Patent Description:
A flow choke can be used in well drilling operations to variably restrict flow of a well fluid. In managed pressure, underbalanced and other types of closed system drilling operations, the flow choke can be used to regulate pressure in a wellbore by variably restricting flow of well fluid from an annulus formed between a drill string and the wellbore.

Therefore, it will be readily appreciated that improvements are continually needed in the art of constructing and utilizing flow chokes and associated well systems. Such improvements may be useful in well operations other than closed system drilling operations (for example, a well control choke manifold could benefit from the improvements disclosed below and in the accompanying drawings).

<CIT> discloses in a sub-sea wellhead insert-type choke valve having a bonnet, a pair of pressure transmitters mounted in the bonnet. One transmitter is connected by a passageway with the annular clearance between the cartridge of the insert assembly and the valve body. This transmitter measures the pressure of the fluid in the clearance and transmits signals indicative thereof to a receiver at surface. The other transmitter is connected by a passageway with the fluid in the valve outlet, measures the pressure of this fluid and transmits signals indicative thereof to the receiver. In this way the high and low pressures upstream and downstream of the choke valve flow trim are monitored by transmitters, which can be serviced by bringing the insert assembly to surface.

<CIT> discloses a wellhead valve system for adjusting the flow, for example, of hydrocarbon, comprising a hydraulic control valve for opening the wellhead made up of a valve body provided with a pipe for the passage of a flow of fluids, having an inlet opening and an outlet opening, interposed between the inlet opening and the outlet opening being an adjustable orifice; an actuator adapted to command the valve to close and open, in which the actuator operates on opening and closing means of the adjustable orifice; and a position gauge adapted to determine the degree of opening of the adjustable orifice, and is characterized in that the position gauge is integral with the opening and closing means of the adjustable orifice. Thanks to the accurate measurements carried out by the position gauge, it is possible to determine the gas/liquid monophase and/or biphase flow rate value accurately and instantly, based upon data measured by a plurality of fluid and/or flow parameters sensors, comprising pressure sensors and temperature sensors, preferably positioned integrally with the valve body.

The invention is as defined in the claims hereof.

Representatively illustrated in <FIG> is a system <NUM> for use with a subterranean well, and an associated method, which can embody principles of this disclosure. However, it should be clearly understood that the system <NUM> and method are merely one example of an application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited at all to the details of the system <NUM> and method described herein and/or depicted in the drawings.

In the <FIG> example, a wellbore <NUM> is being drilled by rotating a drill bit <NUM> connected at a downhole end of a generally tubular drill string <NUM>. A pump <NUM> (such as, a rig mud pump) pumps a well fluid <NUM> through the drill string <NUM>, with the fluid returning to surface via an annulus <NUM> formed radially between the drill string and the wellbore <NUM>.

Note that the term "well fluid" is used herein to indicate that the fluid <NUM> flows in the well. It is not necessary for the well fluid <NUM> to originate in the well, or for characteristics of the well fluid (composition, density, viscosity, etc.) to remain unchanged as it flows in the system <NUM>. For example, the well fluid <NUM> flowed from the wellbore <NUM> in a drilling operation could include fines, cuttings, formation liquids or gas and/or other components, which components may be removed from the well fluid prior to it being re-introduced into the well.

Although not depicted in <FIG>, various items of equipment may be provided in the system <NUM> to facilitate control of pressure in the wellbore <NUM> (for example, in order to prevent undesired fluid loss, fluid influxes, formation damage, or wellbore instability) during actual drilling, and while making connections in the drill string <NUM> or tripping the drill string into or out of the wellbore. The scope of this disclosure is not limited to only the combination of equipment, elements, components, etc., depicted in <FIG>.

