Processes Determining the Composition of Produced Water From Subsea Fields andImplications for Scale Management – Birch Field, UKCS

摘要

Produced water analyses from the Birch Field, UK North Seahave been interpreted and combined with simulation results toexplain the causes of changes in produced water compositionsover time. Preliminary conclusions are that two formationwaters are present in the oil leg, both trapped at the time of oilemplacement. Lower salinity formation water has beenexpelled from the Kimmeridge Clay Formation (KCF) anddominates shallower sections of the reservoir. Higher salinityformation water is thought to be ancient Brae aquifer waterand dominates the deeper sections. Some lateral variability information water compositions is evident. Produced waterfrom individual wells is a mixture of the lower salinityformation water, higher salinity formation water and injectedwater. Trends in produced water compositions over timereflect a relative decrease in formation water production andincrease in injection water production. Depending on theconstituent, reactions occurring as a result of injection of waterinto the reservoir also affect the composition of producedwater. The results have challenged previous concepts relatingto water production at Birch and will be considered in scalemanagement plans in future. They can also be used toconstrain reservoir simulations, to aid enhanced oil recoverydecisions and to provide more reliable tracking of injectionwater and formation waters entering the production wells atBirch.More generally, this study has demonstrated theimportance of evaluating produced water analyses as early aspossible after water breakthrough. Integration of reservoirsimulation studies with the interpretation of produced wateranalyses can provide information that benefits scalemanagement, STOIIP calculations, reservoir models, andtracking of injection water as well as providing analogueinformation that can help reduce uncertainties associated withthe development of deep water and marginal subsea fields.