WELLHEAD PRESSURE GAUGING

Field of the Invention

In one aspect, the present invention relates to a system for gauging pressure at a wellhead. In another aspect, the present invention relates to a method of gauging pressure at a wellhead.

Background of the Invention

Pressure monitoring of pressure equipment is widely applied in various field of industry. An example in the oil and gas industry is well integrity monitoring, which involves surface pressure gauging on a well annulus in a wellhead. Petroleum Technology Company (PTC) has published a white paper under the title "A new approach to Annulus Pressure Monitoring: Improving Data Reliability and Well Integrity, while Reducing Lifecycle Costs" (2016) , which explains the benefits of PTC s "VR Sense" solution.

Traditionally, to monitor annulus pressure, a pressure gauge is installed on an instrument flange, with either one or two gate valves between it and the wellhead side outlet (of the annulus) . It has various drawbacks, including that a free instrument flange must be available on the wellhead or the Christmas tree. Moreover, installation of a pressure gauge in the traditional instrument flange on a wellhead spool on a live (pressurized) well annulus is not trivial and quite elaborate.

Summary of the invention

In one aspect, the invention provides a system for gauging pressure at a wellhead, comprising a valve fluidly connected to a space of interest in the wellhead and a pressure gauge fluidly connected to the valve via a grease injection port of the valve. In another aspect, the invention provides a method of gauging pressure at a wellhead, comprising: fluidly

connecting a pressure gauge to a valve via a grease injection port of the valve, which valve is fluidly connected to the wellhead, and taking at least a pressure reading from the pressure gauge.

Brief description of the drawing

The appended drawing, which is non-limiting, comprises the following figures:

Fig. 1 schematically shows a simplified impression of a wellhead spool including a side outlet valve;

Fig. 2 schematically shows a simplified impression of a gate valve in cross section which can be used as the side outlet valve of Fig. 1;

Fig. 3 schematically shows an external perspective view of a pressure gauge connector;

Fig. 4 schematically shows a cross sectional view of the pressure gauge connector of Fig. 3 being provided with grease fittings and a pressure gauge;

Fig. 5 schematically shows a close-up cross sectional view of the pressure gauge connector of Fig. 3 in neutral position ;

Fig. 6 schematically shows a close-up cross sectional view of the pressure gauge connector of Fig. 3 in

intermediate position;

Fig. 7 schematically shows a close-up cross sectional view of the pressure gauge connector of Fig. 3 in injecting position ;

Fig. 8 schematically shows a close-up cross sectional view of the pressure gauge connector of Fig. 3 in sealing position ; Fig. 9 schematically shows a close-up cross sectional view of the pressure gauge connector of Fig. 3 during mounting of a pressure gauge; and

Fig. 10 schematically shows a cross sectional view of another embodiment of the pressure gauge connector being provided with grease fittings and a pressure gauge.

Detailed description of the invention

The invention will be further illustrated hereinafter by way of example only, and with reference to the non-limiting drawing. The person skilled in the art will readily

understand that, while the invention is illustrated making reference to one or more specific combinations of features and measures, many of those features and measures are functionally independent from other features and measures such that they can be equally or similarly applied

independently in other embodiments or combinations.

According to the present proposal, wellhead pressures (e.g. annulus pressure) can be gauged by a pressure gauge connected to a grease injection port of a valve which is connected to the wellhead. This allows for gauging of the pressure inside the valve without requiring any modification to the valve housing. Valves provided with grease injection ports are regularly employed on wellhead equipment. The term "wellhead" is used in this specification to designate the wellhead including an assembly of spools, valves and fittings mounted on top of the wellhead. This may include a so-called Christmas tree.

Such valves, in particular gate valves, may be employed on a wellhead in a variety of configurations, including as side outlet valve, a wing valve, and a master valve.

