GB2141549A - Method and apparatus for exploration of geological formations in boreholes - Google Patents
Method and apparatus for exploration of geological formations in boreholes Download PDFInfo
- Publication number
- GB2141549A GB2141549A GB08413678A GB8413678A GB2141549A GB 2141549 A GB2141549 A GB 2141549A GB 08413678 A GB08413678 A GB 08413678A GB 8413678 A GB8413678 A GB 8413678A GB 2141549 A GB2141549 A GB 2141549A
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- United Kingdom
- Prior art keywords
- current
- sonde
- focusing
- survey
- response
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
- G01V3/20—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with propagation of electric current
- G01V3/24—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging operating with propagation of electric current using ac
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Geology (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- Geophysics (AREA)
- Geophysics And Detection Of Objects (AREA)
- Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
- Measurement Of Resistance Or Impedance (AREA)
Abstract
For investigating geological formations penetrated by a borehole, a sonde 12 having a plurality of voltage measuring electrodes M0L - - - - - M2U and at least one current emitting electrode A0 is provided and adapted to be lowered into a borehole 14. During exploration, a selected survey current is periodically emitted from the current emitting electrode and selected voltages at various voltage measuring electrodes are recorded. A transfer impedance is calculated utilizing each of these selected voltages and the selected survey current. A selected focusing current is also periodically emitted and similar voltages and transfer impedances are measured and calculated. By utilizing the transfer impedance calculated for the survey current and the focusing current, the amount of focusing current necessary to properly focus the sonde is calculated and with the relationship of focusing current and survey current thus defined, the apparent resistivity of the geological formation may be expressed as a function of the transfer impedances without the necessity of continuously altering the focusing current to focus the sonde. <IMAGE>
Description
SPECIFICATION
Method and apparatus for exploration of geological formations in boreholes
This invention relates to geological formation exploration in general and in particular to the utilization of resistivity measurements in the exploration of geological formations penetrated by a borehole.
Resistivity logging devices are well known in the prior art. Such devices are typically utilized to investigate the characteristics of formations which are penetrated by a borehole. Such formation characteristics correspond to changes in the resistivity of the formation.
It is well known in the prior art that the sedimentary portion of the earth's surface is generally comprised of successive layers or beds which generally do not have a constant thickness. Each of these beds will typically exhibit a certain resistivity characteristic which can be highly useful in the evaluation of a particular borehole with regard to the presence of hydrocarbon deposits.
The resistivity characteristics of a particular formation are generally investigated by introducing a measurement sonde into the borehole. An electrical survey current emitted by the sonde is typically returned to an electrode or "torpedo" which is generally separated from the sonde by a length of insulated cable. Such crude devices function and have been utilized for many years; however, the presence of drilling fluid in the borehole and the high resistivity of the geological formations underinvestigation both tended to diminish the depth into the formation to which the survey current would penetrate. This minimal penetration tended to minimize the amount of useful data regarding formation characteristics which these devices could generate.
In an attempt to overcome the aforementioned problem of minimal penetration, more recent devices have incorporated a second source of current to focus the survey current deeper into the formation. It was soon discovered that the amount of focusing current required to focus the survey current consistently would vary appreciably with the resistivity of the formation under investigation. An analog control loop is generally utilized with such systems to control the focusing current by maintaining as nearly as possible a null voltage gradient at a pair of monitor voltage measuring electrodes. Known analog control loops generally comprises a high gain linear amplifier which is coupled to the output of the monitor voltage measuring electrodes and which emits a focusing current having a polarity and magnitude to counterbalance the voltage gradient senses at the monitor electrodes.
Such analog focused resistivity logging devices have been in use for many years, but have exhibited shortfalls in field operations. Generally, the analog control loop must exhibit extremely high gain to achieve focusing in a wide variety of circumstances and yet the gain of the loop cannot be too great or stability of the loop will be adversely affected.
It is an object of the present invention to enable an improved resistivity logging device to be provided together with an improved method of focusing and an improved method of operating such a device.
