Geological underground utilisation inducing pore pressure changes in underground reservoirs
is generally accompanied by hydro-mechanical processes. Thereby, pore pressure increase
due to fluid injection may trigger ground surface uplift, while a decrease in pore pressure due
to reservoir fluid production is known to induce ground subsidence. Different coupled
hydro-mechanical simulation studies (e.g. Klimkowski et al., 2015, Kempka et al.,
2014, Tillner et al., 2014) indicate that ground surface displacements can achieve a
magnitude of several decimetres, if storage or production operations are being carried
out at an industrial scale. Consequently, detailed knowledge on the parameters
impacting ground surface uplift or subsidence is of major interest for the success of any
geological underground utilisation in order to avoid surface infrastructure damage
by spatially varying deformations. Furthermore, ground subsidence may result
increased groundwater levels as experienced in different underground coal mining
districts.
In the present study, we carried out coupled hydro-mechanical simulations to account for
the impact of caprock permeability on ground surface displacements resulting from
geological underground utilisation. Thereto, different simulation scenarios were investigated
using a synthetic 3D coupled numerical simulation model with varying caprock permeability
and vertical location of the open well section in the target reservoir. Material property ranges
were derived from available literature, while a normal faulting stress state was applied in all
simulation scenarios.
Our simulation results demonstrate that caprock permeability has a significant impact on
the pressure development, and thus on vertical displacements at the ground surface as well as
at the reservoir top. An increase in caprock permeability from 1 x 10-20 m2 by two orders of
magnitude doubles vertical displacements at the ground surface, whereas vertical
displacements at the reservoir top are decreased by almost 10 %. Furthermore, if the vertical
location of the open well section is directly located below the caprock, vertical
displacements at the ground surface are significantly higher compared to a lower open hole
position.
Consequently, a focus in site characterisation in the scope of geological underground
utilisation should be on detailed assessment of caprock permeability. These data
may be derived by well logs and hydraulic tests as well as laboratory tests on core
samples.
Kempka, T., Nielsen, C.M., Frykman, P., Shi, J.-Q., Bacci, G., Dalhoff, F. Coupled
Hydro-Mechanical Simulations of CO2 Storage Supported by Pressure Management
Demonstrate Synergy Benefits from Simultaneous Formation Fluid Extraction (2014) Oil Gas
Sci Technol, doi:10.2516/ogst/2014029.
Klimkowski, Ł., Nagy, S., Papiernik, B., Orlic, B., Kempka, T. Numerical simulations of
enhanced gas recovery at the Załęcze gas field in Poland confirm high storage capacities and
mechanical integrity (2015) Oil Gas Sci Technol (accepted).
Tillner, E., Shi, J-.Q., Bacci, G., Nielsen, C.M., Frykman, P., Dalhoff, F., Kempka, T.
Coupled Dynamic Flow and Geomechanical Simulations for an Integrated Assessment of
CO2 Storage Impacts in a Saline Aquifer (2014) Energy Procedia, 63:2879-2893,
doi:10.1016/j.egypro.2014.11.311. |