In some examples, a closed system may be provided by use of equipment variously known to those skilled in the art as a rotating control device (RCD), rotating control head, rotating drilling head, rotating diverter, pressure control device (PCD), rotating blowout preventer (RBOP), etc. Such equipment isolates the wellbore <NUM> from the atmosphere at surface by sealing off the annulus <NUM>, thereby facilitating pressure control in the wellbore. In other examples, the wellbore <NUM> may be isolated from the atmosphere at surface during well control situations, and not necessarily during drilling operations.

In the <FIG> system <NUM>, a variable flow choke <NUM> is used to restrict flow of the well fluid <NUM> from the annulus <NUM>. In actual practice, the flow choke <NUM> may be part of an overall choke manifold (not shown) comprising multiple redundant chokes, shutoff valves, bypass lines, etc..

It will be appreciated by those skilled in the art that, with the well fluid <NUM> flowing from the annulus <NUM> and through the flow choke <NUM>, restriction to flow of the well fluid through the flow choke can be decreased in order to decrease pressure in the annulus, and the restriction to flow through the flow choke can be increased in order to increase pressure in the annulus. A control system <NUM> can be used to operate the flow choke <NUM> in a manner that maintains a desired pressure in the wellbore <NUM>.

The control system <NUM> can include, for example, a programmable logic controller (PLC) that operates the flow choke <NUM> so that a desired volumetric or mass flow rate of the well fluid <NUM> through the flow choke is maintained, so that a desired pressure is maintained in the annulus <NUM> at the surface, so that a desired pressure is maintained at one or more selected locations in the wellbore <NUM>, or so that another desired objective or combination of objectives is obtained or maintained. In some examples, the PLC could control operation of the flow choke <NUM> using a proportional-integral-derivative (PID) algorithm.

The control system <NUM> may include various configurations of processors, static or volatile memory, input devices, output devices, remote communication devices, software, hardware, firmware, etc. The scope of this disclosure is not limited to any particular components or combination of components in the control system <NUM>, or to use of a PLC controller or PID algorithm.

The control system <NUM> can receive input from a variety of different sources to enable the control system to effectively control operation of the flow choke <NUM>. In the <FIG> example, the control system <NUM> receives an output of a flow meter <NUM> (depicted as a Coriolis-type flow meter) connected downstream of the flow choke <NUM>. Thus, in this example, the control system <NUM> can operate the flow choke <NUM> so that a desired mass or volumetric flow rate of the fluid <NUM> through the flow choke is obtained and maintained. In some examples, other types of sensors (such as, temperature sensors, pressure sensors, pump stroke sensors, etc.) can provide their outputs to the control system <NUM>.

As depicted in <FIG>, fluid conditioning and storage equipment <NUM> used with the system <NUM> can include, for example, a gas separator <NUM>, a solids shaker <NUM> and a mud tank <NUM> connected between the flow meter <NUM> and the pump <NUM>. Of course, other or different fluid conditioning and storage equipment may be used in other examples incorporating the principles of this disclosure.

Referring additionally now to <FIG>, a cross-sectional view of an example of the flow choke <NUM> as used in the system <NUM> and method of <FIG> is representatively illustrated. However, the <FIG> flow choke <NUM> may be used in other systems and methods, in keeping with the scope of this disclosure.

In the <FIG> example, the flow choke <NUM> includes a flow passage <NUM> formed through a body <NUM> of the flow choke. The body <NUM> includes inlet and outlet flanged connections 40a,b for connecting the flow choke <NUM> between the annulus <NUM> (e.g., at a wellhead or RCD, not shown in <FIG>) and the flow meter <NUM> in the system <NUM>. In other examples, the flow choke <NUM> could be connected between other components.

A flow restrictor <NUM> variably restricts flow of the fluid <NUM> through the flow passage <NUM>. In this example, the flow restrictor <NUM> includes a gate or other closure member <NUM> that is displaceable relative to a flow orifice, bean or seat <NUM> that encircles the flow passage <NUM>. Other types of variable flow restrictors may be used in other examples.

