CA3213347A1 - Direct wellhead measurement skid and related uses and methods of operation - Google Patents

Abstract

A measurement skid and related uses and methods for measuring an amount of liquid and gas produced at a wellhead is provided. The measurement skid receives at least a stream of oil/water emulsion and wellhead gas from the wellhead. A gravity separator in the measurement skid receives the oil/water emulsion and wellhead gas and permits the wellhead gas to vent from the gravity separator by a vapour outlet. When the liquid height in the gravity separator exceeds a liquid height threshold a vapour control valve on the gravity separator is selectively closed. The pressure in the gravity separator increases until it is above a pressure threshold, at which point a liquid control valve on the gravity separator is selectively opened to allow liquid to flow from the gravity separator. Flow meters measures flow characteristics of the liquid and gas streams.

Description

DIRECT WELLHEAD MEASUREMENT SKID AND RELATED USES AND
METHODS OF OPERATION
TECHNICAL FIELD
[0001] The present disclosure relates to industrial equipment for measuring the amount of liquid and gas product extracted from a wellhead, and in particular to a direct wellhead measurement skid and related uses and methods of operation.
BACKGROUND

[0002] In the upstream oil and gas industry there are regulatory and operational requirements related to measurement and reporting of the oil, water and gas production from each production well.

[0003] The traditional method to measure production is with a large volume test separator. The fluid produced out of each well is diverted into a test separator on a scheduled basis and allowed a given retention time to separate into its various liquid and gas components. The natural gas production flows out of the top of the separator and is measured with a flow meter while the liquid production flows out of the bottom with the oil and water volumes measured with their own, respective flow meters. Each well could be tested through this system weekly, or even as far apart as monthly.

[0004] These traditional test separators come outfitted in large buildings with numerous types of instrumentation. They are installed on pilings and have multiple .. runs of piping and valving to be able to cycle through each of the wells.
All of this is capital intensive and only gives an operator only a macro view of well production.

[0005] Accordingly, systems and methods that enable accurate and real-time measurement of liquid and gas product extracted from a wellhead remains highly desirable.
SUMMARY OF THE INVENTION

[0006] According to one aspect of the invention, there is provided a measurement skid for measuring an amount of liquid and gas produced at a wellhead, the measurement skid including: a first skid inlet adapted to continuously receive an oil/water emulsion and wellhead gas from the tubing of the wellhead; a second skid inlet adapted to continuously receive wellhead gas from the casing of the wellhead; a Date Recue/Date Received 2023-09-20 gravity separator connected to the first skid inlet, the gravity separator including: a vapour outlet disposed substantially at the top of the gravity separator, the vapour outlet having a vapour control valve disposed thereon and being fluidly connected to the second skid inlet; a liquid outlet disposed substantially at the bottom of the gravity separator, the liquid outlet having a liquid control valve disposed thereon; a liquid level switch adapted to determine a liquid height in the gravity separator; and a pressure meter adapted to determine a pressure in the gravity separator; a gas flow meter adapted to determine a flowrate of a combined stream from the second skid inlet and the vapour outlet; a liquid flow meter adapted to determine a flow rate of the liquid outlet; and at least one skid outlet adapted to continuously discharge the combined stream and the liquid outlet from the measurement skid, wherein when the liquid height in the gravity separator is below a threshold liquid level the liquid control valve is selectively closed and the vapour control valve is selectively opened to allow vapour to vent from the gravity separator by the vapour outlet, and wherein when the liquid height in the gravity separator is above the threshold liquid level the vapour control valve is selectively closed, and wherein when the pressure in the gravity separator is above a threshold pressure the liquid control valve is selectively opened to allow liquid to flow from the gravity separator by the liquid outlet.

[0007] In one embodiment the gravity separator is a cyclone separator. In a further embodiment a bypass line is adapted to permit all or a portion of the oil/water emulsion and wellhead gas from the tubing of the wellhead to bypass the measurement skid. In yet a further embodiment a pressure safety valve is fluidly connected to the gravity separator. In yet a further embodiment the skid outlet consists of a first skid outlet and a second skid outlet, the first skid outlet adapted to continuously discharge the combined stream, and the second skid outlet adapted to discharge flow from the liquid outlet. In yet a further embodiment a check valve is on the first skid outlet and/or the second skid outlet. In yet a further embodiment the liquid flow meter comprises a Coriolis tube. In yet a further embodiment the liquid control valve is a bladder type control valve.

