INTRODUCTION

A hydrocarbon solvent that is insoluble in water is used to leach the fluids from a saturated rock. A special graduated receiving tube may be used to collect the extracted water, thus providing a direct measurement of the water saturation (Figure A2.1). Once the water saturation is known, the oil saturation may be calculated from indirect gravimetric measurement of the rock. The gas saturation is then obtained indirectly by difference because:

Figure A2.1: Equipment for measurement of water saturation by solvent extraction

After extraction of the fluids and drying, the cleaned core may be used for measurement of other petrophysical properties and quantities (permeability, porosity, sieve analysis, mineral grain density, etc).

The boiling point of the hydrocarbon fluid used for the extraction must be higher than the boiling point of water and preferably lower than the boiling point of the hydrocarbons in the core (toluene is the most frequently used solvent: BP = 110.6 C). When the boiling point of the solvent is higher than 212 F (100 C), water vaporizes from the core and travels upward within the rising solvent vapors. The vapors (solvent plus water) are condensed and collected in a side receiver where the water is trapped at the bottom of the tube because its density is higher than the density of the solvent. The excess solvent drains back into the boiling pot where it is reheated to continue the process of extraction.

The crude oil that was originally a part of the core fluids will dissolve in the...