Depending on the function of the valve, the pressure gauged on the grease injection port can be representative of, for example, well annulus pressure or well production tube pressure. Fig. 1 shows a simplified impression of a wellhead spool 50. The wellhead spool may internally be subdivided in multiple annuli, by tubes configured concentrically around a central production tube 51. The example of Fig. 1 has an inner annulus 52 and an outer annulus 53, but this can be varied. Fig. 1 also shows VR Sense units 55 installed on an instrument flanges, as well as side outlet valves 40, which may be gate valves or other types of valves used on

wellheads. These valves typically have some kind of actuator, such as a hand wheel 48, and connecting flanges 43. As will be shown herein, the VR Sense units 55 require separate side outlet openings in addition to the side outlet valve

openings .

Various common types of valves, including gate valves and globe valves, have a grease port to lubricate the mechanism inside. This is illustrated with reference to Fig. 2, which schematically shows a simplified impression of a gate valve for a wellhead and/or Christmas tree.

The gate valve typically comprises a body 41 provided with a flow bore 45. The most common gate valve for wellheads or Christmas trees is one of floating seat type. It comprises a gate 47 which can be moved in or out of a flow bore 45: when in closed position the pressure differential caused by the fluid in the flow bore presses the gate 47 against a gate seat 42, thereby fully sealing off the flow bore 45.

Typically, the gate 47 is moved by sliding transversely to the flow direction 44 in the bore 45. The movement is actuated by an actuator, which may for example be a manual actuator such as hand wheel 48. Hydraulic actuators are also available. The body 41 may comprise connecting flanges 43 to connect the valve to piping.

A grease port 46 is provided, on a gate valve typically on the high-pressure side of the gate 47, which allows to lubricate the gate 47, the gate seat 42 and possibly also parts of the actuator. Usually the grease port 46 is

accessible via an injection fitting 6. The injection fitting 6 may be supplemented by a pressure gauge, for example using T-piece connector between the injection fitting 6 and the grease port 46.

It is recommended to employ a pressure gauge connector between the pressure gauge and the grease injection port, to provide a safety pressure barrier in case the pressure gauge is removed or otherwise leaking. Such pressure gauge

connector may suitably comprise of a housing defining an internal chamber and having an interior space, said housing comprising :

- a pressure gauge port configured to expose a pressure gauging surface to a pressure within in the interior space; and

- a barrier port connectable to the wellhead by means of a connector;

- a pressure-equalizing barrier is configured in the barrier port between the interior space and the space of interest in the wellhead.

Such pressure gauge connector comprises a pressure- equalizing barrier configured in a fluid communication port between the space of interest and the interior space of the internal chamber of the pressure gauge connector. The pressure-equalizing barrier transmits the pressure of a test fluid inside the space of interest to a work fluid which during operation is present within the internal chamber. A pressure gauge may be mounted on the pressure gauge

connector, to monitor the pressure of the work fluid inside the internal chamber.

Under pressure monitoring conditions the internal chamber is a pressure-tight volume, and with the pressure-equalizing barrier in place the work fluid in the interior space of the internal chamber is pressurized by the pressure from the space of interest. To this end, the pressure-equalizing barrier may comprise a flexible barrier, which can change the volume available in the internal chamber. No work fluid flows from the interior space into the space of interest, and no test fluid flows from the space of interest into the interior space. The pressure-equalizing barrier stops equalizing pressure when the internal chamber does not hold the required pressure (i.e. the pressure of the test fluid) within the interior space. In that case the pressure-equalizing barrier creates a seal between the space of interest and the internal chamber thereby blocking flow of pressurized test fluid from the space of interest into the leaking internal chamber while allowing for a pressure drop across the pressure-equalizing barrier .

The pressure-equalizing barrier may be embodied in the form of a pressure-equalizing check valve, which opens a flow passage for excess work fluid to flow from the interior chamber into the space of interest when the amount of work fluid in the interior space exceeds the available volume at the pressure-equalized pressure (i.e. the pressure of the test fluid inside the space of interest) . In such a case, just enough volume of work fluid will bleed from the interior space into the space of interest to restore equilibrium of pressure-equalization without the need to reduce the amount of work fluid inside the interior space.

