Technical Paper: EOS Based Downhole Fluid Characterization

Society: SPE
Paper Number: 114702
Presentation Date: 2008
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Downhole fluid analysis (DFA), together with wireline formation testing tools, provides real-time measurements of reservoir fluid properties such as compositions of four or five components/groups and gas/oil ratio (GOR). With the introduction of a new generation of DFA tools that analyze fluids in situ, the accuracy and reliability of the DFA measurements are significantly enhanced. Furthermore, the downhole measurements of live fluid density and viscosity are integrated into the new tools. Direct pressure and temperature measurements of the flowline ensure capture of accurate fluid conditions. To further enhance these advanced features, a new method of downhole fluid characterization based on the equation of state (EOS) approach is proposed in this work.

The purpose of this work is to develop a new approach to maximize the value of DFA data and perform quality assurance and/or quality control (QA/QC) of DFA data. The basic inputs from DFA measurements are weight percentages of CO2, C1, C2, C3-C5, and C6+; live fluid density; and viscosity. A new method is developed in this work to delump and characterize the measurements of C3-C5 (C2-C5) and C6+ into full-length compositional data. The full-length compositional data predicted by the new method are compared with the laboratory-measured gas chromatograph (GC) data up to C30+ for more than 1,000 fluids, including heavy oil, conventional oil, volatile oil, rich gas condensate, lean gas condensate, and wet gas. A good agreement is reached.

Furthermore, based on the delumped and characterized compositions, an EOS model is established that can be applied to predict fluid phase behavior and physical properties on the basis of DFA data as input. The EOS predictions are validated and compared with the laboratory-measured PVT (pressure/volume/temperature) properties for more than 1,000 fluids. The GOR, formation volume factor (FVF), and density predictions are in good agreement with the laboratory measurements. The established EOS model is then able to predict other PVT properties, and the results are compared with the laboratory measurements in a good accord.

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