This paper presents a coupled reservoir and well model in which the equations are solved simultaneously using Newton's method. The equations for the circulation well include the frictional pressure drop and the heat transfer between tubing flow and annulus flow.
With the coupled reservoir/well model, this paper examines the performance of a horizontal well undergoing cyclic steam injection in a thin bitumen reservoir. It is found that the frictional pressure drop could cause uneven sweep in the reservoir, and that the heat transfer between tubing and annulus flows affected the shape of the sweep zone.
A promising method for the in situ recovery of bitumen with horizontal wells is the steam-assisted gravity drainage (SAGD). Steam is injected continuously above a horizontal producer. The heated oil drains by gravity to the producer and allows the formation and expansion of a steam chamber. In this process, the oil should be removed at the maximum rate without producing any steam1. Steam can be injected through a horizontal well as in AOSTRA's Underground Test Facility2,3, or a vertical well as in Esso's Cold Lake Project4.
The conventional two-well SAGD method is applied to oil sands pay thickness of 25 meters or greater. So, there is a need to find a recovery method for thin reservoirs (thickness less than 25 meters)5,6 - This paper examines through numerical simulation the performance of a single-well SAGD method using cyclic steam injection.
A long horizontal well is placed near the bottom of a thin reservoir (Figure 1). The well which consists of a tubing and a slotted linear, is subject to cyclic steam injection.
During the injection cycle, steam is circulated down the tubing and back through the annulus as shown in Figure 2a. The bitumen and reservoir adjacent to the wellbore is heated by both convection and conduction. Steam leaks into the reservoir through the perforated liner and condenses. The latent heat released raises the temperature of the bitumen and reservoir rock. At the same time, heal is also transferred by conduction through the reservoir rock.
In the production cycle, fluids are produced through the annulus as shown in Figure 2b. Fluids that are liquid in me reservoir may flash in me annulus because of the lower pressure. No flow occurs in the tubing in the production cycle.
A steam chamber can form and grow through a series of injection and production cycles. To model the process, it is necessary to solve the reservoir and wellbore flow equations simultaneously because of the complex interaction between reservoir and wellbore.
This paper describes a simulator that handles rigorously the coupling or reservoir and wellbore, and its application in the predictions of the performance of a single-well SAGD process.
A coupled reservoir/wellbore simulator was previously described in Stone et al7. However, the numerical techniques used in the paper as well as the process simulated are different.