Reservoir Geomechanical Analyses of Joslyn SAGD Steam Release Incident
Creators: Khani, Alireza
Publisher: name: University of Alberta Library
Year: 2022

<p>A noteworthy caprock failure occurred on the Joslyn Steam Assisted Gravity Drainage (SAGD) property in 2006 that continues to have a significant impact on the approval process for future SAGD projects. Two reports were released by Alberta government, which are AER Review and Analysis: Total E&amp;P Canada Ltd. Surface Steam Release of May 18, 2006, Joslyn Creek SAGD Thermal Operation, and Total E&amp;P Canada Ltd., Summary of investigation into the Joslyn, May 18, 2006 Steam Release. Several potential mechanisms were postulated within those studies but without definitive resolution. Therefore, the current study&#39;s main aim is to reassess the possible causes of Joslyn caprock failure and to forensically investigate the different mechanisms that may have contributed to this steam release incident. In addition, the findings of previous studies, including geomechanical simulations, uncertainties, and risk associated with evaluating caprock containment of SAGD operations using different approaches will be analyzed and the Joslyn steam release will be numerically re-analyzed to understand better the possible causes and mechanisms that led to the only known caprock failure in the 30 years of SAGD operations in Alberta.<br><br>
In the current study, numerical simulations were divided into three stages; 1) geomechanical analyses of a fractured medium in the assessment of caprock integrity, 2) hydro-mechanical analyses of the models to explore the impact of fluid flow on the results 3) coupled reservoir geomechanical analysis to investigate effects of SAGD operation on geomechanical response of the models. For the first stage, multiple realizations of the fracture network in caprock were executed to reflect various geomechanical and geometrical properties of fractures. A distinct element code, 3DEC, was utilized to evaluate the possible mechanisms of caprock failure in a fissured and non-fissured caprock. Then, three-dimensional numerical models including caprock and overburden were simulated under different load conditions and properties to assess the impact of steam injection pressure on caprock displacement, surface heave, the joint normal and shear displacements, as well as failure modes. The second stage of the analyses considered fluid flow in the models to investigate the impact of flow on fractures&#39; geometrical parameters, caprock displacement, and surface heave. The last numerical modeling stage was 3D sequentially coupled reservoir geomechanical analyses to simulate the reservoir&#39;s behaviors, caprock, and overburden and examine their complex interactions occurring during SAGD operations from beginning to the end. This stage consists of two sub-sections: first, post-failure simulation to validate the model with actual injection and production data as well as surveillance results installed after the steam release incident and second, using the validated model including all the well pairs and operations from the beginning to the end of the project to better understand the most likely steam release scenario of the failure.<br>
Through the analysis of multiple aspects of the Joslyn steam release incident, it is postulated that a chain of events, each impacting one another, contributed to the surface release. The possible, interacting multiple events that led to this failure have been identified as:<br>
• excessive bottomhole injection pressure;<br>
• potential low quality cement job performed for the abandonment of vertical observation wells;<br>
• presence of a gas zone surrounding the abandoned well within the Upper McMurray and Wabiskaw;<br>
• relatively low quality (less clayey) and thin caprock on the east side of the Joslyn project area;<br>
•  occasionally high water saturation zones within the Upper McMurray Formation; and <br>
• perhaps most critically, the unexpected migration of fluid flow from the west to the east side of the Joslyn project area leading to elevated pore pressures (and hence lower effective confining stresses) in the region (gas streak zone) directly overlying the well pair where the steam release event occurred.<br>
Based on the modeling results in this research which were validated with post-failure SAGD operations monitoring data, it allowed improved confidence in interpreting these complex events and re-adjusting the proposed formula to calculate MOP.</p>