The surveillance of oil and gas production systems for evidence of scale deposition commonly involves trending well inflow performance, pressure, temperature, rate of flow and the composition of produced water. Surveillance using produced water composition data can be improved by the application of geochemical understanding of formation waters, including the processes that controlled the evolution of formation water composition. Also, use of multivariate data analysis (MDA) techniques provides methods that can resolve subtle and significant differences, and increase the reliability of information derived from produced-water composition data. MDA provides a systematic method of evaluating data as a whole as opposed to single variable investigation, which can overlook significant information.

The information derived from geochemical understanding of formation waters and MDA can also benefit reservoir and production management, for example reservoir compartmentalisation studies and subsea production allocation.

Shell Exploration and Production UK Ltd's operations in the North Sea have benefited from a combined application of geochemical understanding of formation waters and MDA. In addition, formation water composition data derived from residual salt analysis (RSA) of reservoir core has provided additional data for several fields, which has assisted produced- water data interpretation and reservoir management. Examples of the benefits include the case of the ETAP Heron Cluster fields, where well-intervention costs in excess of £1 million per well were saved. The Bittern field benefited from postponement of scale-squeeze treatments when erroneous tracer observations suggested injection water breakthrough had occurred. HPHT prospects in the Central Graben have been assessed for the risk of halite deposition before drilling based on regional studies.

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