Steam assisted gravity drainage ("SAGD") is practised in a first section of a reservoir containing heavy oil. When steam/oil ratio rises sufficiently, steam injection into the first section is curtailed or terminated. Non-condensible gas is then injected into the section to pressurize it and production of residual oil and steam condensate is continued. Concurrently with pressurization, SAGD is practised in an adjacent reservoir section. As a result, some of the residual oil in the first section is recovered and steam loss from the second section to the first section is ameliorated.
A flow balancing system for long screen sections particularly useful in high viscosity hydrocarbon production features an annular flow path whose height and length can be varied to provide a predetermined resistance to a given flow rate of a material of a given viscosity. In assembling a long length of screen sections, greater resistance configurations are placed closer to the wellhead end of the screen section with the more remote sections having progressively less restriction until the furthest section of the screen string where low or no resistance to flow internally to the screen section is offered.
