Augmenting a pure and hybrid vertical equilibrium scheme via data-driven surrogate modelling
Pith reviewed 2026-05-18 16:37 UTC · model grok-4.3
The pith
Data-driven surrogates augment hybrid vertical equilibrium schemes to cut simulation times with negligible errors
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
By training and deploying surrogate models to predict gas plume distance, coarse-level mobilities in the VE zone, and the coupling-scheme quantities at model interfaces, the augmented hybrid scheme achieves substantially lower runtimes than traditional mass-and-momentum simulations while introducing only negligible errors and preserving physical properties such as mass conservation.
What carries the argument
Data-driven surrogate models that replace direct computation of gas plume distance, coarse-level mobilities, and coupling terms inside the hybrid vertical equilibrium framework.
Load-bearing premise
The surrogate models must accurately predict gas plume distance, coarse-level mobilities, and coupling quantities over the relevant parameter space without violating physical constraints such as mass conservation.
What would settle it
A benchmark run in which the surrogate-augmented hybrid model either produces a mass-conservation error larger than the non-surrogate hybrid or fails to run faster than a traditional simulation would falsify the performance claim.
read the original abstract
Vertical equilibrium (VE) models have been introduced as computationally efficient alternatives to traditional mass and momentum balance equations for fluid flow in porous media. Since VE models are only accurate in regions where phase equilibrium holds and traditional simulations are computationally demanding, hybrid methods have been proposed to combine the accuracy of the full-dimensional approach with the efficiency of VE model. However, coupling both models introduces computational overhead that can make hybrid simulations slower than fully traditional ones. To address the computational overhead introduced by coupling interfaces in hybrid models, we utilize data-driven surrogates to accelerate the overall scheme. To this end, we predict the gas plume distance and coarse-level mobilities in the VE model, and also enhance the computation of the coupling scheme via surrogates. We focus on surrogate models with short inference times to minimize computational overhead during frequent function calls. The proposed approach preserves key physical properties, such as mass conservation, despite the deployment of data-driven models, while substantially reducing simulation runtimes. Overall, combining data-driven methods with the hybrid VE scheme yields an enhanced model that outperforms traditional simulations in speed while introducing only negligible errors.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes augmenting pure vertical equilibrium (VE) and hybrid VE/full-dimensional schemes for porous-media flow with data-driven surrogate models. Surrogates are trained to predict gas-plume distance and coarse-level mobilities inside VE regions and to accelerate the computation of coupling quantities at VE–full-dimensional interfaces. The authors claim that the resulting scheme retains mass conservation, produces only negligible errors relative to the unsimplified hybrid model, and delivers substantial runtime reductions compared with traditional full-dimensional simulations.
Significance. If the conservation and accuracy claims are rigorously verified, the work would demonstrate a practical route to mitigating the coupling overhead that currently limits hybrid VE models, thereby extending the applicability of reduced-order methods to larger-scale reservoir simulations. The emphasis on short-inference-time surrogates is well-aligned with the requirements of explicit time-stepping schemes.
major comments (2)
- [§4.2 and §5.1] §4.2 and §5.1: The central claim that mass conservation is preserved rests on the assertion that the surrogates for coarse mobilities and interface quantities reproduce the discrete divergence-free property of the underlying finite-volume scheme. No description is given of a projection step, physics-informed loss term, or post-processing correction that would enforce this algebraic identity; standard regression surrogates minimize pointwise error but do not automatically satisfy the local flux-balance condition required at coupling interfaces. Without such a mechanism, accumulated mass drift over hundreds of time steps would invalidate the performance claims.
- [Table 2 and Figure 7] Table 2 and Figure 7: The reported error metrics and runtime speed-ups are presented without baseline comparisons to the original hybrid VE scheme (i.e., without surrogates) or to fully traditional simulations on the same grids. The absence of these controls makes it impossible to quantify whether the observed errors remain negligible once the surrogate-induced perturbations propagate through the coupled system.
minor comments (2)
- [§3.1] Notation for the surrogate inputs (e.g., the precise definition of the coarse mobility vector and the interface flux vector) is introduced inconsistently between §3.1 and the appendix; a single consolidated table of symbols would improve readability.
