Abstract
The incompatibility of injected saline seawater and formation water is the primary cause of scale deposition in offshore developments. Many offshore oilfields are encountering problems with barium sulfate precipitation due to the mixing of sulfate-anion-rich seawater and formation brine with excessive amounts of barium cation. A mechanistic physico-chemical modeling approach is required to predict the amount of scaling to assist operators in making decision regarding scale prevention in oil reservoirs. The predictive model allows various types of flow scenarios to be investigated to reduce the amount of scaling and prevent well damage and eventual loss of well productivities.
Three-dimensional field-scale simulations were performed to investigate the flow and transport of barium and sulfate ions and the significance of barium sulfate precipitation in a typical offshore oil reservoir. The reservoir simulator has the modeling capability of multiphase flow, water reaction chemistry and interaction with the rock, and more significantly the species transport equations that include physical dispersion. The reactions were kept simple with barium and sulfate ions as the only reacting species and sodium, chloride, and calcium ions as non-reacting species. Barium sulfate was considered as the only solid precipitate. Simulations were performed to determine sensitivity to dispersion and mixing in the reservoir, to determine how much solid precipitates in the reservoir and in the wellbore, and to estimate how much sulfate needs to be removed from the injected seawater to prevent the formation damage.
