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Abstract

Disclosed is a gravity-drainage assisted steam flooding process for the recovery of all from thin viscous heavy oil reservoirs using a single horizontal wellbore. Steam is injected through a fully or partially insulated tubing to exit at or near the toe of a long horizontal well penetrating a viscous oil reservoir. Initially, low (10-30%) quality steam is circulated along the well to condition the wellbore and increase the heated radius to about 1 or 2 meters. Oil and reservoir fluids immediately adjacent to the wellbore are produced through the annular space between the insulated tubing string and a slotted liner that surrounds it. After the period of low quality steam circulation, the production outlet is shut in or constrained and steam injection is continued to initiate an active steam chamber zone along a portion of the wellbore. Subsequently, fluid withdrawal is resumed at the production outlet, while the annular liquid level in the vertical section is controlled to maintain a nearly constant pressure at the production outlet. The injection of a higher (50-70% or more) quality steam is continued at a rate similar to or higher than the initial rate to cause the expansion and propagation of the active steam heated volume vertically towards the top of the formation, longitudinally along the horizontal well from the toe towards its heel, and laterally away from the well towards the inter-well boundary with the next row of horizontal well. As steam flows into the reservoir under both gravitational counter current flow and pressure drive, the oil, steam condensate and reservoir fluids heated both conductively and convectively drain towards the slotted liner annulus of the horizontal wellbore and is then pumped to the surface.

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First Claim