Gas sampling for mercury analysis

Abstract

Historically, gas sampling for mercury has been neither accurate nor precise. In some instances, limited understanding of mercury in gas reservoirs has contributed to health, safety and environment (HSE) incidents and project cost escalation. Quality gas sampling for mercury is recognised as a critical element in project planning, best conducted in the exploration and appraisal phases of a field. Early knowledge of mercury concentrations can contribute to the success of development planning, HSE processes and production facility design. Gas Field X on the North West Shelf of Western Australia is in a region of variable mercury-in-gas concentrations. The recent Field X development drilling program commenced with a sampling plan optimised and focussed on mercury analysis using industry best practice operational, logistical and analysis techniques with the intent of building a statistically representative dataset of mercury concentrations. Procedures developed included investigating major sources of scavenging and contamination, innovative pre-job equipment preparation, use of multiple data sources (downhole and surface sampling, offshore and onshore analysis) and blind cross-checking between different laboratories and equipment types. All data has been through rigorous post-analysis quality control. The results of this unprecedented new dataset represent a case study of industry best-practice gas sampling delivering high confidence and repeatable data.