A flow area A between the closure member <NUM> and the seat <NUM> can be varied by displacing the closure member longitudinally relative to the seat. As depicted in <FIG>, downward displacement of the closure member <NUM> relative to the seat <NUM> (along a longitudinal axis <NUM>) will decrease the flow area A, and subsequent upward displacement of the closure member will increase the flow area.

The closure member <NUM> is displaceable by means of an actuator <NUM> connected to the body <NUM>. The actuator <NUM> displaces a thrust rod or stem <NUM> connected to the closure member <NUM>, to thereby vary the flow area A between the closure member and the seat <NUM>.

The actuator <NUM> in this example comprises a linear actuator that displaces the stem <NUM> along the longitudinal axis <NUM>. In some examples, the actuator <NUM> could comprise an axially aligned annular hydraulic motor with planetary gearing, and with a body of the actuator being directly connected to the flow choke body <NUM>. However, the scope of this disclosure is not limited to any particular type of actuator used to operate the flow restrictor <NUM>. In other examples, other types of electrical, hydraulic, pneumatic, etc., actuators or combinations thereof may be used.

The actuator <NUM> is connected to the control system <NUM>, so that operation of the actuator <NUM> (and, thus, the flow restrictor <NUM> and flow choke <NUM>) is controlled by the control system. The restriction to flow of the fluid <NUM> through the flow restrictor <NUM> can be varied by the control system <NUM> to obtain or maintain any of the desired objectives mentioned above. However, the scope of this disclosure is not limited to any particular objective accomplished by operation of the flow restrictor <NUM> by the control system <NUM>.

The control system <NUM> receives outputs from sensors 54a-c connected to external ports 56a-c on the flow choke body <NUM>. In this example, the sensors 54a-c comprise pressure transducers or sensors, but in some examples they may also comprise temperature sensors and/or other types of sensors. The scope of this disclosure is not limited to use of any particular type of sensor or combination of sensors with the flow choke <NUM>.

The ports 56a-c are depicted in <FIG> as including conventional tubing connectors, but other types of connectors may be used in other examples. Alternatively, the sensors 54a-c may be connected directly to the body <NUM>, without use of separate connectors (for example, by threading the sensors into the body at the ports 56a-c). Thus, the scope of this disclosure is not limited to use of any particular type of connector with the ports 56a-c, or to use of separate connectors at all.

As depicted in <FIG>, the flow choke <NUM> is in a fully open configuration. The closure member <NUM> is displaced to its maximum upward stroke extent, so that a longitudinal distance between the closure member and the seat <NUM> is at a maximum, and the flow area A is at a maximum. Relatively unrestricted flow of the fluid <NUM> through the flow passage <NUM> is permitted in this fully open configuration.

Referring additionally now to <FIG>, a somewhat enlarged scale cross-sectional view of a portion of the flow choke <NUM> in the open configuration is representatively illustrated. In this view, components of the flow choke <NUM> may be more clearly seen.

Note that the external port 56a is in fluid communication with the flow passage <NUM> upstream of the flow restrictor <NUM> (relative to a direction of flow of the fluid <NUM>) by means of a fluid line 58a extending through the body <NUM>. Similarly, the external port 56b is in fluid communication with the flow passage <NUM> downstream of the flow restrictor <NUM> (relative to the direction of flow of the fluid <NUM>) by means of a fluid line 58b extending through the body <NUM>.

Thus, the sensors 54a,b (see <FIG>) connected to the respective external ports 56a,b can be used to measure fluid pressure in the flow passage <NUM> respectively upstream and downstream of the flow restrictor <NUM>. A difference between these measured fluid pressures is a pressure differential across the flow restrictor <NUM>. Alternatively, a single pressure differential sensor (not shown) connected to both of the external ports 56a,b could be used to directly measure the pressure differential.

