A method for investigating an area outside a wellbore tubular by applying heat and monitoring acoustic response

Abstract

A method for detecting fluid movement in an annular space between a wellbore and a wellbore tubular includes inducing a temperature change in the wellbore tubular, fluid in the annular space and formations adjacent to the wellbore at a selected depth. Acoustic energy is detected at the selected depth. Fluid movement is determined using the detected acoustic energy.

Description

A METHOD FOR INVESTIGATING AN AREA OUTSIDE A WELLBORE TUBULAR BY APPLYING HEAT AND MONITORING ACOUSTIC RESPONSEBACKGROUND

[0001] This disclosure relates to the field of using wellbore conveyed instruments to detect faults in wellbore construction. More specifically, the disclosure relates to using acoustic instruments to detect fluid flow external to a wellbore that otherwise should be closed to flow by cement surrounding a well conduit such as casing or liner.

[0002] In oil and gas wells, for example, there is sometimes a requirement for checking if an area outside wellbore tubulars (e.g., casing or liner) is sealed, where cement is a typical sealing material placed in an annular space between the wellbore tubulars and the drilled wellbore. Wireline deployed logging tools, so-called cement bond log (CBL tools), are commonly used to check if the cement is bonded to the wellbore tubular and to the drilled wellbore. CBL tools have one or more acoustic transmitters that emit acoustic energy in the 10 to 30 kHz frequency range, and a receiver that detects the acoustic energy after interaction with the well tubular, cement and surrounding wellbore. Generally, attenuation of first compressional wave arrivals at the receiver, and substantial amplitude in later parts of the detected acoustic waves are indicative of good bonding between the wellbore tubular, the cement and the wellbore. However, cement bond logs cannot determine that there are no leaks or crossflow in the area outside the tubular.

[0003] Acoustic logging instruments can be used to detect leaks or crossflow by the detecting the presence of acoustic energy in an otherwise closed-to-flow wellbore, but detecting leaks or crossflow acoustically depends on such events taking place when the acoustic instrument is at the downhole location of interest. Therefore, a method to induce fluid movements and check for leaks or cross flow is required.SUMMARY

[0004] One aspect of the present disclosure is a method for detecting fluid movement in an annular space between a wellbore and a wellbore tubular. A method according to this aspect includes inducing a temperature change in the wellbore tubular, fluid in the annular space and formations adjacent to the wellbore at a selected depth. Acoustic energy is detected at the selected depth. Fluid movement in the annular space is determined using the detected acoustic energy.

[0005] In some implementations, the inducing a temperature change comprises heating.

[0006] In some implementations, the heating comprises moving a well intervention tool having a heating element to the selected depth and activating the heating element.

[0007] In some implementations, the heating element comprises an electrical resistance heater.

[0008] Some implementations further comprise detecting acoustic energy above and below the selected depth to determine a depth of the fluid movement.

[0009] In some implementations, the detecting acoustic energy is performed using an optical fiber distributed acoustic sensor.

[0010] Some implementations further comprise stopping the inducing temperature change and continuing detecting acoustic energy to determine stopping the fluid movement.

[0011] Some implementations further comprise detecting acoustic energy above and below the selected depth to determine at least one depth at which fluid movement stops.

[0012] Some implementations further comprise stopping the inducing temperature change in the wellbore fluid, continuing detecting acoustic energy and determining fluid movement in the annular spaces using the continued detected acoustic energy.

[0013] Some implementations further comprise frequency filtering the detected acoustic energy to attenuate effects of noise generated at surface.

[0014] Other aspects and possible advantages will be apparent from the description and claims that follow.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 shows an example implementation of a wellbore tool deployed in a well according to the present disclosure.DETAILED DESCRIPTION

[0016] In general, methods according to the present disclosure include the following. A wellbore intervention tool having one or more devices to induce temperature change within a wellbore is inserted into subsurface well. In some implementations, the device(s) to induce temperature change comprise a heater or heating element. In some implementations, heating and acoustic sensing are combined in the wellbore intervention tool, where the heating can be performed by the one or more heaters or heating element(s) in or on the wellbore intervention tool deployed in a wellbore to an area (selected depth) of interest. The heating element(s) may be electrical resistance heating element(s). Along or within the wellbore intervention tool, or on accompanying conveyance devices, acoustic sensors can be incorporated. Such acoustic sensors may also be implemented above and / or below the wellbore intervention tool.

[0017] While the present disclosure sets forth a specific implementation using heating element(s) to heat the interior of a wellbore tubular, in principle, a similar effect may be obtained using a device to cool the interior of the wellbore tubular; the scope of the present disclosure is intended to cover both types of implementation to induce temperature change.

