Monitoring and Modelling in Coupled Geomechanics Processes

Abstract

Geomechanics issues are vital in all reservoir processes, but particularly so in weak, unconsolidated sandstones. Coupled stress-flow simulation is necessary to analyse and understand effects such as changes in reservoir volume that arise from heating and pressurization, and non-linear plasticity models that incorporate shear dilatancy are needed to simulate the dilation effects that are observed in any thermal process in sands.Coupling of flow and stress is based on the volume changes that arise with changes in pressur and temperature. Incorporating shear dilation is based on computation of effective stresses from ΔT and Δp, then assessing the state of the rock to see if and how much it shears and dilates. These processes are ill-quantified at present, so it is necessary to monitor.The two monitoring domains that are of greatest interest to coupled geomechanics simulation are the deformation field and the seismic attributes field. More specifically, how these fields evolve in space and with time are the key factors to tracking processes to calibrating geomechanics models, and to the successful optimization of complex in situ processes.A general geomechanics view of how to achieve process monitoring and optimization goals is presented in a general fashion. Further progress in the areas of monitoring, inversion, and geomechanics simulation is needed, although recent developments have advanced these aspects.

Anomalous surface heave induced by enhanced oil recovery in northern Alberta: InSAR observations and numerical modeling

“…One likely candidate for some of the “missing” surface deformation is shear dilation: all our models assume a purely elastic reservoir rock and overburden; however, elevated temperatures and pressures can cause shear failure within the reservoir rock, thereby increasing the porosity and permeability and accelerating the outward expansion of the steam chamber [ Collins , ; Dusseault , ] and enhancing surface deformation compared to the elastic case. The fact that our models assume purely elastic behavior may also explain why compaction effects are visible in our models after about 3–4 years, despite not being visible in the InSAR data: shear dilation would enhance uplift, but since it is not fully reversible, it would also counteract or delay the compaction that takes place following removal of bitumen from the pore space.…”

“…Although geomechanical models aimed at understanding SAGD and optimizing production have already been developed (and continue to be refined) both by industry and researchers in petroleum engineering [e.g., Dusseault and Rothenburg , ; Dusseault , ; Yin et al ., ; Azad and Chalaturnyk , ], the mechanisms leading to deformation within the reservoir and the overburden (observable as heave at the surface) are still not very well understood. A good match to the surface heave observations could likely be obtained by inverting the InSAR data to constrain pressurized elastic sources at reservoir depths.…”

“…It should be noted that the interactions between steam and the oil sand reservoir are not straightforward. Steam injection increases both temperatures and pore pressures within the reservoir, causing strains and heating‐induced changes in material properties of the reservoir [ Collins , ; Dusseault , ]. Thermal expansion, phase changes (steam to water), shear dilation, changes in reservoir properties such as porosity and permeability, and withdrawal of bitumen will all have some influence on the stresses transmitted to the cap rock and thus on the surficial effects of SAGD process.…”

Microscale modeling of fluid flow‐geomechanics‐seismicity: Relationship between permeability and seismic source response in deformed rock joints

“…Human activities create stress perturbations that trigger induced seismicity in underground formations. Intact rock or prestressed fractures subjected to induced stress could fail and release the stored strain energy in the rock suddenly [ Dusseault , ]. Rock rupture involves various scales and generates seismicity with different magnitudes in the forms of acoustic emission, microseismicity, or induced earthquakes [ Bohnhoff et al , ].…”

“…Characterizing the spatial and temporal variations in microseismicity can be used to assess changes in the stress field and hence potentially be used to monitor perturbations in fluid pathways. In addition to mapping the spatial distribution of microseismic events [ Dusseault , ], microseismic source mechanisms can be characterized to study slip direction, slippage plane orientation, and the volumetric deformation of the natural fractures by moment tensor inversion [ Baig and Urbancic , ]. The fractures may have highly variable strength and mechanical properties, allowing them to open or close during failure.…”