Tim CarrGeology 493Reservoir PropertiesReservoir PropertiesGeol472-2009Porosity and PermeabilityPorosity and Permeability• Porosity: % of void space in rock• Permeability: Ease of fluid flow Porosity and PermeabilityPorosity and PermeabilityPorosityPorosity0.5 mmVolume % of open spacePorosityPorosity• Total Porosity (%)• Porosity (Ø)= (bulk volume – grain volume)/bulk volume• Effective Porosity= Interconnected poresTraditional View of Porosity• 0-5% Negligible• 5-10% Poor• 10-15% Fair• 15-20% Good• 20-25% Very GoodFor gas lower porosity is still viableHydrofracturing makes low porosity less of a problemTim CarrGeology 493Primary PorosityPrimary Porosity–Controlled by:• Degree of Uniformity of Grain Size–Sorting• Shape of the Grains• Method of Deposition (Manner of Packing)• Compaction• CementationSortingSortingPoor SortingIntermediate SortingMORE POROUSLESS POROUSWell SortedWell SortedSandSandPoorly SortedPoorly SortedSandSandPorosity Porosity Varies withVaries withSortingSortingPackingPackingCubic Packing 47% porosity in the ideal situationPackingPackingRhombohedral Packing 26% porosity in the ideal situationSecondary PorositySecondary Porosity–Additional open space developed after sedimentation:• Dissolution• Dolomitization• FracturingTim CarrGeology 493Modifications to PorosityModifications to PorositySandstone• Pressure Solution• Cementation• Fracturing– Carbonate• Compaction – 2 to 20%• Solution• Recrystalization – Dolomitization• Fracturing• Cementation– Shale• Compaction – 50%• Bound Water ExpulsionFigure 13.7MORE POROUS LESS POROUSFractured ShaleFractured ShaleUnfracturedUnfracturedShaleShalePorosity Porosity Varies withVaries withFracturingFracturingPorosity Porosity Varies with %Varies with %CementCementSecondary PorositySecondary Porosity2 mmQuarts GrainQuartz cementDissolvedFeldsparWilcox Fm. South TexasDolomitizationDolomitizationCalcite (CaCO3)Antrim Fm. MichiganDolomite CaMg (CO3)2Volume decrease leads to newporosityShaleShaleWet Mud Compacted Sediment(water expelled)Cemented ShaleTim CarrGeology 493ShaleShaleMicrophotographShaleShalePorosityPore sizePorePoreThroatThroatPermeabilityPermeability• Ability to Transmit Fluids• Measure in Darcies or Millidaricies• Permeable– Large Well-Connected Pores• Impermeable– Smaller, Fewer or Less Interconnected PoresDarcy EquationDarcy Equation1 Darcy = 1cm2of Surface Releases 1cm3of Fluid of Unit Viscosity in 1 SecondViscositypermeabilityPermeability Values•1-10 md Fair• 10-100 md Good• 100-1000 md Very goodMd = millidarciesTim CarrGeology 493Permeability Measurements• Porosity can be measured by logs (density, neutron)• Perm. needs cores to do lab injection testsPorosity vs. PermeabilityPorosity vs. PermeabilitySussex SandstoneCapillary PressureCapillary PressureCapillary PressureCapillary PressureSt. Louis Capillary PressureSt. Louis Capillary PressureRelative PermeabilityRelative PermeabilityOilWaterTim CarrGeology 493Buoyancy vs. Capillary PressureBuoyancy vs. Capillary PressureDifferential Entrapment of Oil & GasDifferential Entrapment of Oil &