Suitably, the housing further comprises a work fluid injection port configured to feed the work fluid into the interior space. Suitably, an injection fitting is mounted on the work fluid injection port. With such provisions, the pressure gauge connector can be employed both for gauging of pressure within the space of interest, as well as for injecting of work fluid into the space of interest. No separate T-piece would be needed as the T-piece is

functionally integrated into the pressure gauge connector.

Fig. 3 shows a schematic perspective view of an example pressure gauge connector. A cross sectional view of the same pressure gauge connector features in Fig. 4, combined with some auxiliary elements such as a pressure gauge 7. A housing body 1, which may hereinafter be equally referenced to by the terms housing and/or body, defines an internal chamber providing an interior space 9 within the housing body 1.

The housing 1 is provided with a pressure gauge port 4. The pressure gauge port 4 can accommodate a pressure gauge 7, suitably via a threaded coupling, and it is configured to expose a pressure gauging surface to a pressure within in the interior space 9. The housing 1 is further provided with barrier port 5. A pressure-equalizing barrier 20 is

configured between the interior space 9 and the space of interest 30. The space of interest 30 contains a test fluid, of which the pressure is to be gauged.

The barrier port may comprise connector comprising a threaded male nipple which can be screwed into a female counterpart to provide access to a test fluid in the area of interest . Suitably, barrier port 5 is axially aligned with the pressure gauge port 4. The pressure gauge port 4 may be provided with an internal thread for receiving an external thread of the pressure gauge 7. The pressure gauge port 4 may accommodate a key profile 2, to facilitate making up the connection of the pressure gauge connector to the area of interest .

Optionally, the housing 1 may further comprise one or more work fluid injection ports 3, configured to feed a work fluid into the interior space 9. Suitably, work fluid injection ports 3 can be configured as side ports relative to the barrier port 5 and the pressure gauge port 4. The injection fittings 6 may be thread-connected into the work fluid injection ports 3. Numerous types of grease injection fittings are available on the market which may be employed, such as (vented) capped grease fittings. However, any type of pressure fitting equipment can be employed. The injection fittings 6 are merely shown as examples.

The pressure-equalizing barrier 20 generally transmits a pressure of a test fluid inside the space of interest 30 to a work fluid present inside the interior space 9 of the internal chamber. This means the test fluid pressurizes the work fluid in the interior space 9. The pressure-equalizing barrier 20 seals the access to the interior space 9 when the internal chamber for some reason does not hold the pressure within the interior space 9. This can for instance be the case if the pressure gauge 7 is removed from the pressure gauge port 4, or if one of the injection fittings is opened without providing sufficient back pressure, or when for some reason there is a leak in the housing 1 to ambient.

On the other hand, the pressure-equalizing barrier 20 opens a flow passage for work fluid to flow from the interior space 9 into the space of interest 30 when the work fluid in the interior space 9 is pressurized to a higher pressure than the pressure of the test fluid inside the space of interest 30.

Pressure-equalizing barriers with the properties

described above can be constructed in numerous ways. One non- limiting example is illustrated in Figs. 5-8. In this example, the pressure-equalizing barrier comprises a bore 10. The bore 10 has a cylindrical bore wall section 14, extending along a longitudinal direction and defining a cross sectional contour of the bore 10. The cross sectional contour is the contour of an area available for longitudinal flow of fluid through the bore 10. A chamber-side open end 31 forms a fluid passage from the bore 10 to the interior space 9. A

connector-side open end 32 forms a fluid passage from the bore 10 to the space of 30 interest outside the housing 1. The connector-side open end 32 thus may be in open fluid communication with the space of interest 30 outside the housing 1. An inward sealing shoulder 18 is configured at the chamber-side open end 31 and terminating the bore 10. The shoulder 18 has a flow opening from the bore 10 into the interior space 9 than the area available for longitudinal flow through the bore 10.

