Smart Pad Reservoir Production Machine for Oil Sands SAGD Operations

Abstract

Abstract The Steam Assisted Gravity Drainage (SAGD) process is widely used in the Athabasca oil sands deposit to recover bitumen. Since the viscosity of bitumen is high 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 parameter for evaluating the economics of any SAGD project. The target for many SAGD operations is a SOR lower than 2.5 m3/m3. Here, we explore the use of dynamic distributed steam injection within a pad of SAGD wellpairs controlled via a Proportional-Integral-Derivative (PID) feedback controller, a concept we refer to as Smart Pad. The Smart Pad Reservoir Production Machine is designed to dynamically distribute steam injection along multiple well pairs so that over a period of operation, the pad-scale cSOR is dynamically improved 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 an oil sands reservoir with a top water zone. 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 the "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 reservoir quality zones, i.e. shale barriers, high permeability channel to the top water zone, to lower the local SOR. In this manner, the PID feedback controller provides an efficient method to recovery bitumen in SAGD operation, especially during the first 7-10 years' operation, where it helps to achieve a relatively low cSOR and maintain a normal level of oil recovery. Also, the PID controller reduces the degree of dependence of SAGD operation on the geological conditions of the reservoir. The algorithm described could be applied to any operating or new SAGD pad.