Recent advances in NMR log interpretation for complexlithology formations

Nuclear Magnetic Resonance (NMR) logging measurements respond directly to pore fluids and their interaction with the rock surfaces. Thus, NMR does not suffer many of the drawbacks that affect interpretations of conventional logs, which respond primarily to the rock matrix properties. Conversely, general NMR rock-property interpretation models are explicitly or implicitly developed from clean clastics with single mineralogy and well-connected pore networks at 100% water saturation. When applying these models to interpret more complex lithology, including multi-mineral or carbonate formations, one sometimes faces challenges similar to those encountered when using Archie’s equation for interpreting non-Archie formations. With modifications to the existing interpretation models, and/or use of a more sophisticated pore-scale geometric model, we can take the lithology, mineralogy or pore-structural characteristics information into account to interpret complicated reservoir formations successfully. Essentially, NMR logging applications fall into two categories: those derived from fluid properties only, and those based on fluid and matrix interactions.