Pore Geometry Description Comparison of NMR to Image Results

Dense carbonates reservoirs are beginning to provide a very significant amount of hydrocarbon production in many areas of the world. These formations tend to be difficult to interpret from a traditional log analysis. In many cases, these logs estimate a very low porosity that can be in the 0-4% porosity range. Some of these reservoirs are still very prolific in nature and require some type of log that can provide a definitive and duplicative response that will allow operators to initiate completions with some confidence of a productive and economic result. Nuclear Magnetic Imaging (NMR) logs have been proposed as a potential source of useful information. The response of the NMR device should have some relationship to the textural variations within the formation. These textural changes are fractures that can occur in any formation. Alterations such as vugs or molds are specific to carbonate rocks. All of these require definition if correlations to production can be accomplished. This paper explores responses from NMR devices when compared to known fracture systems, to interconnected vugs and to oomoldic or disconnected vug development. The contribution of these secondary porosity systems to effective porosity and to permeability will be explored.