Down-hole NMR tools are routinely run during the oil and gas exploration process and provide valuable information to the reservoir engineers. The tools measure T2 distribution as a function of depth. T2 can be directly related to pore size and with the correct T2 cut-off can allow the determination of bound fluid versus free fluid in the reserve. These values can then be used to estimate recoverable reserves.
Frequently, logging service companies analyse NMR logs using a single T2 cut-off value for the entire data set. However, this may be lead to inaccurate predictions if the pore size distributions vary at different points in the well. For best results, the down-hole log data should be adjusted by applying the correct T2 cut-off value for each depth. This process is known as well log calibration, and it is carried out by measuring the T2 cut-off value of samples from various depths using a laboratory-based GeoSpec. The correct T2 cut-off value can then be applied to various sections of the NMR well log data, leading to more dependable results.