The present invention provides apparatus for measuring the resistivity of a well bore formation comprising:
a sonde adapted to be lowered to a selected depth in a well bore;
means disposed on said sonde and adapted to emit a selected survey current;
means for measuring the voltage produced by said selected survey current at selected points on said sonde and for computing a first set of transfer impedances in response to said selected survey current and said measured voltages;
means disposed on said sonde and adapted to emit a selected focusing current;
means for measuring the voltage produced by said selected focusing current at selected points on said sonde and for computing a second set of transfer impedances in response to said selected focusing current and said measured voltages; and
means for computing the apparent resistivity of a well bore formation surrounding said sonde as a function of said first and second sets of transfer impedances.
The invention further provides methods of operating and focusing a resistivity sonde having a plurality of voltage measuring electrodes and a plurality of current emitting electrodes, said methods both comprising the steps of:
disposing said resistivity sonde in a well bore at a selected depth;
emitting a selected survey current from at least a selected one of said plurality of current emitting electrodes;
measuring the voltages produced at selected ones of said plurality of voltage measuring electrodes in response to said selected survey current;
computing at least a first transfer impedance utilizing at least one of said voltages produced in response to said selected survey current and said selected survey current and said selected survey current;
emitting a selected focusing current from at least one of said plurality of current emitting electrodes;;
measuring the voltages produced at selected ones of said plurality of voltage measuring electrodes in response to said selected focusing current;
computing at least a second transfer impedance utilizing at least one of said voltages produced in response to said selected focusing current and said selected focusing current.
The focusing method in accordance with the invention further comprises the step of determining the relationship between said selected focusing current and said selected survey current necessary to focus at resistivity sonde in response to said at least a first transfer impedance and said at least a second transfer impedance. The operating method in accordance with the invention, on the other hand, further comprises the step of determining the resistivity of the formation at said selected depth in said wellbore as a function of said at least a first transfer impedance and said at least a second transfer impedance.
By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, wherein:
Figure 1 is a partially schematic view of a resistivity logging system of the present invention suspended in a borehole; and
Figure 2 is a schematic diagram of the circuitry of a resistivity logging system of the present invention.
Referring now to the figures, and in particular to Fig. 1, there is depicted a partially schematic view of resistivity logging system 10 of the present invention. As is shown, system 10 includes a sonde 1 2 suspended in a borehole 14 by means of a wireline cable 16. Electrical conductors disposed within wireline cable 1 6 (not shown) are coupled to various electronic processing devices contained in van 1 8. Sonde 1 2 includes a plurality of voltage measuring electrodes Mou and MOL, M,u and MIL, M2U and M2L which are disposed on the surface of sonde 1 2 symmetrically about the current emitting electrode Ac, the subscripts U and L signifying the upper and lower of each pair of symmetrical electrodes. Sonde 1 2 also includes a pair of focus current return electrodes Aiu and AlL. The particular configuration of electrodes depicted in Fig.
1 is that configuration typically associated with a type of resistivity logging device known as a "spherically focused" tool; however, those skilled in the art will appreciate that the method and apparatus of the present invention will find application with many different types of resistivity measuring devices, including devices with nonsymmetrical arrays of measurement electrodes.
Also depicted in Fig. 1 is a survey current return electrode or "torpedo" 30 which is separated from sonde 1 2 by a length of insulated cable 32, typically referred to as a "bridle." The general parameters within which system 10 operates are quite similar to the operation of known resistivity logging systems. A survey current is emitted from electrode AO and returned at torpedo 30, a typical path followed by the survey current is depicted at reference numeral 34. A focusing or bucking current is also emitted from electrode AO and returned to electrodes A,u and A1L, following typical paths such as those depicted at numerals 36 and 38.However, in a manner unlike known focused resistivity logging systems, the amount of focusing current utilized is not continuously altered to maintain a proper focus. Instead, a series of simple voltage and current measurements are taken and the amount of focusing current necessary to focus the system is calculated and utilized to compute the apparent resistivity of the geological formation without actually focusing the system.
