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1. WO2020112317 - EVALUATION OF FORMATION FRACTURE PROPERTIES USING NUCLEAR MAGNETIC RESONANCE

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[ EN ]

CLAIMS

What is claimed is:

1. An apparatus (10) for estimating fracture properties of a resource bearing formation (12), the apparatus (10) comprising:

a nuclear magnetic resonance (NMR) measurement device (18) configured to be deployed in a region of interest, the region of interest including a tight rock formation region (12), the NMR measurement device (18) including a transmitting assembly (26) configured to transmit an NMR pulse sequence into the tight rock formation region (12), and a receiving assembly (26) configured to detect NMR signals corresponding to a response of the tight rock formation region (12) to the pulse sequence; and

a processor (38) configured to receive the NMR signals and perform:

inverting the NMR signals into a transverse relaxation time ( T2 ) distribution;

separating the T2 distribution (70, 72, 74, 76) based on a cut-off time into a first volumetric indicative of matrix and pore responses and a second volumetric indicative of fracture responses;

estimating a pore size distribution based on the second volumetric; and

calculating a fracture aperture size distribution (80, 82, 84, 86) based on the pore diameter.

2. The apparatus (10) of claim 1, wherein the processor (38) is configured to perform one or more aspects of an energy industry operation based on the fracture aperture size distribution (80, 82, 84, 86).

3. The apparatus (10) of claim 1, wherein the cut-off time is determined based on a maximum pore size and a largest surface relaxivity of the tight rock formation region (12).

4. The apparatus (10) of claim 1, wherein the fracture aperture size distribution (80, 82, 84, 86) is estimated based on a direct correlation between pore diameter and fracture aperture size.

5. The apparatus (10) of claim 4, wherein the direct correlation is based on an assumption that the response of the tight rock formation region (12) is at least substantially a result of surface relaxation, and the response is represented by:


wherein T2, surface is a relaxation time associated with the surface relaxation, and:


wherein p2 is a surface relaxivity, S is a surface area of pores in the tight rock formation region (12), fris a volume of the pores, and S!V is a surface-to-volume ratio of the pores.

6. The apparatus (10) of claim 5, wherein the direct correlation is based on a relationship between the pore diameter and the surface-to-volume ratio, and a relationship between the fracture aperture size (80, 82, 84, 86) and the surface-to-volume ratio.

7. The apparatus (10) of claim 6, wherein the direct correlation is based on an assumption that the tight rock formation region (12) includes spherical pores having a diameter d , and that fractures in the tight rock formation region (12) are planar fractures having an average aperture size w.

8. The apparatus (10) of claim 7, wherein the direct correlation is represented by:


9. The apparatus (10) of claim 1, wherein the NMR measurement device (18) is incorporated into a wireline logging assembly (26) or a logging-while-drilling (LWD) assembly.

10. A method (60) of estimating fracture properties of a resource bearing formation (12), the method (60) comprising:

receiving, by a processor, NMR signals generated by a nuclear magnetic resonance (NMR) measurement device (18) deployed in a region of interest, the region of interest including a tight rock formation region (12), the NMR measurement device (18) including a transmitting assembly configured to transmit an NMR pulse sequence into the tight rock formation region (12), and a receiving assembly (26) configured to detect NMR signals corresponding to a response of the tight rock formation region (12) to the pulse sequence; and inverting the NMR signals into a transverse relaxation time ( T2 ) distribution;

separating the T2 distribution (70, 72, 74, 76) based on a cut-off time into a first volumetric indicative of matrix and pore responses and a second volumetric indicative of fracture responses;

estimating a pore size distribution based on the second volumetric; and

calculating a fracture aperture size distribution (80, 82, 84, 86) based on the pore diameter.

11. The method (60) of claim 10, further comprising performing one or more aspects of an energy industry operation based on the fracture aperture size distribution (80, 82, 84, 86).

12. The method (60) of claim 10, wherein the cut-off time is determined based on a maximum pore size and a largest surface relaxivity of the tight rock formation region (12).

13. The method (60) of claim 10, wherein the fracture aperture size distribution (80, 82, 84, 86) is estimated based on a direct correlation between pore diameter and fracture aperture size, the direct correlation is based on an assumption that the response of the tight rock formation region (12) is at least substantially a result of surface relaxation, and the response is represented by:


wherein T2, surface is a relaxation time associated with the surface relaxation, and:


wherein p2 is a surface relaxivity, S is a surface area of pores in the tight rock formation region (12), Vis a volume of the pores, and S!V is a surface-to-volume ratio of the pores.

14. The method (60) of claim 13, wherein the direct correlation is based on a relationship between the pore diameter and the surface-to-volume ratio, and a relationship between the fracture aperture size and the surface-to-volume ratio.

15. The method (60) of claim 10, wherein the fracture aperture size distribution (80, 82, 84, 86) is calculated in real time and the method further comprises providing a real time assessment of productivity of the tight rock formation region (12).