[0008] According to another aspect of the invention the measurement ski described herein may be use for measuring the amount of liquid and gas produced by the wellhead.

Date Recue/Date Received 2023-09-20

[0009] According to another aspect of the invention, there is provided a method of measuring an amount of liquid and gas produced at a wellhead using the measurement skid described here, the method including: receiving an oil/water emulsion and wellhead gas from the tubing of the wellhead at the first inlet;
receiving wellhead gas at the second inlet of the measurement skid; separating the oil/water emulsion and wellhead gas received at the first inlet by the gravity separator;
selectively discharging wellhead gas from the gravity separator by the vapour outlet;
selectively retaining the oil/water emulsion in the gravity separator;
selectively retaining wellhead gas in the gravity separator by closing the vapour control valve when the liquid level of the oil/water emulsion in the gravity separator exceeds the threshold liquid height; selectively discharging the oil/water emulsion from the gravity separator by opening the liquid control valve when the pressure in the gravity separator exceeds the threshold pressure; measuring a flow rate of the combined stream; and measuring a flow rate in the liquid outlet.
BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[0011] FIG. 1 shows a schematic layout of upstream oil and gas production including a measurement skid according to one embodiment;

[0012] FIG. 2 shows two view of a computerized model of a measurement skid according to one embodiment; and

[0013] FIG. 3 shows a flow chart for a method of measuring an amount of liquid and gas produced at a wellhead according to one embodiment.

[0014] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
DETAILED DESCRIPTION

[0015] Embodiments are described below, by way of example only, with reference to Figs. 1-3.

Date Recue/Date Received 2023-09-20

[0016] A direct wellhead measurement skid and related uses and methods of operation are provided. The measurement skid connects directly to the wellhead, preferably, although not necessarily, before any oil and gas processing steps are completed at the upstream facility. The measurement skid provides real-time measurement of process variables including gas and liquid flows from the wellhead while requiring less material when compared to traditional methods to measure wellhead production. In certain embodiments the liquid flow may be further subdivided into a water flow and an oil flow. The control methodology for a gravity separator of the wellhead measurement skid permits continuous measurement of flow from the wellhead while relieving gas or liquid accumulation as needed. By manually setting a maximum drive gain for a liquid flow meter, measurement difficulties encountered with certain Coriolis flow meters may be overcome leading to a more accurate measurement result.

[0017] With reference to FIG. 1, an example upstream production system 100 is shown including an example measurement skid 110. The system 100 has a wellhead 102 including a casing 102a and a tubing 102b. A surface pump 102c is depicted although other artificial lift systems may be used where preferred.
In certain wells where there is sufficient motive pressure no artificial lifting system may be needed.

[0018] Tubing 102b conveys an oil/water emulsion and/or wellhead gas to pipe 104, which is in turn fluidly connected to a first skid inlet 110b. Casing 102a conveys annulus wellhead gas to pipe 106, which is in turn fluidly connected to a second skid inlet 110a. Valve 104a on pipe 104 and valve 106a on pipe 106 may selectively control or regulate fluid flow from the wellhead. Bypass line 108 is depicted but is not required in all embodiments, and may connect pipe 104 and/or pipe 106 directly to further processing facilities 112 permitting the flow in pipe 104 and/or pipe 106 to bypass the measurement skid 110.

[0019] Measurement skid 110 includes the first skid inlet 110a and the second skid inlet 110b. First skid inlet 110a conveys wellhead gas through a gas flow meter 110f towards skid outlet 110h. Second skid inlet 110b conveys the oil/water emulsion and/or wellhead gas to a gravity separator 110c. In certain embodiments the gravity separator 110c may be a cyclone separator allowing the liquid to be quickly separated Date Recue/Date Received 2023-09-20 from the vapor without substantial foaming; however, alternative gravity separators such as a packed horizontal separator may be used in certain embodiments.

[0020] The gravity separator 110c has a vapour outlet 110d located substantially at the top of the gravity separator, a liquid outlet 110e located substantially at the bottom of the gravity separator, a liquid level switch and a pressure meter. The vapour outlet 110d functions to selectively discharge vapour from the gravity separator 110c by operation of a vapor control valve on the vapour outlet.
Flowmeter 110f measures a combined flow from the vapour outlet 110d and the first skid inlet 110a. Similarly to the vapour outlet 110d, the liquid outlet 110e functions to selectively discharge liquid from the gravity separator 110c by operation of a liquid control valve on the liquid outlet. A pressure safety valve 114 is fluidly connected to the liquid outlet 110d, or alternatively to the gravity separator 110c, and allows for selective venting of vapor if the pressure in the gravity separator or the vapour outlet 110d exceeds a maximum set pressure. The liquid level switch and the pressure meter cooperate to selectively open and close the liquid control valve and the vapor control valve using the control methodologies described below.

