NO20231126A1

NO20231126A1 - Barrier Verification System

Info

Publication number: NO20231126A1
Application number: NO20231126A
Authority: NO
Inventors: Andreas Fliss; Duncan Troup
Original assignee: Archer Oiltools As
Priority date: 2023-10-24
Filing date: 2023-10-24
Publication date: 2025-04-25
Also published as: WO2025089969A1

Description

METHOD AND SYSTEM FOR BARRIER VERIFICATION

INTRODUCTION

The disclosure relates to barrier integrity verification in wellbores. In particular, the disclosure relates to methods, systems and downhole tools for acoustic evaluation of a cement plug in wellbores. The wellbores may e.g. be hydrocarbon wellbores, CCUS wellbores (Carbon capture utilization and storage) or geothermal wellbores.

BACKGROUND

Cement plugs may be placed in the wellbore for temporary or permanent plugging of hydrocarbon wells e.g. in P&A, slot recovery or intervention applications. The cement plugs may be established in e.g. a Perforate, Wash and Cement operation for sealing off the wellbore and the annuli. The wellbore cement plugs are typically placed over a mechanical cement base plug. The cement plug length is typically about 30m (single barrier) or about 60m (dual barrier). The cement plugs must be verified to ensure barrier integrity for establishing a safe barrier in the hydrocarbon wellbore. In current industry practice pressure tests are typically performed from above the cement plug. Acoustic techniques may be used to evaluate the pressure tested cement plugs by looking “sideways” (radially) into the cement barrier looking for leak paths for fluids. These pressure tests may overlook small leaks that develop into bigger leaks over time. In some cases, the cement plug is being drilled out and section logged in a time consuming and costly procedure, typically done only on the first three wells in a certain oil and gas field.

SUMMARY OF THE INVENTION

The invention provides in a first aspect a method for evaluation of a cement plug in a wellbore. The method comprising performing acoustic evaluation of the cement plug from a top side of the cement plug. The method comprising downward acoustic evaluation of the cement plug.

The wellbore may be vertical, horizontal or a deviated wellbore. By “downwards” is meant along the wellbore independent of the orientation of the wellbore. In a high deviation or horizontal wellbore the term "downwards" means "along the hole". In a horizontal or deviated wellbore, the measured depth of the wellbore would be the length along the wellbore instead of the true vertical depth. The true vertical depth would be the length of a vertical wellbore.

The method may further comprise operating an acoustic sensor in a passive mode receiving acoustic signals. The acoustic sensor may comprise a single sensor or a sensor array. An acoustic transmitter may be arranged below the cement plug. An acoustic reflector may be arranged below the cement plug. The acoustic reflector may be arranged on top of a cement base for the cement plug. The method may further comprise varying the pressure in the wellbore.

The method may comprise transmitting an acoustic signal into the cement plug and/or casing and receiving acoustic signals from the cement plug and/or casing. The acoustic signals may be sonic or ultrasound signals.

The invention provides in a further aspect an acoustic system for evaluation of a cement plug in a wellbore. The system comprising an acoustic sensor arranged in the wellbore. The acoustic sensor is adapted for acoustic evaluation of the cement plug from a top side of the cement plug. The acoustic sensor is adapted for downward acoustic evaluation of the cement plug. The acoustic sensor may be a single sensor or a sensor array.

The acoustic system may comprise a transmitter for transmitting at least one acoustic signal arranged below the cement plug. The acoustic system may further comprise a reflector for reflecting acoustic signals arranged below the cement barrier. The reflector may be arranged on top of a cement base for the cement plug. The acoustic system may further comprise a transmitter or transmitter array for transmitting at least one acoustic signal arranged above the cement plug.

The invention provides a further aspect a downhole tool adapted for evaluation of a cement plug in a wellbore. The downhole tool comprising an acoustic sensor. The acoustic sensor is adapted for acoustic evaluation of the cement plug from a top side of the cement plug. The acoustic sensor is a single acoustic receiver or a receiver array. The downhole tool may further comprise a transmitter or transmitter array for transmitting acoustic signals downwards into the cement plug.