- [§4.1] The training-data generation procedure (parameter ranges, number of full-order simulations, and sampling strategy) is described only qualitatively; explicit ranges and sample counts should be stated so that reproducibility can be assessed.
Simulated Author's Rebuttal
We are grateful to the referee for the thorough review and valuable feedback on our manuscript. The comments have helped us identify areas where additional clarifications and comparisons can strengthen the presentation. Below, we address each major comment in detail.
read point-by-point responses
-
Referee: [§4.2 and §5.1] §4.2 and §5.1: The central claim that mass conservation is preserved rests on the assertion that the surrogates for coarse mobilities and interface quantities reproduce the discrete divergence-free property of the underlying finite-volume scheme. No description is given of a projection step, physics-informed loss term, or post-processing correction that would enforce this algebraic identity; standard regression surrogates minimize pointwise error but do not automatically satisfy the local flux-balance condition required at coupling interfaces. Without such a mechanism, accumulated mass drift over hundreds of time steps would invalidate the performance claims.
Authors: We appreciate the referee pointing out the need for explicit justification of mass conservation in the surrogate-augmented scheme. The surrogates are trained directly on data obtained from the original finite-volume discretization, which satisfies the discrete divergence-free condition by construction. The predicted coarse mobilities and interface quantities are therefore approximations to quantities that already fulfill the local flux balance. Our numerical results indicate that the approximation errors are sufficiently small that no significant mass drift occurs over the simulated time horizons. To strengthen the manuscript, we will add a dedicated paragraph in §4.2 explaining this training-based preservation of the algebraic property and include a supplementary figure demonstrating the evolution of global mass error for the surrogate model. revision: partial
-
Referee: [Table 2 and Figure 7] Table 2 and Figure 7: The reported error metrics and runtime speed-ups are presented without baseline comparisons to the original hybrid VE scheme (i.e., without surrogates) or to fully traditional simulations on the same grids. The absence of these controls makes it impossible to quantify whether the observed errors remain negligible once the surrogate-induced perturbations propagate through the coupled system.
Authors: We agree that including baseline comparisons is important for a complete assessment. The current Table 2 and Figure 7 primarily contrast the surrogate-enhanced hybrid model with traditional full-dimensional simulations to emphasize the achieved speed-up. We will revise these to also report results from the original hybrid VE scheme without surrogates. This will allow readers to evaluate the surrogate-induced errors relative to the unsimplified hybrid model and confirm that they remain negligible while still providing substantial runtime improvements over both the baseline hybrid and the full-dimensional approaches. revision: yes
Circularity Check
Data-driven surrogates trained independently on simulation outputs accelerate hybrid VE without reducing claims to self-definition or fitted inputs by construction.
full rationale
The paper trains surrogate models on data generated from the underlying VE and hybrid schemes to predict plume distance, coarse mobilities, and interface quantities. These predictions are evaluated empirically against full simulations for speed and error, with mass conservation preserved through the overall scheme structure rather than by redefining the target quantities in terms of the surrogates themselves. No load-bearing step equates a derived result to its own training inputs or relies on a self-citation chain that assumes the target outcome. The approach remains self-contained against external numerical benchmarks.
