Laboratory Determination of Fluid Saturations .

Conventional Core Analysis Two common methods will be discussed Retort Distillation Solvent Extraction

Retort Distillation Apparatus Core sample Heating element 1000-1100 F Cooling water in Using this technique, the water and oil saturation can be measured directly. Procedure: Heat small sample of rock Water vaporizes first at lower temperature (212º F), The sample temperature remains at 212º F until all pore water is vaporized. After Water is vaporized, the retort temperature increases to 1000-1100 º F vaporizing oil. Both water and oil are condensed into a graduated cylinder Record volumes of water and oil vs time Correct volume of oil for coking and cracking effects Determine volume of water from pores (not counting water of crystallization from clays) Determine saturations volumetrically Cooling water out Condenser Graduated Cylinder

Retort Distillation Method Advantages Rapid (less than one hour) Direct measurement of both oil and water volumes recovered Adequate accuracy

Retort Distillation Method Disadvantages High temperatures (1,000 - 1,100 F): destroys core sample water of crystallization in clays may vaporize – and must be accounted for cracking and coking of oil cracking is breaking of long chain hydrocarbons into smaller chain hydrocarbons, which may not be recondensed coke is impure carbon residue formed from oil

Determining Water of Crystallization Water from pores is recovered first If flattening of curve is not apparent then estimating water recovered from pore space can be innaccurate Later, water of crystallization is recovered at higher temperatures This is destroys the core sample

Effects of Coking and Cracking of Oil Coking and cracking tend to cause only part of oil from pores to be recovered We must scale up the volume of recovered oil to reflect the volume of oil originally in the pores Scaling factor depends on API gravity of oil Coke formation destroys core sample Retort Distillation: Scaling Factor for Recovered Oil

Retort Distillation Calculations Vw = Volume of water, cm3 Vo = Volume of oil, cm3 Vp = Pore volume, cm3 Fcorrection = Volume correction factor, dimensionless

Solvent Extraction Apparatus Condenser Using this technique the water content is measured directly and oil content is measured indirectly from the change in weight Procedure Weigh fresh core sample Apply heat - water in pore space of core vaporizes, then condenses in the condenser and falls into the trap where water volume is measured Boiling point of solvent must be higher than the boiling point of formation water Heating rate must be high enough to ensure that condensation of water occurs in the condenser, so that water falls into the trap Solvent leaches hydrocarbons from the pore space and oil remains in dissolved in the solvent Dry core Re-weigh core Graduate tube Thimble and core Solvent Electric Heater Modified from Amyx, Bass and Whiting, 1960

Solvent Extraction Method Advantages accurate determination of water saturation non-destructive to core samples determination of water saturation by solvent extraction can be made part of the core sample cleaning process for small incremental cost

Solvent Extraction Method Disadvantages slow (can take several days) oil volume not directly measured oil remains in solvent

Solvent Extraction Calculations Wi = Initial core weight, gm Wdry = Core weight after leaching, gm Vw = Volume of water collected, cm3 Vo = Volume of oil, cm3 Vp = Pore volume, cm3 w = Density of water, gm/cm3 o = Density of oil, gm/cm3 g = Density of gas is assumed negligible