Aquifer-plugging steam soak for layered reservoir

A steam soak process for producing oil from a subterranean reservoir in which a relatively viscous oil is contained in a relatively steam impermeable layer overlying a more permeable layer of higher water content, into which reservoir a well is opened into fluid communication with at least a portion of the water layer within which the steam permeability tends to be greater than that in the oil layer because of the absence of the relatively immobile oil, comprising:

• injecting steam through the well and into the resevoir at a relatively high rate and volume sufficent to heat the normally relatively immobile reservoir oil, displace a bank of heated oil radially outward and downward into a portion of the water layer, and cause the steam injectivity to become significantly decreased;
• and
• subsequently producing oil by reducing the pressure in the well borehole and withdrawing fluid from the zone immediately around the well and closer to the well than the so-displaced oil bank, which zone contains relatively highly pressurized hot water and oil.