1. Fluid SaturationsIntroduction

2. Fluid Saturations Definition - The fluid saturation for a particular fluid is thefraction of pore volume occupied by that fluid; H2O, oil or gas Fluid saturation = total volume of the fluid phasepore volume Saturation is an intensive property Equation Form: So=Vo/Vp, Sw=Vw/Vp, Sg=Vg/Vp These fluid volumes are measured under specific conditions of pressureand temperature (e.g. reservoir, or laboratory) reservoir conditions are often noted as in situ 3. Fluid Saturations Fundamental Relationships Pore volume is occupied by fluids (water, oil, and/or gas)= + +S S Sw o g= + +V V V Vp w o g+ +V V Vw o gVp1= for the two phase case, only one of the two saturations isindependent, the other must make the sum of the saturations equalto unity (1) similarly, for the three phase case, only two saturations areindependent 4. Fluid Saturations Fundamental Relationships (continued) Mass of fluids in the pore volume is comprised of: water,oil, and/or gas= + +fluidmass m m mw o g= + + V V Vw w o o g gp [ w w o o g g ]= + +V S S S at laboratory conditions it is often assumed that gas density isnegligible 5. Initial Fluid Saturations in Reservoir Concepts: typical petroleum accumulation scenario pores are initially saturated with water (Sw=1) hydrocarbons migrate up dip into traps due to havingdensity less than water density (gravity force) hydrocarbons (oil and/or gas) is distributed such thatgravity and capillary forces are in equilibrium minimum interstitial water saturation remains in hydrocarbon zone,even after accumulation occurs water wet, drainage accumulation process irreducible wetting phase saturation oil wet, imbibition accumulation process residual non-wetting phase saturation 6. Initial Fluid Saturations in Reservoir Methods for determination of reservoir fluid saturations Direct Measurement Core Analysis of samples obtained from the formation of interest intheir original state and measure saturations directly is ideal. Indirect Measurement Capillary Pressure Measurement Well Log Analysis electrical conductivity depends primarily on water saturation 7. Fluid Saturations - Core Analysis Factors affecting fluid saturations in cores flushing of core by filtrate from drilling fluids (especially foroverbalanced drilling) water filtrate water based mud oil emulsion mud oil filtrate oil based mud inverted oil emulsion mud gas filtrate air drilling foam drilling 8. Fluid Saturations - Core Analysis Factors affecting fluid saturations in cores (continued) Changes in pressure and temperature as core sample isbrought from bottomhole conditions to surface conditions Example: Oil zone at minimum interstitial water saturation,water based drilling mud 9. Application of Core Saturations Application of Core Saturations: Water Based Mud presence of oil zone original oil/gas contact original oil/water contact Application of Core Saturations: Oil Based Mud fairly accurate minimum interstitial water saturation original oil/water contact Other Applications of Core Saturations correlation of indirect methods 10. Estimating Fluid Contact Depths from CoreSaturationsSoGasOilWater0 50DepthSo 0 in gas zoneSo > 0.15 in oil productionzone0 < So < 0.15 in waterproduction zone 11. Maximum Water Saturationfor Oil and Gas ProductionThe trend shown herecontinues for even lowerpermeability, with productivereservoirs existing withSw>0.60 for k