| Vast reserves of oil sand bitumen are located in the Uinta Basin in northeast Utah. The Steam-Assisted Gravity Drainage (SAGD) process is a potentially viable method for the economic recovery of this valuable resource. Although both numerical simulators and analytical computer models have been used to analyze the horizontal-well SAGD process, no computer studies have addressed the use of vertical injection and production wells.; A series of analytical computer models have been developed for the simulation of the SAGD process for various combinations of vertical and horizontal wells. A horizontal-well analytical model was developed to predict chamber-to-reservoir interface shapes, production rates, and oil-to-steam ratios for the SAGD process using a horizontal injector in combination with a horizontal producer. A vertical-well model was developed to predict similar output in the simulation of the SAGD process for a vertical injector in combination with a vertical producer. A third model was developed to simulate the SAGD process for a vertical injector in combination with a horizontal producer. For each of the well configurations, the effect of confinement by adjacent wells or well pairs was investigated.; Output from the analytical models indicated that the horizontal-well SAGD process predicted the highest production rate, although the equivalent process for a vertical injector in combination with a horizontal producer resulted in a consistently lower, yet comparable, production rate. The vertical-well SAGD process model predicted a significantly lower production rate than either of the SAGD processes involving horizontal producers. Results of the analytical-model simulations were confirmed by numerical simulation using CMG's commercial thermal simulator, STARS.; One of the most important inputs to the analytical-model simulations is the chemical structure of the oil sand bitumen. A method for determining the carbon-number and Z-number distributions of bitumen saturate fractions using GC/MS was developed and demonstrated using samples from the Sunnyside, Asphalt Ridge, and Whiterocks deposits in the Uinta Basin, Utah.; Bitumen viscosity is strongly dependent on the chemical structure of the bitumen. Likewise, the production rate, as predicted by the SAGD process, is strongly dependent on the bitumen viscosity. A viscosity model was proposed for predicting bitumen viscosity as a function of temperature and composition. |
