Events

Dr. Rick Chalaturnyk, professor in the Department of Civil and Environmental Engineering at the University of Alberta, will give a talk entitled "Reservoir - Geomechanical Challenges Associated with In Situ Thermal Recovery in the Alberta Oil Sands" as part of the Claude R. Hocott Graduate Seminar Series.

Abstract:
Reservoir geomechanics is the integrated study of the state of stress, pore pressure and physical properties of reservoirs, natural fractures/faults, caprocks and the formations in the overburden. It provides a context within which to understand the interactions between geological conditions and engineering and production practices. The importance of geomechanics in problems such as wellbore stability, hydraulic fracturing and subsidence is well known and increasingly, a growing awareness of the importance of the link between fluid flow and geomechanics in the management of stress-sensitive reservoirs.  In contrast to conventional hydrocarbon reservoirs where flow in the pore space dominates the physics of recovery, exploitation of unconventional reservoirs typically involves recovery processes that produce complex thermal, chemical and stress changes within the reservoir that can significantly influence recovery. For oil sands reservoirs, the steam assisted gravity drainage recovery process results in a complex interaction of geomechanics and multiphase flow in primarily cohesionless porous media (sand) but also significant interactions with intra-formational shale facies and shale dominated caprocks. The geomechanical response of an oil sands reservoir to fluid pressure changes or to temperature changes results in stress and deformations that affect formation shearing, hydraulic properties such as absolute and relative permeability and the stability of underground openings. Temperature increase causes thermal expansion of the sand grains and sand structure and pore pressure increase during steam injection decreases the effective confining stress. For anisotropic in situ stress state in the reservoir, pore pressure will also generate shear stresses and shear strains in the sand structure. These processes combine to result in a net change in reservoir pore volume and permeability.  These issues will be explored within the context of the current challenges of SAGD development with the oil sands of Alberta. The seminar will also discuss a caprock integrity event that occurred in 2006 that has changed the focus of reservoir geomechanics for SAGD projects in Alberta.  It is estimated the Joslyn lease, located within the boreal forest, has 7.5 billion barrels of bitumen. The Total E&P Canada Ltd. (Total) Joslyn Creek SAGD project was located about 60 km north of Fort McMurray, Alberta. The target reservoir is located about 70 m below surface and is confined above by 50 m to 60 m of Clearwater Formation shale (caprock) and below the Devonian carbonates (underburden). On May 18, 2006, a loss of caprock containment occurred at the project, following the 4-month circulation period at well pad 204. This resulted in a steam release at ground surface, which lasted nearly 5 minutes, forming a 75 m by 125 m surface crater, threw rocks nearly 300 m away from the release point, and created 1 km dust plume (ERCB, 2010). The affected wells were shut down and pressures in neighboring wells were reduced following the incident. Further, the ERCB imposed a MOP restriction of 1,250 kPa for the Joslyn Creek project, a significant decrease from the original operating pressure of 1,800 kPa. The ERCB initiated these activities in part to address caprock integrity of SAGD developments in the Athabasca Oil Sands; since that time, Total has suspended the SAGD development. Post-failure analyses of the causes for caprock failure at Joslyn Creek are not entirely conclusive. Total (2007) stated that upward pressure migration induced by the steam chamber caused the loss of caprock containment and shear failure. An independent review of the Joslyn Creek failure by Carlson (2010) and Carlson (2011) did not entirely support the findings of Total (2007) and ERCB (2010), stating that considerable time, on the order of years, were needed to develop shear failure conditions in the caprock at the designed, operating conditions. Moreover, peak shear conditions in the caprock develop after about 5 years of SAGD operation and not early in the project life when the induced loadings and pore pressure increases are relatively low.  The ERCB (2010) agreed with the Total (2007) interpretation; however, suggested that naturally occurring fractures within the caprock and steam migration along abandoned wells may have also contributed to the steam release.