Nuclear magnetic resonance borehole logging apparatus and method for ascertaining a volume of hydrocarbons independent of a diffusion coefficient

摘要

A nuclear magnetic resonance (NMR) logging technique reveals the volume of hydrocarbons in an earth formation. The differences in viscosity among gas, oil and water are used to distinguish among these three fluids. During NMR logging, a parameter of a sequence of magnetic field pulses is altered, causing echo signal strengths to vary due to the diffusion of the fluids in the formation. The volume of hydrocarbons in the formation is determined from detected spin echo strengths. The invention applies to wireline NMR logging and NMR logging-while-drilling techniques.