oa Value of NMR logging to heavy oil reservoir characterization

Recent advancements in nuclear magnetic resonance (NMR) logging have made it possible to address the particularly challenging heavy-oil reservoir characterization problem. Because viscosity varies substantially in different heavy-oil fields, no single NMR technique works for all situations. Three methods were employed for characterizing heavy-oil reservoirs in clean sands, shaly sands, and formations containing bitumen/tar, respectively. In clean sand or some carbonate formations, direct NMR fluid-typing is usually sufficient for quantifying heavy oils. For shaly sands, where NMR responses to heavy oil and bound water significantly overlap, we developed a conventional log-constrained inversion technique to better discern heavy oil from bound water. For bitumen at<br>low-reservoir temperature, NMR relaxation time is too short to detect by the current NMR logging tools; analysis of porosity deficit is a robust means to identify and quantify tar mats. Those techniques have been successfully employed in Venezuela, Kazakhstan, Canada, USA and the Middle East. In contradistinction to cuttings, NMR logs allow us to precisely determine the depth of heavy oil that is crucial for water-flooding applications. Also, NMR can quantify movable water in the heavy-oil reservoirs – critical information for predicting producibility. Furthermore, NMR provides crude oil constituent information far beyond a single bulk-viscosity estimate. This can be used for identifying sweet spots in heavyoil reservoirs. The component analysis is essential for<br>separating light and heavy oil volumes with their corresponding viscosities in dual-charged reservoirs where each charge to the reservoir brought in oils having different viscosities.