A flexible barrier, which in the example is embodied in the form of a traveler 11, is arranged in the bore 10 in sliding engagement with the cylindrical bore wall 14. The traveler 11 in the figures is represented as a floating sphere. However, alternatives are within scope of the present disclosure, including a piston, a bellow, or the like. The traveler 11 has freedom to slide longitudinally through the bore 10 over a stroke range bound on one side by the inward sealing shoulder 18 at the chamber-side open end 31. On the other side, the stroke range is bound by a spring retainer 16, the function of which will be explained hereinbelow.

As is best viewed in Fig. 6, the traveler 11 separates a chamber-side section 33 of the bore 10 from a connector-side section 34 of the bore 10. The traveler 11 seals the interior space 9 from the connector-side section 34 of the bore 10, when the traveler 11 engages with the inward sealing shoulder 18, as shown in Fig. 8. The traveler 11 thus functions as a barrier against loss of containment of test fluid from the space of interest 30 when the traveler 11 seals against the inward shoulder 18.

The inward sealing shoulder 18 may be shaped in a variety of ways. For example, it may be shaped in the form of a tapered low angle seat, whereby the traveler 11 completes a fluid tight seal as it shoulders into engagement with the inward sealing shoulder 18. The inward sealing shoulder 18 may be formed out of, or comprise, a soft elastomeric and/or soft metallic material.

The stroke range of the traveler 11 can be divided into two distinct subranges: a floating range and a non-floating range .

In the floating range, which is illustrated in Fig. 6, the traveler 11 slidingly floats in the bore 10 thereby separating the chamber-side section 31 of the bore 10 from a connector-side section 32 of the bore 10. When the traveler 11 is in the floating range, the test fluid can enter into the connector-side section 34 of the bore 10 and push against the traveler 11. As schematically indicated by arrow 35, the traveler 11 is capable of transmitting the pressure of the test fluid to the work fluid that is present inside the interior space 9.

At an extremity of the floating range, where the traveler 11 is furthest removed from the internal sealing shoulder 18, the floating range transitions into the non-floating range. This is illustrated in Fig. 7. A bypass flow path 37 is open when the traveler is located in the non-floating range. The bypass flow path 37 fluidly connects the chamber-side section 33 of the bore 10 with the space of interest 30. In this case, excess work fluid, which can be additional work fluid and/or be a result of a reduction of volume available in the internal chamber, pushes the traveler into the non-floating range. As stated above, a spring retainer 16 is provided. This spring retainer 16 supports a spring-loaded seat 24 configured at the connector side 34 of the bore 10. The traveler 11 engages with the spring-loaded seat 24 when the traveler 11 is in the non-floating range. The spring 15 loads - li as the traveler 11 moves away from the inward sealing seat 18. The spring 15 unloads as the traveler 11 moves from towards the floating range and the inward sealing seat 18. The traveler 11 is disengaged from spring-loaded seat 24 when the traveler 11 is located in the floating range.

As can be best seen in Fig. 5, preferred embodiments of the pressure gauge connector comprise provisions to separate the pressure gauging surface from the work fluid in the interior space 9 of the internal chamber. If fauling of the pressure gauging surface by the work fluid is of no

significant concern, such provisions may not be necessary. However, to illustrate the option, the embodiment as shown further comprises an auxiliary traveler 12 arranged between the pressure gauge port 4 and the interior space 9. Herewith, a gauge fluid chamber 38 is defined between the gauging surface of the pressure gauge, and the interior space 9. The gauge fluid chamber 38 is pressure-equalized with the interior space 9. The gauge fluid chamber 38 may be filled with a suitable, clean, gauge fluid such as clean oil. The auxiliary traveler 12 separates work fluid in the interior space 9 from any gauge fluid that may be present in the gauge fluid chamber 38.

