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Technical Paper: Evaluating Formation Fluid Properties During Sampling-While-Drilling Operations

Society: IADC
Paper Number: 173152
Presentation Date: 2015
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Abstract

Recent experience with a newly introduced sampling-while-drilling service has shown that it is possible to make reliable downhole formation fluid property estimates during sampling-while-drilling operations. Such fluid properties, derived by means of downhole optical spectrometry, include hydrocarbon composition (C1 through C5 and C6+), carbon dioxide (CO2) concentration, gas/oil ratio (GOR), formation volume factor (FVF), and, asphaltene content. Oil-based mud filtrate contamination estimates made during the sample cleanup process enable assessing the quality of the pumped fluid in real time. These property and contamination estimates facilitate the management of the entire while-drilling sampling process by aiding sample-capture decisions and allowing the best possible utilization of the sample bottles currently available on a drilling bottomhole assembly. Moreover, the contamination estimates together with the real-time fluid property estimates enable prediction of the uncontaminated fluid properties. These may be the only available estimates of clean-fluid properties in zones where fluid scanning was performed with no physical sample recovery. The real-time while-drilling fluid property predictions made during sampling-while-drilling operations performed in a Gulf of Mexico deepwater exploration well are compared to the properties measured during pressure/volume/temperature (PVT) laboratory analysis performed on recovered samples. Furthermore, the predicted clean-fluid properties are compared to uncontaminated properties derived using an equation-of-state (EoS) after mathematically “removing” the contamination from the composition of the laboratory-analyzed samples. The downhole estimated fluid properties are found to be in good agreement with the properties measured in the PVT laboratory on recovered samples. Similarly, the downhole predicted clean-fluid properties are found to be in good agreement with the laboratory cleaned estimates obtained by the EoS approach.

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