[0018] The wellbore intervention tool is deployed into the wellbore to the selected depth. When the wellbore intervention tool is disposed at the selected depth, the acoustic sensor(s) is / are activated and used throughout the remainder of the method as follows:1. Keep the wellbore intervention tool at a fixed depth in the wellbore, and using the acoustic sensor(s), detect if one or several leaks outside the tubular(s) may be detected.It may be inferred that detecting acoustic energy above a nominal background amplitude, such as may be caused by equipment operating at surface, is a result of one or more active leaks of fluid outside the wellbore. In some implementations, background acoustic energy may be frequency-filtered from the detected acoustic energy, it beingobserved that energy originating near surface may have relatively low frequency by reason of propagation through the Earth to the depth of interest, while leak-sourced energy may have relatively higher frequencies by reason of a very short propagation path through formations and cement outside the wellbore.If substantially no above-background acoustic energy is detected (filtered or not), then the method may proceed as explained below.2. One or more heating elements in the wellbore intervention tool may be activated, while continuing to detect acoustic energy. Increase in detected acoustic energy may be inferred to be caused by induced leaks outside the wellbore, e.g., by reason of a temperature gradient inducing a fluid pressure gradient in the heated cement and formations outside the wellbore.3. Switch off the heating element(s), and allow cooling of the area to take place, while continuing to detect acoustic energy. The acoustic sensor(s) may be point sensor(s) as a geophone accelerometer or the like, or distributed fiber optic acoustic sensors. In particular, cessation or attenuation of detected acoustic energy after cooling may result from the fluid movement through the leak(s) stopping as a result of cooling and loss of the temperature gradient. In some cases, acoustic energy may attenuate or stop while heating is maintained within the wellbore as the wellbore components reach thermal equilibrium. Commencing cooling may reestablish fluid movement in the annular space until thermal equilibrium is once again obtained.

[0019] A method according to the present disclosure may be performed using a wellbore intervention tool as may be better understood with reference to FIG. 1. A subsurface wellbore (1) drilled through earthen formations (1 A) has cemented in place a conduit such as a liner or casing (2). The cement (not shown) is disposed in an annular space (IB) between the wellbore (1) and the liner or casing(2). The annular space (IB) may comprise cement, and mud or fluid filled voids (3) between the wellbore (1) and the casing (2).

[0020] A wellbore intervention tool (4) is lowered into the casing (2) using a conveyance (5) which may be, for example, armored electrical cable, coiled or jointed tubing or other conveyance into the casing (2) to a depth of interest. The wellbore intervention tool (4)may comprise at one longitudinal end a cable head (6) or similar device to connect the wellbore intervention tool (4) mechanically and electrically to the conveyance (5).

[0021] The wellbore intervention tool (4) comprises devices to provide heat, as well as acoustic sensing. Acoustic sensing may be obtained using, for example, geophones or accelerometers (9) disposed within the wellbore intervention tool (4), or using a distributed acoustic sensor (DAS), shown generally at (8). The DAS (8) may be, for example, an optical fiber having a plurality of longitudinally spaced apart Bragg gratings each having a different grating spacing. Acoustic sensing may also be implemented as any of the above, within the conveyance (5).

[0022] A heater (7), such as an electrical resistance heater, may be disposed as shown at one end of the wellbore intervention tool (4) or at any other convenient place within or about the wellbore intervention tool (4).

[0023] The wellbore intervention tool (4) may further comprise a controller (10) to operate at times chosen by a user the heater (7). The controller may also accept as input signals from the geophone or accelerometer (9) or DAS (8) and communicate signals over the conveyance (5) to surface for interpretation.

[0024] A method according to the present disclosure may detect leaks without the need to penetrate the wellbore tubulars such as casing or liner, and may detect leaks not otherwise determinable using cement bond logging techniques and instruments known in the art.

[0025] In light of the principles and example implementations described and illustrated herein, it will be recognized that the example implementations can be modified in arrangement and detail without departing from such principles. The foregoing discussion has focused on specific implementations, but other configurations are also contemplated. In particular, even though expressions such as in “an implementation," or the like are used herein, these phrases are meant to generally reference implementation possibilities, and are not intended to limit the disclosure to particular implementation configurations. As used herein, these terms may reference the same or different implementations that are combinable into other implementations. As a rule, any implementation referenced herein is freely combinable with any one or more of the other implementations referenced herein,and any number of features of different implementations are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A method for detecting fluid movement in an annular space between a wellbore and a wellbore tubular, comprising: inducing a temperature change in the wellbore tubular, fluid in the annular space and formations adjacent to the wellbore at a selected depth; detecting acoustic energy at the selected depth; and determining fluid movement in the annular space using the detected acoustic energy.

2. The method of claim 1 wherein the inducing temperature change comprises heating.

3. The method of claim 2 wherein the heating comprises moving a well intervention tool having a heating element to the selected depth and activating the heating element.

4. The method of claim 3 wherein the heating element comprises an electrical resistance heater.

5. The method of claim 1 further comprising detecting acoustic energy above and below the selected depth to determine a depth of the fluid movement.

6. The method of claim 4 wherein the detecting acoustic energy is performed using an optical fiber distributed acoustic sensor.

7. The method of claim 1 further comprising stopping the inducing temperature change and continuing detecting acoustic energy to determine stopping the fluid movement.

8. The method of claim 7 further comprising detecting acoustic energy above and below the selected depth to determine at least one depth at which fluid movement stops.

9. The method of claim 8 wherein the detecting acoustic energy is performed using an optical fiber distributed acoustic sensor.

10. The method of claim 1 further comprising stopping inducing temperature change in the wellbore tubular, fluid in the annular space and formations adjacent to the wellbore; continuing detecting acoustic energy; and determining fluid movement in the annular spaces using the continued detected acoustic energy.

11. The method of claim 1 further comprising frequency filtering the detected acoustic energy to attenuate effects of noise generated at surface.

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