CO2BLOCKSEISM

An analytical tool for screening subsurface CO₂ storage resources constrained by induced seismicity

CO2BLOCKSEISM extends the tool CO2BLOCK, which estimates and optimizes CO₂ storage capacity subject to reservoir injectivity limitations. To learn more about the theory behind CO2BLOCKSEISM, please refer to the following paper:

• Kivi, I.R., De Simone, S. and Krevor, S., 2024. A simplified physics model for estimating subsurface CO₂ storage resources constrained ‎by fault slip potential. EarthArXiv. https://doi.org/10.31223/X5KM65

The CO2BLOCKSEISM tool is provided here in the context of two demonstration studies: Oklahoma seismicity and Utsira storage capacity. A general version of the code that can be applied to any study will be provided soon in this repository.

Should you have any questions/comments/suggestions, please contact Iman R. Kivi through the email i.rahimzadeh-kivi@imperial.ac.uk

CO2BLOCKSEISM is open-source software. If you use it for academic purposes, please cite the reference paper above.

Code structure

The tool comprises a number of scripts and functions as detailed below:

• “CO2BLOCKSEISM.m”: this is the main script, where all input data for the study are specified. This script calls several functions to perform the required calculations,
• “read_data.m”: this function reads the input parameters from the input Excel file,
• “hydrogeology.m”: this function involves analytical solutions of the pressure response of saline aquifers to multi-site CO₂ injection at time-varying rate,
• “Geomech_prob.m”: this function develops a Monte Carlo-type probabilistic model for evaluating the probability of fault slip under inherent uncertainties of the geomechanical parameters of the subsurface,
• “Analytical_solution.m” and “FD_Nor_2zones.m”: these functions calculate pressure changes in a saline aquifer in response to two phase flow of CO₂ and water around a single injection site based on the analytical solution by Nordbotten et al. (2005). A simplified solution for single phase flow of water is used for the demonstration study of induced seismicity in Oklahoma,
• “stress_projection.m”: this function projects shear and normal stress components onto the fault planes for different realizations of the Monte Carlo simulation,
• “eos.m”: this function returns brine viscosity and CO₂ density and viscosity using appropriate equations of state,
• “plot.m”: this script visualizes the output data through appropriate plots. Scientific colormaps developed by Fabio Crameri (2018) are used in these plots. The functions, database and instructions for using Crameri’s colormaps are also provided.

Input

Input parameters are introduced to the tool either directly within the script “CO2BLOCKSEISM.m” or through the input .xlsx file. The input file involves average values of the hydraulic properties of the aquifer required to estimate injection-induced pressure changes and the geomechanical properties of the seismogenic rock layers needed to estimate the potential for induced seismicity. The seismogenic layer can be the storage aquifer or hydraulically connected formations overlying or underlying the storage aquifer. Note that the input file has a fixed structure and the order of the input variables must not be changed. There is a set of strictly required parameters, while there is the possibility of using default values for the others, as explained in the example input data files. Although default values provide reasonable estimations, we recommend the use of precise data which would allow for a more accurate prediction of the storage capacity.

Information about the statistical distributions of uncertain geomechanical parameters, discretization in time and space, injection schedules and distributions of injection sites and faults are specified in the script “CO2BLOCKSEISM.m”. The script reads data for the distributions of the injection sites and faults from separate input .xlsx files. Additional information, e.g., geographical data or induced seismicity records may be added for use in the plots.

Output

The main outputs of the tool are the spatial and temporal evolution of injection-induced pore pressure changes, fault slip probability, possible earthquake magnitudes and the maximum CO₂ storage capacity that can be safely achieved. The tool saves the plots in the specified directory.

The results of the tool calculations for the two demonstration studies are provided as “Results_Utsira.mat” and “Results_OK.mat”. One may simply load the results and just run the script “plot.m” to reproduce all figures presented in the reference paper mentioned above. Alternatively, the script “CO2BLOCKSEISM.m” with the provided input data can be run to regenerate the results.

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