Development
of Predictive Model for Carbon Dioxide Sequestration In Deep Saline Aquifers
Abstract
Although deep saline aquifers are found in all
sedimentary basins and provide very large storage capacities, a little is known
about them because they are rarely a target for the exploration. Furthermore,
nearly all the experiments and simulations made for CO2 sequestration in deep
saline aquifers are related to the sandstone formations. The aim of this study
is to create a predictive model to estimate the CO2 storage capacity of the
deep saline carbonate aquifers since a little is known about them. To create a
predictive model, the variables which affect the CO2 storage capacity and their
ranges are determined from published literature data. They are rock properties
(porosity, permeability, vertical to horizontal permeability ratio), fluid
properties (irreducible water saturation, gas permeability end point, Corey water and gas coefficients), reaction properties
(forward and backward reaction rates) and reservoir properties (depth, pressure
gradient, temperature gradient, formation dip angle, salinity), diffusion
coefficient and Kozeny-Carman Coefficient. Other
parameters such as pore volume compressibility and density of brine are
calculated from correlations found in literature. To cover all possibilities,
Latin Hypercube Space Filling Design is used to construct 100 simulation cases
and CMG STARS is used for simulation runs. By using least squares method, a
linear correlation is found to calculate CO2 storage capacity of the deep
saline carbonate aquifers with a correlation coefficient 0.81 by using variables
found from literature and simulation results. Numerical dispersion effects have
been considered by increasing the grid dimensions. It has been found that
correlation coefficient decreased to 0.77 when the grid size was increased from
250 ft to 750 ft. The sensitivity analysis shows that the most important
parameter that affects CO2 storage capacity is depth since the pressure
difference between formation pressure and fracture pressure increases with
depth. Also, CO2 storage mechanisms are investigated at the end of 300 years of
simulation. Most of the gas (up to 90%) injected into formation dissolves into
the formation water and negligible amount of CO2 reacts with carbonate. This
result is consistent with sensitivity analysis results since the variables affecting
the solubility of CO2 in brine have greater affect on storage capacity of
aquifers. Dimensionless linear and nonlinear predictive models are constructed
to estimate the CO2 storage capacity of all deep saline carbonate aquifers and
it is found that the best dimensionless predictive model is linear one
independent of bulk volume of the aquifer.
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