Secondary Recovery of Oil in the United States and Canada
Oil and .gas reservoirs exist under pressure within the pore spaces of rock structures or traps. Wells are drilled to produce these reservoirs. Under primary operation, the natural energy of expanding fluids in and adjacent to the reservoir forces or drives oil and gas to the wells. There are three basic sources of energy: dissolved gas, water, and gas cap. Typical recovery by ,primary rmethods is only 10 to 25 per cent of the oil in place for the dissclved ,gas drive 'but is generally higher for the others.