ELECTROMAGNETIC LOGGING IN TIME DOMAIN WITH USE OF SPECIFIC CURRENT PULSES

• US 20100191469A1
• Filed: 10/12/2009
• Published: 07/29/2010
• Est. Priority Date: 01/27/2009
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Mogilatov, Vladimir S.
• Granted Patent: US 9,405,034 B2
• Time in Patent Office: Days
• US Class Current: 702/6
• CPC Class Codes: G01V 3/26 operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device with electromagnetic waves G01V3/30

Abstract

A method for estimating a property of an earth formation in a zone of investigation, the earth formation having the zone of investigation and another zone, the method including: applying a compound pulse of electromagnetic energy to the earth formation, the compound pulse having a shape to induce a predominately greater amount of current in the zone of investigation than in the another zone, wherein the compound pulse includes a first pulse and a second pulse, the first pulse having an amplitude different from the amplitude of the second pulse; receiving a response of electromagnetic energy from the current induced by the compound pulse; and estimating the property from the response of electromagnetic energy.

Claims

1. A method for estimating a property of an earth formation in a zone of investigation, the earth formation comprising the zone of investigation and another zone, the method comprising:

applying a compound pulse of electromagnetic energy to the earth formation, the compound pulse comprising a shape to induce a predominately greater amount of current in the zone of investigation than in the another zone, wherein the compound pulse comprises a first pulse and a second pulse, the first pulse comprising an amplitude different from the amplitude of the second pulse;

receiving a response of electromagnetic energy from the current induced by the compound pulse; and

estimating the property from the response of electromagnetic energy.

2. The method of claim 1, wherein the first pulse is derived from a first pulse of direct current in a transmitter coil and the second pulse is derived from a second pulse of direct current in the transmitter coil.

3. The method of claim 2, wherein the first pulse of direct current comprises a constant amplitude and the second pulse of direct current comprises a constant amplitude.

4. The method of claim 1, wherein the first pulse is applied before the second pulse and the amplitude of the first pulse is greater than the amplitude of the second pulse.

5. The method of claim 1, wherein a duration of the first pulse is greater than a duration of the second pulse.

6. The method of claim 1, wherein a polarity of the first pulse is opposite of a polarity of the second pulse.

7. The method of claim 1, wherein the compound pulse further comprises a third pulse, wherein the first pulse amplitude is greater than the second pulse amplitude and the second pulse amplitude is greater than an amplitude of the third pulse.

8. The method of claim 7, wherein each of the first pulse, the second pulse and the third pulse comprise a same polarity.

9. The method of claim 1, wherein the property comprises conductivity.

10. The method of claim 9, wherein estimating the conductivity comprises solving the equation:

${\mathrm{Emf}}_D=\frac{M_z<br><br>q<br><br><br><br>\mathrm{\mu <br><br>}}{32<br><br>\mathrm{\pi <br><br>}<br><br>\sqrt{\mathrm{\pi <br><br>}}}·<br><br>\frac{\partial <br><br>}{\partial <br><br>t}<br><br>\left\{{\left(\frac{\mathrm{\mu <br><br>}<br><br><br><br>\mathrm{\sigma <br><br>}}{t}\right)}^{5/2}·<br><br>{\int <br><br>}_{r_1}^{r_2}<br><br>{\int <br><br>}_{{\stackrel{\_}{z}}_1}^{{\stackrel{\_}{z}}_2}<br><br>\frac{r^3<br><br>{\mathrm{<br><br>}}^{-\frac{\mathrm{\mu <br><br>}<br><br><br><br>\mathrm{\sigma <br><br>}}{4<br><br>t}<br><br>\left(r^2+{\stackrel{\_}{z}}^2\right)}<br><br><br><br><br><br>r<br><br><br><br><br><br>\stackrel{\_}{z}}{{\left[r^2+{\left(z-\stackrel{\_}{z}\right)}^2\right]}^{3/2}}\right\}$

where;

Emf_D represents a voltage induced by the response of electromagnetic energy;

M_z represents a vertical magnetic moment aligned along a longitudinal axis of a borehole penetrating the earth formation;

q represents an effective cross-sectional area of a receiver coil for receiving the response of electromagnetic energy;

μ

represents magnetic permeability of the earth formation;

σ

represents conductivity;

t represents time;

r represents a radial distance from the longitudinal axis;

z represents a distance measured along the longitudinal axis; and

z represents an observation point at the longitudinal axis;

wherein the zone of investigation is a cylindrical volume centered about the longitudinal axis, the cylindrical volume having a minimum radius of r₁ and a maximum radius of r₂ and a length extending from z₁ to z₂.

11. The method of claim 1, wherein the property comprises a boundary.

12. The method of claim 1, wherein the second pulse follows the first pulse with substantially no delay.

13. An apparatus for estimating a property of an earth formation in a zone of investigation, the earth formation comprising the zone of investigation and another zone, the apparatus comprising:

a logging instrument;

a transmitter;

a receiver; and

a processing system configured to implement the following instructions;

applying a compound pulse of electromagnetic energy to the earth formation, the compound pulse comprising a shape to induce a predominately greater amount of current in the zone of investigation than in the another zone, wherein the compound pulse comprises a first pulse and a second pulse, the first pulse comprising an amplitude different from the amplitude of the second pulse;

receiving a response of electromagnetic energy from the current induced by the compound pulse; and

estimating the property from the response of electromagnetic energy.

14. The apparatus of claim 13, wherein the transmitter comprises a coil.

15. The apparatus of claim 14, wherein a plane of the coil is aligned perpendicular to a longitudinal axis of a borehole penetrating the earth formation.

16. The apparatus of claim 13, wherein the receiver comprises a coil.

17. The apparatus of claim 13, wherein the receiver is disposed a distance from the transmitter.

18. A computer program product stored on machine-readable media comprising machine-executable instructions for estimating a property of an earth formation in a zone of investigation, the earth formation comprising the zone of investigation and another zone, by implementing a method comprising:

applying a compound pulse of electromagnetic energy to the earth formation, the compound pulse comprising a shape to induce a predominately greater amount of current in the zone of investigation than in the another zone, wherein the compound pulse comprises a first pulse and a second pulse, the first pulse comprising an amplitude different from the amplitude of the second pulse;

receiving a response of electromagnetic energy from the current induced by the compound pulse; and

estimating the property from the response of electromagnetic energy.

19. The computer program product of claim 18, wherein the property comprises at least one of conductivity and a boundary.