The Emergent Impacts of Small Scale Capillary Heterogeneity on Field
Scale CO2 Flow and Trapping
Abstract
We employ a multi scale approach combining experiments and modelling to
elucidate the impacts of small scale (sub-seismic resolution
<10m) capillary pressure heterogeneities in field scale CO2
flow and trapping. We analyse 48 rock cores (~3cm
length, 4cm diameter) covering the entire 100m interval of the Captain D
sandstone in the Goldeneye field, UK North Sea. We experimentally
measure porosity, capillary pressure, absolute permeability, relative
permeability and trapping characteristics for the cores, which are used
to create 3D numerical models with heterogeneities defined at the mm
scale. These models are validated by predicting experimental X-Ray CT
observations of saturation (mm scale) and pressure measurements (cm
scale) at various flow rates and fractional flows of gas-water. The
intrinsic, core scale properties are then used to populate 2D meso scale
numerical simulations (50m x 10m size), with heterogeneities defined at
cm scale using a geostatistical representation. We vary the correlation
length and variance of the fields within the bounds of the experimental
observations to investigate the impacts of small scale heterogeneity on
vertical and lateral CO2 plume migration under different Capillary, Bond
and Gravity numbers. At low flow potential, layered capillary pressure
heterogeneities can speed up lateral plume migration by up to 20%, with
gravitational segregation significantly enhancing the migration (See
Fig. 1). In the vertical case, layered heterogeneities can significantly
increase CO2 trapping, which is further enhanced with the inclusion of
capillary pressure hysteresis. Finally, we derive capillary limit,
upscaled equivalent properties from the meso scale simulations, which
incorporate the impacts of small scale heterogeneity. These are used to
represent the grid block properties in a full field 3D numerical model
of the Goldeneye field (lateral ~5 km, depth 200m). We
analyse the impact of varying relative permeabilities (with anisotropy)
on the field scale plume migration and trapping. We see large
differences compared to cases using intrinsic rock properties,
indicating that proper inclusion of small scale heterogeneity is needed
in upscaling workflows when predicting and assessing uncertainty in low
flow potential CO2 plume migration at the field scale.