HAS Drive (Heated Annulus Steam Drive) is an in-situ thermal process for recovering bitumen from tar sands. This paper presents the results of a numerical simulation of the HAS Drive process in repeated, elongated well patterns. Results show that the process can effectively recover bitumen from tar sands. In a basic configuration, the cumulative recovery in ten years is predicted to be high, but the rate of production is low during the early steam-injection period. Several well configurations and operating procedures were investigated to accelerate the early year production. The recovery mechanisms and the sensitivity of the process to various parameters are also discussed in process to various parameters are also discussed in this paper.
Bitumen is a naturally occurring mixture of viscous hydrocarbons. The total reserves of bitumen in the world are estimated to be over four trillion barrels. Bitumen is characterized by its low gravity (6 to 13 deg. API) and extremely high viscosity (approximately 0.1 to 10 million centipoise at reservoir conditions).
In its naturally occurring state, bitumen is not recoverable at a commercial rate through a well. Conventional steamflooding cannot work satisfactorily because bitumen ahead of the heated zone does not have sufficient mobility to flow to the production well. production well. HAS Drive is an in-situ thermal process for recovering bitumen from tar sands. The process utilizes a horizontal, cased, unperforated pipe running between a vertical steam-injection well and a vertical production well (see Fig. 1). High pressure, high temperature steam is first pressure, high temperature steam is first circulated through the HAS pipe which heats the surrounding tar sand by conduction. In time, a heated annulus is formed around the HAS pipe. Continuous steam injection and production at the vertical wells begin when sufficient mobility,, around the HAS pipe has been established. The heated annulus acts pipe has been established. The heated annulus acts as a communication path between the injection and production wells. production wells. As the injected steam contacts the bitumen, the bitumen is mobilized. Both the bitumen and steam condensates drain to the HAS pipe where they are swept to the vertical production well by the pressure gradient maintained between the production pressure gradient maintained between the production and injection wells. Steam circulation in the PAS pipe is maintained at a sufficient rate to keep the pipe is maintained at a sufficient rate to keep the communication path between production and injection wells open throughout the life of the project.
The reservoir descriptions used in this simulation study are hypothetical; they are intended to be representative of a homogeneous Athabasca oil sand. The bitumen is assumed to be a non-volatile, single-component oil. The reservoir porosity is assumed to be 35% and the initial oil saturation is 65%. The total original oil in place (OOIP) is 1765 bbl per acre-foot. Table 1 lists reservoir properties used as input. properties used as input. The viscosity of bitumen is shown as a function of temperature in Figure 2. At reservoir conditions, the bitumen viscosity is 0.1 million cp. It decreases to 30 cp at 260 deg. F. Thermal conductivity of the tar sand is assumed to be 31 BTU/(ft-day-F).
Relative permeability curves for water-oil and oil-gas systems are shown in Figure 3.