System and methods for T1-based logging

• US 7,755,354 B2
• Filed: 11/04/2008
• Issued: 07/13/2010
• 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): Shrivastav; Brij B
• Application Number:
  US12/264,637
• Publication Number:
  US 20090093962A1
• Time in Patent Office: 616 Days
• Field of Search: 324300-322
• 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 (MR) 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. A method for analyzing geologic formations, comprising the steps of:

obtaining a first set of T₁ NMR measurements of the geologic formation;

obtaining at least one second set of T₂ NMR measurements of the geologic formation; and

processing said first and at least one second sets of NMR measurements to derive an estimate of one or more of;

diffusivity, gas to oil ratio (GOR) and viscosity at reservoir conditions, wherein the estimate is obtained from the T₁ NMR measurements and the T₂ NMR measurements as a function of T_2,hc, T_1,hc, G, TE, where G is the gradient of the magnetic field and the T₁ NMR measurements are used to approximate T₂ NMR measurements with an infinitely short T_E.

2. The method of claim 1, wherein an estimate of diffusivity is obtained for diffusivity of low viscosity light hydrocarbons.

3. The method of claim 1, wherein an estimate of diffusivity D₀ is obtained directly from the T₁ NMR measurements and the T₂ NMR measurements using:

4. The method of claim 1, wherein an estimate of GOR is obtained by combining a D₀ estimate and T₁ values.

5. The method of claim 1, further comprising a step of pre-polarizing the geologic formation.

6. The method of claim 1, further comprising a step of compensating for insufficient polarization within the geologic formation.

7. The method of claim 1, further comprising a step of delineating reservoir fluids based on the one or more derived estimate.

8. The method of claim 1, further comprising a step of identifying hydrocarbon bearing zones based on the one or more derived estimate.

9. The method of claim 1, further comprising the step of processing the T₁ NMR measurements and an estimate of diffusivity.

10. The method of claim 1, further comprising the step of plotting the T₁ NMR measurements and an estimate of diffusivity.

17. The method of claim 9, wherein the step of processing the T₁ NMR measurements and the estimate of diffusivity is used to derive formation properties.

18. The method of claim 9, wherein the step of processing the T₁ NMR measurements and the estimate of diffusivity is used to derive fluid properties.

11. A system for analyzing geologic formations, comprising:

means for obtaining a first set of T₁ NMR measurements of the geologic formation;

means for obtaining at least one second set of T₂ NMR measurements of the geologic formation; and

means for processing said first and at least one second sets of NMR measurements to derive an estimate of one or more of;

diffusivity, gas to oil ratio (GOR) and viscosity at reservoir conditions, wherein the means for processing said first and at least one second sets of NMR measurements is configured to derive an estimate from the T₁ NMR measurements and the T₂ NMR measurements as a function of T_2,hc, T_1,hc, G, TE, where G is the gradient of the magnetic field and the T₁ NMR measurements are used to approximate T₂ NMR measurements with an infinitely short T_E.

12. The system of claim 11, wherein the means for processing said first and at least one second sets of NMR measurements is configured to derive an estimate of diffusivity for diffusivity of low viscosity light hydrocarbons.

13. The system of claim 11, wherein the means for processing said first and at least one second sets of NMR measurements is configured to derive an estimate of diffusivity D₀ directly from the T₁ NMR measurements and the T₂NMR measurements using:

14. The system of claim 11, wherein the means for processing said first and at least one second sets of NMR measurements is configured to obtain an estimate of GOR based on a D₀ estimate and T₁ values.

15. The system of claim 11, further comprising means for pre-polarizing the geologic formation.

16. The system of claim 11, wherein the means for processing said first and at least one second sets of NMR measurements is configured to compensate for insufficient polarization within the geologic formation.

19. The system of claim 11, further comprising means for processing the T₁ NMR measurements and an estimate of diffusivity.

20. The system of claim 19, wherein the means for processing the T₁ NMR measurements and the estimate of diffusivity is used to derive formation properties.

21. The system of claim 19, wherein the means for processing the T₁ NMR measurements and the estimate of diffusivity is used to derive fluid properties.

22. The system of claim 11, further comprising means for plotting the T₁ NMR measurements and an estimate of diffusivity.