Claims
- 1. A method for making nuclear magnetic resonance (NMR) measurements of a geologic formation using an NMR logging tool, comprising the steps of:(a) applying downhole one or more forced magnetization recovery pulse sequences; (b) applying at least one T1 saturation-recovery sequence following the one or more forced magnetization recovery pulse sequences; (c) receiving NMR echo signals in response to pulse sequences applied in steps (a) and (b); and (d) processing the received NMR echo signals to determine properties of the geologic formation.
- 2. The method of claim 1, wherein the one or more forced magnetization recovery pulse sequences are given by the expression:[τi−π/2(+x)−[tcp−π−tcp−echo]j−tcp−π/2(−x)]k where τi is a variable delay, and i≧1; j≧1; k≧1; and +x and −x denote phases of the Larmor frequency of the carrier of the pulse with respect to a continuous wave Larmor frequency signal; tcp is the Carr-Purcell spacing, wherein the echo train defined by tcp and j in the sequence is shorter than the longest expected characteristic signal decay time component T2.
- 3. The method of claim 2, wherein the phase of all π pulses is y.
- 4. The method of claim 2, wherein the phase of all π pulses is x.
- 5. The method of claim 2, wherein for k≧2 the index i is held fixed.
- 6. The method of claim 2, wherein for k≧2 the index i is varied, resulting in variable delay τi times.
- 7. The method of claim 6, wherein i=k.
- 8. The method of claim 2, wherein τ1>>τi, where i=2, 3, . . . , N and N is an integer.
- 9. The method of claim 8, wherein τ1≧1 second.
- 10. The method of claim 1, wherein step (b) of applying at least one T1 saturation-recovery sequence comprises the step of:applying one or more times a chirped pulse sequence, comprising a radio frequency (RF) pulse covering a relatively wide range of frequencies to saturate nuclear magnetization in a volume within the geologic formation and a readout pulse sequence at a frequency within the range of covered frequencies, the readout pulse sequence following a predetermined wait time after the saturation pulse.
- 11. The method of claim 10, wherein the chirped sequence is repeated using different saturation recovery times.
- 12. The method of claim 11, wherein the selection of different saturation recovery times is made based on desired data points on a T1 relaxation curve.
- 13. The method of claim 12, wherein the chirped sequence is repeated using saturation recovery times including two or more of the following: 1 ms, 10 ms, 30 ms, 100 ms, 300 ms, 1000 ms, 3000 ms.
- 14. The method of claim 10, wherein the range of frequencies is covered using a rapid succession of short radio frequency pulses.
- 15. The method of claim 10, wherein the range of frequencies is covered using a single pulse in a frequency sweep.
- 16. The method of claim 1 further comprising the step of monitoring the motion of the tool with respect to the borehole.
- 17. The method of claim 16, wherein the step of processing comprises discarding echo signals obtained during measurement intervals when motion tool acceleration values exceed predetermined threshold.
- 18. The method of claim 1, wherein steps (a), (b) and (c) are performed concurrently with the step of drilling a borehole in said geologic formation.
- 19. The method of claim 1, wherein the step of processing comprises computation of T1 relaxation times.
- 20. The method of claim 1, wherein the phase of the π pulses is alternated between +y and −y for incremental values of the index i.
- 21. A system for making nuclear magnetic resonance (NMR) measurements of a geologic formation using an NMR logging tool, comprising the steps of:(a) means for applying downhole one or more forced magnetization recovery pulse sequences; (b) means for applying at least one T1 saturation-recovery sequence following the one or more a forced magnetization recovery pulse sequences; (c) means for receiving NMR echo signals in response to NMR pulse sequences; and (d) means for processing the received NMR echo signals to determine properties of the geologic formation.
- 22. The system of claim 21, wherein the one or more a forced magnetization recovery pulse sequences are given by the expression:[τi−π/2(+x)−[tcp−π−tcp−echo]j−tcp−π/2(−x)]k where τi is a variable delay, and i≧1; j≧1; k≧1; and +x and −x denote phases of the Larmor frequency of the carrier of the pulse with respect to a continuous wave Larmor frequency signal; tcp is the Carr-Purcell spacing, wherein the echo train defined by tcp and j in the sequence is shorter than the longest expected characteristic signal decay time component T2.
- 23. The system of claim 21, wherein the means for applying at least one T1 saturation-recovery sequence comprises:means for applying one or more times a chirped pulse sequence, comprising a radio frequency (RF) pulse covering a relatively wide range of frequencies to saturate nuclear magnetization in a volume within the geologic formation and a readout pulse sequence at a frequency within the range of covered frequencies, the readout pulse sequence following a predetermined wait time after the saturation pulse.
- 24. The system of claim 21 further comprising the step of monitoring the motion of the tool with respect to the borehole.
- 25. The system of claim 21 further comprising a drill bit for drilling a borehole in said geologic formation, and at least the means in (a), (b) and (c) are capable of operating concurrently with the drilling of a borehole.
Parent Case Info
This application is a continuation of application Ser. No. 09/874,029, filed Jun. 5, 2001 now U.S. Pat. No. 6,531,868, which is a continuation-in-part of application Ser. No. 09/552,160 filed Apr. 18, 2000, now U.S. Pat. No. 6,242,913, which is a continuation of application Ser. No. 08/996,720 filed Dec. 23, 1997, now U.S. Pat. No. 6,051,973, which is a continuation of provisional application No. 60/033,986 filed Dec. 30, 1996, which are incorporated herein by reference.
US Referenced Citations (6)
Foreign Referenced Citations (1)
Number |
Date |
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WO 9210768 |
Jun 1998 |
DE |
Provisional Applications (1)
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Number |
Date |
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60/033986 |
Dec 1996 |
US |
Continuations (2)
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09/874029 |
Jun 2001 |
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10/385539 |
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08/996720 |
Dec 1997 |
US |
Child |
09/552160 |
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US |
Continuation in Parts (1)
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09/552160 |
Apr 2000 |
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09/874029 |
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