The auxiliary traveler 12 is shown in the form of a second floating sphere. However, alternatives including pistons, bellows, and the like are conceived within the scope of the present disclosure. The auxiliary traveler 12 may be kept in position by two, relatively weak, auxiliary springs: gauge-side spring 13 and chamber-side spring 14. Auxiliary spring retainers 17 may be provided as necessary or desired. The auxiliary traveler 12 does not need to form a pressure- tight seal. In fact, not fully sealing can be advantageous to ensure accurate pressure read out, regardless of the position of the auxiliary traveler 12. An internal port 8 may be provided to grant fluid communication access from the gauge fluid chamber 38 to the interior space 9 if the auxiliary sphere is pressured into the chamber-side spring 14 in case of excess gauge fluid in the gauge fluid chamber 38. This is illustrated in Fig. 9. Arrows 39 show the flow of gauge fluid from gauge fluid chamber 38 though the ports 8. If this causes excess fluid (work fluid, mixed with some gauge fluid) in the interior space 9, traveler 11 may be pushed into the non-floating range causing the bypass flow path 37 to open as well to bleed excess work fluid into the space of interest.

Optionally, the chamber-side spring 14 supports an auxiliary spring-loaded seat . When the auxiliary traveler 12 engages with the spring-loaded seat it loads the auxiliary spring 14 and opens the auxiliary bypass flow path 39 between the gauge fluid chamber 38 and the interior space 9.

If, after installing the pressure gauge connector, the traveler 11 is seated against the inward sealing shoulder 18, the volume available in the internal chamber may be decreased and/or the amount of work fluid in the internal chamber may be increased to push the traveler 11 into the bore 10 against the pressure prevailing in the connector-side section 34 of the bore 10. This may be accomplished for example by screwing a pressure gauge 7 in the pressure gauge port 4 and/or by injecting additional work fluid via one of the work fluid injection ports 3. Eventually, the traveler 11 can end up in the non-floating position as shown in Figs. 5 and 7, in which case some of the work fluid will be injected into the space of interest 30 via the bypass flow path 37.

As long as the traveler 11 is not seated against the inward sealing shoulder 18, it forms a pressure-equalizing barrier enabling read out of the pressure via the pressure gauge 7. However, in case there is a leak (for instance if the pressure gauge 7 is removed) then the traveler 11 will sealingly seat against the inward sealing shoulder 18 and thus form a full pressure barrier capable of retaining the pressure in the pressure equipment. Assuming no leaks are present, the test fluid pressure in the space of interest 30 can be measured to a maximum pressure increase which is determined by the volume available in the chamber-side section 33 of the bore 10 and the effective (cumulative) compressibility of the fluids contained within the internal chamber of the housing (this may include pockets of trapped air) . Pressure readings can be made, as long as the traveler 11 is not seated against the inward seating shoulder 18.

It will be understood that the pressure gauge connector of the previous Figures is merely an example. Various configurations can be employed, including configurations comprising only one injection fitting 6 and/or configurations where the injection fitting 6 is aligned on a straight line with the barrier port 5 so that it can be aligned with the the grease port 46 as the same way as the injection fitting is usually aligned with the grease port 46.

Fig. 10 is an example wherein the pressure gauge

connector is embodied in the form of a T-piece connector. As with the preceding example, a pressure-equalizing barrier 20 is configured between the interior space 9 and the space of interest 30. However, this is optional and the pressure gauge connector can be further simplified by omitting the pressure- equalizing barrier 20. It is further noted that in the example of Fig. 10 there is no separate provision to separate the pressure gauging surface of the pressure gauge 7 from the work fluid (grease) in the interior space 9 of the internal chamber. However, such provision, for example one involving an auxiliary traveler as explained above, or a flexible membrane, or any other suitable provision, may be included. Finally, it may also be possible to integrate the pressure sensor in the injection fitting or within the pressure gauge connector. Miniature pressure sensors are commercially available, some having wireless read-out.

The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims.