MEASURING CURRENT FROM AN ELECTRODE USING A NON-LINEAR ELEMENT

Abstract

An arrangement for generating a resistivity image having a drill bit with cutters configured to be placed within a wellbore, the cutters configured to create further sections of the wellbore upon rotation, the drill bit having an end with threads for engagement, at least one section of drill string connected to the drill bit through a matching set of threads for engagement, a receiver toroid connected to the at least one section of drill string along at least a portion of the drill string, a transmitter toroid connected to the at least one section of drill string and located at least a portion of the drill string away from the receiver toroid, at least one stabilizer connected to the at least one section of drill string, a power source connected to the transmitter toroid and the receiver toroid, an electrode arrangement placed at the drill bit, wherein the electrode arrangement is electrically connected to the drill bit through a non-linear circuit element and a computer arrangement connected to the receiver toroid.

Claims

1. An arrangement for drilling a wellbore, comprising: a drill bit with cutters; at least one section of drill string connected to the drill bit; a receiver toroid connected to the at least one section of drill string; a transmitter toroid connected to the at least one section of drill string; and an electrode arrangement placed at the drill bit, wherein the sensor is electrically connected to the drill bit through a non-linear circuit element.

2. The arrangement according to claim 1, wherein the electrode is placed at a gauge pad of the drill bit.

3. The arrangement according to claim 1, wherein the cutters are polycrystalline diamond cutters.

4. The arrangement according to claim 1, wherein the non-linear circuit element comprises: a diode with an anode and a cathode; and an electrode connected to the cathode of the diode.

5. The arrangement according to claim 4, wherein the electrode further comprises: an insulator placed to at least one exterior side of the electrode.

6. The arrangement according to claim 4, wherein the non-linear circuit element is configured such that excitation of the transmitter toroid will cause a current flowing out of the electrode to be at least twice an excitation frequency of the transmitter.

7. The arrangement according to claim 1, further comprising: at least one contact point arrangement on the at least one section of drill string, the at least one contact point arrangement connecting the at least one section of drill string and a geological formation.

8. The arrangement according to claim 1, wherein the at least one contact point arrangement is a stabilizer.

9. The arrangement according to claim 1, further comprising: at least one computing arrangement, the at least one computing arrangement connected to the receiving toroid, the computing arrangement configured to receive data from the receiver toroid to produce a resistivity image.

10. An arrangement for generating a resistivity image, comprising: a drill bit with cutters configured to be placed within a wellbore, the cutters configured to create further sections of the wellbore upon rotation, the drill bit having an end with threads for engagement; at least one section of drill string connected to the drill bit through a matching set of threads for engagement; a receiver toroid connected to the at least one section of drill string along at least a portion of the drill string; a transmitter toroid connected to the at least one section of drill string and located at least a portion of the drill string away from the receiver toroid; at least one stabilizer connected to the at least one section of drill string, the stabilizer configured to stabilize the at least one section of drill string and the drill bit upon rotation of the connected drill string and the drill bit by contacting an exterior portion of the wellbore; a power source connected to the transmitter toroid and the receiver toroid; an electrode arrangement placed at the drill bit, wherein the electrode arrangement is electrically connected to the drill bit through a non-linear circuit element; and a computer arrangement connected to the receiver toroid, the computer arrangement configured to receive data from the receiver toroid and generate a resistivity image.

11. The arrangement according to claim 10, wherein the power source is one of a downhole battery and a turbine arrangement configured to convert fluid motion in the wellbore to electrical energy.

12. The arrangement according to claim 10, wherein the non-linear circuit element is a diode arrangement.

13. The arrangement according to claim 10, wherein the computer arrangement connected to the receiver toroid is positioned outside of the wellbore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the disclosed subject matter, and advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0012] FIG. 1 is a perspective view of an electrode embedded in a drill bit.

[0013] FIG. 2 is a side elevation view of a drilling tool using a resistivity based technique to obtain data from a geological formation.

[0014] FIG. 3 is a side view of an electrode and insulator arrangement in position next to a geological formation.

DETAILED DESCRIPTION

[0015] Referring to FIG. 1, an electrode embedded bit arrangement 10 is illustrated. The electrode embedded bit arrangement 10 is connected to the remainder of the drill system through a thread connection 18. In the illustrated embodiment, an American Petroleum Institute (“API”) thread connection is used. Other mechanical fastening arrangements may be used such that rotation of a drill string, in turn, causes the electrode embedded bit arrangement 10 to rotate. Rotation of the electrode embedded bit arrangement 10 may be accomplished through a rotary table or top drive assembly, as non-limiting embodiments.

[0016] Upon rotation, the electrode embedded bit arrangement 10 contacts a geological formation through use of cutters 12 placed on the crown 20 of the electrode embedded bit arrangement 10. The cutters 12 are configured such that rotation of the electrode embedded bit arrangement 10 causes the geological formation to break, shear or otherwise be compromised by the cutters 12. In the illustrated embodiment, the cutters 12 illustrated are configured in a round shape. The material used in the cutters 12, in a non-limiting embodiment, is a polycrystalline diamond compact arrangement, hereinafter (“PDC”). In other non-limiting embodiments, tungsten insert carbide cutters may be used. In still another non-limiting embodiment, a ridged diamond element bit may be used. In another further non-limiting embodiment, rotating cutters may be used to limit the amount of wear on the contact face of the cutter 12.

[0017] Gauge pads 14 are placed on the electrode embedded bit arrangement 10 around selected positions on the periphery of the electrode embedded bit arrangement 10. An electrode insulator arrangement 16, described later, is placed along one gauge pad of the electrode embedded bit arrangement 10. Although illustrated as a single electrical sensor, the description should not be considered to be limited to such a configuration. The gauge pads 14 are placed on the periphery of the drill bit arrangement 10 to provide an outward contact limit of the electrode embedded bit arrangement 10 within the wellbore. The gauge pads 14 may be diamond impregnated surfaces to limit overall wearing of the gauge pads 14. On the top side surface of the gauge pads 14, a cutting element may be placed such that pull-out of the wellbore by the electrode embedded bit arrangement 10 can be facilitated and stick may be minimized. In the illustrated embodiment depicted in FIG. 1, the electrode embedded bit arrangement 10 is rotated counter clockwise such that the flat portions of the PDC cutters 12 contact the geological formation. Ports 22, may be added to the arrangement 10 such that fluid may be pumped through the drill string, through the thread connection 18 and out the ports 22. The purpose of the drilling fluid pumped through the ports 22 is to remove degraded rock, soil and minerals from the wellbore through the fluid being pushed up an annulus of the drill string.

[0018] The matrix materials used to create the body of the arrangement 10 in the illustrated embodiment may be varied to achieve a sufficiently rigid body to support the cutters 12. The base matrix materials used to create the body of the arrangement may not only have ports 22 but also inserted nozzles such that fluid may be more evenly dispersed or dispersed to areas needed in the drill bit arrangement 10. In the illustrated embodiment, a configuration is provided where 5 ports 22 are illustrated. In this embodiment, the number of ports is limited to allow for larger openings so that removed materials from the geological formation do not clog the port(s). In the case where materials broken from the geological stratum are not of sufficient size to clog the ports 22, the number of ports 22 may be increased.

[0019] Referring to FIG. 2, a side elevation of an arrangement placed in an oil based mud is illustrated. In the illustrated embodiment, a receiver toroid 26 is placed upstream from a transmitter toroid 23. In this embodiment, one cutter of a drill bit arrangement 10 is insulated from an electrically connected bit body through a non-linear circuit element, such as that disclosed in FIG. 3 and FIG. 1.

[0020] FIG. 2, illustrates how the bit resistivity measurement in an oil-based mud works with a tool. One toroid transmitter 23 positioned over the drill collar generates an alternating current voltage across the drill collar or drill string after receiving power from an electrical circuit, such as a battery arrangement. The battery arrangement can be located inside the drill string of the bottom hole assembly. Since the bit arrangement 10 is the only part of the bottom hole assembly in contact with the geological formation below the transmitter toroid 23, current will flow out from the bit arrangement 10 and return higher up the bottom hole assembly where there is some contact with the formation, for example, on a stabilizer 24. A receiver toroid 26 is used to measure the current flowing along the collar as illustrated. In the illustrated embodiment, the receiver toroid 26 is placed as close to the stabilizer 24 such that signal attenuation is prevented.

[0021] In this non-limiting embodiment provided in FIG. 2, the current flowing out of the cutter/electrode will be at two times the excitation frequency of the transmitter. This current harmonic can be measured by the receiver toroid 26 in addition to the fundamental (if the toroid and measuring circuit are sufficiently linear themselves). In this way, the current leaving just the electrode can be distinguished from the current leaving the rest of the bit body and used to generate a resistivity image.

[0022] A computer arrangement may be connected to the receiver toroid 26 such that signals received from the receiver toroid 26 may be converted into a resistivity image. In the illustrated embodiment, the computer arrangement is positioned at the well head and the signal may be transported from the receiver toroid though various methods and apparatus, such as wired drill pipe. The computer arrangement may have a visual display apparatus to pictorially represent data to an operator in real time so that operator decisions may be made related to drilling progress. The computer arrangement may be a personal computer, laptop or portable handheld unit to aid the operators in making drilling decisions.

[0023] In the arrangement shown in FIG. 2, an oil based mud is used to enhance the overall signal capabilities of the system. Such oil based muds are typically non-conductive muds which aid in resistivity signal generation for the geological formation. Other types of muds that are non-conductive may be used, such as synthetic based systems from M-I. SWACO, Inc. Alternative configurations may include diesel-based fluid systems or mineral oil type systems.

[0024] Referring to FIG. 3, a side elevation of an electrode insulator arrangement 16 is illustrated. The electrode insulator arrangement 16 may be used in the configuration presented in FIG.1 and FIG. 2, above. In the electrode insulator arrangement 16, a diode 302 is connected to an electrode 304. Around the periphery of the electrode 304, an insulator 306 is positioned to insulate the electrode 304 from contacts other than the diode 302 and directly in contact with the formation 308. Surrounding metal 310, such as that from a drill bit arrangement 10, may be located to house the diode 302, insulator 306 and the electrode 304.

[0025] The diode 302 is positioned, in the illustrated embodiment, with the cathode side positioned toward the formation side. This positioning allows for one way flow of electricity through the diode 302 toward the formation. The diode 302 may be constructed from silicon, selenium or germanium as applicable. The overall electrode insulator arrangement 16 may be designed such that the expected temperatures that the arrangement 16 will encounter will not deleteriously compromise the integrity of the diode 302.

[0026] In one non-limiting embodiment, an arrangement for drilling a wellbore, is disclosed having a drill bit with cutters, at least one section of drill string connected to the drill bit, a receiver toroid connected to the at least one section of drill string; a transmitter toroid connected to the at least one section of drill string and an electrode arrangement placed at the drill bit, wherein the electrode arrangement is electrically connected to the drill bit through a non-linear circuit element.

[0027] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may also be configured wherein the electrode arrangement is placed at a gauge pad of the drill bit.

[0028] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may also be configured wherein the cutters are polycrystalline diamond cutters.

[0029] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the non-linear circuit element comprises a diode with an anode and a cathode and an electrode connected to the cathode of the diode.

[0030] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the electrode further comprises an insulator placed to at least one exterior side of the electrode.

[0031] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the non-linear circuit element is configured such that excitation of the transmitter toroid will cause a current flowing out of the electrode to be at least twice an excitation frequency of the transmitter.

[0032] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may further comprise at least one contact point arrangement on the at least one section of drill string, the at least one contact point arrangement connecting the at least one section of drill string and a geological formation.

[0033] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the at least one contact point arrangement is a stabilizer.

[0034] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may further comprise at least one computing arrangement, the at least one computing arrangement connected to the receiving toroid, the computing arrangement configured to receive data from the receiver toroid to produce a resistivity image.

[0035] In another non-limiting embodiment, an arrangement for generating a resistivity image is disclosed comprising a drill bit with cutters configured to be placed within a wellbore, the cutters configured to create further sections of the wellbore upon rotation, the drill bit having an end with threads for engagement, at least one section of drill string connected to the drill bit through a matching set of threads for engagement, a receiver toroid connected to the at least one section of drill string along at least a portion of the drill string, a transmitter toroid connected to the at least one section of drill string and located at least a portion of the drill string away from the receiver toroid, at least one stabilizer connected to the at least one section of drill string, the stabilizer configured to stabilize the at least one section of drill string and the drill bit upon rotation of the connected drill string and the drill bit by contacting an exterior portion of the wellbore, a power source connected to the transmitter toroid and the receiver toroid, an electrode arrangement placed at the drill bit, wherein the sensor is electrically connected to the drill bit through a non-linear circuit element and a computer arrangement connected to the receiver toroid, the computer arrangement configured to receive data from the receiver toroid and generate a resistivity image.

[0036] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the arrangement according to claim 10, wherein the power source is one of a downhole battery and a turbine arrangement configured to convert fluid motion in the wellbore to electrical energy.

[0037] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the non-linear circuit element is a diode arrangement.

[0038] In another non-limiting embodiment, the arrangement for drilling a wellbore described above may be configured wherein the computer arrangement connected to the receiver toroid is positioned outside of the wellbore.

[0039] Although methods for inverting electromagnetic logging measurements have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.