USE OF NMR FOR ROCK TYPING

Transcription

1 USE OF NMR FOR ROCK TYPING MARC FLEURY S.A.I.D. 29 novembre 26

2 VARIOUS CONCEPTS OF CLASSIFICATION Rock typing eefal rock Leached channels in r Particle diameter = 5 Particle diameter = 3 Particle diameter = Moldic grainstone Flow units Permeability, md. Grainstone, pore diameter declining Vuggy dolomite Wackestone Packstones, Lime mud Coccolith chalk pore diameter <. Wackestones Mudstones 2 Porosity, % Fractures Compaction and cementing 3 Leaching Facies, electrofacies Main objective: link permeability with some measurable log quantity 2 2

3 BACKGROUND: NUCLEAR MAGNETIC RESONANCE MEASUREMENTS Measured: M(t) t M ( t) Ai exp( i T 2i ) M(t) Excitation (B pulse) Temps Time Distribution (a.u.) Origin of magnetization: nuclear spins Water volume... Relaxation times T 2 (s) Inverse Laplace transform: calculate amplitude A i 3 3

4 BACKGROUND: NMR AND PORE SIZE not dependant on shape fbulk=-es/v f surf bulk T 2 T 2 surf T 2 bulk f T e T 2bulk 2surf S V V S r 2 : surface relaxivity fsurf= es/v e T 2 T 2B r 2 S V 4 4

5 BACKGROUND: NMR AND PORE SIZE (LAB. AND LOG) r S V 2 T2 T2 Bulk nm pore sizes between. and ms Pore size V/S (micron) Fast diffusion limit 4r 2 V/S << D r 2 = m/s r 2 = m/s T 2b Measured T 2 (ms) log lab 5 5

6 NMR PERMEABILITY EQUATIONS Timur, 968 Sandstones 6 6

7 GENERAL APPROACH FOR PERMEABILITY (WBM) kw a T 2 F b T 2 is a characteristic pore size T 2peak, T 2ml, T 2matrix.. a and b must be adjusted using lab. measurements permeability is obtained at best within a factor of 2 it is not a direct method 7 7

8 INTERPRETATION OF NMR FOR ROCK TYPING: CONDITIONS bitumen water Water-based mud Non viscous oil in place 8 8

9 SANDSTONES Unité arbitraire Clay Intergranular porosity Porosité cumulée (%) Obtained: - dominant pore size - water associated with clay Useful and robust information 5 E+ E+ E+2 E+3 T2 (ms) 9 9

10 EXAMPLE: SHALY SANDSTONES.3 Cluster.2 Cluster Cluster 3.2 Cluster

11 CARBONATE SYSTEM Kw (md),,,,2,3,4,5 Porosity kw RRT kw RRT2 kw RRT3 kw RRT4 kw RRT5 kw RRT6

12 CARBONATE: NMR SIGNATURE AND PERMEABILITY k=2 md F=.27 k=.5 md F=.5 k=68 md F=.29 k=267 md F=.28 T2 (ms) 2 2

13 NMR SIGNATURE VS. ROCK TYPE RRT RRT2 RRT3 RRT4 RRT Normalized amplitude Normalized amplitude Normalized amplitude Normalized amplitude Normalized amplitude T2 (ms) T2 (ms) T2 (ms) T2 (ms) T2 (ms) 3 3

14 NMR PERMEABILITY RELATIONSHIP Same set of sample 4 4 kw (md) 3 2 kw (md) kw estimate (md) T2 peak (ms) In carbonate, porosity may be a poor indicator of permeability 4 4

15 LINK BETWEEN NMR AND MERCURY INJECTION Microporosity: MICP limit: 2 m NMR limit: 2 ms Vincent et al. Applied Geophysics 2 5 5

16 LINK BETWEEN NMR AND MERCURY INJECTION Mesoporosity 6 6

17 LINK BETWEEN NMR AND MERCURY INJECTION Conclusion: micro-macro porosity limit of 2 ms Mesoporosity not evidenced by NMR 7 7

18 NMR-MERCURY INJECTION COMPARISON CRE Estaillade.9.8 NMR r 2 = 3.2 m/s Rapport des modes: r 2 = 5 m/s Rapport des modes: V/S, d HG ( m) V/S, d HG NMR surface relaxivity calibrated by BET surface ( m) 8 8

19 EXCEPTIONS Bimodal Unimodal Pore coupling effect Unimodal Bimodal Pore structure effect 9 9

20 NMR ROCK-TYPING IN SHALES? NMR cryoporometry P * ds/dp Mercury injection (sister plug) Pore entry diametre ( m) NMR T 2 relaxation (same sample) Diffusive pore coupling effect Problem: due to pore coupling effects, NMR is more representative <V>/<S> than a distribution of V/S 2 2

21 STUDY OF A CAPROCK (METHANE STORAGE) Still possible to find K-T2 relationship but small range of variation 2

22 CONCLUSION NMR data can provide information for rock typing/zonation in many situations Sensitive to pore size Can be a good indicator of permeability even in carbonates Cannot be performed without laboratory validation Some exceptions exist But rock typing studies using mainly NMR are not common (?) 22

23 Find us on: I F P E N

24 NMR AND PERMEABILITY: FONTAINEBLEAU SANDSTONE D/Dm Fontainebleau F Kw=64 md phi=.55 A=.88 S/V=.4 Lc=5.4 r 2 [ m/s] Ld (micron) 5. V/S (micron) Fontainebleau Kw (md) Small variation of V/S 24

25 25 NMR PERMEABILITY AND WTLOG