Axiom & Free-Parameter Ledger
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We employ data-driven models to enhance both a pure VE model and a hybrid formulation... linear regression and spline interpolation models stand out for their exceptionally fast evaluations
-
IndisputableMonolith/Foundation/Atomicity.leanatomic_tick unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the proposed approach preserves key physical properties, such as mass conservation
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
Technical report, Gas Infrastructure Europe (2021)
Europe, G.I.: Picturing the value of underground gas storage to the euro- pean hydrogen system. Technical report, Gas Infrastructure Europe (2021). https://www.gie.eu/wp-content/uploads/filr/3517/Picturing%20 the%20value%20of%20gas%20storage%20to%20the%20 FINAL 140621.pdf
work page 2021
-
[2]
Energy Reports 9, 6251– 6266 (2023) https://doi.org/10.1016/j.egyr.2023.05.236
Al-Shafi, M., Massarweh, O., Abushaikha, A.S., Bicer, Y.: A review on underground gas storage systems: Natural gas, hydrogen and carbon sequestr ation. Energy Reports 9, 6251– 6266 (2023) https://doi.org/10.1016/j.egyr.2023.05.236
-
[3]
Energy Storage M aterials 63, 103045 (2023) https://doi.org/10.1016/j.ensm.2023.103045
Liu, W., Li, Q., Yang, C., Shi, X., Wan, J., Jurado, M.J., Li, Y., Jiang, D., C hen, J., Qiao, W., Zhang, X., Fan, J., Peng, T., He, Y.: The role of underground salt c averns for large- scale energy storage: A review and prospects. Energy Storage M aterials 63, 103045 (2023) https://doi.org/10.1016/j.ensm.2023.103045
-
[4]
Wan, J., Sun, Y., He, Y., Ji, W., Li, J., Jiang, L., Jurado, M.J.: Developm ent and technology status of energy storage in depleted gas reservoirs. Internatio nal Journal of Coal Science & Technology 11(1), 29 (2024) https://doi.org/10.1007/s40789-024-00676-y
-
[5]
In: SPE Energy Tr ansition Symposium
Aluah, R., Fadairo, A., Opeyemi, O., Ni, R., Foerster, I.: An experime ntal study on the caprock integrity of reservoirs to assess the repurposing deplet ed bakken formation oil and gas fields for underground hydrogen storage. In: SPE Energy Tr ansition Symposium. SPE Energy Transition Symposium, vol. SPE Energy Transition Symposium , pp. 012–002002 (2024)...
-
[6]
Natural Gas Industry B 9(4), 383–393 (2022) https://doi.org/10.1016/j.ngib.2022.07.002
Luo, A., Li, Y., Chen, X., Zhu, Z., Peng, Y.: Review of co2 sequestra tion mechanism in saline aquifers. Natural Gas Industry B 9(4), 383–393 (2022) https://doi.org/10.1016/j.ngib.2022.07.002
-
[7]
Celia, M.A., Bachu, S., Nordbotten, J.M., Bandilla, K.W.: Status of co2 storage in deep saline aquifers with emphasis on modeling approaches and pract ical simulations. Water Resources Research 51(9), 6846–6892 (2015) https://doi.org/10.1002/2015WR017609 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015WR017609
-
[8]
Das, M., Mukherjee, P., Muralidhar, K.: Modeling Transport Pheno mena in Porous Media with Applications, p. 241. Springer, ??? (2018). https://doi.org/10.1007/978-3-319-69866-3
-
[9]
Water Resources Research 47(5) (2011) https://doi.org/10.1029/2010WR009075
Gasda, S.E., Nordbotten, J.M., Celia, M.A.: Vertically averaged appr oaches for co2 migration with solubility trapping. Water Resources Research 47(5) (2011) https://doi.org/10.1029/2010WR009075
-
[10]
Nordbotten, J., Celia, M.: Geological storage of co: Modeling app roaches for large-scale sim- ulation. Geological Storage of CO2: Modeling Approaches for Large -Scale Simulation, (2011) https://doi.org/10.1002/9781118137086.fmatter
-
[11]
Vahabzadeh, E., Buntic, I., Nazari, F., Flemisch, B., Helmig, R., Nias ar, V.: Applicability of the vertical equilibrium model to underground hydrog en injection and withdrawal. International Journal of Hydrogen Energy 106, 790–805 (2025) https://doi.org/10.1016/j.ijhydene.2025.01.201