The measured pressure differential can be used to determine a flow rate of the fluid <NUM> through the flow choke <NUM>, for example, as a "check" or verification of the flow rate measurements output by the flow meter <NUM> (see <FIG>), or in the event of malfunction of the flow meter <NUM> or inaccuracies in its measurements (for example, due to excessive two-phase flow through the flow meter). A previously empirically determined flow coefficient or flow factor for the flow choke <NUM> may be used to calculate the flow rate of the fluid <NUM>, based on the measured pressure differential.

In the case of an empirically determined flow coefficient (Cv), the following equation (<NUM>) may be used: <MAT> in which Q is the volumetric flow rate in US gallons per minute, SG is the specific gravity of the fluid <NUM>, and ΔP is the differential pressure in pounds per square inch.

Solving for the flow rate Q results in the following equation (<NUM>): <MAT>.

Thus, with an empirically derived flow coefficient Cv, known specific gravity SG and measured differential pressure ΔP, the flow rate Q can be conveniently calculated. A similar calculation may be used in the case of an empirically determined flow factor (Kv) in SI metric units.

The flow rate calculation may be performed by the control system <NUM> in this example. The calculated flow rate may be used by the control system <NUM> to directly control operation of the flow choke <NUM> (such as, by varying the flow restriction to obtain and maintain a desired flow rate set point), or the calculated flow rate may be used in further calculations (for example, to obtain and maintain a desired pressure in the wellbore <NUM>). The scope of this disclosure is not limited to any particular use for the calculated flow rate through the flow choke <NUM>. Calculation of the flow rate may not be necessary or may not be performed in other examples.

In a closed configuration, the closure member <NUM> can be displaced by the actuator stem <NUM> into contact with a sealing surface 46a on the seat <NUM>. Another sealing surface 46b is formed on an opposite end of the seat <NUM>, so that the seat can be reversed in the flow choke <NUM>, in the event that the sealing surface 46a becomes damaged, eroded or otherwise unable to function satisfactorily in sealingly engaging the closure member <NUM>. When the seat <NUM> is reversed, the closure member <NUM> can be displaced by the actuator stem <NUM> into contact with the sealing surface 46b.

The closure member <NUM> is also reversible. Near one end, the closure member <NUM> has a sealing surface 44a for engagement with the sealing surface 46a or 46b of the seat <NUM>. Another sealing surface 44b is formed near an opposite end of the closure member <NUM>, so that the closure member can be reversed in the flow choke <NUM>, in the event that the sealing surface 44a becomes damaged, eroded or otherwise unable to function satisfactorily in sealingly engaging the seat <NUM>.

The fluid line 58b is in communication with the flow passage <NUM> via openings 60a formed through a sleeve <NUM> positioned in the body <NUM>. The sleeve <NUM> provides erosion resistance about the flow passage <NUM> downstream of the seat <NUM>.

An annular recess <NUM> in the body <NUM> enables the fluid line 58b to communicate with all of the openings 60a circumferentially about the sleeve <NUM>. The sleeve <NUM> is reversible in the body <NUM>, so that the fluid line 58b can communicate with the flow passage via openings 60b formed through the sleeve near an opposite end of the sleeve.

A seal <NUM> (depicted in <FIG> as a stack of V- or chevron-type packing) sealingly engages an exterior surface of the stem <NUM>. The seal <NUM> is preferably suitable to isolate an interior of the actuator <NUM> from the fluid <NUM> in the flow passage <NUM> (e.g., with a pressure rating appropriate to resist the fluid pressure in the flow passage).

In the event of a leak past the seal <NUM>, the fluid <NUM> will accumulate in an annular chamber <NUM> formed radially between the stem <NUM> and an adapter <NUM> used to interface the actuator <NUM> with the valve body <NUM>. The fluid line 58c is in communication with the chamber <NUM>, and so the sensor 54c (connected to the external port 56c, see <FIG>) can detect if the fluid <NUM> has leaked past the seal <NUM>.