In order to understand the method and apparatus illustrated by the drawings it is necessary to understand the operation of a conventionally focused resistivity logging system.
Generally, a survey current 1, is emitted by the central electrdde Ao (see Fig. 1) and returned at a remote electrode 30. A focusing current 12 is emitted by Ao and returned at a nearby pair of electrodes namely A, upper, and A, lower, labeled A,u and AlL. The ratio between survey current and focusing current is constantly adjusted to satisfy:
(The subscripts U and L denote upper and lower electrodes respectively.)
With the balanced condition of equation (1) achieved, the tool response is computed in accordance with equation (2):
where K is the geometric coefficient specific to the sonde utilized.In order to simplify the equation, the average voltage of symmetrical electrodes, without U and L subscripts, is written using the rule expressed in equation (3).
Similarly, the sum of currents flowing from (or to) symmetrical electrodes will be written without U or L subscripts: I1 = (Iiu + IlL) (4)
With this simplified notation, equation (1) becomes: VM. VM2 = (5) and the tool response equation (2) takes the simplified form:
to be applied to the tool at a focused condition.
In comparison, the operation of the apparatus described herein proceeds without constant adjustments to the ratio of survey current and focusing current as follows:
A selected survey current, 11, is transmitted between Ao and return electrode 30.
The actual amount of survey current is measured along with the following two voltage levels:
The following two transfer impedances are then calculated:
Next, the supply of survey current is turned off and a selected amount of focusing current, 12 is transmitted from current emitting electrode Ao to return electrodes A1U and A1,. It should be noted that the amount of focusing current transmitted is not necessarily the amount required to focus the sonde, and that the focusing current may be transmitted simultaneously with the survey current at a different frequency.
The actual amount of focusing current is now measured along with the same two voltage levels which were measured while the survey current was transmitted.
Two more transfer impedances are then calculated utilizing the focusing current measured and the voltage levels:
In order to satisfy the focused condition expressed in equation (5), one must select a focusing current and survey current such that: a2212 +a12l1 = 0 (11)
This condition will be satisfied if one chooses a focusing current such that: It = 1 and: 12 = a12 (12)
a22
Since the system described is a linear system, the total voltage present at each point on sonde 1 2 must be a linear combination of the voltage contributions from each current source.
Therefore, for any number of currents selected, it is possible to compute the total voltage present on the sonde by utilizing the transfer impedances. Thus, the total voltage present on the sonde when the currents Il and i2 are selected can be expressed as depicted in equation (3):
By substituting the value of 12 chosen in equation (12) the voltage present on sonde 1 2 during the predicted balance condition is expressed in equation (14):
Equation (14) may now be easily substituted into the tool response equation (6), recalling that I, has been selected as unity, to yield a new tool response equation (15), which is a function of the previously computed transfer impedances, completely independent of any voltage or current values::
Referring now to Fig. 2, there is depicted a schematic diagram of one embodiment of the electronic circuitry which may be utilized in apparatus of the present invention. Survey and focusing current are provided by oscillator 40, filter 42 and amplifier 44. Switch 46 is utilized to alternately provide a current path between return electrode 30 and electrode Ao or between Ao and return electrodes A,u and A". Resistor 48 is utilized to permit scaling of the applied currents should the computed values fall outside of the limits imposed by the software utilized to compute the transfer impedances.
The voltage at electrode Ao is coupled, via transformer 50, td amplifier 52. The output of amplifier 52 is coupled through a detector circuit 54 and filter 56 to switch 58. Switch 58 may be selectively closed to couple the detected and filered output through analog-to-digital converter 60 to computer 62. Computer 62 may be implemented utilizing an appropriately programmed electronic data processing device such as a microprocessor or microcomputer.
The series connected secondaries of transformer 64 and 66 are utilized to implement equations (8) and (9), and will directly yield
and are coupled to amplifier 68. The output of amplifier 68 is coupled to detector 70, filter 72 and switch 74 in a manner similar to the output of amplifier 52. Similarly, the centre-tapped primaries of transformers 64 and 66, in addition to the voltage divider formed by resistors 76, 78, 80 and 82 are utilized to implement a portion of equation (2) directly yielding the following voltage:
As above, the outputs of the center-tapped primaries and voltage dividers are coupled to amplifier 84, detector 86, filter 88 and switch 90.