The downhole tool may be an imaging tool.

The method, system or downhole tool as disclosed may be used for evaluating an in-situ cement barrier.

The method, system or downhole tool as disclosed may be used for acoustic imaging of the cement plug.

The method, system or downhole tool as disclosed may be used in well integrity applications within PP&A, temporary P&A, slot recovery, well intervention or drilling.

The disclosed downward acoustic solution is adapted for evaluation of a cement plug along its length (axial) instead of the current industry standard to look “sideways” (radially). The in-situ cement plug is evaluated in a reliable and cost efficient way. The solution enables detection of small leaks and leak paths in the cement barrier. The solution enables the possibility for barrier verification of all cement plugs in a well. The solution may e.g. be used in hydrocarbon, CCUS or geothermal wells. The solution also enables acoustic «imaging» of the barrier.

BRIEF DESCRIPTION OF DRAWINGS

Example embodiments are described with reference to the following drawings. The example embodiments are only examples and not limiting for the invention.

Figure 1 illustrates an exemplary embodiment of a passive acoustic mode using an acoustic sensor with a single sensor (receiver Rx).

Figure 2 illustrates an exemplary embodiment of a passive acoustic mode using an acoustic sensor with a sensor array (receiver Rx array).

Figure 3 illustrates an exemplary embodiment of a sensor array located on finger touching casing with single transmitter Tx or array of transmitters Tx above the cement plug and with an acoustic reflector arranged on a cement base for the cement plug. The cement plug may be evaluated in passive or active mode.

Figure 4 illustrates an exemplary embodiment of a sensor array located on a finger of a tool, where the finger touching a casing of the wellbore. A single transmitter Tx or array of transmitters Tx are placed below the cement plug on top of the cement base for the plug. The cement plug may be evaluated in passive or active mode.

DETAILED DESCRIPTION

Example embodiments are described with reference to the drawings. The example embodiments are not limiting for the disclosure. The drawings are illustrations for understanding of the principles of the disclosed solution. The same reference numerals are used for the same or similar features in all the drawings and throughout the description.

Figures 1 and 2 illustrate a cement plug in a wellbore. The cement plug is arranged in a main bore of the wellbore inside a casing and arranged outside the casing in the annulus of the wellbore. In Figures 3 and 4 the cement plug in the main bore is arranged on top of a mechanical cement base plug.

The method provides evaluation of a cement plug in a wellbore. The evaluation of the cement plug is performed from a top side of the cement plug. This is a downward acoustic evaluation of the cement plug. The downward acoustic evaluation of the cement plug is performed along the length of the casing. The wellbore may be vertical, horizontal or a deviated wellbore. By “downwards” is meant along the wellbore independent of the orientation of the wellbore. In a high deviation or horizontal wellbore the term "downwards" means "along the hole". In a horizontal or deviated wellbore, the measured depth of the wellbore would be the length along the wellbore instead of the true vertical depth. The true vertical depth is the length of a vertical wellbore. Figures 1-4 illustrates cement plugs in a vertical wellbore for illustration purposes only, but this is not to be considered limiting for the invention as explained above. Both the cement plug main bore and cement plug annulus may be evaluated for cement quality and cement bonding. The downward acoustics is evaluation from a top side of the cement plug. The acoustic waveforms travel downwards and upwards with receivers placed above the cement plug. There are two general modes. One active mode with transmitting acoustic signals into the cement plug and or casing and receiving acoustic signals from the cement plug and or casing and a passive mode with just receiving acoustic signals from the cement plug and or casing. The acoustic evaluation may be performed by use of an acoustic sensor. The acoustic sensor may be arranged on a downhole tool. An acoustic transmitter may be arranged on the downhole tool. The downhole tool may be an imaging tool. Evaluating may be performed of the in-situ cement barrier. Typical barrier placed: 30m (single barrier) to 60m (dual barrier).

