WO2013142484A2

WO2013142484A2 - Apparatus and method for remotely determining the structural intergrity of a well or similar structure

Info

Publication number: WO2013142484A2
Application number: PCT/US2013/032949
Authority: WO
Inventors: John S. Laudo; Raphael J. WELSH
Original assignee: Battelle Memorial Institute
Priority date: 2012-03-19
Filing date: 2013-03-19
Publication date: 2013-09-26
Also published as: WO2013142484A3

Abstract

A well includes a bore formed in the earth and a casing disposed within the bore so as to define an annular space between an outer surface of the casing and an inner surface of the bore. Cement is disposed in the annular space, and at least one sensor is disposed within the cement. A source of an electromagnetic field electrically connected to the casing and adapted to send the electromagnetic field through the casing to interrogate the sensors. The casing is adapted to deliver power to the sensors and to receive signals from the sensors.

Description

TITLE

APPARATUS AND METHOD FOR REMOTELY DETERMINING THE STRUCTURAL INTEGRITY OF A WELL OR SIMILAR STRUCTURE

BACKGROUND OF THE INVENTION

[0001 ] This invention relates in general to apparatuses and methods for remotely sensing one or more relevant characteristics of a structure. In particular, this invention relates to an apparatus and method for determining the structural integrity of a well or similar structure from a surface above the well.

[0002] A wellbore is an elongated hole that is drilled or otherwise formed downwardly into the earth from the surface thereof, typically for the purpose of accessing and withdrawing a desired material, such as oil or gas, for example. After the wellbore is created, a casing is typically inserted into the wellbore to prevent collapsing of the wellbore, deter cross-contamination between the various layers of the earth, and provide a pressure boundary for the well. In many instances, the casing is a hollow cylindrical pipe that is inserted within the wellbore from the surface of the earth to the bottom of the wellbore. The hollow cylindrical pipe is typically formed from a rigid metallic material, such as a steel alloy, and is somewhat smaller in size than the wellbore in which it is disposed. As a result, an annular space is defined between the outer surface of the casing and the inner surface of the wellbore that extends from the surface of the earth to the bottom of the wellbore. This annular space is then filled with cement to protect and seal the wellbore, as well as prevent contaminants from entering into or exiting from the wellbore.

[0003] It is important that the cement surrounding the casing in the wellbore be of good integrity, both when the cement is initially inserted and subsequently thereafter. A variety of conditions can affect the integrity of the cement, including pressure, temperature, pH, moisture content, stress/strain and the like. By measuring one or more of these conditions, a reasonable evaluation of the integrity of the cement can be made.

[0004] U.S. Patent No. 6,408,943 discloses a method and system for passively monitoring cement integrity within a wellbore. Different types of sensors (pressure, temperature, resistivity, rock property, formation property, etc.) are "pumped" into place by placing them in a suspension of cement slurry at the time the casing is being cemented. The sensors are either battery operated or externally excited (such as by EMF energy, acoustic energy, RF energy, etc.) to operate the sensor, which sends a signal conveying the desired information. The sensor is then energized and interrogated using a separate piece of wellbore-deployed equipment whenever it is desired to monitor cement conditions. This wellbore-deployed equipment can be, for example, a wireline tool.

[0005] Nonetheless, there still exists a need for an improved apparatus and method for determining the structural integrity of a well or similar structure that is relatively simple and inexpensive.

SUMMARY OF THE INVENTION

[0006] This invention relates to an improved apparatus and method for determining the structural integrity of a well or similar structure that is relatively simple and inexpensive. In particular, this invention provides an improved apparatus and method for placing sensors in a wellbore to monitor the integrity of a cement filler. One aspect of this invention is to deploy and interrogate embedded sensors in the cement in the most unobtrusive means possible. In certain embodiments, the method uses a steel or other metallic casing in the wellbore as a conduit for electromagnetic fields that interrogate miniature embedded sensors, which report point measurements throughout the cement structure. The system has the ability to operate from the surface to get the diagnostic data without the need for shutting down the well. Also, this new method does not require plumbed lines or wires in the cement, which simplifies installation of the sensing devices. In this method, the sensors can be mixed with the liquid cement and poured into the wellbore prior to curing. Extended operation of the sensor network is anticipated because the method does not use sensitive glass components, such as fiber optics, or other materials that can darken or otherwise fail over time. The cost of deployment can also be contained because of the simplicity of the proposed ceramic sensor circuits.

[0007] Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Fig. 1 is a schematic sectional elevational view of a well including a wellbore having a casing surrounded by cement containing a plurality of sensors in accordance with this invention.

[0009] Fig. 2 is an enlarged view of the upper portion of the well showing how the cement and the sensors can be inserted within the annular space defined between the outer surface of the casing and the inner surface of the wellbore.

[0010] Fig. 3 is a schematic view of an embodiment of this invention in which a sensor embedded within the cement employs a loop antenna to couple to a standing electromagnetic field.

[0011 ] Fig. 4 shows an alternative embodiment for a sensor antenna having an inductively loaded split wire pair structure for coupling to an E-field driven system.

[0012] Fig. 5 illustrates an embodiment of a ceramic sensor using an LC circuit for frequency modulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Referring now to the drawings, there is illustrated in Fig. 1 a well, indicated generally at 10, including a wellbore 11 that is drilled or otherwise formed

downwardly from the surface of the earth for the purpose of accessing and

withdrawing a desired material 12, such as a quantity of oil or gas, for example. After the wellbore 11 is drilled in a conventional manner, a casing 13 is inserted into the wellbore 11. In the illustrated embodiment, the casing 13 is a hollow cylindrical pipe that is formed from a rigid metallic material, such as a steel alloy. As shown in Fig. 1, the casing 13 is somewhat smaller in size than the wellbore 11 in which it is disposed. As a result, an annular space is defined between the outer surface of the casing 13 and the inner surface of the wellbore 11. This annular space, which extends from the surface of the earth to the bottom of the wellbore 11, is filled with cement 14 in a conventional manner.

[0014] One or more sensors 15 are disposed within the cement 14 throughout the annular space of the wellbore 11. The sensors 15 may be provided within the cement

14 in any desired manner and at any desired locations. For example, after the wellbore 11 has been formed and the casing 13 has been inserted into the wellbore 11, a slurry of the cement 14 can be created and pumped into the wellbore 11 in a well known manner. The sensors 15 can be inserted within the slurry of cement 14 as the slurry is being pumped into the wellbore 11. By inserting the sensors 15 within the slurry of cement 14 at predetermined time intervals as it is being pumped into the wellbore 11, the sensors 15 can be spaced apart from one another at approximately desired intervals, such as shown in Fig. 1.

[0015] Fig. 2 shows one method how the cement 14 and the sensors 15 can be inserted within the annular space defined between the outer surface of the casing 13 and the inner surface of the wellbore 11. As shown therein, each of the sensors 15 can be fabricated on or otherwise attached to a carrier 16. The carrier 16 is preferably formed from material that will dissolve in the cement 14 over time. For example, the carrier 16 may be formed from paper cellulose, wax, or other relatively soft material. However, the carrier 16 may be formed from any other desired material. Preferably, the carrier 16 is formed having a relatively long aspect ratio and is considerably larger than the sensor 15. For example, the carrier 16 may be several inches in length and one to two inches in width. The purpose of the carrier 16 is to help orient the sensors

15 as they are being pumped into the wellbore 11. This can be accomplished by providing the carrier 16 with a sufficiently large surface area for the laminar flow of the cement 14 to maintain a generally vertical orientation within the annular space defined between the outer surface of the casing 13 and the inner surface of the wellbore 11. The cellulose or other material of the carrier 16 preferably dissolves during curing of the cement 14 and, therefore, will not adversely influence the binding of the cement 14. Predominantly laminar flow of the cement 14 holds the orientation of the sensors 15 during the insertion thereof within the wellbore 11.

[0016] Another aspect of this method contemplates that the sensors 15 be fed into the flow of cement 14 by an orienting jig 17 located at the surface of the well 10 where the cement 14 is inserted into the wellbore 11. The orienting jig 17 may be embodied as a flat funnel-like insertion tool that will allow the sensors 15 to properly orient at the point of contact with the cement 14. As a result, as the sensors 15 enter the flow of cement 14, the drag of the cement 14 will pull the sensors 15 preferentially along the length of the casing 13 and help to maintain a desired orientation for optimal use.

[0017] The method of remote measurement capitalizes on the use of the existing steel casing 13 in the wellbore 11 as a backbone for both (1) delivering power to the sensors 15 dispersed within the cement 14 and (2) receiving signals back from those sensors 15 for analysis. In this manner, the system "illuminates" the well 10 with an active sensing capability to provide diagnostics on the integrity of the cement 14. As will be explained further below, this is accomplished by sending a relatively large current electromagnetic wave through the casing 13 from the top of the wellbore 11 toward the bottom thereof. This E-field travels down the steel casing 13, which acts like an inverted monopole antenna. Standing waves are set up in the casing 13, and the energy in this field radiates into the cement 14 that encases and surrounds the casing 13.

[0018] Two exemplary forms of sensors 15 are among those that may be used, which are based on a chosen antenna design, namely, either an H-field (magnetic) coupling or an E-field (electric) coupling. In the first case, a simple wire loop can be used as the sensor antenna, which undergoes an induced current when the driving field is present in the casing 13. When the driving field is shut off, the current in the sensor 15 decays and radiates an opposing B-field, which couples to the steel casing 13 and produces a small electromotive force (emf) signal that propagates upwardly along the casing 13 to the surface of the well 10. Fig. 3 is a schematic view of an embodiment of this invention in which the sensor 15 embedded within the cement 14 employs a loop antenna to couple to the standing field.

[0019] The second antenna type is an inductively loaded split wire pair or dipole, which can couple directly to the E-field of the casing 13. Such a split wire antenna offers smaller dimensions for equivalent coupling and may afford better overall performance at lower frequency. Fig. 4 shows an inductively loaded split wire pair antenna for coupling to an E-field driven system.

[0020] The choice between driving with E or H fields may be determined by the specific conditions of the application and sensor size constraints. The overall dimensions of the sensors 15 are preferably as small as possible to allow dispersion in the cement 14 without influencing the structural integrity thereof. The sensors 15 can, for example, be in the range of from about 1mm to about 10mm of linear size dimensions and be made of ceramic materials to withstand the expected high pressure and high temperature conditions of the application (which can reach 400°F and 15,000 psi). However, any desired sensor or combination of sensors 15 may be used. It is contemplated that many (perhaps hundreds) sensors 15 may be deployed in the cement 14 as it is poured in the wellbore 11 during fabrication. Such sensors 15 should withstand the journey down the wellbore 11 and the subsequent curing of the cement 14 so that they become embedded passive devices for repeated interrogation throughout the life of the well 10. The choice of an E or H field antenna may be based upon the frequency desired to be used. Because of the size of the sensors, a good candidate will be a loop type antenna operating in the induction mode (near field) since the separation distance between the sensor 15 and the casing 13 is relatively small.

[0021 ] Each sensor 15 may have a unique characteristic frequency of operation that will allow it to be interrogated specifically by tuning the frequency of the surface driver wave to the sensor. By stepping through multiple frequencies, many sensors 15 can be interrogated separately, thereby enabling a network of reporting from the illuminated well 10. [0022] To reach a high density of sensors 15 throughout the well 10, the time- domain of operation can also be used to sequester sections of the long wellbore 11 (which could run 10,000 feet deep). By time gating appropriately (on the nanosecond time scale) so that the receiver is allowed to only look at a portion of the return signals at a specific time of their return, the locations of the various sensors 15 can be isolated down to one meter or less with relatively low uncertainty. The return frequency of a given sensor 15 can be modulated by the physical cement parameter of interest, such as, for example, the pressure of the cement 14 at that point. Readings of the resonant frequency for a sensor 15 over time can be monitored to see the variation in pressure upon curing and over longer timeframes.

[0023] One example of a sensor 15 is an LC circuit whose resonant frequency changes as a function of the deflection of a portion of the device. Fig. 5 illustrates an example of a ceramic sensor 15 using an LC circuit for frequency modulation.

