Determining petrophysical properties using sodium nuclear magnetic resonance (NMR) logs

摘要

The presence of hydrocarbons in a subsurface formation fluid may be inferred from a determined salt concentration. A sodium nuclear magnetic resonance (NMR) measurement of a subsurface formation is obtained and a salt concentration of the fluid in the subsurface formation is determined from the sodium NMR measurement. Various operations may be performed using the determined salt concentration such as tracking injected water, monitoring flood fronts, improving reserves estimation, and designing enhanced oil recovery. A sodium index may be determined and used in conjunction with one or more other logs to determine a saturation of the subsurface formation. The one or more other logs may include a resistivity log, a dielectric log, a capture cross section (sigma) log, and a proton NMR log. Differentiation between bound water and free water can also be achieved using the sodium nuclear magnetic resonance measurement.