Effect of Dispersion on Transport and Precipitation of Barium and Sulfate in Oil Reservoirs

摘要

The incompatibility of injected saline seawater and formationwater is the primary cause of scale deposition in offshoredevelopments. Many offshore oilfields are encounteringproblems with barium sulfate precipitation due to the mixingof sulfate-anion-rich seawater and formation brine withexcessive amounts of barium cation. A mechanistic physicochemicalmodeling approach is required to predict the amountof scaling to assist operators in making decision regardingscale prevention in oil reservoirs. The predictive modelallows various types of flow scenarios to be investigated toreduce the amount of scaling and prevent well damage andeventual loss of well productivities.Three-dimensional field-scale simulations were performedto investigate the flow and transport of barium and sulfate ionsand the significance of barium sulfate precipitation in a typicaloffshore oil reservoir. The reservoir simulator has themodeling capability of multiphase flow, water reactionchemistry and interaction with the rock, and more significantlythe species transport equations that include physicaldispersion. The reactions were kept simple with barium andsulfate ions as the only reacting species and sodium, chloride,and calcium ions as non-reacting species. Barium sulfate wasconsidered as the only solid precipitate. Simulations wereperformed to determine sensitivity to dispersion and mixing inthe reservoir, to determine how much solid precipitates in thereservoir and in the wellbore, and to estimate how muchsulfate needs to be removed from the injected seawater toprevent the formation damage.