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Electrical Properties of Reservoir Rocks

Electrical Properties of Reservoir Rocks. DETERMINING FLUID SATURATIONS. Conventional core analysis Capillary pressure measurements Well log analysis. Methods of Determining Saturations. Well Log. SP. Resistivity. OPENHOLE LOG EVALUATION. Most abundant data for formation evaluation and

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Electrical Properties of Reservoir Rocks

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  1. Electrical Properties of Reservoir Rocks

  2. DETERMINING FLUID SATURATIONS • Conventional core analysis • Capillary pressure measurements • Well log analysis Methods of Determining Saturations

  3. Well Log SP Resistivity OPENHOLE LOG EVALUATION Most abundant data for formation evaluation and determination of fluid saturations From NExT, 1999

  4. RHOMBIC PACKING OF SPHERES • Electrical properties of reservoirs vary strongly with porosity and characteristics of the fluids in the pore space; usually, basic properties are determined assuming: • “clean” reservoir rock (non-shaly) • Sw = 1.00 (water saturated rock)

  5. RESISTIVITY • Resistivity • Resistivity is an intensive rock/fluid property, and is a measure of (the inverse of) the electrical flow capacity of the rock • Resistance is extensive and for linear, 1-D electrical flow, r=(R ·L)/A • r electrical resistance,  • R electrical resistivity, ·m • L length of electrical flow path, m • A cross-sectional area perpendicular to electrical flow path, m2

  6. RESISTIVITY – DEFINITION OF THE OHM-METER From Halliburton (EL 1007)

  7. RESISTIVITY • Resistivity • Resistivity is determined by measuring the voltage required to pass a measured amount of electrical current through the rock. • For a rock cube with sides of 1 m, if electrical potential of 1 V (Volt) is required for current flow of 1 A (Ampere), then resistivity is 1 ·m (Ohm ·meter)

  8. RESISTIVITY • Resistivity • Electrical resistance () is inverse of Electrical conductance (S, Siemens) • 2  = (1/2) S • Resistivity is the inverse of conductivity • 2 ·m = (1/2) S/m

  9. RESISTIVITY OF EARTH MATERIALS (1) Rock (2) Gas (3) Oil (4) Fresh Water (5) Salt Water Resistivity Conductivity Common Notations • Ro = Resistivity of non-shaly rock saturated (Sw=1) with formation water (ohm-m) • Rt = True formation resistivity (ohm-m) • Rw = Formation water resistivity (ohm-m) From J. Jensen, PETE 321 Lecture Notes

  10. ELECTRICITY AND EARTH MATERIALS • Primarily, conduction is by ions in water • Na+ and Cl- are very common • Other monovalent ions K+ and OH- • Bivalent ions, too: Ca++, Mg++ • But, clays can conduct electricity also Modified from J. Jensen, PETE 321 Lecture Notes

  11. Electricity and Earth Materials • Water resistivity controlled by • Ion concentrations • Type of ions • Temperature • Chart GEN-4 to convert to NaCl equiv • Chart GEN-5 for temp/resist for NaCl From J. Jensen, PETE 321 Lecture Notes

  12. Factors Affecting Electrical Resistivity • Resistivity of water • Porosity of the formation, • Pore geometry - tortuosity • Lithology of the formation • Degree of cementation, and • Type and amount of clay in the rock From J. Jensen, PETE 321 Lecture Notes

  13. (1) Rock (2) Gas (3) Oil (4) Fresh Water (5) Salt Water Increasing Resistivity Increasing Conductivity Saturation Equation Rock containing pores saturated with water and hydrocarbons Formation Factor Equation Non-shaly rock, 100% saturated with water having resistivity, Rw Rt Cube of water having resistivity, Rw • = 20% Sw = 20% Ro • = 20% Sw = 100% Resistivity Rw • = 100% Sw = 100%

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