Determination of Initial Fluid Saturations Using Traced Drilling Media

Initial saturations of hydrocarbons and water, that exist in porous media, control reserves in place and, in many cases, the deliverability/recovery of these reserves. Hence, their accurate determination is essential for proper economic and reservoir engineering evaluation and optimization. Electric logging techniques are commonly used to estimate initial fluid saturations, but may suffer from problems with accurate determination of the log calibration constants for a given reservoir rock, as well as the accurate determination of in-situ water resistivity in some situations. Advanced logging techniques, such as magnetic resonance, have been used in recent years to estimate the saturation of bound and free water. The use of these techniques is increasing, but cost and other factors have limited their widespread usage. Various types of reactive tracers and other in-situ techniques for the determination of initial fluid saturations have also been used to attempt to determine initial fluid saturations with varying degrees of success. Another family of techniques, on which this paper concentrates, is the actual measurement of in-situ initial or swept zone fluid saturations on samples of appropriately obtained, preserved, handled and analyzed core material. Different coring techniques and fluid and coring procedures will be discussed, along with the relative merits and advantages/disadvantages of each. Illustration of the results of of various techniques will be given with respect to their cost, effectiveness and accuracy of the data generated.