These figures will be based off of the EIA projections for consumption in 2030.

petroleum: 239 quadrillion Btu (70 trillion kWh equiv.) – 5% used for electrical power generation
natural gas: 163 trillion cubic feet (50 trillion kWh equiv.) – 35% used for electrical power generation

International Energy Outlook 2007
Energy Calculator

non-electrical consumption
—
petroleum: 66 trillion kWh equiv.
natural gas: 31 trillion kWh equiv.

Assume the most electricity-intensive process, vapor compression, is used 100%. A vapor-compression evaporator can make clean water from any water source.

vapor compression: 10-15,000 kWh/AF (1 acre foot = 325,851.4 U.S. gallons)
Seawater Desalination – Energy Use

48 billion gallons ~= 150,000 AF => 2.2 billion kWh / day = 800 billion kWh / year

note: That amount of water would account for 0.03% of the projected global non-irrigation water usage in 2025.
Water consumption, non-irrigation

0.7 * 66 trillion + 0.95 * 31 tillion + 800 billion ~= 80 trillion kWh / year

80 trillion kWh / year ~= 9 TW

Compare this to the previous figure of 3.5 TW for 2006 global electric generator capacity producing ~12% of current helium extraction.

This usage projection would produce ~30% of current helium extraction, for a total of ~42%.