In operation, the circuitry of Fig. 2 is selectively activated for each reading and a relay controller (not shown) is utilized to alternately couple a selected survey current and a selected focusing current to the appropriate electrodes. The voltage and current measurements described above are taken and computer 64 is utilized to calculate the four transfer impedances described above which are necessary to compute the apparent resistivity of the geological formation.
Those skilled in this art should appreciate that the apparatus and methods just described can yield an improved result over known analog focused systems due to the lack of physical constraints found in this system.
While the embodiments disclosed is that of a spherically focused resistivity logging device, it should be understood that this m,ethod and apparatus may be applied to various alternate types of resistivity logging devices. Similarly, instead of alternately applying the survey and focusing current, it is possible to simultaneously apply survey and focusing current at different frequencies, with each current return electrode designed to accept a specific current.
Claims (10)
1. A method of operating a resistivity sonde having a plurality of voltage measuring electrodes and a plurality of current emitting electrodes, comprising:
disposing said resistivity sonde in a well bore at a selected depth;
emitting a selected survey current from at least a selected one of said plurality of current emitting electrodes;
measuring the voltages produced at selected ones of said plurality of voltage measuring electrodes in response to said selected survey current;
computing at least a first transfer impedance utilizing at least one of said voltages produced in response to said selected survey current and said selected survey current;
emitting a selected focusing current from at least one of said plurality of current emitting electrodes;;
measuring the voltages produced at selected ones of said plurality of voltage measuring electrodes in response to said selected focusing current;
computing at least a second transfer impedance utilizing at least one of said voltages produced in response to said selected focusing current and said selected focusing current; and
determining the resistivity of the formation at said selected depth in said wellbore as a function of said at least a first transfer impedance and said at least a second transfer impedance.
2. A method of focusing a resistivity sonde having a plurality of voltage measuring electrodes and a plurality of current emitting electrodes, comprising:
disposing said resistivity sonde in a well bore at a selected depth:
emitting a selected survey current from at least a selected one of said plurality of current emitting electrodes;
measuring the voltages produced at selected ones of said plurality of voltage measuring electrodes in response to said selected survey current;
computing at least a first transfer impedance utilizing at least one of said voltages produced in response to said selected survey current and said selected survey current;
emitting a selected focusing current from at least one of said plurality of current emitting electrodes;;
measuring the voltages produced at selected ones of said plurality of voltage measuring electrodes in response to said selected focusing current;
computing at least a second transfer impedance utilizing at least one of said voltages produced in response to said selected focusing current and said selected focusing current; and
determining the relationship between said selected focusing current and said selected survey current necessary to focus at resistivity sonde in response to said at least a first transfer impedance and said at least a second transfer impedance.
3. Apparatus for measuring the resistivity of a well bore formation comprising:
a sonde adapted to be lowered to a selected depth in a well bore;
means disposed on said sonde and adapted to emit a selected survey current;
means for measuring the voltage produced by said selected survey current at selected points on said sonde and for computing a first set of transfer impedances in response to said selected survey current and said measured voltages;
means disposed on said sonde and adapted to emit a selected focusing current;
means for measuring the voltage produced by said selected focusing current at selected points on said sonde and for computing a second set of transfer impedances in response to said selected focusing current and said measured voltages; and
means for computing the apparent resistivity of a well bore formation surrounding said sonde as a function of said first and second sets of transfer impedances.
4. The apparatus according to Claim 3 wherein said selected survey current and said selected focusing current are emitted during alternate periods of time.
5. The apparatus according to Claim 3 wherein said selected survey current and said selected focusing current are emitted at different frequencies.
6. The apparatus according to Claim 3 wherein said means for computing said first and second set of transfer impedances comprises an appropriately programmed microprocessor.
