olavau

• Kane, Birane; Jettestuen, Espen; Sandve, Tor Harald; Helland, Johan Olav; Landa-Marbán, David & Aursjø, Olav (2026). Data-Driven Modeling of Hysteresis in Porous Media: Neural-Network Surrogates Coupled with the OPM Flow Reservoir Simulator. Transport in Porous Media. ISSN 0169-3913. 153. doi: 10.1007/s11242-026-02337-x. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Relative permeability hysteresis in porous media presents a significant challenge for accurate reservoir simulation due to its path-dependent nature. Traditional empirical and geometric models often fall short in capturing the complexity of hysteresis, especially under cyclic drainage and imbibition conditions. This study investigates the use of machine learning (ML), specifically neural networks, as surrogate models to approximate relative permeability relationships, including hysteresis effects, with high fidelity for applications in reservoir simulations. Focusing on two-phase oil–water systems, the study uses separate training datasets derived from classical hysteresis models (Killough and Carlson) and pore-scale simulation results from a workflow using level set and lattice Boltzmann models (LS-LBM) to generate training data. The proposed ML models incorporate saturation history to predict relative permeability. Three surrogate models are developed: ML-Killough and ML-Carlson, trained on synthetic/model-generated datasets, and ML-LS-LBM, trained on a physics-based dataset. To demonstrate practical applicability, the proposed ML surrogates are applied to a core-scale simulation case implemented in the OPM Flow reservoir simulator. Results demonstrate that the ML surrogates accurately reproduce scanning curves and nonlinear hysteresis effects, perform well on test data drawn from the same distribution, and maintain physical consistency. Their differentiable structure and computationally efficient inference make them suitable for integration into full-field reservoir simulators, offering a promising alternative for simulation-time prediction in enhanced oil recovery and CO2 storage applications.

• Helland, Johan Olav; Jettestuen, Espen & Aursjø, Olav (2026). Pore-Scale Simulation of Relative Permeability Hysteresis from a Workflow of Level-Set and Lattice-Boltzmann Methods: The Case of Consolidated Media with Low Pore-to-Throat Aspect Ratio. Transport in Porous Media. ISSN 0169-3913. 153. doi: 10.1007/s11242-026-02308-2. Fulltekst i vitenarkiv Vis sammendrag

  We present a workflow, based on level-set and lattice-Boltzmann methods, for numerical estimation of relative permeability and capillary pressure curves with hysteresis in capillary-dominated flow on segmented 3D rock images. Calculation of relative permeability from rock images has commonly been limited to studies of the bounding hysteresis loop and conventional porous media. Here, we demonstrate the workflow on an almost unexplored case, a consolidated sandstone with low pore-to-throat aspect ratio, and obtain a complex relative permeability hysteresis behavior, consistent with the few studies available for such media. The pore-scale simulations include primary drainage, followed by the main bounding hysteresis loop and scanning curves for secondary drainage and secondary imbibition. We also explore the impact of initial saturation after primary drainage on hysteresis and phase trapping. The relative permeability hysteresis is larger for the non-wetting phase than for the wetting phase, yet the extent of both decreases with increasing initial wetting-phase saturation. For the non-wetting-phase relative permeability, imbibition and drainage curves may cross, while scanning curves cross each other and exhibit a more significant hysteresis than the bounding loop. The role of trapped ganglia makes secondary processes different from primary. The behavior complies with hysteresis in phase connectivity, in which snap-off/coalescence breaks/recovers pathways. The results deviate significantly from the nested hysteresis loops seen for unconsolidated media and show that hysteresis in scanning curves cannot be neglected, indicating that flexible machine learning methods are better suited approaches than standard hysteresis models to implement this complex relative permeability behavior in reservoir simulators.

