USC_Sec_6_SP_Log_doc

USC_Sec_6_SP_Log_doc - University of Southern California...

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University of Southern California Department of Petroleum Engineering Fall, 2007 PTE-461 Formation Evaluation Section 6: Spontaneous Potential Donald G. Hill, Ph.D. California Registered Geophysicist 170 California Registered Geologist 6043 Kentucky Registered Professional Geologist 1624 Texas Licensed Professional Geophysicist 6289 Consulting Petrophysicist: Petrophysics, Shallow Geophysics, Borehole Geophysics, and Subsurface Geology Planning, Oversight, and Interpretation 1012 Hillendale Ct +(925) 437-5748 Cell Walnut Creek, CA +(309) 420-7354 FAX USA 94596 +(925) 947-1541 Home http://www.hillpetro.com <dgh@hillpetro.com>
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USC PTE-461, Basic Petrophysics - Fall, 2007 Section 6: Spontaneous Potential Donald G. Hill, Ph.D., R.Gp, R.G., R.P.G., L.P.Gp. Page: 6-2 dgh@hillpetro.com Table of Contents Subject Page Introduction 6-4 Electrolytes 6-4 Spontaneous Potential 6-6 Measurement of SP 6-6 Historical Background 6-8 SP Mechanism 6-9 Generalized Thermodynamics of Coupled Flows 6-9 Dissociation of Electrolyte Salts in Water 6-12 Clay Minerals 6-12 Electro-Chemistry of the Double Layer 6-13 Streaming Potential 6-14 Membrane Potential 6-15 Junction Potential 6-18 SP R w Epilog 6-19 The SP as a Sand/Shale Indicator 6-20 Linear V sh Model 6-20 The Bi-Modal Model and SP V sh 6-20 SP Log Shale Volume Disclaimer 6-21 References 6-22 Vendor Websites 6-28 Other Websites 6-28 Tables No Tables Figures Figure 6.1: Equivalent Conductivities of Some Uni-Valent Electrolytes in Very Dilute Solutions at 25°C 6-5 Figure 6.2: Temperature-Resistivity-Salinity Chart for NaCl Solutions 6-6 Figure 6.3: NaCl Equivalent Multipliers for Common Oil Field Brine Ions 6-7 Figure 6.4: Schematic Rendering of Spontaneous Potential Measurement 6-7 Figure 6.5: Borehole Streaming Potential, Due to Pressure Differences Between the Mud and Formation Across the Mud Cake 6-8 Figure 6-6: Membrane Potential due to Salinity Differences between the Mud Filtrate and Formation Waters, Across a Low Permeability Material 6-9 Figure 6.7 Schematic Representation of Dissociation of NaCl in Water 6-12 Figure 6.8: Schematic Representation of Bound Water Molecules and Formation of the Helmholtz Double Layer in Water Adjacent to a Clay Mineral Surface 6-12
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USC PTE-461, Basic Petrophysics - Fall, 2007 Section 6: Spontaneous Potential Donald G. Hill, Ph.D., R.Gp, R.G., R.P.G., L.P.Gp. Page: 6-3 dgh@hillpetro.com Figure 6.9: Schematic Representation of a Pore Throat Completely Filled by the Helmholtz Double Layer Forming a Cation Selective Membrane 6-14 Figure 6.10: Schematic Representation of a Pore Throat, Lined with Clay Minerals and their Double Layers 6-14 Figure 6.11: Schematic Representation of SP Development Due to Mud Filtrate Less Saline than Formation Waters 6-15 Figure 6.12: Liquid Junction SP Mechanism 6-15 Figure 6.13 Borehole Model and Analogue Circuit 6-16 Figure 6.14 Nomograph for Nernst Equation Interpretation of SP Anomalies 6-17 Figure 6.15 R w /R weq (R mf /R mfeq ) Conversion Chart 6-18 Figure 6.16 Bi-Modal Grain Size Model 6-19 Figure 6.17 Sieve Analysis for a Recent Gulf Coast Shaly Sand Interval, with Two Dominant Grain Sizes 6-20 Figure 6-18 Total and Effective Porosity for a Bi-Modal grain Size Shaly-Sand Model with Ø sd - Ø sh = 40% 6-21
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USC_Sec_6_SP_Log_doc - University of Southern California...

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