Automated Sample Capture, Separation and Analysis with the Use of X-Ray Fluorescence to Monitor Produced Water Composition and Sulphate Scaling Risks for Individual Wells

Abstract A proof of concept pilot-scale emulsions rig, with analytical instrumentation, to capture, concentrate, stabilise and analyse brine and produced gas from a 3 phase flow is presented. X-ray fluorescence (XRF) spectroscopy has been evaluated for monitoring produced water for 1 specific field case with the aim of determining the fraction of formation, sea and low sulphate sea water and associated scaling risks. In addition, H2S sensors have been evaluated for long-term measurements in produced gas. A 3 phase flow loop capable of recirculating 40 L/min of liquid and 100 Std L/min of gas was built and used to test sample collection and develop a process that could be automated. Single phase samples were collected, stabilised and transferred in a controlled way to the analytical instruments. Synthetic brine mixtures were used to assess the suitability of using XRF in a single field case for compositional (and scaling risk) analysis. The impact of contamination of the samples was assessed for both the XRF and H2S sensors. Sample collection and separation with increased water cut compared to the emulsion was demonstrated. Procedures for the controlled depressurisation and transfer of the sample were also developed. Analysis of the selected (heavier) elements and H2S at the concentrations of interest was possible. The system could be used without any analytical reagents or cleaning fluids other than fresh water and nitrogen which should allow long term operation between service visits. Operational sequences were developed that would allow operation without onsite human intervention. Following the proof of concept tests, a specification for the field sampling skid has been prepared and sequence logic drafted for the operation of the sampling skid on the normally unmanned Hugin B wellhead platform. Identifying the composition of produced water samples from complex water floods is essential to understanding the reservoir's behaviour and managing the scale risks due to mixing incompatible waters. With well streams being mixed upstream of any manned installations, the ability to automate this is essential. This paper presents a step towards the goal of routine well monitoring on unmanned installations and further demonstrates the utility of XRF spectroscopy in oilfield applications.