In response to an indication from the sensor 54c that a leak has occurred, or that fluid has otherwise accumulated in the chamber <NUM>, the control system <NUM> may record data corresponding to the leak event (e.g., time, level, pressure, etc.), provide an indication that the seal <NUM> requires service, and/or provide an alarm (such as, a visual, audible, textual and/or tactile alarm). An early indication of seal <NUM> leakage can help to ensure that the problem is mitigated at the earliest appropriate opportunity.

Referring additionally now to <FIG>, the flow choke <NUM> is representatively illustrated in the closed configuration. In this example, flow of the fluid <NUM> through the passage <NUM> is completely prevented, due to sealing engagement between the closure member <NUM> and the seat <NUM>.

In other examples, engagement between the closure member <NUM> and the seat <NUM> may result in substantially complete (but not entirely complete) prevention of flow through the flow restrictor <NUM>. In these examples, engagement between the closure member <NUM> and the seat <NUM> may result in maximum resistance to flow through the passage <NUM>, and a separate shutoff valve may be used when complete prevention of flow is desired.

Note that engagement between the closure member <NUM> and the seat <NUM> is not required. In some examples, there may be no direct contact between the closure member <NUM> and the seat <NUM> when maximum resistance to flow through the flow choke <NUM> is achieved. In addition, if the flow restrictor <NUM> is of another type, the closure member <NUM> and seat <NUM> may not be used. Thus, the scope of this disclosure is not limited to any particular configuration, combination or manner of operation of components in the flow restrictor <NUM>.

A more detailed view of the flow restrictor <NUM> in the closed configuration is representatively illustrated in <FIG>, and is described more fully below.

Referring additionally now to <FIG>, another cross-sectional view of the flow choke <NUM> is representatively illustrated. The view depicted in <FIG> is rotationally offset (rotated about the longitudinal axis <NUM>) relative to the view depicted in <FIG>, so that another external port 56d in the body <NUM> is visible.

The external port 56d is in fluid communication via a fluid line 58d with an annular chamber <NUM> formed radially between the body <NUM> and the adapter <NUM>. The chamber <NUM> is isolated from the passage <NUM> by one or more seals <NUM>.

In the event of a leak past the seals <NUM>, the fluid <NUM> will accumulate in the annular chamber <NUM>. The fluid line 58d is in communication with the chamber <NUM>, and so a sensor 54d connected to the external port 56d can detect if the fluid <NUM> has leaked past the seals <NUM>. The sensor 54d may be the same as, or similar to, the sensors 54a-C.

In response to an indication from the sensor 54d that a leak has occurred, or that fluid has otherwise accumulated in the chamber <NUM>, the control system <NUM> may take any of the actions mentioned above (record data corresponding to the leak event, provide an indication that the seals <NUM> require service, or provide an alarm). However, the scope of this disclosure is not limited to any particular actions taken by the control system <NUM> in response to an indication of seal <NUM> or seals <NUM> leakage.

Referring additionally now to <FIG>, a more detailed cross-sectional view of the flow restrictor <NUM> is representatively illustrated in the closed configuration. In this view, a pressure balancing feature of the flow restrictor <NUM> is more clearly seen.

In the example depicted in <FIG>, the closure member <NUM> has one or more openings 44c formed longitudinally through the closure member. The closure member <NUM> is also slidingly and sealingly received in a sleeve 68a extending downwardly (as viewed in <FIG>) from the adapter <NUM>.

One or more seals <NUM> are sealingly engaged between the sleeve 68a and an exterior surface of the closure member <NUM>. Thus, with the closure member <NUM> in sealing engagement with the seat <NUM> (e.g., with the <FIG> sealing surfaces 44a or b, and 46a or b, sealingly engaged with each other), fluid flow through the flow restrictor <NUM> and passage <NUM> is prevented.

