Sonic data logging system

• US 6,205,087 B1
• Filed: 11/16/1998
• Issued: 03/20/2001
• Est. Priority Date: 01/31/1996
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Tejada, Mauricio, Fukuhara, Masafumi
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): JOLLY, ANTHONY S
• Application Number:
  US09/117,514
• Time in Patent Office: 855 Days
• Field of Search: 367/26, 367/27, 367/25, 367/34, 367/30, 367/31, 367/43, 367/45, 367/69, 367/33, 367/86, 367/32, 181/102
• US Class Current: 367/69
• CPC Class Codes: G01V 1/48 Processing data

Abstract

A sonic logging method involves the pre-processing of a detection signal by a downhole processing device to determine the arrival time of a sonic signal at a receiver which is then transmitted to the surface. A suitable sonic logging downhole tool includes a control device for controlling generation and reception of the sonic signal, an A-D converter for digitizing the detected signal at a predetermined sampling interval, a first memory for storing the digitized waveform, a second memory for storing a program for processing the digitized waveform, and a microprocessor capable of executing the stored program so as to determine an arrival time of the sonic signal arriving at the receiver.

Claims

1. A sonic logging method for determining characteristics of a formation through which a borehole passes using a downhole tool which is located in the borehole so as to be moveable up and down and coupled to ground surface processing apparatus by means of a logging cable, the downhole tool including:

(i) at least one sonic wave generator and at least once receiver spaced apart from each other; and

(ii) a downhole processing device operatively coupled to the generator and receiver and also to the ground surface processing apparatus through the logging cable, the method comprising;

(a) locating the downhole tool in the borehole;

(b) generating a sonic wave signal with the at least one generator;

(c) receiving the sonic wave signal with the at least one generator;

(d) processing a received signal using the downhole processing device and determining an arrival time for the sonic wave signal at the receiver; and

(e) transmitting the determined arrival time to the ground surface processing equipment through the logging cable.

2. A method as claimed in claim 1, wherein the step of processing the received signal comprises:

(i) setting an arrival time detection period;

(ii) identifying a point in the arrival time detection period at which the received signal first exceeds a predetermined threshold level; and

(iii) determining the point as the arrival time.

3. A method as claimed in claim 2, wherein the step of processing the received signal comprises:

(i) setting an offset detection period earlier than the arrival time detection period;

(ii) detecting, during the offset detection period, any DC offset in the received signal baseline; and

(iii) determining, from the determined offset, a zero level of the received signal.

4. A method as claimed in claim 2, wherein the step of processing the received signal comprises:

(i) setting a noise detection period earlier than the arrival time detection period;

(ii) detecting, during the noise detection period, any noise in the received signal baseline; and

(iii) evaluating a reliability for the determined arrival time from the detected noise.

5. A method as claimed in claim 1, wherein the step of processing the received signal comprises:

(i) sampling the received signal at a predetermined sampling interval;

(ii) converting the sampling signal into a digital form;

(iii) storing the digital form in memory; and

(iv) processing the digital form so as to determine the arrival time.

6. A method as claimed in claim 5, wherein the step of processing the digital form comprises:

(i) setting an arrival time detection period;

(ii) identifying a point in the arrival time detection period at which the digital form first exceeds a predetermined threshold level; and

(iii) determining the point as the arrival time.

7. A method as claimed in claim 6, wherein the step of processing the digital form comprises:

(i) setting an offset detection period earlier than the arrival time detection period;

(ii) detecting, during the offset detection period, any DC offset in the digital form baseline; and

(iii) determining, form the determined offset, a zero level of the digital form.

8. A method as claimed in claim 6, wherein the step of processing the digital form comprises:

(i) setting a noise detection period earlier than the arrival time detection period;

(ii) detecting, during the noise detection period, any noise in the digital form baseline; and

(iii) evaluating a reliability for the determined arrival time from the detected noise.

