three - phase separation is achieved downhole in a production well by forming an oil / liquid separation zone in the well between two packers which are positioned between producing and disposal zones . gas is permitted to separate above the top packer . a pump is used to pump an oil / water mixture from above the top packer into the separation zone . adequate residence time is permitted in the separation zone to achieve the separation . a check valve in the bottom packer is used to provide pressure to raise the oil to the wellhead . a control valve at the wellhead is used to control pressure in the separation zone and the relative sizes of the streams issuing therefrom .