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. 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 use 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.
Introduction
If performed during drilling (when filtrate invasion is not fully developed), fluid scanning—where formation fluid is pumped and analyzed within the sampling-while-drilling tool without taking a sample—affords the opportunity to characterize the formation fluid at potential sampling depths before committing sample chambers. The success of such an approach depends on how completely the in-situ fluid can be characterized and how free of contamination the assessed properties are.
By use of downhole optical spectrometry, it has been shown recently that it is possible to estimate in real time at least the following formation-fluid properties: fluid color and type, hydrocarbon composition at various levels, carbon dioxide (CO2) content, gas/oil ratio (GOR), formation volume factor (FVF), and asphaltene content.
