The giant Al Shaheen oil field, located within the Qatar Arch, exhibits variation in reservoir fluid properties, for example the oil API gravity ranges from 15° to 35°. The cause of the variability in oil density is believed to be due to multiple charges events ( ), and the subtle bacterial alteration ( ). Nowadays the field development is challenged to lower quality reservoirs units and in such condition a continuous information of hydrocarbon fluid quality is required.

An example of application in a horizontal well drilled in the Mauddud Formation proves that the monitoring in near real-time of a series of molecular parameters enables the observations of oil quality variations along the well bore.

In the future, the information supplied by the advanced mudlogging could evolve in a more detailed API gravity model, applicable to Al Shaheen field, provided by a sufficient number of downhole fluid samples.

In any case the methodology, also thanks to its synergy and complementarity with LWD, offers a unique data set for geological interpretation and can give a fundamental contribution to the improvement of fluid sampling program and, ultimately, to a reduction of the costs for downhole sampling.


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