Saturation • Volume of phase to pore volume • Wettability • Tortuosity • Mobile vs immobile 1) Swir -irreducible water saturation, below which water cannot flow. 2) Swc -connate water saturation existing on discovery of the reservoir. It may or may not be irreducible. 3) Swi -may mean irreducible, connate, or interstitial, which means saturation among the interstices, or pores. Interstitial may or may not signify irreducible. It may be the value on discovery of the reservoir, or the value at any time thereafter. Swi may also mean initial or original, which truly means the water saturation on discovery, but it may or may not be irreducible.Saturation Saturation distribution in a reservoirSaturationFactors affecting fluid saturations • Fluid invasion • Release of confining pressure • Thermal affectsFactors affecting fluid saturationsFactors affecting fluid saturations Influence of mud type on saturations Oil67.6%Wtr32.4%Oil53.4%Oil26.7%67.6%Wtr46.6%Wtr38.5%Gas34.8%OriginalAfterflushingAtsurfaceWater-based Muds Oil50.9%Wtr49.1%Oil32.9%Oil26.7%Wtr49.1%Wtr47.7%OriginalAfterflushingAtsurfaceOil-based MudsFiltrate18%Gas 25.6%Measurement of Fluid Saturation 1. Retort method - evaporation of the fluids in the pore space 2. Dean-Stark extraction method - the leaching of fluids in the pore spaceMeasurement of Fluid Saturation Retort method • sample is sealed inside an aluminum cell and then heated in stages from 400 F to 1100 F • Advantages: fast, multiple samples run Picture of a conventional retort [CoreLab,1983]Measurement of Fluid Saturation Disadvantages of Retort method Retort oil correction curve [CoreLab, 1983] Retort water calibration curves [CoreLab,1983] • Coking effect - heating process burns oil to the pore surfaces. • results in oil recovery less than the initial amount in the sample. • Empirical correction • removal of both pore water and water of crystallization. • Results in high water recovery Volume of water in pores Crystallized waterMeasurement of Fluid Saturation Dean-Stark extraction method • vapor of a solvent rises through the core and leaches out the oil and water. • water condenses and is collected in a graduated cylinder. • solvent and oil continuously cycle through the extraction process. • A typical solvent is toluene, miscible with the oil but not the water. • Advantage: accurate • Disadvantage: long time o*pVwtrWdryWwetWoSMeasurement of Fluid Saturation Example of Dean-Stark extraction method to determine saturations • Obtain the mass of the saturated sample = 57 gms. • Determine the bulk volume by nondestructive means = 25 cc • Determine the oil density = 0.88 gm/cc • Place the sample in the extraction apparatus and heat the solvent. Record the volume of water collected and when the reading becomes constant – stop. Vw = 1.4 ml • After cooling, remove the core and dry, obtain dry weight = 53 gms. • Using the saturation method, resaturate the sample with fresh water ( = 1.00 gm/cc) and weigh. = 58 gms.Measurement of Fluid Saturation Example of Dean-Stark extraction method to determine saturations • Calculate the pore volume and porosity, • Calculate the water saturation • Calculate the oil saturation • Calculate the gas saturation %20255cc500.15358pV%2854.1wS %5988.0*500.1*4.15357oS %1359.028.01gS