Steam Assisted Gravity Drainage (SAGD) is an enhanced oil recovery technology for producing heavy crude oil and bitumen involving an advanced form of steam stimulation.
Two horizontal wells are drilled into the oil reservoir, one a few meters above the other. High-pressure steam is continuously injected into the upper well and into the reservoir to heat the oil and reduce its viscosity, causing the heated oil and condensed steam to drain into the lower wellbore, where it flows under natural pressure or via pumps to the surface for further processing.
Initially developed in Canada for application in the Oil Sands, SAGD is applicable to any heavy oil development which is too deep for surface mining and/or requires oil viscosity reduction to enable the oil to be moved to the surface.