TABLE OF CONTENTS Table E-1 describes tools and techniques to determine residual oil saturation (S or) and remaining oil saturation (ROS). In using these techniques, one should keep the following in mind:
Each measurement technique has different capabilities and limitations
Use several measurement techniques to establish confidence in the final answer
In open-hole environments, the NML (nuclear magnetism logs) Mn EDTA logging method yields the best accuracy
In cased-hole environments, the PNC (pulsed neutron capture) Log-Inject-Log method yields the best accuracy
| Method | Advantages | Disadvantages |
| Material Balance | Straightforward calculation Produced oil usually known accurately | ROS seldom known accurately Multi-zone completions complicate allocation Areal reservoir distribution seldom known accurately |
| Cores | ||
| Conventional | Direct measurement Services widely available | Core bleeds fluids when pressure released and dis solved gases expand |
| Pressure | Maintains reservoir pressure, thereby pre-venting oil from escaping | Expensive Poor recovery Special labs required |
| Sponge | Preserves oil expelled while pressure drops | Potentially more core jamming and shorter barrel than conventional core |
| Core Flood | Direct measurement | Must preserve wettability Core may not be representative of reservoir Core may be damaged |
| Method | Advantage Open Hole Logs | Disadvantage |
| Resistivity | Inexpensive | Many sources of error in interpretation |
| Can measure either invaded or uninvaded zone | ||
| High Frequency | Inexpensive | Many sources of error in interpretation |
| Dielectric Logs | Straightforward interpretation Can run in variable formation water salinities | Very shallow depth of investigation; sensitive to borehole rugosity |
| Low Frequency | Inexpensive | Not accurate with current interpretation techniques |
| Dielectric Logs | Operates... |