• Vaseghnia, Hamed; Jettestuen, Espen; Giljarhus, Knut Erik Teigen; Aursjø, Olav; Vinningland, Jan Ludvig & Hiorth, Aksel (2025). Enhanced double distribution function lattice Boltzmann method for simulation of viscoelastic and shear-thinning fluids flow. Journal of Non-Newtonian Fluid Mechanics. ISSN 0377-0257. 344, s. 105467–105467. doi: 10.1016/j.jnnfm.2025.105467. Fulltekst i vitenarkiv Vis sammendrag

  In this study, we use a two-dimensional multiple relaxation time (MRT) approach for simulating polymeric fluids. A correction term is introduced into the source term to remove non-physical terms and improve numerical accuracy of the simulations. The correction term preserves the locality of the collision process and ensures numerical stability across a range of Weissenberg numbers when coupled with non-linear constitutive equations. This approach is applied to the Phan-Thien-Tanner (PTT) model and the Oldroyd-B model, where the first exhibits viscoelastic and shear-thinning behavior while the second is purely viscoelastic. To evaluate the numerical accuracy and stability of the proposed MRT-LBM approach, we apply it to planar Poiseuille flow as well as simplified four-roll mill benchmarks. In the case of the four-roll mill, we specifically examine the effects of shear-thinning and viscoelasticity in steady elongational flows and their transitions to oscillatory and chaotic or turbulent behaviors, known as elastic instability. Our results indicate that the non-linearity in the stress-strain rate relationship and the microstructural dynamics of polymer chains, as described by non-linear constitutive models, make the standard BGK-LBM approach incapable to accurately capture the complex behavior of polymers without introducing numerical artifacts. On the other hand the MRT-LBM method maintains numerical stability and accuracy across a broad range of Weissenberg (up to Wi = 20) and should therefore be the method of choice when simulating these types of flows.

• Zeynolabedini, Mohammadsajjad; Jettestuen, Espen; Aursjø, Olav & Helland, Johan Olav (2025). Discrete-Domain Model for Hysteresis and its Application on Porous Rocks. EarthDoc. 2025, s. 1–16. doi: 10.3997/2214-4609.202531055. Fulltekst i vitenarkiv Vis sammendrag

  Water-alternate-gas injections for improved recovery, slug-wise CO2 injections for permanent storage, and seasonal storage of natural gas and hydrogen are all processes that lead to cyclic flows of drainage and imbibition in the reservoir. Reservoir simulations of these processes need flow functions with hysteresis, which is typically implemented using correlations and hysteresis loop logic that could be inaccurate, especially for the description of higher-order scanning curves. Typically, measuring enough hysteresis-loop data from core-scale experiments is not feasible, and pore-scale simulation of these relations directly on micro-CT images is computationally demanding. The discrete-domain model (DDM) represents an efficient, physics-based, method to describe hysteresis. DDM divides the porous rock into a set of compartments where each compartment is described by a Helmholtz energy and a local saturation. These energy functions describe a rugged energy landscape where hysteresis occurs due to irreversible jumps across energy barriers separating the local energy minima. For pressure-controlled displacement, the evolution equations of the local saturations are uncoupled, while for saturation-controlled (or, rate-controlled) displacement they are coupled by global saturation constraints where capillary pressure is a Lagrange multiplier. The global coupling leads to fluid redistribution among compartments (cooperative behavior) and pressure fluctuations. Thus far, the DDM has only employed simple phenomenological energy functions. The objective of this work is to explore the applicability of the DDM on realistic data from rock samples. For that purpose, we simulate primary drainage, imbibition, and subsequent scanning loops, on segmented micro-CT images of Castlegate sandstone, using a level set model (LSM) for capillary-controlled displacement. The generated data is used to calculate the energy functions for different compartment architectures in the DDM. From the data we also explore how the interfacial area leads to differences in the energy between drainage and imbibition. We find that the DDM reproduces the capillary pressure curves from both the pressure- and saturation-controlled LSM simulations using the energy functions from the saturation-controlled case. A finer compartment division of the rock sample leads to more energy minima and smoother results. Using the same energy landscape for either drainage or imbibition on all processes (including scanning curves) leads to a slight deviation from the LSM results, whereas the case with different energy landscapes for drainage and imbibition shows excellent agreement. Hence, the DDM emerges as a suitable pore-to-core upscaling approach for hysteresis as its compartmental description is based on extensive properties.

