NanoTags for Improved Cuttings Depth Correlation

Abstract

During a drilling operation, rock cuttings are often sampled off a shale shaker for lithology and petrophysical characterization. These analyses play an important role in describing the subsurface, and it is important that the depth origin of the cuttings be accurately determined. Traditionally, mud loggers determine the depth origin of the sampled cuttings by calculating the lag time required for the cuttings to travel from the bit to the surface. These calculations, however, can contain inaccuracies in the depth correlation due to the shuffling and settling of cuttings as they travel with drilling fluid to the surface, due to unplanned conditions like drilling an overgauge hole, and due to other unforeseen drilling events, especially critical in horizontal sections. We, therefore, aimed to remedy these inaccuracies by developing a series of styrene-based nanoparticles that tagged the cuttings as they were generated at the drill bit. These “NanoTags” were tested while drilling in Q4 2019, and the results indicated that the NanoTags did, in fact, have the potential to identify some systematic errors compared with traditional mud-logging calculations.