NMR and Carbonates

1. Forward Modelling NMR Log Response Using the Carbonate Rock catalogue Adam Moss, ResLab ART Simon Stromberg, Reservoir Management Ltd

3. NMR Interpretation Data (T2 Distribution) 0.1 1.0 10.0 100.0 1000.0 10000.0 Rock Bulk Volume Rock Matrix Clay Clay bound water Total Porosity Effective Porosity Capillary bound water Free water Hydrocarbons Minerals T2 cutoff NMR is unique it measures total porosity and can be partitioned into pore-size and fluid component

5. Hydrocarbon effect on T2 distribution 100% Brine Saturated Water wet with oil Producible water (free fluid) Bound fluid (irreducible water) Producible hydrocarbon (free fluid) Bound fluid (irreducible water) T2 increases since hydrocarbon Is not limited by pore-size T2 is limited by pore size in 100% Sw rocks

6. CPMG pulse sequence f s s s s s s f f f f f 90  180  180  180  echo echo 90  180  180  180  180  180  180 

7. The echo-train of a complex system, e.g. fluid in pore system, comprises many exponential decays. Time Domain T 2 Domain INVERSION Magnetization amplitude T 2 amplitude Time (ms)

10. Chalk NMR and Mercury Injection Open Forams Matched Peaks

11. Diagenetic Chalk NMR and Mercury Injection Large Pores Matched Peaks

12. Microcrystalline Dolomite NMR and Mercury Injection Surface irregularities possibly associated with fractures Matched Peaks

13. Oolites NMR and Mercury Injection Large pores are genuine rock features, seen in BESI. Intergranular pores associated with ooids Matched Peaks

14. Vuggy Dolomite NMR and Mercury Injection Large pores are genuine rock features, seen in BESI. Intergranular pores assoc. with ooids Diffusion Diffusive pore coupling

15. Analogue Data (Carbonate Rock Catalogue) chalk Diagenetic chalk Microcryst Dolomite Oolite Sucrosic dolomite Vuggy Dolomite

18. NMR Logs

19. Analogue Data (Carbonate Rock Catalogue) chalk Diagenetic chalk Microcryst Dolomite Oolite Sucrosic dolomite Vuggy Dolomite

21. Inversion T 2 x T 2 y T 2 z

22. Inversion T 2 x T 2 y T 2 z T 2 x T 2 y T 2 z T2x, y and z are T2 bins, or if scaled to pore size, pore size bins. Height of column is pore volume

23. Modelling T 2 x T 2 y T 2 z T 2 x T 2 y T 2 z T2x, y and z are T2 bins, or if scaled to pore size, pore size bins. Height of column is pore volume

25. Fluid modelling: Fluid and T2 bulk relaxation Oil viscosity and T2 (150 degF) Density of gas (150 degF)

26. Density and diffusion coefficient of gas 150 deg F

28. Spectral Bound Fluid Model Bound fluid = Capillary bound + Surface film b W = f(T2) Carbonate Model: m = 0.0113; b = 1.

29. Fluid Substitution Method Spectral bound fluid = Swirr 2. Remove free-fuid (water) 3. Add in free fluid water so that T2LM of free fluid = T2 predicted for hydrocarbon 1.

30. Modelling Example 1: Optimising Inversion of Log Data Inversion: SVD T1 min = 0.3 T2 max = 3000 No Bins = 30 T2 maximum is not long enough to capture Long T2 associated with carbonate Analogue Model Inversion

31. Modelling Example 1: Optimising Inversion of Log Data Inversion: SVD T1 min = 5 T2 max = 5000 No Bins = 30 Analogue Model Inversion New bin range better captures the full T2 spectrum

32. Modelling example 2: Fluid Substitution 3 CP Oil T2 = 1130 msec (150 deg F) Analogue Model Inversion Fluid Sub

33. Modelling Example 3: Decreased Wait Time (1 sec) Analogue Model Inversion Fluid Sub Tw = 1 sec Lost porosity With Tw = 1 sec