[0021] During start-up, the vapor control valve is open and the liquid control valve is closed allowing liquid to accumulate in the gravity separator 110c.
The level of the retained liquid rises until it exceeds a threshold liquid level as determined by, for example, the height of the liquid level switch on the gravity separator 110c, at which time the vapour control valve is closed preventing further vapor from escaping through the vapor outlet 110d. At this point both the vapor control valve and the liquid control valve are closed. The pressure in the gravity separator 110c begins to rise until the pressure meter on the gravity separator measures a threshold pressure, at which time the liquid control valve is opened allowing liquid to escape through the liquid outlet 110e. Liquid in the liquid outlet 110e flows through a liquid flow meter 110g and may be discharged from the measurement skid 110 by the skid outlet 110i.
In certain embodiments a check valve may be present downstream of the liquid flow meter 110g to prevent back flow of fluid towards the liquid flow meter.

[0022] In one control strategy, when or if the liquid level in the gravity separator 110c falls below the threshold liquid level, for example if a slug of wellhead gas is received at the gravity separator, the pressure in the gravity separator falls and the Date Recue/Date Received 2023-09-20 liquid control valve is subsequently closed preventing further flow of liquid through the liquid outlet 110e and the vapor control valve is opened re-establishing flow of vapor through the vapor outlet 110d until such time that the liquid level again exceeds the threshold liquid level. Following the process described above, the vapor control valve may thereafter be closed allowing the pressure in the gravity separator 110c to rise, and the liquid control valve is opened once the pressure in the gravity separator reaches the threshold pressure.

[0023] In an alternative control strategy, when or if the liquid level in the gravity separator 110c falls below the threshold liquid level, the liquid control valve is closed and the vapor control valve is opened for a pre-set length of time. In a preferred embodiment the vapor control valve will remain open and the liquid control valve will remain closed for between about 0.3 seconds and 30 seconds, and in a particularly preferred embodiment the vapor control valve will remain open and the liquid control valve will remain closed for between about 1.0 seconds and 1.5 seconds, after which time the liquid control valve will be automatically re-opened and the vapor control valve will be closed. This procedures may be repeated as required.

[0024] Described above is an example where then tubing 102b is producing a mixture of oil/water emulsion and wellhead gas, but where the tubing 102b is producing predominantly wellhead gas then the above described control methodology may still be followed except the system will predominantly operate in the state with the vapor control valve open and the liquid control valve closed. This configuration allows wellhead gas to substantially free-flow from the first skid inlet 110b to the vapor outlet 110d where it rejoins with the second skid inlet 110a. Conversely, if the tubing 102b is producing predominantly an oil/water emulsion then the system will predominantly operating in the state with the vapour control valve closed and the liquid control valve open, allowing liquid to substantially free-flow from the first skid inlet 110b to the liquid outlet 110e.

[0025] It will be appreciated that while flows are described with respect to the tubing and casing of a wellhead, the oil/water emulsion and wellhead gas flows may be delivered to the measurement skid by other wellhead components or piping particular to the wellhead configuration or production methodology.

Date Recue/Date Received 2023-09-20

[0026] The geometry of the gravity separator 110c, the threshold liquid height, and the threshold pressure depend on the circumstances of each well. For example, in certain embodiments it may be desirable to have the threshold pressure be sufficiently high to aid liquid flow from the gravity separator 110c but low enough to minimize the chance or amount of liquid flashed as a vapour should the pressure in the gravity separator begin to decrease as liquid flows from the gravity separator. In other embodiments it may be desirable to have the threshold pressure be sufficiently low to permit more continuous flow of liquids out of the liquid outlet 110e.

[0027] The term pressure meter, as used in the present description, broadly indicates a component that can determine the pressure in the gravity separator 110c.
The pressure meter may be a pressure gauge or a pressure transmitter in certain embodiments. In one embodiment the liquid control valve may be a bladder type control valve allowing the liquid control valve to automatically open when a bladder set pressure is reached. In this embodiment the bladder set pressure would correspond to the threshold pressure in the gravity separator 110c, and the pressure meter would be the bladder on the bladder type control valve as the bladder is able to determine the pressure in the gravity separator.