-
[12]
Becker, B., Guo, B., Buntic, I., Flemisch, B., Helmig, R.: An adaptive hybrid vertical equilibrium/full-dimensional model for compositional multiph ase flow. Water Resources Research 58(1), 2021–030990 (2022) https://doi.org/10.1029/2021WR030990 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021WR030990. e2021WR030990 2021WR030990
-
[13]
Computational Geosciences 23(1), 1–20 (2019) https://doi.org/10.1007/s10596-018-9775-z
Møyner, O., Nilsen, H.M.: Multiresolution coupled vertical equilibrium model for fast flexible simulation of co2 storage. Computational Geosciences 23(1), 1–20 (2019) https://doi.org/10.1007/s10596-018-9775-z
-
[14]
Computational Geos ciences 29(2), 11 (2025) https://doi.org/10.1007/s10596-025-10351-z
Buntic, I., Schneider, M., Flemisch, B., Helmig, R.: A fully-implicit solvin g approach to an adaptive multi-scale model - coupling a vertical-equilibrium and full-dime nsional model for compressible, multi-phase flow in porous media. Computational Geos ciences 29(2), 11 (2025) https://doi.org/10.1007/s10596-025-10351-z
-
[15]
Sun, L., Gao, H., Pan, S., Wang, J.-X.: Surrogate modeling for fluid flows based on physics- constrained deep learning without simulation data. Computer Metho ds in Applied Mechanics and Engineering 361, 112732 (2020) https://doi.org/10.1016/j.cma.2019.112732
-
[16]
In: AISyS 2024 : The First International Conference on AI-based Systems and Services
Kavana, S., Kulkarni, K., K¨ ostler, H.: An advanced surrogate m odel approach for enhancing fluid dynamics simulations. In: AISyS 2024 : The First International Conference on AI-based Systems and Services. AISyS 2024, p. 6 (2024)
work page 2024
-
[17]
Wen, H., Khan, F., Amin, M.T., Halim, S.Z.: Myths and misconceptions o f data-driven meth- ods: Applications to process safety analysis. Computers & Chemica l Engineering 158, 107639 (2022) https://doi.org/10.1016/j.compchemeng.2021.107639
-
[18]
Schultzendorff, P.V., Sandve, T.H., Kane, B., Landa-Marb´ an, D ., Both, J.W., Nord- botten, J.M.: A machine-learned near-well model in opm flow 2024(1), 1–23 (2024) https://doi.org/10.3997/2214-4609.202437033 22
-
[19]
Water Resources Research 54(7), 4347–4360 (2018) https://doi.org/10.1029/2017WR022303
Becker, B., Guo, B., Bandilla, K., Celia, M.A., Flemisch, B., Helmig, R.: An adap- tive multiphysics model coupling vertical equilibrium and full multidimens ions for mul- tiphase flow in porous media. Water Resources Research 54(7), 4347–4360 (2018) https://doi.org/10.1029/2017WR022303
-
[20]
Brooks, R.H., Corey, A.T.: Hydraulic properties of porous media. Hydrology Papers 3 (1964)
work page 1964
-
[21]
Zhang, D.: 6 - two-phase flow. In: Zhang, D. (ed.) Stochastic Methods for Flow in Porous Media, pp. 262–296. Academic Press, San Diego (2002). https://doi.org/10.1016/B978-012779621-5/50007-3 . https://www.sciencedirect.com/science/article/pii/B9780127796215500073
-
[22]
Becker, B.: Development of efficient multiscale multiphysics models accounting for reversible flow at various subsurface energy storage sites. Disse rtation, Universit¨ at Stuttgart, Institut f¨ ur Wasser- Umweltsystemmodellierung, St uttgart (June 2021). https://doi.org/10.18419/opus-11753 . http://dx.doi.org/10.18419/opus-11753
-
[23]
Nordbotten, J.M., Dahle, H.K.: Impact of the capillary fringe in vertically integrated models for co2 storage. Water Resources Research 47(2) (2011) https://doi.org/10.1029/2009WR008958 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009WR008958
-
[24]
Computers & Geosciences 169, 105207 (2022)
Wen, G., Li, Z., Azizzadenesheli, K., Anandkumar, A., Durlofsky, L .J.: Fourier neural operator for multiphase flow simulation in carbon sequestration. Computers & Geosciences 169, 105207 (2022)
work page 2022
-
[25]
