NMR on the Ogbon-1 Well

One Pass, Many Answers

The chapter ends on the well, with everything NMR delivers on a single track. The NMR porosity is split by the cutoff into bound water and free fluid: in the clean oil pay the free slice dominates, in the shales almost all of the porosity is bound. From that same split the Timur-Coates permeability is computed foot by foot and laid against the core truth.

Matrix-Free and Physical

Two things stand out on the log. The NMR porosity needs no matrix density, yet it tracks the conventional porosity through clean sand and shale alike, the lithology-independence promised at the start of the chapter, made good. And the Coates permeability, built only from BVI and FFI, follows the core permeability closely, a log permeability with a physical basis in pore size rather than a fitted $S_{wi}$ that fails in the transition zone.

The Most Complete Log

That is what makes NMR the most complete single measurement in formation evaluation: a matrix-free porosity, an irreducible water with no resistivity, a permeability from the pore sizes, and a fluid type from T1, T2, and diffusion, all from one pass of the tool. It does not replace the density, neutron, and resistivity logs, it cross-checks and completes them. With the log suite now exhausted, from gamma ray to NMR, the course turns to the integration that turns all these curves into a reservoir: capillary pressure and saturation-height, net pay and cutoffs, and the volumetric answer the whole evaluation was built to produce.

References

• Coates, G. R., Xiao, L., and Prammer, M. G. (1999). NMR Logging Principles and Applications. Halliburton Energy Services.
• Allen, D. et al. (2000). Trends in NMR logging. Oilfield Review, 12(3).