7. The apparatus according to Claim 3 wherein said means disposed on said sonde and adapted to emit a selected survey current and said means disposed on said sonde and adapted to emit a selected focusing current comprise a single current emitting electrode.
8. Apparatus for measuring the resistivity of a well bore formation, substantially as described herein with reference to, and as illustrated by, the accompanying drawings.
9. A method according to claim 1, substantially as described herein with reference to the accompanying drawings.
10. A method according to claim 2, substantially as described herein with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US49927483A | 1983-05-31 | 1983-05-31 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8413678D0 GB8413678D0 (en) | 1984-07-04 |
| GB2141549A true GB2141549A (en) | 1984-12-19 |
Family
ID=23984596
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08413678A Withdrawn GB2141549A (en) | 1983-05-31 | 1984-05-29 | Method and apparatus for exploration of geological formations in boreholes |
Country Status (3)
| Country | Link |
|---|---|
| FR (1) | FR2547064A1 (en) |
| GB (1) | GB2141549A (en) |
| NO (1) | NO842170L (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5159978A (en) * | 1991-08-13 | 1992-11-03 | Halliburton Logging Services, Inc. | Connecting apparatus for logging tools including electrical feedthrough and isolation system with bridle assembly |
| US5852363A (en) * | 1995-10-20 | 1998-12-22 | Schlumberger Technology Corporation | Methods and apparatus for measuring characteristics of a formation around a borehole using computed focusing |
| CN102141534A (en) * | 2011-01-18 | 2011-08-03 | 中国地质调查局水文地质环境地质调查中心 | Seawater invasion monitoring method and distributed conductivity geological disaster monitoring device |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB728564A (en) * | 1952-06-06 | 1955-04-20 | Schlumberger Well Surv Corp | Improvements in or relating to well logging apparatus |
| GB979223A (en) * | 1961-06-19 | 1965-01-01 | Continental Oil Co | Electrical well logging device |
| GB2019004A (en) * | 1978-01-21 | 1979-10-24 | Schlumberger Ltd | Well Logging Methods and Apparatus |
| GB2042735A (en) * | 1978-12-04 | 1980-09-24 | Dresser Ind | Dual focused resistivity logging method and apparatus |
-
1984
- 1984-05-29 FR FR8408402A patent/FR2547064A1/en not_active Withdrawn
- 1984-05-29 GB GB08413678A patent/GB2141549A/en not_active Withdrawn
- 1984-05-30 NO NO842170A patent/NO842170L/en unknown
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB728564A (en) * | 1952-06-06 | 1955-04-20 | Schlumberger Well Surv Corp | Improvements in or relating to well logging apparatus |
| GB979223A (en) * | 1961-06-19 | 1965-01-01 | Continental Oil Co | Electrical well logging device |
| GB2019004A (en) * | 1978-01-21 | 1979-10-24 | Schlumberger Ltd | Well Logging Methods and Apparatus |
| GB2042735A (en) * | 1978-12-04 | 1980-09-24 | Dresser Ind | Dual focused resistivity logging method and apparatus |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5159978A (en) * | 1991-08-13 | 1992-11-03 | Halliburton Logging Services, Inc. | Connecting apparatus for logging tools including electrical feedthrough and isolation system with bridle assembly |
| US5852363A (en) * | 1995-10-20 | 1998-12-22 | Schlumberger Technology Corporation | Methods and apparatus for measuring characteristics of a formation around a borehole using computed focusing |
| CN102141534A (en) * | 2011-01-18 | 2011-08-03 | 中国地质调查局水文地质环境地质调查中心 | Seawater invasion monitoring method and distributed conductivity geological disaster monitoring device |
| CN102141534B (en) * | 2011-01-18 | 2013-09-04 | 中国地质调查局水文地质环境地质调查中心 | Seawater invasion monitoring method and distributed conductivity geological disaster monitoring device |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8413678D0 (en) | 1984-07-04 |
| NO842170L (en) | 1984-12-03 |
| FR2547064A1 (en) | 1984-12-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |