Improved method for sample mixing, handling and analysis in high water cut samples

Operating production facilites in mature fields globally pose both measurement challenges and opportunities. When production depletes, facility operations may transition from three-phase to two-phase production separation resulting in allocation measurement of oil and water mixtures.

There are two common approaches used for production allocation measurement to determine water cut: online water cut analyzers (WCA) and sampling.Sampling can be spot or automatic, with automatic sampling preferred for custody applications when water content is less than 5 % by volume. Spot sampling is the common method used for field verifying WCA. The most common technique for determining water content in a sample is by centrifuge; however, the centrifuge methods lack published reproducibility and repeatability data at high water cuts (>5 % water in oil by volume). Sample handling and mixing with high water concentrations are also a severe challenge, especially with light oils and products which don't mix well. As WCAs are used more and more in high water cut production allocation, an accurate methodology for verifying the instruments is required for broad industry acceptance but the current industry guidance is very limited.

This paper describes an improved method for sample handling, and mixing and describes the proof of concept of using existing methods for analysis of high water cut samples for production allocation measurement developed in support of WCA verification. The testing described in this paper used water cuts 15–95 % by volume, and three hydrocarbons: two crudes and one distillate oil. The data demonstrates the range of the standard methods (API 10.3 and API 10.4) could be expanded while meeting or exceeding the current reproducibility requirements of API MPMS Ch 8 and Ch 10.