Introduction

expreccs is a simplified and flexible framework for testing a two-stage approach with dynamic pressure boundary conditions in regional and site-scale CO2 storage simulations. It can generate integrated modeling studies or project dynamic boundary conditions between existing OPM Flow models with nonconforming grids.

Core concept

The two-stage workflow connects a computationally efficient regional model with a higher-resolution site model:

1. Simulate the regional model through all report steps.

2. Identify the regional connections corresponding to the site-model boundary.

3. Project regional pressures, pressure increases, fluxes, or pore-volume effects to the site boundary.

4. Simulate the site model with dynamically updated boundary conditions.

5. Compare the site result with a higher-resolution reference model when one is available.

This approach accounts for regional pressure interference without requiring the complete regional grid resolution inside every site-scale simulation.

Supported model sources

expreccs supports two main ways of defining a study.

Integrated configuration

A configuration file can generate the reference, regional, and site models together with their rock properties, faults, wells, schedules, and boundary conditions.

Existing OPM Flow models

Existing regional and site OPM Flow decks can be supplied directly. Their grids do not need to conform. expreccs identifies the overlapping region, constructs the boundary mappings, processes the regional results, and writes the dynamic boundary updates required by the site model.

Core workflows

• Generate corner-point grids for reference, regional, and site models.

• Define heterogeneous rock and saturation properties.

• Add faults, hysteresis, salinity, wells, and operational schedules.

• Run complete, reference-only, regional-only, site-only, or regional-and-site workflows.

• Project pressure, pressure increase, flux, or pore-volume effects.

• Apply dynamic conditions to regular or irregular site boundaries.

• Interpolate projected values between regional report steps.

• Construct projections by corresponding FIPNUM regions when the regional and site models have a vertical offset.

• Compare reference, regional, and site simulations.

• Generate figures for pressure, gas saturation, well behavior, sensor pressure, and boundary effects.

• Support model coarsening, optimization, and reproducible research workflows.

Basic usage

Run an integrated study defined by a TOML file:

expreccs -i examples/example1.toml -o hello_world

Project dynamic boundary conditions between existing regional and site models:

expreccs -i "tests/regional/REGIONAL tests/site/SITE" -o projected

Display the available command-line options:

expreccs --help

Use Command-line reference for exact syntax, defaults, and option compatibility. See Examples for complete integrated, existing-deck, regular-boundary, and irregular-boundary workflows.

Research development

The expreccs Python tool was used to generate the published results for the hierarchical regional-to-site modeling study:

Tveit, S., Gasda, S. E., Landa-Marbán, D., and Sandve, T. H. (2025). A hierarchical approach for modeling regional pressure interference in multi-site CO2 operations. Geoenergy Science and Engineering, 248, 213733. https://doi.org/10.1016/j.geoen.2025.213733

The scripts and configurations used to reproduce that study are available in the examples/paper_2025 directory.

The directory contains four study folders:

• Case1

• Case2

• Case3

• Case4

These cases use expreccs and implement the regional-to-site modeling and dynamic boundary-condition studies described in the paper. They remain available as publication-supporting examples in the repository but do not have a separate reproduction page in the online documentation.

Related project publications

The expreccs repository also hosts the reproducibility material for TCCS-13 and ECMOR 2026. These studies are contributions from the broader expreccs research project and address model coarsening, pressure communication, and large-scale CO2 storage simulation.

Unlike the 2025 hierarchical regional-to-site study, the TCCS-13 and ECMOR 2026 reproduction workflows do not use the expreccs Python executable. They are hosted in this repository because they were developed within the same research project and share its OPM Flow modeling, preprocessing, visualization, and reproducibility infrastructure.

TCCS-13

The TCCS-13 page documents the Troll aquifer coarsening and optimization study. Its workflow uses OPM Flow, pycopm, plopm, Everest, ResInsight, and supporting Python and shell scripts. It does not invoke the expreccs executable.

ECMOR 2026

The ECMOR 2026 page documents the explicit non-net-cell treatment study for improving pressure communication in coarsened aquifer models. Its workflow uses OPM Flow, pycopm, plopm, ResInsight, ParaView, and supporting Python and shell scripts. It does not invoke the expreccs executable.

About the project

expreccs is funded by Harbour Energy, Equinor, Shell, and the Research Council of Norway under project number 336294.

See the project description for additional information about the project objectives and partners.

Where to continue

• Complete the Installation and verify expreccs and OPM Flow.

• Use Configuration reference to define integrated regional, reference, and site studies.

• Browse Examples for configuration-based, existing-deck, regular-boundary, and irregular-boundary workflows.

• Review the 2025 publication cases for the research workflows that use the expreccs Python tool.

• Open TCCS-13 for the related Troll aquifer coarsening and optimization study hosted by the expreccs project. This workflow does not use the expreccs executable.

• Open ECMOR 2026 for the related explicit non-net-cell treatment study hosted by the expreccs project. This workflow does not use the expreccs executable.

• Use Command-line reference for exact CLI options, defaults, and workflow compatibility.

• Review Output folder for generated preprocessing, simulation, postprocessing, mapping, and boundary-condition files.

• Browse expreccs Python API for the Python modules, classes, and functions.

• See Contributing to report issues, request features, or contribute to expreccs.

• Explore Related projects for complementary OPM Flow simulation, preprocessing, and visualization tools.