The openings 44c provide for fluid communication between the flow passage <NUM> downstream of the flow restrictor <NUM>, and an annular chamber <NUM> formed radially between the stem <NUM> and the adapter sleeve 68a. The chamber <NUM> is also positioned longitudinally between the seal <NUM> and the seals <NUM>.

However, the scope of this disclosure is not limited to use of the openings 44c in the closure member <NUM> for providing fluid communication between the passage <NUM> and the chamber <NUM>. In other examples, fluid communication could be provided via one or more openings or other fluid flow paths in the stem <NUM>, in a retainer <NUM> used to releasably secure the closure member <NUM> to the stem, or in another component of the flow choke <NUM>.

Pressures in the annular chamber <NUM> and in the flow passage <NUM> are equalized in the open configuration depicted in <FIG> (and in intermediate positions of the closure member <NUM> between its open and closed positions). Thus, there is no net force exerted on the closure member <NUM> in the longitudinal direction (along the longitudinal axis <NUM>) due to the pressure in the flow passage <NUM> and annular chamber <NUM>. The closure member <NUM> is, therefore, pressure balanced in the longitudinal direction.

The actuator <NUM> (via the stem <NUM>) can exert a longitudinal force on the closure member <NUM>, for example, to maintain the closure member in its closed position or to displace the closure member to its open position or an intermediate position. Note that, in order to exert a net downward biasing force on the closure member <NUM>, the actuator <NUM> will apply to the stem <NUM> a downward force only greater than an upward force due to the pressure in the flow passage <NUM> applied across a cross-sectional area of the stem (and not across a cross-sectional area of the closure member <NUM>, since the closure member is pressure balanced). This reduces a need for the actuator <NUM> to apply such large longitudinal forces.

Referring additionally now to <FIG>, another example of the flow choke <NUM> is representatively illustrated. In this example, additional ports 56e,f and sensors 54e,f are provided. The sensor 54e is in fluid communication with the flow passage <NUM> upstream of the flow restrictor <NUM> via the port 56e, and the sensor 54f is in fluid communication with the flow passage <NUM> downstream of the flow restrictor <NUM> via the port 56f.

The sensors 54e,f measure a density of the fluid <NUM> flowing through the passage <NUM>, respectively upstream and downstream of the flow restrictor <NUM>. A suitable density sensor for use as the sensors 54e,f with the <FIG> flow choke <NUM> is marketed by Rheonics, Inc. of Sugar Land, Texas, USA. A "DV" family of sensors available from Rheonics can measure viscosity in addition to density. However, any suitable density sensor may be used for the sensors 54e,f in keeping with the principles of this disclosure.

A combination of flow rate, density, and temperature measurements (from the sensors <NUM>, 54a,b,e,f) can provide much of the same capability as a typical Coriolis flow meter (e.g., measurement of mass flow rate), with the additional capability of the adjustable flow restrictor <NUM> downstream of the sensors 54a,e and upstream of the sensors 54b,f. For example, from the density measurements, the fluid <NUM> specific gravity SG can be more accurately determined to improve flow rate Q calculation (see equation <NUM> above) in real-time. In addition, measurement of density upstream and downstream of the flow restrictor <NUM> will provide more information, for example, to determine if there is a phase change to the fluid <NUM> as it flows through the flow choke <NUM>.

Note that the sensors 54e,f and ports 56e,f are depicted in <FIG> as being positioned in a same lateral plane as the sensors 54a,b and ports 56a,b. However, in other examples, the sensors 54e,f or ports 56e,f may not be positioned in the same lateral plane as the sensors 54a,b and ports 56a,b.

Although separate sensors 54a,e and 54b,f are depicted in <FIG> respectively upstream and downstream of the flow restrictor <NUM>, any or all of these sensors could be combined, or different combinations of sensors could be used. The sensors 54a,e are depicted in <FIG> as being in fluid communication with the flow passage <NUM> via separate flow paths or fluid lines formed in the body <NUM>, but the flow paths could be combined or could intersect in the body (as depicted for the sensors 54b,f) in other examples. Thus, the scope of this disclosure is not limited to any particular combination, arrangement, configuration or number of the sensors 54a,b,e,f or ports 56a,b,e,f, or to any manner of placing the sensors in fluid communication with the flow passage <NUM>.