• Jettestuen, Espen; Aursjø, Olav & Cayeux, Eric (2025). Lattice Boltzmann simulations of non-Newtonian fluids in annular geometries. Geoenergy Science and Engineering. ISSN 2949-8929. 254. doi: 10.1016/j.geoen.2025.214039. Fulltekst i vitenarkiv Vis sammendrag

  A lattice Boltzmann scheme is introduced to model the interaction between a drill string and a non-Newtonian drilling fluid, as fluid–drill–string interactions can give significant force contributions on the drill string. The method uses a fast look-up-table approach to include non-Newtonian rheological behavior. In addition, an immersed boundary method was developed to model the interaction between the fluid and the drill string. The method is used on both Newtonian and Quemada fluids for a prescribed drill-string motion. The analysis of the simulations shows that the fluid viscosity had less influence on the integrated forces from the fluid on the drill string, for fairly rapid changes in the drill string center of mass movement, than on the integrated torque on the drill string. A comparison between a quasi two dimensional radial annular geometry and a true three dimensional annular geometry was conducted for a Quemada fluid. Also here we observed that the differences were most pronounced in the integrated torque measurements. The fluid motion is complex, but there is a noticeable correlations between the drill-string kinetics and the integrated forces and torques acting on the drill string from the fluid. And, even though this model is too computational demanding to be used in real-time drilling operations, it will make a good basis for data driven reduced order methods that can be used in actual real time applications.

• Jettestuen, Espen; Aursjø, Olav; Helland, Johan Olav; Vinningland, Jan Ludvig & Hiorth, Aksel (2024). Workflow for Direct Pore-Scale Simulation of Relative Permeability and Capillary Pressure Curves with Hysteresis at Low Capillary Numbers, SPE Norway Subsurface Conference, April 17, 2024, Bergen, Norway. Society of Petroleum Engineers. ISSN 9781959025344. doi: 10.2118/218427-MS. Fulltekst i vitenarkiv Vis sammendrag

  We propose an efficient workflow to estimate relative permeability and capillary pressure curves directly from pore-scale images for capillary dominated flows. In this workflow, we use a method to determine saturation configurations, and by coupling these configurations to a single-phase lattice Boltzmann fluid flow solver, we can impose higher order boundary conditions at the phase interfaces and avoid spurious currents and phase mixing. This removes some of the common drawbacks when employing multiphase fluid solvers: it improves numerical accuracy

• Vaseghnia, Hamed; Jettestuen, Espen; Giljarhus, Knut Erik Teigen; Aursjø, Olav & Hiorth, Aksel (2024). Evaluation of the non-Newtonian lattice Boltzmann model coupled with off-grid bounce-back scheme: Wall shear stress distributions in Ostwald-de Waele fluids flow. Physical Review E (PRE). ISSN 2470-0045. 110(1). doi: 10.1103/PhysRevE.110.015305. Fulltekst i vitenarkiv
• Jettestuen, Espen; Aursjø, Olav; Vinningland, Jan Ludvig & Hiorth, Aksel (2023). A generalized bodyforce scheme for lattice Boltzmann simulations of incompressible flow in complex geometries. Physics of Fluids. ISSN 1070-6631. 35(2). doi: 10.1063/5.0134569. Fulltekst i vitenarkiv Vis sammendrag

  We present a general procedure for reducing compressibility effects in pressure driven lattice Boltzmann simulations involving complex geometries. We do this by introducing a preconditioning step for the flow system in order to reduce these often undesirable effects, rather than directly modifying the flow algorithm itself. The method consists of determining the geometry dependent contribution to a pressure field induced by a given set of pressure boundary conditions. We show that this may be done through solving a set of Laplace's equations that do not need re-evaluation during flow simulations. This preconditioning method is not limited to stationary flows but is directly applicable to time-varying flows, without any recalculation of the preconditioning step. In this paper, we apply the procedure to the lattice Boltzmann algorithm, but it may be utilized in any flow simulation algorithm based on artificial compressibility methods. The method is demonstrated in both stationary and non-stationary flow situations. This includes examples from flow in porous media and hemodynamics. All the presented examples are compared to conventional methods for implementing pressure driven flow in lattice Boltzmann. In all the examples, it is shown that the proposed method considerably reduces the undesirable features exhibited by the conventional methods.