Pressure (P) modulates the resonant frequency of the device. One approach can be to modify a sensor 15 to withstand much higher pressures and, thus, enable it for this application. This is just one of many possible sensor designs, however. Temperature, pH, moisture content and other parameters that modify the resonant frequency by modulating the dielectric constants of the circuit are also possible in a format very similar to the circuit shown in Fig. 5. Either type of antenna used with the sensors (loop or split wire) is most optimally coupled if aligned with the respective driving field from the casing 13.

[0024] In a particular example of the method, the coupling efficiency of the approach was studied. A wire loop of approximately one centimeter diameter was used as an antenna/receiver/transmitter. A current source modulated with a square wave at 83Hz and six amps of current was used to drive a steel casing 13 having a diameter of about 1.5 inch and having copper contacts at each end of its length of about fourteen inches. The loop signal is captured by a 24-bit data acquisition system and filtered for lHz bandwidth at the drive frequency. The result was a 100-200 microvolt signal in that detection window. Both the loop and the casing 13 were used as transmitter and receiver with similar results. The pipe had about a 0.7 ohm resistance. A crude coupling factor was calculated based on this data which showed approximately 25e-6 coupling in one direction for the transmitter-receiver pair.

Estimating that a transmit and receive will be no better than the product of two couplings (one to the receiver and one back to the casing 15), the product of 25e-6 squared is approximately 6e-10. So for a ten volt drive signal, the expected return signal would be no bigger than about six nanovolts. Other factors, such as additional resistance and higher permeability of cement, can be taken into account as the work progresses. Because femtovolt detection of signals is achievable with standard high end equipment, the approach is feasible. The size of the sensors may be shrunk, and this will directly reduce the signal strength. Thus, a balance can be struck between the parameters, which also include the drive frequency. For this initial experiment, a low frequency was used. At higher frequencies, the efficiency of coupling should increase linearly with higher values. This can be limited by the increased skin resistance of the steel casing 15.

[0025] The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims

What is claimed is:

1. A method for monitoring a condition in a bore comprising the steps of: positioning sensors in the bore; and

sending an electromagnetic field through an object present in the bore to interrogate the sensors.

2. A method for monitoring cement integrity in a wellbore comprising the steps of:

embedding sensors in the cement; and

sending an electromagnetic field through a casing present in the wellbore to interrogate the sensors.

3. The method of claim 2 wherein the casing delivers power to the sensors and receives signals from the sensors.

4. The method of claim 3 wherein the electromagnetic field is sent through the casing from the top of the well, and electromagnetic energy radiates into the cement around the casing.

5. The method of claim 4 wherein the sensors are H-field sensors or E-field sensors.

6. The method of claim 2 wherein the sensors are embedded in the cement by being mixed with the liquid cement and poured into the wellbore prior to curing.

7. The method of claim 6 which further comprises using a sensor insertion tool to orient the sensors in the cement.

8. The method of claim 6 which further comprises positioning the sensors on carriers before mixing them with the liquid cement.

9. The method of claim 2 wherein the sensors have multiple frequencies of operation, and wherein the method includes interrogating different sensors by tuning the electromagnetic field to different frequencies.

10. An apparatus for monitoring cement integrity in a wellbore comprising: sensors embedded in the cement;

a casing disposed in the wellbore inside of the cement; and

a source of an electromagnetic field electrically connected to the casing and adapted to send the electromagnetic field through the casing to interrogate the sensors.

11. The apparatus of claim 10 wherein the casing is adapted to deliver power to the sensors and to receive signals from the sensors.

12. The apparatus of claim 11 wherein the source of the electromagnetic field is located outside the top of the well.

13. The apparatus of claim 12 wherein the sensors are H-field sensors or E- field sensors.

14. The apparatus of claim 10 which further comprises a sensor insertion tool to orient the sensors in the cement.

15. The apparatus of claim 10 which further comprises carriers for positioning the sensors before embedding them in the cement.

16. The apparatus of claim 10 wherein the sensors have multiple frequencies of operation, so that different sensors can be interrogated by tuning the

electromagnetic field to different frequencies.

17. A well comprising:

a bore formed in the earth;

a casing disposed within the bore so as to define an annular space between an outer surface of the casing and an inner surface of the bore;

cement disposed in the annular space;

at least one sensor disposed within the cement; and

18. The well of claim 17 wherein the casing is adapted to deliver power to the sensors and to receive signals from the sensors.