Journal of Computational Physics 337, 275–288 (2017) https://doi.org/10.1016/j.jcp.2017.02.041
Voskov, D.V.: Operator-based linearization approach for mode ling of multiphase multi- component flow in porous media. Journal of Computational Physics 337, 275–288 (2017) https://doi.org/10.1016/j.jcp.2017.02.041
-
[26]
Khait, M., Voskov, D.V.: Operator-based linearization for gener al purpose reser- voir simulation. Journal of Petroleum Science and Engineering 157, 990–998 (2017) https://doi.org/10.1016/j.petrol.2017.08.009
-
[27]
Springer, Berlin, Heidelberg (2006)
Bishop, C.M.: Pattern Recognition and Machine Learning (Inform ation Science and Statis- tics). Springer, Berlin, Heidelberg (2006)
work page 2006
-
[28]
Murphy, K.P.: Machine Learning: A Probabilistic Perspective. The MIT Press, ??? (2012)
work page 2012
-
[29]
Boor, C.: A Practical Guide to Splines. Springer, New York (1978 )
work page 1978
-
[30]
http://www.iapws.org/IF97-Rev.pdf , Lucerne, Switzerland (1997)
Water, I.T.I.A., Steam): Revised Release on the IAPWS Industria l Formulation 1997 for the Thermodynamic Properties of Water and Steam. http://www.iapws.org/IF97-Rev.pdf , Lucerne, Switzerland (1997)
work page 1997
-
[31]
Buntic, I., Coltman, E., Flemisch, B., Ghosh, T., Gl¨ aser, D., Gr¨ un inger, C., Hommel, J., Keim, L., Kelm, M., Koch, T., Kostelecky, A.M., Lipp, M., Oukili, H., Schneide r, M., Utz, M., Wang, Y., Weishaupt, K., Wendel, K., Winter, R., Wu, H.: DuMux 3.8.0. D aRUS (2023). https://doi.org/10.18419/darus-3788
-
[32]
Koch, T., Gl¨ aser, D., Weishaupt, K., Ackermann, S., Beck, M., Becker, B., Burbulla, S., Class, H., Coltman, E., Emmert, S., Fetzer, T., Gr¨ uninger, C., Heck, K., Hommel, J., Kurz, T., Lipp, M., Mohammadi, F., Scherrer, S., Schneider, M., Seitz, G., Stadler, L., Utz, M., Weinhardt, F., Flemisch, B.: Dumux 3 – an open-source simulator for solving flow and...
-
[33]
Computers & Mathematics with Applications 81 (Jan
Bastian, P., Blatt, M., Dedner, A., Dreier, N.-A., Engwer, C., Fritz e, R., Gr¨ aser, C., Gr¨ uninger, C., Kempf, D., Kl¨ ofkorn, R., Ohlberger, M., Sander, O.: The dune fra mework: Basic concepts and recent developments. Computers & Mathematics with Applicatio ns 81, 75–112 (2021) https://doi.org/10.1016/j.camwa.2020.06.007
-
[34]
Journal of Machine Learning Research 12, 2825–2830 (2011)
Pedregosa, F., Varoquaux, G., Gramfort, A., Michel, V., Thirion, B., Grisel, O., Blondel, M., Prettenhofer, P., Weiss, R., Dubourg, V., Vanderplas, J., Passo s, A., Cournapeau, D., Brucher, M., Perrot, M., Duchesnay, E.: Scikit-learn: Machine learn ing in Python. Journal of Machine Learning Research 12, 2825–2830 (2011)
work page 2011
-
[35]
developers, O.R.: ONNX Runtime. https://onnxruntime.ai/. Version: 1.18.0 (2021)
work page 2021
-
[36]
http://www.gnu.org/software/gsl/
Galassi, M.e.a.: GNU Scientific Library Reference Manual (3rd Ed.) . http://www.gnu.org/software/gsl/
-
[37]
Water Resources Research 52(8), 6490–6505 (2016) https://doi.org/10.1002/2016WR018714
Guo, B., Bandilla, K.W., Nordbotten, J.M., Celia, M.A., Keilegavlen, E., D oster, F.: A multiscale multilayer vertically integrated model with vertical dynamic s for co2 sequestra- tion in layered geological formations. Water Resources Research 52(8), 6490–6505 (2016) https://doi.org/10.1002/2016WR018714
-
[38]
Reid, R.C., Prausnitz, J.M., Poling, B.E.: The Properties of Gases an d Liquids. McGraw-Hill Inc., ??? (1987). https://www.osti.gov/scitech/biblio/6504847
-
[39]
Journal f¨ ur die reine und angewandte Mathematik 1, 65–84 (1826) 24
Abel, N.H.: M´ emoire sur les ´ equations alg´ ebriques o` u on d´ emo ntre l’impossibilit´ e de la r´ esolution de l’´ equation g´ en´ erale du cinqui` eme degr´ e. Journal f¨ ur die reine und angewandte Mathematik 1, 65–84 (1826) 24
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.