• Pettersson, Per; Aursjø, Olav; Helland, Johan Olav & Jettestuen, Espen (2023). Constrained optimization of offshore wind turbine positions under uncertain wind conditions with correlated data. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 2626(1). doi: 10.1088/1742-6596/2626/1/012056. Fulltekst i vitenarkiv Vis sammendrag

  Offshore wind power production is subject to substantial uncertainty due to variability in wind conditions. Planning of new wind parks should take these uncertainties into account by means of stochastic modeling and uncertainty quantification. Wind speed and wind direction exhibit dependence that needs to be properly modeled to yield reliable uncertainty estimates. In particular, the dependence is strong when data are averaged over a short time-horizon, e.g., on a monthly rather than an annual basis. In this work we introduce a stochastic model for wind speed and wind direction using Rosenblatt transformation and an empirical model. This allows efficient numerical quadrature that replaces thousands of Monte Carlos samples by a few tens of model evaluations at quadrature points in parametric space. A robust design formulation for maximizing power production honoring dependent data is proposed and demonstrated on data from the North Sea site Sørlige Nordsjø II.

• Aursjø, Olav; Jettestuen, Espen; Vinningland, Jan Ludvig & Hiorth, Aksel (2018). On the inclusion of mass source terms in a single-relaxation-time lattice Boltzmann method. Physics of Fluids. ISSN 1070-6631. 30(5). doi: 10.1063/1.5024641. Fulltekst i vitenarkiv
• Aursjø, Olav; Jettestuen, Espen; Vinningland, Jan Ludvig & Hiorth, Aksel (2017). An improved lattice Boltzmann method for simulating advective–diffusive processes in fluids. Journal of Computational Physics. ISSN 0021-9991. 332, s. 363–375. doi: 10.1016/j.jcp.2016.12.014. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Jettestuen, Espen; Aursjø, Olav; Madland, Merete Vadla & Hiorth, Aksel (2017). Mineral Dissolution and Precipitation Rate Laws Predicted from Reactive Pore Scale Simulations. I Ukjent, Ukjent (Red.), 19th European Symposium on Improved Oil Recovery/IOR Norway 2017. European Association of Geoscientists and Engineers (EAGE). ISSN 9789462822092. doi: 10.3997/2214-4609.201701792. Fulltekst i vitenarkiv
• Nermoen, Anders; Madland, Merete Vadla; Korsnes, Reidar Inge; Aursjø, Olav; Kjørslevik, Trygve Alexander Carlsen & Østensen, Geir (2017). How Stress and Temperature Conditions Affect Rock-Fluid Chemistry and Mechanical Deformation. I Toussaint, Renaud; Sandnes, Bjørnar; Koehn, Daniel; Szymczak, Piotr & Aharonov, Einat (Red.), Flow and Transformations in Porous Media. Frontiers Media SA. ISSN 9782889450770. s. 130–149. doi: 10.3389/fphy.2016.00002. Fulltekst i vitenarkiv
• Nermoen, Anders; Korsnes, Reidar Inge; Aursjø, Olav; Madland, Merete Vadla; Kjørslevik, Trygve Alexander Carlsen & Østensen, Geir (2016). How stress and temperature conditions affect rock-fluid chemistry and mechanical deformation. Frontiers in Physics. 4(2). doi: 10.3389/fphy.2016.00002. Fulltekst i vitenarkiv Vis sammendrag

