Reservoir-fluid sampling and characterization - Key to efficient reservoir management

Reservoir-fluid properties play a key role in the design and optimization of injection/production strategies and surface facilities for efficient reservoir management. Inaccurate fluid characterization often leads to high uncertainties in in-place-volume estimates and recovery predictions, and hence affects asset value. Reservoir-fluid pressure/volume/temperature (PVT) characterization begins with acquisition of adequate volumes of representative fluid samples followed by PVT-data measurement with strict quality-assurance/quality-control (QA/QC) protocols and phase-behavior modeling through best-practice methods. In this paper, key steps involved in accurate fluid characterization are discussed for a wide spectrum of fluid types ranging from extraheavy oils to highly volatile near-critical fluids and lean gas condensates undergoing a wide range of production processes from simple depletion to complex tertiary recovery. Selection of appropriate sampling methods and tools, design of tool strings, and customizing procedures are demonstrated through these examples. Routine and special laboratory-fluid-analysis strategies for various fluid types and for different production strategies are highlighted. Fluid-modeling techniques including optimum-component selection, accurate C7+ characterization, robust Gibb's energy minimization, and gravity/ chemical equilibrium calculations are demonstrated through appropriate field examples. Copyright 2007 Society of Petroleum Engineers.