What is Saturation Logging
Saturation logging, also known as resistivity and saturation log, is a type of geophysical logging method used to measure the amount of hydrocarbons present in a potential oil reservoir. The two main measurements taken using the method are the electrical resistivity and the saturation of water. The resistivity is a measure of how much resistance a material has to electricity and the saturation is the amount of water being held in the pore spaces of the rock. Both measurements are then used to determine the amount of hydrocarbons present.
Resistivity logs are run on wells that have been logged with a gamma ray logging tool. The gamma ray logs provide information on the lithology or rock type, and the resistivity logs allow the operator to make more accurate interpretations of the reservoir. A resistivity log measures the amount of resistance to a charged current, which is measured in ohms, a unit of electrical resistance.
Saturation logs are run in conjunction with the resistivity logging tool to determine the amount of water present in the rock. Saturation logs measure the saturation level of water present in the reservoir. This measurement is taken by examining the amount of radio frequency energy returned from the borehole wall when logged.
The data from the logging tools is then compiled onto a log plot….
Saturation logs are important because they tell the operator the amount of hydrocarbons present in a potential reservoir. The hydrocarbon saturation level is a combination of both the resistivity log measurements and the saturation log measurements. If the hydrocarbon saturation is high, then the potential reservoir is likely to contain a good amount of hydrocarbons. The hydrocarbon saturation is then used to predict the producible content of the reservoir and make decisions as to what development and extraction strategies should be used.
For example, if the resistivity log data shows a high hydrocarbon saturation, but the saturation log data shows a low water saturation, then it is likely that the reservoir will produce a large amount of oil but with a limited amount of gas. This type of information is invaluable in making projections about the future performance of a reservoir.
Saturation logging is a critical element of reservoir evaluation and provides key information for decision making. Without saturation logging, it would be much more difficult to make accurate estimations of the potential content and productivity of a reservoir.
