Determination of initial fluid saturations using traced drilling media

Initial saturations of hydrocarbons and water, existing in porous media, co ntrol 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 sat urations, but may suffer from problems with accurate determination of the l og calibration constants for a given reservoir rock, as well as the accurat e determination of in situ water resistivity in some situations. Advanced l ogging techniques, such as magnetic resonance, have been used in recent yea rs to estimate the saturation of bound and free water. The use of these tec hniques is increasing, but cost and other factors have limited their widesp read usage. Various types of reactive tracers and other in situ techniques for the determination of initial fluid saturations have also been used to a ttempt to determine initial fluid saturations with varying degrees of succe ss. Another family of techniques, on which this paper concentrates, is the actu al measurement of in situ initial or swept zone fluid saturations on sample s of appropriately obtained, preserved. handled and analysed core material. Different coring techniques and fluid and coring procedures will be discus sed, along with the relative merits and advantages/disadvantages of each, I llustration of the results of various techniques will be given with respect to their cost, effectiveness, and accuracy of the data generated.