Non-Uniform SAGD Steam Chambers: Evolution, Control, and Optimization

Steam-Assisted Gravity Drainage (SAGD) is a key in-situ recovery process being used today to extract oil from oil sands reservoirs. In SAGD, an oil-depleted chamber of steam grows within the oil sands formation along a pair of horizontal wells and heats bitumen-laden oil sands at its edge. The viscosity of bitumen drops by up to five orders of magnitude when heated to about 200°C and mobilized bitumen at the chamber edge flows under gravity to a production well located at the base of the chamber. A necessary condition for an efficient steam-based bitumen recovery process is full utilization of the steam injection well and creation of a uniform steam chamber along the length of the well. If only a fraction of the oil sands surrounding the well is heated, then only a fraction of the bitumen around the well is mobilized. There are several reasons why steam may not be delivered uniformly along the well, for example, instabilities at the edge of the steam chamber, reservoir heterogeneities, and wellbore hydraulics. These diverse causes result non-uniform steam conformance along the wellpair length. In this thesis, causes of non-uniform steam chamber development have been discussed and corrective measures to improve non-uniform steam conformance have been outlined. Potentially, the evolution of non-uniform steam conformance can be mitigated by implementing smart well technology. The central thrust of the thesis is the analysis of non-uniformities of SAGD steam chambers and the use of smartwells (wells with adjustable steam injection or fluid production capabilities along the length of the wellpair) to offset non-uniformities arising from instabilities and geological heterogeneities.