It may now be fully appreciated that the above disclosure provides significant advancements to the art of constructing and utilizing flow chokes and associated well systems. In examples described above, the flow choke <NUM> is provided with the external ports 56a,b,e,f that can facilitate determining fluid flow rate through the flow choke, external ports 56c,d that can facilitate early detection of seal <NUM>, <NUM> leakage, sealing of the actuator stem <NUM> against the fluid <NUM> and pressure in the flow passage <NUM>, and pressure balancing of the closure member <NUM>.

The above disclosure provides to the art a flow choke <NUM> for use with a subterranean well. In one example, the flow choke <NUM> can include a variable flow restrictor <NUM> configured to restrict flow through a flow passage <NUM> extending through the flow choke <NUM>, a first external port 56a in communication with the flow passage <NUM> upstream of the flow restrictor <NUM>, a second external port 56b in communication with the flow passage <NUM> downstream of the flow restrictor <NUM>, and at least one sensor 54a,b in communication with the first and second external ports 56a,b.

The "at least one" sensor may comprise first and second pressure sensors 54a,b. The first pressure sensor 54a may be in communication with the first external port 56a, and the second pressure sensor 54b may be in communication with the second external port 56b.

The "at least one" sensor may comprise first and second density sensors 54e,f. The first density sensor 54e may be in communication with an external port 56a or e, and the second density sensor 54f in communication with the second external port 56b or f.

The flow choke <NUM> may include an actuator <NUM> including a displaceable stem <NUM>. A restriction to the flow through the flow passage <NUM> may be varied in response to displacement of the stem <NUM>.

A stem seal <NUM> may sealingly engage the stem <NUM> and isolate the actuator <NUM> from fluid pressure in the flow passage <NUM>. The stem seal <NUM> may isolate the actuator <NUM> from the fluid pressure in the flow passage <NUM> downstream of the flow restrictor <NUM>, in a closed configuration of the flow choke <NUM>.

The flow choke <NUM> may include a third external port 56c in communication with a stem chamber <NUM> surrounding the stem <NUM>. The third external port 56c may be isolated by the stem seal <NUM> from the fluid pressure in the flow passage <NUM>.

The flow choke <NUM> may include a fourth external port 56d in communication with a sleeve chamber <NUM>. The sleeve chamber <NUM> may be positioned external to a sleeve 68a in which a closure member <NUM> of the flow restrictor <NUM> is slidingly and sealingly received. The sleeve chamber <NUM> may be isolated from the flow passage <NUM> by a sleeve seal <NUM>.

In open and intermediate configurations of the flow choke <NUM>, a longitudinally displaceable closure member <NUM> of the flow restrictor <NUM> may be pressure balanced in a longitudinal direction.

A method of controlling flow of a well fluid <NUM> is also provided to the art by the above disclosure. In one example, the method can include the steps of: flowing the well fluid <NUM> through a flow passage <NUM> formed through a body <NUM> of a flow choke <NUM>, the flow choke <NUM> including a flow restrictor <NUM>, the flow restrictor <NUM> being operable to variably restrict flow through the flow passage <NUM>; measuring a pressure differential ΔP between first and second external ports 56a,b of the flow choke <NUM>, the first and second external ports 56a,b being in communication through the body <NUM> with respective upstream and downstream sides of the flow restrictor <NUM>; and operating the flow restrictor <NUM>, thereby varying a restriction to the flow through the flow passage <NUM>, in response to the measured pressure differential ΔP.

The varying step can include varying the restriction to the flow through the flow passage <NUM> in response to a change in the measured pressure differential ΔP.