  We report the results from a series of chalk flow-through-compaction experiments performed at three effective stresses (0.5, 3.5, and 12.3MPa) and two temperatures (92 and 130◦C). The results show that both stress and temperature are important to both chemical alteration and mechanical deformation. The experiments were conducted on cores drilled from the same block of outcrop chalks from the Obourg quarry within the Saint Vast formation (Mons, Belgium). The pore pressure was kept at 0.7MPa for all experiments with a continuous flow of 0.219M MgCl2 brine at a constant flow rate; 1 original pore volume (PV) per day. The experiments have been performed in tri-axial cells with independent control of the external stress (hydraulic pressure in the confining oil), pore pressure, temperature, and the injected flow rate. Each experiment consists of two phases; a loading phase where stress-strain dependencies are investigated (approximately 2 days), and a creep phase that lasts for 150–160 days. During creep, the axial deformation was logged, and the effluent samples were collected for ion chromatography analyses. Any difference between the injected and produced water chemistry gives insight into the rock-fluid interactions that occur during flow through the core. The observed effluent concentration shows a reduction in Mg2+, while the Ca2+ concentration is increased. This, together with SEM-EDS analysis, indicates that magnesium-bearing mineral phases are precipitated leading to dissolution of calcite. This is in-line with other flow-through experiments reported earlier. The observed dissolution and precipitation are sensitive to the effective stress and test temperature. Higher stress and temperature lead to increased Mg2+ and Ca2+ concentration changes. The observed strain can be partitioned additively into a mechanical and chemical driven component.

• Aursjø, Olav & Pride, Steven R (2015). Lattice Boltzmann method for diffusion-limited partial dissolution of fluids. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 92(1). doi: 10.1103/PhysRevE.92.013306. Fulltekst i vitenarkiv
• Aursjø, Olav; Erpelding, Marion; Tallakstad, Ken Tore; Flekkøy, Eirik Grude; Hansen, Alex & Måløy, Knut Jørgen (2014). Film flow dominated simultaneous flow of two viscous incompressible fluids through a porous medium. Frontiers in Physics. 2, s. 1–9. doi: 10.3389/fphy.2014.00063. Fulltekst i vitenarkiv Vis sammendrag

  We present an experimental study of two-phase flow in a quasi-two-dimensional porous medium. The two phases, a water-glycerol solution and a commercial food grade rapeseed/canola oil, having an oil to water-glycerol viscosity ratio M = 1.3, are injected simultaneously into a Hele-Shaw cell with a mono-layer of randomly distributed glass beads. The two liquids are injected into the model from alternating point inlets. Initially, the porous model is filled with the water-glycerol solution. We observe that after an initial transient state, an overall static cluster configuration is obtained. While the oil is found to create a connected system spanning cluster, a large part of the water-glycerol clusters left behind the initial invasion front is observed to remain immobile throughout the rest of the experiment. This could suggest that the water-glycerol flow-dynamics is largely dominated by film flow. The flow pathways are thus given through the dynamics of the initial invasion. This behavior is quite different from that observed in systems with large viscosity differences between the two fluids, and where compressibility plays an important part of the process.

