Conventional mud logging techniques cannot reliably distinguish the organic-rich, micro-porous Athel silicilyte reservoir cuttings from shale. Yet, a simple gamma ray log resolves most uncertainties in this respect. Spectral Gamma Ray logging on cuttings was introduced in South Oman in 1995 as a practical and cost effective means to optimise operational decisions on Athel wells. Target applications included picking casing setting depth, selecting coring points, and confirming TD. Equipment was designed and constructed, procedures were created, and personnel were trained. The "Cuttings Spectral Gamma Ray" has since become an integral component of the mud logging suite on many exploration wells in South Oman. In this environment, the technique proves technically and economically more attractive than alternative solutions involving wireline or MWD logging.

The original objectives were met, and new applications evolved as experience and confidence in the system grew. They include: depth-matching mud logs to wireline logs; correcting driller's depth; logging to the deepest point in the well; data assurance in case of hole problems; logging after completion or abandonment (where cuttings have been stored); and, in hindsight, a qualitative hole cleaning efficiency indicator. The paper reviews design considerations, operating procedures, and aspects of data processing. Using field data and comparisons with wireline logs, the discussion then focuses on current capabilities and inherent limitations of the system, to conclude with a brief assessment of the potential for a cuttings-based wellsite formation evaluation package.

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