Complex Lithology and Hydrocarbon Fluid Characterizations while Drilling from Advanced Mud Logging Technologies

The pre-salt plays in block BM-C-33 (Campos Basin, offshore Brazil) show complexity that is bringing new challenges. Drilling wells proved to be extremely difficult and losses compromise wireline logging operations. In this context, Repsol Sinopec Brasil realized the need for additional techniques to mitigate the risk of traditional borehole logging technologies not providing all the necessary information for reservoir evaluation. For the first time in a pre-salt ultra-deepwater well, enhanced drill cuttings characterization and advanced mud-gas analysis were deployed in a 12-¼” hole. The objectives were to decrypt complex lithology and characterize the hydrocarbon fluids by API gravity and GOR. In today´s market, for this borehole size, there is no elemental spectrometry tool, and therefore, no mineralogy assessment available from LWD. Moreover, whatever the hole size, there is no LWD tool capable of evaluating API gravity and GOR. While drilling, mud-logging X-ray diffraction analyses of cuttings led to the recognition and characterization of lithology in a complex setting. In parallel, API and GOR logs were generated in real time, and continuously, from an in-house model using advanced mud gas data. Trends in the hydrocarbon column were observed. Data are adequate for early operational decisions.