[0028] A skilled person will appreciate that a certain liquid fraction may be present in vapor flows and certain vapor fractions may be present in liquid flows.
Liquid entrained in vapor may be managed or removed using known techniques, such as by including bleeder valves in the measurement skid 110 or by retaining sufficient vapor pressure in the measurement skid 110 to purge the liquid fraction along with the vapor flow. A significant vapor fraction in the liquid flow of the liquid outlet 110e may affect the flow rate measurement of the liquid flow meter 110g, particularly in the embodiment where the liquid flow meter is a Coriolis flow meter because the entrained vapor may dampen oscillation of the Coriolis tube leading to imprecise flow measurement.

[0029] Certain flow meters, such as, for example, a Micro MotionTM
Advanced Phase Measurement flow meter, may correct measured flow rates of liquids having non-negligible vapour flow using a drive gain parameter. The drive gain is a measure of the amount of power input required to power the drive coils for a Coriolis tube to ensure consistent amplitude and vibration. The drive gain is useful for correcting Date Recue/Date Received 2023-09-20 measured flow rates because when biphasic flow is present in a system, or when there is significant entrained gas in a Coriolis tube, more energy is required power the drive coils. The Micro MotionTM Advanced Phase Measurement flow meter compares a measured drive gain to a maximum drive gain expected for single-phase fluid flow .. under the measured operating conditions. When the ratio of the measured drive gain to the maximum drive gain becomes too high the flow meter will switch to using the measured mass flow rates along with a remediation functionality based on historical density values, as opposed to measured density values, to calculate fluid flow properties.

[0030] The inventors of the present application have noticed that because of process fluctuations and variations in process conditions present in applications where the measurement skid 110 is intend to operate, Coriolis flow meters may not accurately switch to using remediation functionality when appropriate and therefore may report incorrect flow properties. Therefore, a maximum drive gain value is set for the liquid flow meter by evaluating when data from a liquid flow meter becomes overly chaotic or inconsistent with flow properties expected for given process conditions.

[0031] Turning now to FIG. 2, FIG. 2 shows a first view 200a and a second view 200b of a measurement skid according to one embodiment. The first view 200a shows a first skid inlet 210a and a second skid inlet 210b, which correspond to the first skid inlet 110a and second skid inlet 110b, respectively. The second view 200b shows the skid outlet 210h and the skid outlet 210i, which correspond with the skid outlet 110h and the skid outlet 110i, respectively. Also shown is a pressure safety valve 214, which corresponds to the pressure safety valve 114, and a liquid flow meter 210g, which corresponds to the liquid flow meter 110g.

[0032] Additionally shown in FIG. 2 is a liquid level switch 210j on a gravity separator, a liquid control valve 210k on a liquid outlet from the gravity separator, and a drain valve 2101. The liquid level switch 210j and the liquid control valve 210k have the same functionality as described for the liquid level switch and the liquid control valve with respect to Figure 1. The drain valve 2101 may selectively open to allow draining of the gravity separator during maintenance procedures, for example.

Date Recue/Date Received 2023-09-20

[0033] FIG. 3 a flow chart for an example method 300 of measuring an amount of liquid and gas produced at a wellhead using a measurement skid described herein.
The method includes, at step 302, receiving an oil/water emulsion and wellhead gas from the tubing of the wellhead at the first inlet and at step 304 receiving wellhead gas at the second inlet of the measurement skid. As described herein, how the flow components are received at the measurement skid may be determined by the piping configuration of the wellhead or by operating philosophy.

[0034] At step 306 the oil/water emulsion and wellhead gas are separated at the gravity separator and at step 308 wellhead gas is selectively discharged from the gravity separator by selectively opening the vapour control valve on the vapour outlet and the oil/water emulsion is selectively retained in the gravity separator by selectively closing the liquid control valve on the liquid outlet.

[0035] Using the control methodology described herein, at step 310 wellhead gas is selectively retained om the gravity separator by selectively closing the vapour control valve on the vapour outlet and the oil/water emulsion is selectively discharged from the gravity separator by selectively opening the liquid control valve on the liquid outlet. At step 312, flow meters on the discharged liquid and gas streams can measure flow properties of the discharged fluids.

[0036] It would be appreciated by one of ordinary skill in the art that the system and components shown in Figures 1 to 3 may include components not shown in the drawings. For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, are only schematic and are non-limiting of the elements structures. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. A system of one or more computers can be configured to perform particular operations or actions described herein by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions.

