The main productive formation of the Ku Maloob Zaapfield offshore Mexico in the Bay of Campeche presentsseveral challenges to successfully logging andcharacterizing the formation in a complete and efficientmanner. A complete evaluation of all wells is neededto accurately upscale the data to the reservoir model forcompletion decisions and for future planning.The main reservoir is the Upper and Middle Cretaceousthat is brecciated in the upper portion and dolomitizedthroughout much of the section. The section is alsohighly fractured, and most of the drilling is performedwithout returns. Logs are typically run on wireline, buton many occasions are not possible operationallybecause of unstable well conditions and the presence ofgas or because of mechanical collapse of the wellbore. Inthese cases, logging-while-drilling (LWD) is used.More advanced tools have been run in the past yearincluding a multifunction LWD tool that uses a pulsedneutron generator (PNG) instead of a chemical neutronsource. The use of a PNG allows the measurement offormation sigma, elemental capture spectroscopy, andneutron porosity, in addition to sourceless neutrongamma density which provides a deeper measurementthan a conventional density. The spectroscopymeasurement allows characterization of lithologyincluding clay content and distinguishing calcite fromdolomite. The sigma measurement gives an alternatemethod of determining hydrocarbon saturation anddetecting oil-water contacts. Borehole images usingresistivity and density for fracture determination werealso run along with advanced sonic tools acquiringStoneley wave data for detection of fractures anddetermination of whether the fractures are open orclosed. The borehole images were also used to detectthe presence of vugs and were combined with the densitymeasurements at two depths of investigation to betterquantify the vugular porosity.By acquiring data that allows measurement of porosity,lithology, and saturation, more complete formationcharacterization was possible in wells where wirelinecould not be run. By having a complete data set acrossthe field, future production and field optimizationdecisions can be made in an informed manner. In casesin which fractured carbonates were evaluated usingLWD measurements in this challenging loggingenvironment, the measurements enabled betterevaluation of the reservoir, determinations of porosityand fluid contacts, and identification of both location anddensity of fractures in the formation.
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