Fluid characterization and correct volumetric assessment can be very difficult to quantify in saturated fluid systems. Commonly, during initial fluid sampling, the flowing sand face pressure condition is less than saturation pressure, leading to multiphase flow. In this common unconventional production situation, appropriate in-situ fluid characterization is critical for valid resource assessment.
Simplified protocols have been developed for saturated fluid characterization and a continuous volumetric assessment approach is developed across variable fluid phases. A broad range of Montney fluid systems, defined by valid Pressure-Volume-Temperature (PVT) characterization, are described relative to field production results and commonly available routine fluid sample diagnostics. In order to accurately describe in-situ fluid character three recombination paths are followed after field sampling of separator liquids and gases at multiple drawdowns. The three paths are: increasing pressure to force single-phase behavior with subsequent equilibration at reservoir pressure; incremental addition of separator gas to separator liquid while maintaining reservoir pressure; equilibration at reservoir pressure at the lowest sampling gas-oil ratio (GOR).
The application of a fluid characterization method utilizing the concept of a pseudo formation volume factor for gas system hydrocarbon in-place assessment is described. Continuous volumetric assessment across variable phases is established with a simple predictive link to the formation volume factor and the pseudo formation volume factor concept with the normalized molecular weight of the pressured lower phase separator liquid C4+.
Linking valid PVT laboratory protocols with observed producing fluid components is critical for accurate fluid characterization and volumetric assessment. In complex fluid systems consisting of both coexisting gas and oil systems, oil in-place estimates can fluctuate +/-50% based upon the relative allocation of phase, demonstrating the importance of appropriate characterization and resource assessment in the monetization of assets. Volatile fluid systems, that is, saturated or near saturated reservoirs, can produce fluid samples that exhibit complex recombined fluid character. Field and lab workflows for sampling and characterization materially impact the assessment of hydrocarbon in-place. This paper provides a simple accurate approach to characterize volatile fluid systems to ultimately drive field development decisions.
The team who produced this paper were comprised of laboratory, production testing, field sampling, exploration/development and reserves/asset evaluation individuals.