[0037] Although certain components and steps have been described, it is contemplated that individually described components, as well as steps, may be combined together into fewer components or steps or the steps may be performed Date Recue/Date Received 2023-09-20 sequentially, non-sequentially or concurrently. Further, although described above as occurring in a particular order, one of ordinary skill in the art having regard to the current teachings will appreciate that the particular order of certain steps relative to other steps may be changed. Similarly, individual components or steps may be provided by a plurality of components or steps. One of ordinary skill in the art having regard to the current teachings will appreciate that the system and method described herein may be provided by various combinations of software, firmware and/or hardware, other than the specific implementations described herein as illustrative exam pies.

Date Recue/Date Received 2023-09-20

Claims (10)

CLAIMS:

1. A
measurement skid for measuring an amount of liquid and gas produced at a wellhead, the measurement skid comprising:
a first skid inlet adapted to continuously receive an oil/water emulsion and wellhead gas from the tubing of the wellhead;
a second skid inlet adapted to continuously receive wellhead gas from the casing of the wellhead;
a gravity separator connected to the first skid inlet, the gravity separator comprising:
a vapour outlet disposed substantially at the top of the gravity separator, the vapour outlet having a vapour control valve disposed thereon and being fluidly connected to the second skid inlet;
a liquid outlet disposed substantially at the bottom of the gravity separator, the liquid outlet having a liquid control valve disposed thereon;
a liquid level switch adapted to determine a liquid height in the gravity separator; and a pressure meter adapted to determine a pressure in the gravity separator;
a gas flow meter adapted to determine a flowrate of a combined stream from the second skid inlet and the vapour outlet;
a liquid flow meter adapted to determine a flow rate of the liquid outlet;
and at least one skid outlet adapted to continuously discharge the combined stream and the liquid outlet from the measurement skid, wherein when the liquid height in the gravity separator is below a threshold liquid level the liquid control valve is selectively closed and the vapour control valve Date Recue/Date Received 2023-09-20 is selectively opened to allow vapour to vent from the gravity separator by the vapour outlet, and wherein when the liquid height in the gravity separator is above the threshold liquid level the vapour control valve is selectively closed, and wherein when the pressure in the gravity separator is above a threshold pressure the liquid control valve is selectively opened to allow liquid to flow from the gravity separator by the liquid outlet.

2. The measurement skid of claim 1 wherein the gravity separator is a cyclone separator.

3. The measurement skid of claim 1 further comprising a bypass line adapted to permit all or a portion of the oil/water emulsion and wellhead gas from the tubing of the wellhead to bypass the measurement skid.

4. The measurement skid of claim 1 further comprising a pressure safety valve fluidly connected to the gravity separator.

5. The measurement skid of claim 1 wherein the skid outlet consists of a first skid outlet and a second skid outlet, the first skid outlet adapted to continuously discharge the combined stream, and the second skid outlet adapted to discharge flow from the liquid outlet.

6. The measurement skid of claim 5 further comprising a check valve on the first skid outlet and/or the second skid outlet.

7. The measurement skid of claim 1, wherein the liquid flow meter comprises a Coriolis tube.

8. The measurement skid of claim 1, wherein the liquid control valve is a bladder type control valve.

9. Use of the measurement skid of any one of claims 1 to 8 for measuring the amount of liquid and gas produced by the wellhead.

10. A method of measuring an amount of liquid and gas produced at a wellhead using the measurement skid according to claim 1, the method comprising:

Date Recue/Date Received 2023-09-20 receiving an oil/water emulsion and wellhead gas from the tubing of the wellhead at the first inlet;
receiving wellhead gas at the second inlet of the measurement skid;
separating the oil/water emulsion and wellhead gas received at the first inlet by the gravity separator;
selectively discharging wellhead gas from the gravity separator by the vapour outlet;
selectively retaining the oil/water emulsion in the gravity separator;
selectively retaining wellhead gas in the gravity separator by closing the vapour control valve when the liquid level of the oil/water emulsion in the gravity separator exceeds the threshold liquid height;
selectively discharging the oil/water emulsion from the gravity separator by opening the liquid control valve when the pressure in the gravity separator exceeds the threshold pressure;
measuring a flow rate of the combined stream; and measuring a flow rate in the liquid outlet.

Date Recue/Date Received 2023-09-20