Figure 1 illustrates an exemplary embodiment for evaluation of a cement plug in a wellbore. The method in Figure 1 illustrates operation of an acoustic sensor in a passive acoustic mode. An acoustic sensor in the form of a single sensor (receiver Rx) is used. The acoustic sensor is arranged inside the casing. The acoustic sensor may be arranged on a downhole tool. The acoustic sensor performs acoustic evaluation of the cement plug from a top side of the cement plug. The acoustic sensor performs downward acoustic evaluation of the cement plug.

Figure 1 illustrates an acoustic signal from leaks inside the inside cement travelling upwards towards the sensor. The single sensor performs passive listening to the acoustic signals. The single acoustic sensor is arranged on top of the cement plug. «Passive listening» is performed by the single acoustic sensor for acoustic signal(s) from potential leak(s) across the cement plug. The passive evaluation of the cement plug may or may not include pressure variation/manipulation in the wellbore. Although not shown in Figure 1, a mechanical cement base plug may be arranged under the cement plug main bore. The mechanical cement base plug may be provided with either transmitters or acoustic reflector(s). The sensor may be used for obtaining an acoustic image of plug with potential leak.

Figure 2 illustrates an exemplary embodiment for evaluation of a cement plug in a wellbore. The method in Figure 2 illustrates operation of an acoustic sensor in a passive acoustic mode. An acoustic sensor in the form of a sensor array (receiver Rx array) is used. The acoustic sensor is arranged inside the casing. The acoustic sensor array may be arranged on a downhole tool. The acoustic sensor performs acoustic evaluation of the cement plug from a top side of the cement plug. The acoustic sensor performs downward acoustic evaluation of the cement plug.

Figure 2 illustrates an acoustic signal from leaks inside the inside cement travelling upwards towards the sensor array. The sensor array performs passive listening to the acoustic signals. The acoustic sensor array is placed on top of the cement plug. «Passive listening» is performed by the acoustic sensor array for acoustic signal(s) from potential leak(s) across the cement plug. The passive evaluation of the cement plug may or may not include pressure variation/manipulation in the wellbore. Although not shown in Figure 2, a mechanical cement base plug may be arranged under the cement plug main bore. The mechanical cement base plug may be provided with either transmitters or acoustic reflector(s). The acoustic receiver array may be linear or spatial.

For the embodiments in Figures 1 and 2 a combination of pressure testing with high bandwidth acoustic sensor (20 Hz [audible sound frequency range] - 250KHz [Ultra sound frequency range]) or sensor array placed above cement plug may be performed. Typical applications may be in barrier integrity yes/no (leak or no leak).

Figure 3 illustrates an exemplary embodiment for evaluation of a cement plug in a wellbore. A mechanical cement base plug is arranged below the cement plug in the main bore. A reflector for acoustic signals is arranged on top of the cement base plug below the cement plug in the main bore. The reflector is arranged between the top of the cement base plug and the cement plug. The method in Figure 3 illustrates operation of an acoustic sensor in an active acoustic mode. The acoustic sensor may however also be operated in a passive acoustic mode. The modes may be active or passive sonic and/or ultrasonic modes. The frequency range may be from 20 Hz [audible sound frequency range] - 250KHz [ultra sound frequency range]). The acoustic sensor is arranged inside the casing. The acoustic sensor array may be arranged on a downhole tool. The acoustic sensor performs acoustic evaluation of the cement plug from a top side of the cement plug. The acoustic sensor performs downward acoustic evaluation of the cement plug. The acoustic sensor has a sensor array of receivers (Rx array). The acoustic sensor array of receivers may have a variable bandwidth. The bandwidth may vary between (20 Hz [audible sound frequency range] - 250KHz [ultra sound frequency range]). The acoustic array of transmitters may be combination of monopole and dipole transmitters. In Figure 3, the receiver array has multiple finger mounted sensors (i.e. multi-finger tool). The receiver array is located circumferentially touching the casing above cement plug. There may be at least two sensors or more. In Figure 3, the sensor array of receivers is located on fingers. In Figure 3, there is a sensor on each finger. The fingers may be attached to a tool. The receivers Rx on the fingers touch the inside of the casing. The exemplary embodiment illustrated in Figure 3 has an array of transmitters (Tx array). The transmitter may however also be a single transmitter. The transmitter array is arranged on the downhole tool. As illustrated in Figure 3, the transmitter array is located on the front part of the downhole tool. This location of the transmitter array allows the transmitter to be arranged directly above the top of the cement plug and transmitting acoustic signal(s) downwards into the cement plug. The acoustic signal(s) travel downwards into the cement plug and are reflected by the acoustic reflector on top of the cement base. The reflected acoustic signal(s) travel upwards through the cement plug and are received by the sensors Rx on the fingers that touch the inside of the casing. The exemplary embodiment in Figure 3 may also be operated in a passive mode by not sending an acoustic signal and only listening with the acoustic receivers Rx.

