Assessment of Micro-Fracture Density Using Combined Interpretation of NMR Relaxometry and Electromagnetic Logs

Assessment of micro-fracture density in hydrocarbon-bearing reservoirs is of special interest for designing production plans and selecting zones for fracture treatment. NMR (nuclear magnetic resonance) T2 (spin-spin relaxation time) distribution has been traditionally considered insensitive to the presence of fractures. However, in a recent publication, we documented a measureable NMR sensitivity to the existence of micro-fractures and proposed a new concept of fracture-pore diffusional coupling. The quantification of micro-fracture density in multipleporosity systems is a challenging issue, and distinguishing fractures from pore space is not possible from NMR T2 measurement alone. However, the inclusion of additional borehole measurements, such as induction logs, enables evaluation of micro-fracture density. In this paper, we introduce a new method to evaluate the porosity associated to micro-fractures and intra-/inter-granular pores in complex formations using combined interpretation of NMR and EM (electromagnetic) measurements.