A complex carbonate oilfield in Saudi Arabia required pressure support to sustain production. Saudi Aramco was looking to achieve sustained production using the best-in-class reservoir management practices. This article describes a comprehensive, long-term injectivity test whose objective was to characterize reservoir sweep patterns so the optimum number and location of injectors could be determined. The pilot injectivity tests ultimately proved to be successful, with dynamic data that included pressure transient analysis removed several faults from the geological model. At least 13 injector wells were dropped from the field development plan because of uncertainties about the tar mat sealing were redefined. System design issues successfully resolved to address test goals and result in almost 96% uptime. It was determined that lower powered water injector pumps were required because the injectivity index turned out to be better than expected, and ESPs proved more reliable than diesel-powered pumps.