Abstract
Nuclear Magnetic Logging was introduced to the industry by Pan Geo Atlas Corp. in 1959. As today, expectations were high. Following an initial period of enthusiasm, interest declined as solutions were not provided. Since then the technology has been periodically reintroduced to the oil industry. The SPWLA Bibliography of NMR Applications"2 records 458 technical references on the subject related to the oil industry. Interest in the technology is understandable considering the prospect of permeability prediction, lithology independent total porosity, effective porosity, wettability determination, hydrocarbon typing, residual oil saturation, and estimate of movable formation water. Today, the newest generation logging tools, CMR* and MRIL+, offer improved signal to noise ratio, faster logging speeds, and superior vertical resolution. The preponderance of recent technical papers highlight the successful application of NMR in clastic reservoirs. Carbonate reservoirs are proving more challenging. Complex pore geometry, varying wettability, intragranular / matrix microporosity, chaotic pore throat / pore size ratios, connected and non-connected vugs, and weak surface relaxivity make interpretation difficult. This paper documents ADMA-OPCO's experience with the CMR in a mixed wet / intermediate wet carbonate reservoir exhibiting high immobile water saturation. CMR total porosity underestimated core / neutron – density – sonic porosity. A T2 cutoff of 280 msec failed to predict the water free oil production obtained. An investigative core analyses program which followed did not provide a unique T2 cutoff, but several, varying from 120 msec to 486 msec. The usefulness of this technology for evaluation of ADMA-OPCO's carbonate reservoirs is judged.