The exemplary embodiment with a Tx array above cement plug and reflector below cement plug on top of cement base is more complicated as waveforms have to pass twice through cement. This sensor system may be used to obtain acoustic image of plug with potential leak, plug length, strength, CBL-VDL (Cement Bond Log)-(Variable Density Log).

Figure 4 illustrates an exemplary embodiment for evaluation of a cement plug in a wellbore. A mechanical cement base plug (CB) is arranged below the cement plug in the main bore. A transmitter Tx or transmitter Tx array for transmitting acoustic signals is arranged on top of the cement base plug below the cement plug in the main bore. The transmitter Tx or transmitter Tx array is arranged between the top of the cement base plug and the cement plug. The acoustic transmitter array may be combination of monopole and dipole transmitters. The method in Figure 4 illustrates operation of an acoustic system in an active acoustic mode. The acoustic system may however also be operated in a passive acoustic mode. The modes may be active or passive sonic and/or ultrasonic modes. The frequency range may be from 20 Hz [audible sound frequency range] - 250KHz [ultra sound frequency range]). The acoustic sensor is arranged inside the casing. The acoustic sensor array (Rx array) may be arranged on a downhole tool. The acoustic sensor performs acoustic evaluation of the cement plug from a top side of the cement plug. The acoustic sensor performs downward acoustic evaluation of the cement plug. The acoustic sensor has a sensor array of receivers (Rx array). The acoustic sensor array of receivers may have a variable bandwidth. In Figure 4, the receiver array has multiple finger mounted sensors (i.e. multi-finger tool). The receiver array is located circumferentially touching the casing above cement plug. There may be at least two sensors or more. In Figure 4, the sensor array of receivers is located on fingers. In Figure 4, there is a receiver on each finger. The fingers are attached to a tool. The receivers Rx on the fingers touch the inside of the casing. The acoustic signal(s) from the transmitter or transmitter array travel upwards through the cement plug. The acoustic signal(s) are received by the sensors Rx on the fingers that touch the inside of the casing. The exemplary embodiment in Figure 4 may also be operated in a passive mode by not sending an acoustic signal and only listening with the acoustic receivers Rx.

This sensor system of a transmitter below plug on top of cement base and receiver with multiple arms clamped onto or touching casing above, may be used to measure flexwave/3rd echo interface and CBL-VDL ((Cement Bond Log)-(Variable Density Log). This may create a sector image of the cement plug.

The method and sensor system may be used to measure and confirm plug length, plug strength/density, potential leak and may also provide an acoustic image of the plug with plug length, plug strength/density, potential leak.

Active acoustic verification downwards of placed cement barriers (in-situ). Typical applications may be well integrity applications within PP&A, temporary P&A, well intervention, slot recovery, drilling.

Passive acoustic verification downwards of placed cement barriers (in-situ).

Typical applications may be well integrity applications within PP&A, temporary P&A, well intervention, slot recovery, drilling.

A combination of pressure testing with variable bandwidth acoustic transmitter array placed above or below cement plug (combination of monopole and dipole transmitters) and receiver array located circumferentially touching the casing above cement plug may be performed. Receiver array may include multiple finger mounted sensors (i.e. multi-finger tool) with at least two sensors or more. This may e.g. be used for barrier integrity measuring acoustic properties of at least but not limited to compressional, shear and flexural wave forms (CBL type amplitude, cement casing bonding, cement outside casing bonding, barrier geometry – length internal and annulus, compressional strength of cement).

