METHOD OF AND APPARATUS FOR LOGGING WHILE DRILLING

• US 3,789,355 A
• Filed: 12/28/1971
• Issued: 01/29/1974
• Est. Priority Date: 12/28/1971
• Status: Expired due to Term

• Current Assignee: Bobbie J. Patton
• Original Assignee: Bobbie J. Patton
• Inventors: Patton, Bobbie J.
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Moskowitz, N.
• Application Number:
  US05/213,061
• Time in Patent Office: 763 Days
• Field of Search: 340/18P,18LD
• US Class Current: 367/137
• CPC Class Codes: E21B 47/18 through the well fluid , e.g. mud pressure pulse telemetry
• CPC Class Codes: E21B 47/20 by modulation of mud waves, e.g. by continuous modulation

Abstract

A method and apparatus is described for monitoring at a remote location downhole conditions encountered while drilling a well. A sensed downhole condition is represented by a binary coded acoustic signal which is transmitted by way of a liquid path, provided by drilling liquid, to the surface of the earth. The acoustic signal, whose phase state represents bit values, is detected at the surface and decoded by way of a coherent system. Coherency is provided by deriving from the received signal a reference signal which is compared with the received signal to produce an output representative of the sensed condition.

Claims

1. In a logging-while-drilling system for transmitting downhole measured conditions to the surface of the earth during the drilling of a well utilizing a flowing drilling liquid including an acoustic generator having a movable member which when driven at a constant speed produces in the liquid a continuous acoustic wave signal having a first phase state and having a frequency proportional to the speed of movement of said movable member, driving means for said member, and a downhole transducer, the improvement comprising:

means responsive to the output of said transducer for momentarily changing the speed of said member and then reestablishing said constant speed to change the phase of said acoustic signal from the first phase state to a second phase state.

2. The system of claim 1 wherein said acoustic signal is coded in m-ary coded bit lengths, where m is any integer greater than 1, means for initiating said bits at a selected rate, and means for varying the bit initiation rate to vary the time duration over which said acoustic signal representing each bit is generated.

3. The system of claim 2 where m 2, 4 or 8.

4. The system of claim 1 wherein the movable member for generating the acoustic signal comprises a rotating valve for interrupting liquid flow, means for generating pulses at a predetermined repetition rate to control the rotation of said valve, means responsive to the rotation of said valve for producing a signal representative of the rate of rotation of said valve, means for comparing said pulses and said signal to produce an error signal when said valve is operating at a phase other than a preselected phase, and means responsive to said error signal to adjust the rate of rotation of said valve to regain said preselected phase and return said error signal to zero.

5. The system of claim 1 including a plurality of means for sensing downhole conditions and for generating analog signals representative of said conditions, cycling means for multiplexing said signals, an analog-to-digital converter for converting said analog signals into digital words represented by two states '"'"''"'"''"'"''"'"'0'"'"''"'"''"'"''"'"' and '"'"''"'"''"'"''"'"'1,'"'"''"'"''"'"''"'"' an encoder responsive to said digital words to produce an output signal only upon the occurrence of one of said states, means for introducing to said system a sync signal at the beginning of each cycle of said means for multiplexing, and wherein said means for momentarily changing the speed of said member responds to each output signal from said encoder for reversing the phase of said acoustic signal.

6. The system of claim 5 in which said means for introducing said sync signal introduces alternately two sync signals, one the complement of the other.

7. The system of claim 5 including means for generating said states at a selected rate, and means for varying the state generation rate to vary the time duration over which said acoustic signal representing each state is generated.

8. In the drilling of a well employing a drilling liquid and a drill string within the well, the method of logging said well comprising driving a movable member of an acoustic generator at a constant speed to produce in the liquid a continuous acoustic wave signal having a first phase state and having a frequency proportional to the speed of movement of said movable member, sensing at least one downhole condition and in response to said sensed condition changing the speed of said member and then re-establishing said constant speed to change the phase of said acoustic signal from the first phase state to a second phase state.

9. The method of claim 8 wherein said acoustic signal is modulated in a nonreturn to zero mode in which phase conditions are different phase states of said acoustic signal with reference to the phase state of said signal during a preceding time interval.

10. In a well logging tool, the combination comprising:

an elongated housing adapted to be inserted into a well and into contact with liquid within said well, said housing having a liquid flow passage therein, an acoustic generator supported by said housing and including a movable member which when driven at a constant speed produces in the liquid a continuous acoustic wave signal having a frequency proportional to the speed of movement of said movable member, means for regulating the operation of said generator at a selected frequency, a plurality of transducers supported by said housing for producing analog signals representative of sensed downhole conditions, means for converting said analog signals to serial digital signals, multiplexer means for serially applying the signals from said transducers to said converting means, and means for momentarily changing the speed of said member and then re-establishing said constant speed to change the phase of said acoustic signal in response to said digital signals.

11. The combination of claim 10 wherein said means for regulating the operation of said generator comprises:

clock means for generating a primary timing function representative of said selected frequency, pulse generating means associated with said generator for generating a secondary timing function representative of the actual operating frequency of said generator, means for comparing said primary and secondary timing functions, and means for adjusting the operating frequency of said generator in response to the deviation of said secondary timing function from said primary timing function.

12. In a well logging system having a logging tool movable lengthwise through a well filled with liquid and including an acoustic generator for imparting to the well liquid an acoustic signal whose frequency is proportional to the speed of a motor driving the acoustic generator, and having one or more transducers for producing output signals representative of sensed downhole conditions, the improvement comprising:

a signal source of constant frequency, signal means driven by said motor for generating within said well liquid an acoustic output signal having a frequency proportional to the speed of said motor, means for producing a signal proportional to the speed of the motor, means responsive to said constant frequency and to said signal representative of motor speed for producing a resultant output signal varying with phase differences between them, means responsive to said last-named output signal for maintaining said motor at a constant speed with a resultant fixed-phase relationship between said constant frequency and said acoustic output signal, an uphole transducer acoustically coupled to said well liquid for generating an output signal having the same frequency as that of said acoustic output signal, an oscillator for producing a reference frequency, means including a phase detector for adjusting said oscillator for maintaining a fixed-phase relationship between that of said reference frEquency and said acoustic output signal, means responsive to each transducer carried by said logging tool for applying to said driving motor a series of control pulses of magnitude and duration for producing transient changes in the speed of said motor to change by predetermined amounts the phase of said acoustic output signal relative to that of said reference frequency, and means including a phase detector responsive to said changes in phase due to said transient speed changes for producing output pulses corresponding with said control pulses.

13. In a logging-while-drilling system for transmitting data via a flowing drilling liquid between spaced points during the drilling of a well utilizing an acoustic generator for producing a continuous wave having a movable member which when driven at a constant speed produces in the liquid a continuous wave signal having a first phase state and having a frequency proportional to the speed of movement of said movable member, driving means for said member, and a signal source, the improvement comprising:

means responsive to the output of said signal source for momentarily changing the speed of said driving means and then re-establishing said constant speed to change the phase of said acoustic signal from the first phase state to a second phase state.