Addassi, Mouadh

Alam, Mohammad Monzurul

Fabricius, Ida Lykke

Katika, Konstantina

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Differences in the Texture of Chalk as observed by NMRKatika, Konstantina; Addassi, Mouadh; Alam, Mohammad Monzurul; Fabricius, Ida LykkePublication date:2014Link back to DTU OrbitCitation (APA):Katika, K., Addassi, M., Alam, M. M., & Fabricius, I. L. (2014). Differences in the Texture of Chalk as observedby NMR. Poster session presented at 12th International Bologna Conference on Magnetic Resonance in PorousMedia, Wellington, New Zealand.Acknowledgement The financial support from DONG energy, Maersk oil, Danish energy agency and DTU is gratefully acknowledged.   Differences in the Texture of Chalk as observed by NMR  Konstantina Katika, Mouadh Adassi, M. Monzurul Alam and Ida Lykke Fabricius  In this study, three cases under investigation illustrate how changes in the surface-to-volume ratio of chalk affect the low-field Nuclear Magnetic Resonance signal: 1. Outcrop chalk  saturated with high  salinity brine showed  that saturation with  divalent ions can  cause major shifts  in the T2 curve. Low field NMR was successfully used to identify changes in the surface-to-volume ratio. Samples with high surface-to-volume ratio result in smaller relaxation times. Samples saturated with Mg-rich brines, brines containing precipitants, and chalk with different texture illustrate this.       2. Fluid samples  where precipitation  reactions caused  shifts in the T2 curve due to the  creation of crystals within the fluid.  3. Two types of chalk  with different  surface-to-volume  ratio, saturated with  the same brines  produced different NMR signals. NMR Signal Relaxation Time Long distance from the pore walls means long decay times. NMR Signal Relaxation Time In smaller distances, NMR relaxation is affected by the solid.  NMR signal decay time (known as relaxation) is affected by the solid phase:  NMR Relaxation in the homogenous system of brine saturated chalk: NMR Signal Relaxation Time  Dry solid (water film) NMR Signal Relaxation Time Liquids  NMR Signal Relaxation Time Exponential inversion Amplitude T2 (ms)  Outcrop chalk with low surface-to-volume ratio saturated with divalent ions:  Brines that contain precipitants after contact with chalk:   Outcrop chalk with high surface-to-volume ratio saturated with divalent ions: • Austad, T. et al., Seawater in Chalk: An EOR and Compaction Fluid, SPE Reservoir Evaluation and Engineering, 11 (4), 648-654, (2007). • Katika et al., Nuclear magnetic resonance and sound velocity measurements of chalk saturated with magnesium rich brine, Poromechanics V, 678-684, (2013).  • Kenyon, W. E., Petrophysical principles of applications of NMR logging: Log Analyst, 38, 21-43, (1997). • Madland M. V. et al., Chemical Alterations Induced by Rock-Fluid Interactions When Injecting Brines in High Porosity Chalks,  Transp Porous Med, 87, 679-702, (2011).  030006000900012000150001800010 100 1000Amplitude (m.u) T2 (ms) T2 Distribution of chalk saturated with divalent ions saturation with  MgCl2 solution saturation with CaCl2 and Na2SO4 solution saturation with Deionized Water and NaCl solution 030006000900012000150001800010 100 1000Amplitude (m.u) T2 (ms) T2 Distribution of chalk with high vs. low  surface-to-volume ratio 0500010000150002000025000300003500040000100 1000 10000Amplitude (m.u) T2 (ms) T2 Distribution of solutions that contain precipitants Deionized WaterMagnesium Chloride solutionCalcium Chloride solutionParameter ST-Samples Porosity (%) ~42 Grain density (g/cm3) ~2.71 Permeability (mD) ~6 Carbonate content (%) ~99 Specific surface (m2/g) ~1.7 Specific surface of the IR (m2/g) ~50 Surface relaxivity (μm/s) ~0.9 Parameter MA-Samples Porosity (%) ~38 Grain density (g/cm3) ~2.70 Permeability (mD) ~5 Carbonate content (%) ~99 Specific surface (m2/g) ~1.6 Specific surface of the IR (m2/g) ~70 Surface relaxivity (μm/s) ~1.5 Brines with precipitants Concentration (g/L) Magnesium chloride solution 58.1 Calcium chloride solution 67.7  Transverse relaxation rate, 1/T2 :    ρ: surface relaxivity S/V: surface-to-volume ratio  Differences in the rock texture  Precipitants within the pore space  Variations in the bound water thickness  may affect the transverse relaxation time by altering the surface relaxivity or the surface-to-volume ratio in the following equation:    as observed from the following results: low S/V high S/V 

Differences in the Texture of Chalk as observed by NMR

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Differences in the Texture of Chalk as observed by NMR

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