Maximum depth of investigation of measurements in a formation

Patent metadata

Field	Value
Publication number	US-9043153-B2
Application number	US-201113048833-A
Country	US
Kind code	B2
Filing date	Mar 15, 2011
Priority date	Mar 15, 2011
Publication date	May 26, 2015
Grant date	May 26, 2015

Abstract

The present disclosure relates to a method to determine a volume of clearance surrounding a wellbore. A logging tool is provided. The logging tool may be disposed on a wireline, a drill string, or a wired drill pipe. A formation property is obtained using the logging tool. The formation property may include a voltage, a bulk resistivity, a horizontal resistivity, a vertical resistivity, a porosity, a permeability, a fluid saturation, an NMR relaxation time, a borehole size, a borehole shape, a borehole fluid composition, an MWD parameter, or an LWD parameter. The maximum depth of investigation into the subsurface formation is determined using a model response and a noise level, and the volume of clearance is determined using the determined maximum depth of investigation. The maximum depth of investigation and volume of clearance may be determined even though no boundary layers are detected.

First claim

What is claimed is:

1. A method to determine a volume of clearance surrounding a wellbore, comprising:
placing a logging tool into the wellbore;
obtaining a signal response from the logging tool corresponding to a measurement of a subsurface formation property of the wellbore, wherein the measurement of the subsurface formation property relates to one or more characteristics of materials along a trajectory of the wellbore at a plurality of depths; and
using a processor configured to:
determine the strength of the signal response of the logging tool as a function of radial depth of investigation distance with respect to the axis of the logging tool, wherein the signal response is modeled using the measurement obtained by the logging tool;
select a noise threshold based at least partially upon the electrical noise of the logging tool and a frequency at which a signal is transmitted from the logging tool to obtain the measurement;
determine a point of intersection between the signal response strength and the noise threshold, wherein the radial depth of investigation distance corresponding to the point of intersection represents a maximum radial depth of investigation; and
determine the volume of clearance using the determined maximum radial depth of investigation.

2. The method of claim 1 , wherein the obtaining the signal response corresponding to the measurement of the subsurface formation property comprises transmitting and receiving an electromagnetic signal transmitted at a certain frequency, or transmitting and receiving a plurality of electromagnetic signals, each of the electromagnetic signals being transmitted at different frequencies.

3. The method of claim 1 , wherein the subsurface formation property includes at least one of a voltage, a bulk resistivity, a horizontal resistivity, a vertical resistivity, a porosity, a permeability, a fluid saturation, an NMR relaxation time, a magnetic field, a sonic response, a borehole size, a borehole shape, a borehole fluid composition, an MWD parameter, and an LWD parameter.

4. The method of claim 1 , wherein no boundary layers are detected.

5. The method of claim 1 , wherein the model response is derived from a formation model comprising three or more layers.

6. The method of claim 1 , further comprising displaying the volume of clearance.

7. The method of claim 6 , wherein the displaying comprises color-coding one or more formation property boundaries.

8. The method of claim 6 , wherein the displaying comprises adjacently placing multiple circles or ellipsoids of different size and shape.

9. The method of claim 6 , wherein the displaying comprises plotting a 3-D, spatially oriented volume of clearance positioned in a 3-D environment along a wellbore's trajectory.

10. A system comprising:
an electromagnetic logging tool having a plurality of transmitter-receiver measurement couplings, wherein the electromagnetic logging tool is configured to be disposed within a subsurface formation of a wellbore and configured to obtain electromagnetic measurements corresponding to a measurement of a subsurface formation property of the wellbore, and wherein the electromagnetic measurements relate to one or more characteristics of materials along a trajectory of the wellbore at a plurality of depths; and
a processor configured to:
receive the electromagnetic measurements from the electromagnetic logging tool disposed in the subsurface formation;
determine a noise threshold based upon a selected transmitter-receiver measurement coupling of the electromagnetic logging tool and the electrical noise of the electromagnetic logging tool;
determine a resistivity ratio based upon the received electromagnetic measurements;
model a signal response of the electromagnetic logging tool using the resistivity ratio;
plot a first curve representative of the signal response as a function of signal strength and depth of investigation distance and a second curve representative of the noise threshold; and
determine a maximum depth of investigation into the subsurface formation as the depth of investigation distance corresponding to where the first and second curves intersect on the plot.

11. The system of claim 10 , wherein no boundary layers are detected.

12. The system of claim 10 , wherein the processor is capable of determining a volume of clearance surrounding a wellbore in which the electromagnetic logging tool is disposed based on the maximum depth of investigation.

13. The system of claim 12 , further comprising displaying the volume of clearance.

14. The system of claim 10 , wherein the selected transmitter-receiver measurement coupling is one that provides the greatest depth of investigation for the electromagnetic logging tool relative to all other transmitter-receiver measurement couplings of the electromagnetic logging tool.

15. A method for determining a maximum depth of investigation comprising:
disposing an electromagnetic logging tool having a plurality of transmitter-receiver spacings into a borehole formed in a subsurface formation;
obtaining electromagnetic measurements from the electromagnetic logging tool corresponding to a measurement of a subsurface formation property of the borehole, wherein the electromagnetic measurements relate to one or more characteristics of materials along a trajectory of the borehole at a plurality of depths;
using a processor to:
determine a noise threshold based at least partially upon a selected transmitter-receiver spacing of the electromagnetic logging tool and the electrical noise characteristic of the electromagnetic logging tool;
determine a resistivity ratio based upon the obtained electromagnetic measurements;
model a signal response of the electromagnetic logging tool using the resistivity ratio;
plot a first curve representative of the signal response as a function of signal strength and depth of investigation distance;
plot a second curve representative of the noise threshold on the same plot as the first curve; and
determine a maximum depth of investigation into the subsurface formation as the depth of investigation distance corresponding to where the first and second curves intersect on the plot.

16. The method of claim 15 , wherein the electromagnetic measurements comprise a horizontal resistivity and a vertical resistivity.

17. The method of claim 16 , wherein the resistivity ratio is determined as a ratio of horizontal resistivity to a user-defined resistivity that results in a desired resistivity contrast.

18. The method of claim 15 , wherein the selected transmitter-receiver spacing is one that provides the greatest depth of investigation for the electromagnetic logging tool relative to all other transmitter-receiver spacings of the electromagnetic logging tool.

19. The method of claim 15 , wherein the maximum depth of investigation is used to determine a volume of clearance centered on the axis of the electromagnetic logging tool.

20. The method of claim 15 , wherein when the first curve and second curve intersect at more than one point, the point corresponding to a lesser depth of investigation distance is selected as the maximum depth of investigation.

Assignees

• Denichou Jean-Michel
• Schlumberger Technology Corp

Inventors

• Denichou Jean-Michel

Classifications

• G01V3/18 Primary

  specially adapted for well-logging · CPC title