• Aursjø, Olav; Løvoll, Grunde; Knudsen, Henning Arendt; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2011). A Direct Comparison Between a Slow Pore Scale Drainage Experiment and a 2D Lattice Boltzmann Simulation. Transport in Porous Media. ISSN 0169-3913. 86(1), s. 125–134. doi: 10.1007/s11242-010-9611-y. Fulltekst i vitenarkiv
• Aursjø, Olav; Knudsen, Henning Arendt; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2010). Oscillation-induced displacement patterns in a two-dimensional porous medium: A lattice Boltzmann study. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. ISSN 1539-3755. 82(2). doi: 10.1103/PhysRevE.82.026305. Fulltekst i vitenarkiv
• Pride, Steve; Flekkøy, Eirik Grude & Aursjø, Olav (2009). Mechanisms of seismic EOR. World Oil. ISSN 0043-8790. s. 49–52. Fulltekst i vitenarkiv
• Pride, Steve; Flekkøy, Eirik Grude & Aursjø, Olav (2008). Seismic stimulation for enhanced oil recovery. Geophysics. ISSN 0016-8033. 73(5), s. O23–O35. doi: 10.1190/1.2968090. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Zeynolabedini, Mohammadsajjad; Jettestuen, Espen; Helland, Johan Olav & Aursjø, Olav (2026). Three-phase hysteresis in porous rock characterized with a discrete-domain model and direct pore-scale simulations. doi: https:/events.interpore.org/event/58/attachments/1265/2530/Book%20of%20Abstracts%20(2).pdf. Fulltekst i vitenarkiv
• Helland, Johan Olav; Jettestuen, Espen & Aursjø, Olav (2026). Pore-scale level-set simulation of drainage and imbibition of trapped gas in the presence of oil and water during reservoir pressure cycling. doi: https:/events.interpore.org/event/58/attachments/1265/2530/Book%20of%20Abstracts%20(2).pdf. Fulltekst i vitenarkiv Vis sammendrag

  Depressurization in hydrocarbon reservoirs can mobilize trapped gas in the presence of residual oil and water and lead to improved recovery. The effects of reservoir pressure cycling are also important for storage applications in depleted reservoirs, like temporary storage of natural gas and hydrogen, and in permanent CO2 storage, where reservoir pressure may drop temporarily due to fault activation or leakage. Traditionally, drainage and imbibition processes in the reservoir have been studied by fluid invasion and displacement at the pore scale, that may lead to trapping. Here, we will instead focus on the drainage and imbibition characteristics that occur due to the expansion and compression of the trapped gas in the presence of residual oil and water when the reservoir pressure changes. To this end, we use a level set model for capillary-controlled displacement with local volume conservation as a basis for the investigations [1]. The model enforces volume conservation of disconnected ganglia by modifying their pressure to prevent volume changes, and it also conserves volume during ganglion splitting and merging. Thus, simulations predict the pressures of trapped ganglia, which is a prerequisite for describing pressure-volume behaviour of ganglia under various processes, such as Ostwald ripening of trapped gas [2]. Here, we extend the model to handle local mass conservation of a compressible gas, in the presence of incompressible oil ganglia and water, when the (uniform) reservoir pressure changes stepwise. The strategy is to first calculate the equilibrium gas pressures for trapped ganglia from which we calculate the number of moles of gas from an equation of state (EOS). Then, for each stepwise change in reservoir pressure, we combine the EOS with the volume conservation equation to find the gas pressure in each level set iteration that corresponds to the volume for the current reservoir pressure. In the case of cubic EOS, the resulting gas pressure equation is a fourth order polynomial which we solve numerically. The reservoir pressure is changed once a static three-phase fluid configuration is achieved. Using the developed model, we perform quasi-static simulation of depressurization followed by re-pressurization on trapped gas configurations (using CH4 and CO2) in the presence of residual oil ganglia and water achieved from the simulation of a conventional gas-water invasion cycle on a 3D segmented micro-CT image of sandstone. We monitor changes in average ganglia capillary pressure as a function of trapped gas saturation and show the hysteresis behaviour. The simulations show that gas ganglia coalesce as they expand during depressurization, leading to oil displacement. Eventually, a percolating gas cluster forms and the critical gas saturation is calculated. Re-pressurization results in snap-off of large ganglia as they get compressed. The gas connectivity, quantified by the Euler characteristic, also displays hysteresis. Further, the hysteresis from reservoir pressure cycling is different from standard injection-displacement experiments due to the expansion and compression behaviour of the gas, which is further demonstrated by the comparison of fluid configurations in the two cases. Hence, reservoir pressure cycling calls for other hysteresis models in reservoir simulation. References: [1] Jettestuen, E., Friis, H. A., Helland, J. O. (2021). A locally conservative multiphase level set method for capillary-controlled displacements in porous media. Journal of Computational Physics 428, 109965. https://doi.org/10.1016/j.jcp.2020.109965. [2] Singh, D., Friis, H.A., Jettestuen, E., Helland, J. O. (2023). Pore-scale Ostwald ripening of gas bubbles in the presence of oil and water in porous media. Journal of Colloid and Interface Science 647, 331–343 (2023). https://doi.org/10.1016/j.jcis.2023.05.070.

