Understanding and Checking the Validity of PVT- reports

Tuesday, 07 October 2014 Read 7700 times
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Information about fluid properties is a required input for every stage in the oil and gas industry from the reservoir to the refinery. It is therefore of utmost importance for reservoir, facility and corrosion engineers to understand the volumetric behaviour and the transport properties of the produced fluid. These fluid properties can be obtained from PVT reports generated either in-house or in external labs. In both cases, engineers should be able to perform a consistency check on the data before including it in their respective tasks.

This presentation provides an overview of tools for verifying the consistency of PVT data. Among them are mass balance, cross plots and the Y-function for the constant composition experiment (CCE) and for the differential liberation experiment (DLE) for oils. As well, basic quantities, like thermal expansion or oil compressibility always have to lie within a certain order of magnitude. The formation volume factor Bo, the compressibility and the viscosity of oil depend more on the amount and only to a lesser degree on the composition of solution gas. Based on the idea of ideal solutions one can find estimates for Bo,Co,µo.

Correlations for oils applicable to different oil provinces complete the checks for oil. For gas-condensates the CCE gives valuable insights into the quality of the experiment. The constant volume depletion (CVD) for gas-condensates is more difficult to check, but calculating the K-values can serve as a quality control. In both cases, black oil and compositional, it is customary to model the experiments with equations of state (EOS).

About the Author

Klaus Potsch is a retired Senior Expert from OMV and also serves as a consultant for Fluid Studies. He holds a BS and MS in Physics, and a PhD in Mechanical Engineering from the Technical University of Vienna, where he also worked as an Assistant Professor. For the last 4 years he has been a guest lecturer for "Reservoir Fluids and their Modeling" at the Mining University of Leoben, Austria. In his professional career he headed the team of Mathematics, Reservoir Engineering and finally High Pressure Technology in the Laboratory of Exploration and Production of OMV. Within SPE he has held several positions in the Vienna Basin Section board and from 2003-2008 served on the International Board of SPE as the Regional Director for South, Central and Eastern Europe. Klaus was also on the SPE Distinguished Lecturer Committee from 2003-06.

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