An Evaluation of the Application of Low Field NMR in the Characterization of Carbonate Reservoirs

Abstract

ACKNOWLEDGEMENTS iv LIST OF FIGURES ix LIST OF TABLES xi 24 4.0 NMR APPLICATIONS 4.1 Pore size distribution 4.2 Porosity 27 4.3 Bound and free fluid fractions 30 4.4 Permeability 4.4.1 Free Fluid model 34 4.4.2 Mean T 2 (SDR) model 5.0 PROCEDURE 38 vi 5.1 Sample preparation 38 5.2 Air permeability 39 5.3 Gas expansion 41 5.4 Brine saturation 42 5.5 Brine permeability 44 5.6 NMR measurements 45 5.7 Computerized Tomography (CT) scanning 47 5.8 Centrifuging 48 6.0 POROSITY DETERMINATION 49 6.1 Porosity measurements 49, 6.1.1 Gas expansion 49 6.1.2 Archimedes principle 49 6.1 .3 NMR 51 6.1.4 CT (wet cores) 53 6.1.5 CT (dry cores) 56 6.2 Porosity comparisons 6.2.1 NMR porosity at d i fferent echo spacings 6.2.2 Brine saturation and gas expansion 6.2.3 NMR and brine saturation 6.2.4 NMR and gas expansion 6.2.5 CT (wet) and gas expansion 62 6.2.6 CT (thy) and gas expansion 63 6.2.7 CT (wet) and CT (thy) 63 7.0 EVALUATION OF IRREDUCIBLE WATER SATURATION (55 7.1 Investigation of end effects 65 7.2 S,j determination from mass balance 68 7.3 S determination from NMR 71 7.4 S,j comparison between mass balance and NMR 72 8.0 DETERMINING CORRELATIONS TO ESTIMATE IRREDUCIBLE WATER SATURATION 75 8.1 T2toff determination 75 8.2 Relationships between T2utoff and characteristics of NMR spectra 79 8.3 Relationships between S wi and characteristics of NMR spectra 87 9.0 DETERMINATION OF VUGGY AND NON-VUGGY POROSITY 91 9.1 Vuggy and non-vuggy porosity determination 9.2 Observed relationships between various parameters vii 92 96 10.0 PERMEABILITY 10.1 Air and brine permeability 10.2 Permeability models 10.2.1 Evaluation of existing permeability models using NMR data 10.2.2 Development of a new permeability model 12.0 CONCLUSIONS AND RECOMMENDATIONS 12.1 Conclusions 114 11.2 Recommendations 116

Application of NMRT2to Pore Size Distribution and Movable Fluid Distribution in Tight Sandstones

“…However, tight sandstones have more pores with a large pore throat ratio, resulting in poor reservoir connectivity. − Hence, a new approach to obtain C is essential for transforming NMR T 2 into PSD. In addition, movable fluid percentage is a critical parameter to evaluate formation flowability, which is always obtained by the empirical value of T 2cutoff based on NMR tests and centrifugations. ,,,− And predecessors are always focused on sandstone and carbonate in earlier research. , However, the pores and throats in tight sandstones are in micronano degrees, and traditional methods may not be applicable. Therefore, the research of movable fluid percentage for tight sandstones is greatly urgent.…”

“…21,23,26,30−36 And predecessors are always focused on sandstone and carbonate in earlier research. 35,36 However, the pores and throats in tight sandstones are in micronano degrees, and traditional methods may not be applicable. Therefore, the research of movable fluid percentage for tight sandstones is greatly urgent.…”