Estimating scale deposition through reservoir history matching in the Janice field

Inorganic scale precipitation and deposition in production wells can be a significant impediment to effective reservoir management. In extreme cases scale can cause the well to be abandoned as a result of reservoir formation damage in the near wellbore area and the narrowing of the production tubing annulus thus preventing fluid flow. The prediction of the time and location of scale formation is therefore essential for scale management. This study is focused on sulphate scales, which form when sulphate rich seawater mixes with formation brines, rich in barium, strontium and calcium, and which are amongst the most difficult types of scale to prevent and remove. Formation brines in reservoirs with a tendency for sulphate scale deposition can have a very different makeup when compared to seawater, which may be injected for pressure support. Having such different chemistries allows seawater and formation brine to be tracked. In this study, two different types of water are considered, formation brine and injected seawater.

The objective of this work is to predict uncertainty in sulphate scale deposition from multiple history matched reservoir models, by tracking injected seawater in the Janice Field. There are many examples in the literature where conventional reservoir history matching, namely gas rate, oil rate and bottom hole pressure, are used to generate an ensemble of good history matched models, which will determine the uncertainty of a hydrocarbon reservoir production forecast. In this study, the same approach will be adopted, but including produced water chemistry, in particular seawater breakthrough. This approach provides a methodology to predict the uncertainty of the formation brine and the injected seawater mixing zone within the reservoir formation. The methodology provides a Bayesian confidence interval (P10-P50-P90) in time and space for the injected seawater, identifying which wells will be at risk based on seawater breakthrough and in which zones of the reservoir mixing is more likely to occur.