SAGD has been proven to be a commercially viable method to extract bitumen from oil sands reservoirs in Western Canada. To understand the influences of steam injection on reservoir and surrounding rocks and potential impacts of surface deformation on the environment, instrumentations such as piezometers, thermocouples, extensometers, tiltmeters, geophones and 4D seismic survey have been applied in SAGD projects. The effects of geomechanics on SAGD have been well documented. Collecting essential geomechanical data, interpreting them properly and incorporating them into numerical models are necessary to ensure meaningful history matching and understanding of reservoir performances.
This paper outlines geomechanical data acquisition and field monitoring methods from a reservoir engineering perspective, and the applications of geomechanics in SAGD design and history matching. Minimum data acquisition programs to collect the necessary geomechanical data for different analysis purposes in SAGD projects are suggested. Primary instrumentations are briefly overviewed and recommendations to instrumentation selection are provided. Using generic Canadian oil sands reservoir and rock properties, the subsurface and surface deformation including permeability changes, reservoir movements, strains and surface uplifts etc. are simulated. The method to couple the results of geostatistics modeling, reservoir simulation and geomechanics in SAGD simulation and to link them with 4D seismic in history matching is provided. Simulations are completed with the widely applied thermal simulator, STARS ®, and its limitations are also discussed.
Steam Assisted Gravity Drainage (SAGD) has been proven to be a commercially viable method to extract bitumen from oil sands reservoirs in Western Canada(1)–(3). In SAGD process, high temperature steam is injected into the reservoir with pressures closed to or higher than initial reservoir pressures. Steam temperature in the reservoir could be over 200 °C and pressure up to 5 or 6 MPa. This can cause significant geomechanical effects on the reservoir and surrounding rocks, and may also affect surface facilities and the surface surrounding environment.
The influences of SAGD on bitumen recovery from oil sands have been investigated by a number of researchers such as Chalaturnyk(4), Collins(5), and Li(6), and some of their findings will be referred to in his paper. In addition to ensuring safe SAGD operations, geomechanics understanding will be necessary to investigate the potential breaking of interbedded mudstone and IHS (Inclined Heterolithic Stratification), a commonly found geological feature that often are baffle to the upward growth of a SAGD steam chamber. As demonstrated by Li(6), if these IHS can be broken, SAGD bitumen recovery would increase significantly where IHS is prevalent.
Several types of field monitoring methods have been applied in SAGD projects to understand geomechanical responses and steam chamber dynamics. Piezometers and thermocouples are commonly used to monitor pressures and temperatures at observation wells and SAGD injectors and producers(4). Downhole extensometers and inclinometers (tiltmeters) were also installed in the UTF project to measure vertical strains and displacements(4). Tiltmeters are applied to monitor surface deformations and triaxial geophones to detect microseismic events during SAGD recovery(7).