The method may include the step of determining a flow rate Q of the well fluid <NUM> through the flow passage <NUM>, based on the measured pressure differential ΔP.

The method may include the steps of: connecting at least one pressure sensor 54a,b to the first and second external ports 56a,b; receiving an output of the at least one pressure sensor 54a,b by a control system <NUM>; and the control system <NUM> operating an actuator <NUM> of the flow choke <NUM>.

The "at least one pressure sensor" may comprise first and second pressure sensors 54a,b. The connecting step may include connecting the first and second pressure sensors 54a,b to the respective first and second external ports 56a,b. The output received by the control system <NUM> can comprise outputs of the first and second pressure sensors 54a,b.

The operating step may include longitudinally displacing a closure member <NUM> of the flow restrictor <NUM>. The method may further include balancing pressure across the closure member <NUM> in a longitudinal direction when the closure member <NUM> is not engaged with a seat <NUM> of the flow restrictor <NUM>.

The operating step may include displacing an actuator stem <NUM> of the flow choke <NUM>. The method may further include sealing about the actuator stem <NUM>, thereby isolating the actuator <NUM> from the flow passage <NUM>.

The method may include measuring density of a fluid <NUM> in the flow passage <NUM>. The density measuring step may include measuring the density upstream and downstream of the flow restrictor <NUM>.

Also described above is a system <NUM> for use with a subterranean well. In one example, the well system <NUM> can include a pump <NUM> that pumps a well fluid <NUM>, a flow choke <NUM> comprising a variable flow restrictor <NUM> that restricts flow of the well fluid <NUM> through a flow passage <NUM> extending through the flow choke <NUM>, the variable flow restrictor <NUM> being operable by an actuator <NUM> that includes a displaceable stem <NUM>, and the flow choke <NUM> further comprising a stem seal <NUM> that isolates the actuator <NUM> from the well fluid <NUM> in the flow choke <NUM>, and a control system <NUM> that operates the actuator <NUM>.

The stem seal <NUM> may isolate the actuator <NUM> from fluid pressure in the flow passage <NUM> upstream of the flow restrictor <NUM>, in a closed configuration of the flow choke <NUM>.

Although various examples have been described above, with each example having certain features, it should be understood that it is not necessary for a particular feature of one example to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example's features are not mutually exclusive to another example's features. Instead, the scope of this disclosure encompasses any combination of any of the features.

Although each example described above includes a certain combination of features, it should be understood that it is not necessary for all features of an example to be used. Instead, any of the features described above can be used, without any other particular feature or features also being used.

It should be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of this disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments.

In the above description of the representative examples, directional terms (such as "above," "below," "upper," "lower," etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein.

The terms "including," "includes," "comprising," "comprises," and similar terms are used in a non-limiting sense in this specification. For example, if a system, method, apparatus, device, etc., is described as "including" a certain feature or element, the system, method, apparatus, device, etc., can include that feature or element, and can also include other features or elements. Similarly, the term "comprises" is considered to mean "comprises, but is not limited to.

Claim 1:
A flow choke (<NUM>) for use with a subterranean well, the flow choke (<NUM>) comprising:
a variable flow restrictor (<NUM>) configured to restrict flow through a flow passage (<NUM>) extending through the flow choke (<NUM>), in which, in open and intermediate configurations of the flow choke (<NUM>), a longitudinally displaceable closure member (<NUM>) of the flow restrictor (<NUM>) is fully pressure balanced in a longitudinal direction, such that there is no net force exerted on the-closure member (<NUM>) in the longitudinal direction, due to well pressure acting on opposite ends of the flow restrictor (<NUM>);
a first external port (56a) in communication with the flow passage (<NUM>) upstream of the flow restrictor (<NUM>);
a second external port (56b) in communication with the flow passage (<NUM>) downstream of the flow restrictor (<NUM>); and
at least one sensor (<NUM>) in communication with the first and second external ports (56a,b).