CONTINENTAL SHELF FRESHWATER WATER RESOURCES AND IMPROVED OIL RECOVERY BY LOW-SALINITY WATER FLOODIN

This study assesses the feasibility of utilizing offshore freshwater for improved oil recovery in passive-margin marine environments. Low-salinity water flooding (< 5 ppt) has recently been shown, on average, to improve oil recovery by 14%. Hydrogeologists estimate that up to 3x10⁵ km³ of fresh (< 1 ppt) water are sequestered in shallow (< 500 m), permeable, poorly-lithified sand, sandstone and carbonate aquifers along passive margins, within 100 km of the present-day coastline in ocean water depths up to about 50m (164 ft). The offshore distribution of fresh-brackish water is analyzed for five vertical cross-sections from offshore Australia, Suriname, Indonesia and the United States. The distribution of offshore freshwater is compared to offshore platform locations in three oil producing marine basins including the North Sea, the Gulf of Mexico, and the Niger Delta. The continental shelf cross-sections host between 0.8 to 8.6 km³ of fresh-brackish water (< 5 ppt) per km of shoreline, most within 20 to 100 km from the coast in water depths of 10 to 50m. Because the majority of the offshore oil platforms are located less than 100 km (60 miles) from the shore, these resources could be utilized for low-salinity recovery. Cross sectional aquifer models of offshore fresh-brackish production indicate that a single, 1000m long horizontal well could produce 19,200 m³/day from a relatively permeable aquifer (10^-11 to 10^-12 m²) overlain by a moderately tight (~10^-15 m²) confining unit for the typical life span of a well (30 years).