Design of the Monitoring Program For AOSTRA's Underground Test Facility, Phase B Pilot

Abstract

Abstract A monitoring program for an oil sands thermal recovery pilot project is described. New methods of monitoring were used to monitor the steam-assisted gravity drainage process, and to observe the reservoir's geo-mechanical response. In addition, the performance of the access tunnels and of the production wells' surface casings were also monitored. The types, quantities, and locations of instrumentation are described. Rationale for the selection of instrumentation is presented, and approximate costs are provided. Background The Alberta Oil Sands Technology and Research Authority's Underground Test Facility (AOSTRA UTF) is located 20 km west of Syncrude in the Athabasca oil sands deposit of north-eastern Alberta. The reservoir bottom is at a depth of 160 m and the pay is 20 m thick. At the reservoir temperature of 7 °C, the viscosity of this 1.014 kg/l (8 ° gravity) bitumen is 5 Pa •s. The underburden consists of massive, underformed Waterways Formation limestone. Open pit mining of this reservoir is uneconomic because of the low pay to overburden ratio, and the relatively thin pay is uneconomic to recover with in-situ processes from vertical wells. Instead, the UTF project uses the Shaft And Tunnel Access Concept (SATAC) to gain access to the reservoir from tunnels within the limestone underburden. Horizontal well pairs were drilled into the oil sands from the tunnels. Steam injection is concurrent with the bitumen and water production. The process operates at a constant pressure (below fracture pressure) and relies on gravity drainage to deplete the reservoir(1). The phase A "laboratory scale" pilot consisted of three pairs of 160 m wells, each with 55 m of completion, and was successful(2). The subsequent Phase B pilot is operating, and consists of three pairs of 600 m wells, with 500 m completions. Purpose The intent of the monitoring program was to ensure the safety of the tunnels and wells, to quantify the success of the process, to confirm the geomechanical observations made during the Phase A laboratory scale pilot, and to assess methods of monitoring a commercial-scale project. The SATAC approach to bitumen recovery was novel enough to warrant extensive instrumentation of the shaft and tunnels. The Phase A tunnels, which provide access to the underground wellheads, had to be safe for personnel, isolate them from the pressurized steam chamber and allow for the continuous flow of steam and produced fluids between the wells and the surface. Given the observed integrity of the Phase A tunnels and the extremely consistent geology of the limestone underlying the UTF lease. The new Phase B tunnels have a reduced number of instrumented stations(3). The program is sufficiently flexible to allow for supplementary instrumentation if warranted. FIGURE 1: Plan of Phase A wells. (Available in full paper) For interpreting the process results, the data obtained from surface instrumentation in the Phase A pilot was extremely useful. It was expected that the behavior observed in the Phase A pilot would be applicable to the Phase B pilot and would therefore avoid the costs of using closely-spaced wells for monitoring small-scale phenomena.