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Title: Automated Control for Oil Sands SAGD Operations
Author: Guo, Tao
Advisor: Gates, Ian
Keywords: Engineering--Chemical
Issue Date: 14-Jan-2014
Abstract: The Steam Assisted Gravity Drainage (SAGD) process is widely used in the Athabasca oil sands deposit to recover extra heavy oil, also referred to as bitumen. Since the viscosity of bitumen is high, typically over 1 million cP, at original reservoir conditions, heat is required to lower its viscosity to the point it becomes mobile enough to be recovered under gravity drainage. To heat the reservoir, steam is injected into the formation and thus SAGD is energy intense – on average, the steam-to-oil ratio (SOR) is equal to about 3.5 m3 (expressed as cold water equivalent) of steam injected per m3 of bitumen produced. Given that the fuel used to generate steam is the largest operating cost, the SOR is a key control on the economics of any SAGD project. The target for many SAGD operations is a SOR lower than 2.5m3/m3. However, very few field operations have achieved this threshold. Here, the use of dynamic distributed steam injection within a pad of SAGD wellpairs controlled via a Proportional-Integral-Derivative (PID) feedback controller to lower the SOR is explored, a concept we refer to as Smart Pad. The Smart Pad is designed to dynamically distribute steam injection along multiple well pairs so that over a period of operation, the pad-scale cSOR is lowered as the process evolves. First, a method to condition the PID control gains is described and second, the controller is applied to a multiple well pair SAGD pad in a typical Athabasca oil sands reservoir. The results demonstrate that automated control can lead to improvements of the SOR over that of constant pressure. The results show that automated PID control is able to detect “sweet spots” (oil zones with better geological properties) in the reservoir and dynamically deliver more steam to that region. Meanwhile, it reduces the steam injection towards relatively worse quality zones, i.e. shale barriers, to lower the local SOR. In this manner, the PID feedback controller provides an effective method to control SAGD operations, especially over the first 7 to 10 years of operation, where for the same amount of steam injection, it helps to achieve reduced cSOR and increased oil recovery. Also, since the PID controller dynamically controls the process according to its performance, the method appears to reduce the degree of dependence of SAGD operation on knowledge of the geological conditions of the reservoir. The algorithm described could be applied to any operating or new SAGD pad.
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