System and methods for T1-based logging

• US 7,501,818 B2
• Filed: 03/29/2007
• Issued: 03/10/2009
• Est. Priority Date: 10/03/2003
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Akkurt, Ridvan
• Primary Examiner(s): Arana; Louis M
• Application Number:
  US11/731,121
• Publication Number:
  US 20070241750A1
• Time in Patent Office: 712 Days
• Field of Search: 324/303, 324/306, 324/307, 324/300
• US Class Current: 324/303
• CPC Class Codes: G01N 24/081 Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
• CPC Class Codes: G01R 33/50 based on the determination of relaxation times , e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences
• CPC Class Codes: G01R 33/5617 using RF refocusing, e.g. RARE
• CPC Class Codes: G01V 3/32 operating with electron or nuclear magnetic resonance

Abstract

System and methods for using nuclear magnetic resonance (NMR) T₁ measurements for wireline, LWD and MWD applications and down-hole NMR fluid analyzers. The T₁ measurements are characterized by insensitivity to motion, as the detrimental effects arising from tool motion or fluid flow are effectively reduced or eliminated. T₁ measurements alone or in combination with other standard oil field measurements are shown to provide efficient data acquisition resulting in compact and robust data sets, the potential for substantially increased logging speeds, and simple methods for fluid typing, including direct and robust identification of gas.

Claims

1. An NMR method for analyzing geologic formations, comprising the step of:

providing a distribution of NMR T₁ relaxation times corresponding to an NMR log of the geologic formation obtained with a maximum wait time T_wmax such that T_wmax<

α

T_1max, where T_1max is the longest component in the T₁ spectrum of the NMR signal and α

is a constant less than 5; and

computing a correction for insufficient polarization of the NMR log based solely on the provided distribution of NMR T₁ relaxation times and acquisition parameters of the NMR log.

2. The method of claim 1 further comprising the step of obtaining an NMR log of the geologic formation.

3. The method of claim 1, wherein the constant α

is between about 1 and 3.

4. The method of claim 1, wherein for I wait times in the NMR log measurements, and KT₁ components, the uncorrected T₁ spectrum is computed using a solution to the linear system A_cx=d, in which d_(I×

l) is the data vector;

A<sub>c(I×

K)</sub> is a constrained matrix the elements of which are defined as

A(i,k)=(1−

e<sup>−

Twi/T1k</sup>)e<sup>−

Te/T2k</sup>, and (1−

e<sup>−

Twi/T1k</sup>)=1, for i=I

and the vector of uncorrected T₁ spectrum components is x<sub>(I×

l)</sub>.

5. The method of claim 4, wherein the post-inversion correction factors c_k, given the amplitudes x_k from inversion, are defined by:

6. The method of claim 1 further comprising the step of computing a correction for insufficient polarization of a T₂ NMR log based solely on the provided distribution of NMR T₁ relaxation times and acquisition parameters of the NMR log.

7. An NMR method for analyzing geologic formations, comprising the steps of:

providing a distribution of NMR T₁ relaxation times corresponding to an NMR log of the geologic formation obtained with a mixed polarization profile including pre-polarization, where magnetization originating from pre-polarization (B₀>

0, B₁=0) is mixed with standard magnetization; and

computing a correction for pre-polarization of the NMR log based solely on the provided distribution of NMR T₁ relaxation times, and acquisition parameters of the NMR log, said acquisition parameters including the logging speed.

8. The method of claim 7 further comprising the step of obtaining an NMR log of the geologic formation.

9. The method of claim 7, wherein the correction for pre-polarization for a set of acquisition parameters is computed a-priory.

10. The method of claim 8, wherein the maximum wait time are approximately 3 seconds.

11. A system for implementing the method steps in accordance with claim 7.

12. An NMR system for analyzing geologic formations, comprising:

means for providing a distribution of NMR T₁ relaxation times corresponding to an NMR log of the geologic formation obtained with a maximum wait time T_wmax such that T_wmax<

α

T_1max, where T_1max is the longest component in the T₁ spectrum of the NMR signal and α

is a constant less than 5; and

means for computing a correction for insufficient polarization of the NMR log based solely on the provided distribution of NMR T₁ relaxation times and acquisition parameters of the NMR log.