4D-3C geomechanical study of in-situ bitumen recovery in NW Canada using Toe-to-Heel Air Injection

Recent observations of shear-wave splitting in the near surface have been interpreted as a consequence of the stress state rather than the presence of fractures. The analysis of such shallow anisotropy measurements from shear-wave splitting on converted-wave data allows us to evaluate caprock integrity and detect areas where the stress in the caprock may deviate from the regional faulting regime. This information is vital in discerning whether the caprock is able to withstand recovery of shallow in-situ bitumen and heavy oil. Moreover, using time-lapse multi-component data, we can use the changes in splitting azimuth and time delay to monitor overburden and reservoir changes occurring during production. Here we show that converted-wave splitting changes, observed at the Conklin Demonstration Project between 2008 and 2009, can be directly correlated to changes occurring in the overburden. Additionally, we show that the stress state of the overburden, and in particular the transition from one stress regime to another with depth, is considerably more complex than has generally been assumed.