9. A method as claimed in claim 6, wherein the step of identifying the point at which the digital form exceeds the threshold comprises:

(i) identifying a first sample point in the arrival time detection period at which the digital form first exceeds the predetermined threshold; and

(ii) interpolating between the first sample point and a sample point immediately preceding the first sample point and identifying a point exceeding the threshold level at a time interval smaller than the sampling interval, which point is determined as the arrival time.

10. A method as claimed in claim 1, further comprising determining an amplitude for the received signal in the downhole processing device and transmitting this amplitude to the ground surface processing equipment.

11. A method as claimed in claim 10, wherein the step of processing the received signal comprises:

(i) determining a threshold for detecting arrival of a signal;

(ii) detecting a point at which the received signal exceeds the threshold;

(iii) identifying a largest amplitude in the received signal after the point at which the received signal exceeds the threshold; and

(iv) adjusting the threshold to be a predetermined portion of the largest amplitude.

12. A method as claimed in claim 11, wherein the received signal is subsequently re-processed using the adjusted threshold to determine the arrival time by identifying a point at which the received signal exceeds the adjusted threshold for the first time.

13. A method as claimed in claim 5, further comprising determining an amplitude for the digital form in the downhole processing device and transmitting this amplitude to the ground surface processing equipment.

14. A method as claimed in claim 13, wherein the step of processing the received signal comprises:

(i) determining a threshold for detecting arrival of a signal;

(ii) detecting a point at which the digital form exceeds the threshold;

(iii) identifying a largest amplitude in the digital form after the point at which the received signal exceeds the threshold; and

(iv) adjusting the threshold to be a predetermined portion of the largest amplitude.

15. A method as claimed in claim 14, wherein the digital form is subsequently re-processed using the adjusted threshold to determine the arrival time by identifying a point at which the digital form exceeds the adjusted threshold for the first time.

16. A sonic logging method for determining characteristics of a formation through which a borehole passes using a downhole tool which is located in the borehole so as to be moveable up and down and operatively coupled to ground surface processing apparatus, the downhole tool including:

(i) at least one sonic wave generator and at least one receiver spaced apart from each other; and

(ii) a downhole processing device operatively coupled to the generator and receiver and in communication with the ground surface processing apparatus, the method comprising;

(a) locating the downhole tool in the borehole;

(b) generating a sonic wave signal with the at least one generator;

(c) receiving the sonic wave signal with the at least one receiver;

(d) processing a received signal using the downhole processing device and determining an arrival time for the sonic wave signal at the receiver; and

(e) transmitting the determined arrival time to the ground surface processing equipment.

17. A sonic logging downhole tool for determining characteristics of a formation through which a borehole passes, comprising:

(a) at least one sonic wave generator;

(b) at least one receiver capable of receiving the sonic wave after it has traveled through the formation;

(c) a control device for controlling the generation and reception of the sonic wave, the control device comprising;

(i) an analog-to-digital converter for digitizing a detection signal waveform from the at least one receiver at a predetermined sampling interval;

(ii) a first memory for storing the digitized waveform;

(iii) a second memory for storing a predetermined program for processing the stored digitized waveform; and

(iv) a microprocessor capable of executing the program stored in the second memory so as to process the digitized waveform stored in the first memory to determine an arrival time of a sonic wave generated by the generator and received by the receiver.

18. A sonic logging system for determining characteristics of a formation through which a borehole passes, comprising a ground surface processing apparatus, and a downhole tool in communication with the ground surface processing apparatus and comprising:

(a) at least one sonic wave generator;

(b) at least one receiver capable of receiving the sonic wave after it has traveled through the formation;

(c) a control device for controlling the generation and reception of the sonic wave, the control device comprising;

(i) an analog-to-digital converter for digitizing a detection signal waveform from the at least one receiver at a predetermined sampling interval;

(ii) a first memory for storing the digitized waveform;

(iii) a second memory for storing a predetermined program for processing the stored digitized waveform; and

(iv) a microprocessor capable of executing the program stored in the second memory so as to process the digitized waveform stored in the first memory to determine an arrival time of a sonic wave generated by the generator and received by the receiver.