b does not emerge at the bore 12 to be orientated towards bore axis 16 but are instead orientated towards bore internal surface 24 and/or the region between the internal surface 24 and bore axis 16. Accordingly, as the primary fluid flow 23 flows axially through the constriction and passed injector port 18, the secondary fluid flow 22 induces rotational motion 39 to the primary flow 23 around bore axis 16. The embodiment of figure 5 (to induce a rotational or helical flow path within the primary flow) may be supplementary to the embodiment of figure 1 (to create a secondary fluid flow 22 aligned counter to the primary fluid flow 23) that provides a flow stabilising effect. Accordingly, the multiphase fluid flowing through valve 10 may be stabilised, regulated and in addition effected to adopt a rotational helical flow path downstream of the valve 10.