Chapter 4: Fluid Sampling

Many general petroleum engineering texts have sections covering the measurement of phase behavior or pressure/volume/temperature (PVT) analysis, but few have detailed descriptions of fluid-sampling practices. This chapter covers the sampling of all produced reservoir fluids. It is intended to provide an overview of sampling methods, guidelines for selecting suitable methods, and detailed procedures for the most common practices.

An enormous range of reservoir fluids exists, and this means that the limited measurements of produced oil and gas properties that can be made in the field are far from adequate to provide the detailed characterization that modern petroleum engineering requires. In addition to PVT analysis, of fundamental importance to reservoir management, measurements relating to corrosion potential, solids formation, and nonhydrocarbon constituents have the potential to produce serious effects on the design of production facilities, on compatibility with pipeline transport, on product sales value, on refinery maintenance costs, and on reservoir asset values in general. The lack of such data could easily represent more risk than that tolerated when the decision to perform sampling and laboratory studies is taken. Examples of the financial impact of errors in fluid-property measurements are given elsewhere. ¹  Fluid samples are thus required to enable advanced physical and chemical analyses to be carried out in specialized laboratories. Samples must be collected from a wide range of locations, including separators, pipelines, tanks, wellbores, and the formation itself. This chapter primarily targets the sampling of fluids under pressures above atmospheric, where numerous tools and procedures have been developed that are essentially specific to the petroleum industry. Best practices are proposed for fluid sampling, reporting of data, and quality control of samples.