Properties
The steam is injected into a resistive oil reservoir (Fig. 487) and decreases its resistivity (Fig. 488). The amount of change in the resistivity depends on a variety of reservoir parameters, which can include temperature, salinity, and wettability [MMW93], [MBR12].
In addition, the surrounding geologic layers have differing resistivities, as indicated in the Table 1. The overlying layers consist of glacial till, paleo-channels, sands, and shales while the reservoir itself is a unconsolidated sand that contains the heavy oil. Below the reservoir lies a limestone basement unit, separated by an unconformity. Prairie Evaporites (or salts) may exist along the unconformity. The Aspen case history describes an airborne EM method which was used to recover the resistivities of the upper geologic layers.
The table below shows the resistivity values and thickness variations for each geologic layer and the steam chambers. A synthetic model was created with a single well pad that contains three sets of horizontal wells. An EM survey is used to monitor the growth of the steam chambers over time.
Table 1: The resistivity values and thickness variations for each geologic layer and the steam chambers.
Unit |
Description |
Thickness (m) |
Resistivity (Ohm-m) |
Quaternary deposits |
Glacial till, paleo-channels |
60 - 100 |
29 |
Grand Rapids Formation |
Shales and sands |
30 - 110 |
24 |
Clearwater Formation |
Shale |
65 - 90 |
12 |
Wabiskaw Formation |
Shales and sands |
5 |
46 |
McMurray Formation |
Oil sands |
45 - 115 |
147 |
Steam |
Steam |
n/a |
16 |
Devonian basement |
Limestone |
n/a |
56 |