Back Analysis of Joslyn Failure Using DEM Geomechanical Model

Abstract

At Joslyn creek, about 5:15 a.m. on May 18, 2006, the caprock (Clearwater Formation) which was supposed to be a barrier for steam inside the bitumen reservoir breached and caused a 125 by 75 meter surface disturbance, hurling rocks and trees, and leaving large craters. Joslyn creek steam assisted gravity drainage (SAGD), at that time, was operated by Deer Creek Energy Limited, a subsidiary wholly owned by Total E&P Canada Ltd. (Total). Long time after steam release, Total and Energy Resources Conservation Board (ERCB) released 1140-page and 177-page reports about this phenomenon respectively. Total and others have provided several scenarios for steam release and so far nobody knows what exactly has been caused the failure in this shallow reservoir during a short time of operation. Total's report states that “further work is needed especially to improve the quality of the geomechanical data (stresses and mechanical properties) and achieve two way coupling between the reservoir simulator and the geomechanical simulator”. It is challenging to simulate the behavior of unconventional reservoirs in an accurate manner when several physical models like geomechanics are not properly considered. Because of this fact that the geomechanical properties of reservoir such as in situ stress, deformation, porosity and compressibility change during operation and their values are completely different in compared to the original; thus, a reliable geomechanical model is needed in the conventional reservoir simulator. In traditional geotechnical engineering, back analysis of failed slopes or earth structures are used to test the models used to predict the factor of safety and the accuracy of laboratory testing. For the Joslyn Creek event, this is one of the only cases for SAGD where the Factor of Safety of the reservoir was unity (ie the applied forces where equal to resisting forces), therefore this presents a unique opportunity for a back analysis. This paper presents the initial work on the creating the geomechanical and flow models and the coupled reservoir geomechanical simulation approach which will be used for the back analysis. The model includes Discrete Fracture Network modeling, discontinuum modeling and coupling with CMG-STARS as a reliable representative for complicated geometry of fractured media. This approach may provide an opportunity to model real complex systems of a heterogeneous and anisotropic reservoir systems.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016