Having described example embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.

Claims

1. Method for evaluation of a cement plug in a wellbore, the method comprising performing acoustic evaluation of the cement plug from a top side of the cement plug.

2. Method according to claim 1, wherein the method comprising downward acoustic evaluation of the cement plug.

3. Method according to claim 1 or claim 2, wherein the method further comprising operating an acoustic sensor in a passive mode receiving acoustic signals.

4. Method according to claim 3, wherein the acoustic sensor comprising a single sensor or a sensor array.

5. Method according to claim 3, wherein an acoustic transmitter is arranged below the cement plug.

6. Method according to claim 3 or claim 4, wherein an acoustic reflector is arranged below the cement plug.

7. Method according to claim 6, wherein the acoustic reflector is arranged on top of a cement base for the cement plug.

8. Method according to one of claims 1-7, the method further comprising varying the pressure in the wellbore.

9. Method according to one of claims 1-8, wherein the method further comprising transmitting an acoustic signal into the cement plug and/or casing and receiving acoustic signals from the cement plug and/or casing.

10. Method according to one of claims 1-9, wherein the acoustic signals are sonic or ultrasound signals.

11. An acoustic system for evaluation of a cement plug in a wellbore, the system comprising an acoustic sensor arranged in the wellbore, wherein the acoustic sensor is adapted for acoustic evaluation of the cement plug from a top side of the cement plug.

12. Acoustic system according to claim 11, wherein the acoustic sensor is adapted for downward acoustic evaluation of the cement plug.

13. Acoustic system according to one of claims 11-12, wherein the acoustic sensor comprising a single sensor or a sensor array.

14. Acoustic system according to one of claims 11-13, the system further comprising a transmitter for transmitting at least one acoustic signal arranged below the cement plug.

15. Acoustic system according to one of claims 11-14, the system further comprising a reflector for reflecting acoustic signals arranged below the cement barrier.

16. Acoustic system according to claim 15, wherein the reflector is arranged on top of a cement base for the cement plug.

17. Acoustic system according to one of claims 11-13, the system further comprising a transmitter or transmitter array for transmitting at least one acoustic signal arranged above the cement plug.

18. Downhole tool adapted for evaluation of a cement plug in a wellbore, the downhole tool comprising an acoustic sensor, wherein the acoustic sensor is adapted for acoustic evaluation of the cement plug from a top side of the cement plug.

19. Downhole tool adapted for evaluation of a cement plug in a wellbore, the downhole tool comprising an acoustic sensor, wherein the acoustic sensor is adapted for downward acoustic evaluation of the cement plug.

20. Downhole tool according to claim 18 or claim 19, wherein the acoustic sensor is a single acoustic receiver or a receiver array.

21. Downhole tool according to one of claims 18-20, wherein the downhole tool further comprising a transmitter or transmitter array for transmitting acoustic signals downwards into the cement plug.

22. Downhole tool according to one of claims 18-21, wherein the downhole tool is an imaging tool.

23. Method for evaluation of a cement plug in a wellbore, wherein the method comprising performing downward acoustic evaluation of a cement plug.

24. Method according to claim 23, wherein the method further comprising at least one of claims 3-10.

25. An acoustic system for evaluation of a cement plug in a wellbore, the system comprising an acoustic sensor arranged in the wellbore, wherein the acoustic sensor is adapted for downward acoustic evaluation of the cement plug.

26. Acoustic system according to claim 25, the system further comprising at least one of claims 13-17.

27. Use of the method according to one of claims 1-11, 23-24 or system according to one of claims 12-17, 25-26 or downhole tool according to one of claims 18-22, for evaluating an in-situ cement barrier.

25. Use of the method according to one of claims 1-11, 23-24 or system according to one of claims 12-17,25-26 or downhole tool according to one of claims 18-22, for acoustic imaging of the cement plug.

26. Use of the method according to one of claims 1-11, 23-24 or system according to one of claims 12-17,25-26, or downhole tool according to one of claims 18-22, in well integrity applications within PP&A, temporary P&A, slot recovery, well intervention or drilling.