Secondary Porosity, Image Log and Nuclear Magnetic Resonance Log Definition

Carbonate reservoirs offer difficult challenges to evaluation due to the frequent incidence of secondary porosity features in the form of fractures and vugs. Image logs are useful to help identify the presence of these features, but they do not quantify their contribution to permeability or to production. Nuclear Magnetic Resonance (NMR) logs provide characterization of the unaltered formation along with an evaluation of the contribution to porosity and permeability of the secondary porosity features. Even very difficult portions of the formation can now be characterized and potential production predicted. This paper compares the results from image logs and NMR logs in different carbonate reservoirs. The increased value of the asset created by the enhanced porosity and permeability from secondary porosity can now be considered when contemplating completion attempts in complex carbonates.