• Helland, Johan Olav; Jettestuen, Espen & Aursjø, Olav (2026). Relative permeability hysteresis data calculated using LS-LB workflow on Castlegate sandstone. doi: 10.6084/M9.FIGSHARE.31084654. Fulltekst i vitenarkiv
• Jettestuen, Espen; Aursjø, Olav & Vinningland, Jan Ludvig (2025). GitHub - Lattice Boltzmann code extended for particle transport. doi: https:/github.com/eje74/BADChIMP-cpp.git. Fulltekst i vitenarkiv Vis sammendrag

  A general-purpose lattice Boltzmann solver .

• Helland, Johan Olav; Jettestuen, Espen & Aursjø, Olav (2025). Pore-scale level-set simulation of drainage-imbibition cycles of trapped gas during decline and incline of reservoir pressure. doi: https:/events.interpore.org/event/56/attachments/1242/2271/InterPore2025%20Book%20of%20Abstracts.pdf. Fulltekst i vitenarkiv Vis sammendrag

  New uses of subsurface reservoirs such as temporary storage of natural gas and hydrogen, involve seasonal gas injection and production schedules accompanied by seasonal inclines and declines in reservoir pressure, respectively. In the gas withdrawal stage, rising water will trap gas in the gas/water transition zone below the producing gas cap. The injection and production of gas leads to drainage and imbibition processes in the reservoir which traditionally have been studied by two-phase displacement of continuous flow of gas and water at the pore scale. Here, we will instead focus on the drainage and imbibition characteristics that occur due to the expansion and compression of the trapped gas when the reservoir pressure changes. To this end, we use a level set model for capillary-controlled displacement with local volume conservation as a basis for the investigations. The model enforces volume conservation of disconnected ganglia by modifying their pressure (that is, the normal level-set velocity) to prevent volume changes, and it also conserves volume during ganglion splitting and merging. Thus, simulations predict the pressures of trapped ganglia, which is a prerequisite for describing pressure-volume behaviour of ganglia under various processes, such as Ostwald ripening of trapped gas. Here, we extend the model to handle local mass conservation of a compressible gas when the (uniform) reservoir pressure changes stepwise. The strategy is to first calculate the equilibrium gas pressures for trapped ganglia from which we calculate the number of moles of gas from an equation of state (EOS). Then, for each stepwise change in reservoir pressure, we combine the EOS with the volume conservation equation to find the gas pressure in each level set iteration that corresponds to the volume for the current reservoir pressure. In case of Peng-Robinson EOS the resulting pressure equation is a fourth order polynomial which we solve either numerically or analytically in each level set iteration. The reservoir pressure is changed once a static fluid configuration is achieved. Using the developed model, we perform quasi-static simulation of pressure incline followed by pressure decline on trapped gas configurations after imbibition on a 3D segmented micro-CT image of sandstone. We monitor changes in average ganglion pressure as a function of trapped gas saturation and show the hysteresis behaviour. The simulations also show that pressure incline results in snap-off of large ganglia as they get compressed. Further, both coalescence and snap-off are observed during pressure decline when ganglia grow and extend into nearby pores.

• Zeynolabedini, Mohammadsajjad; Jettestuen, Espen; Aursjø, Olav & Helland, Johan Olav (2025). Development of ANN models for constitutive multiphase flow relationships in porous media accounting for hysteresis. doi: https:/2025.iaiss.cc/. Fulltekst i vitenarkiv
• Zeynolabedini, Mohammadsajjad; Jettestuen, Espen; Aursjø, Olav & Helland, Johan Olav (2025). Discrete-Domain Model for Hysteresis and its Application on Porous Rocks. doi: 10.3997/2214-4609.202531055. Fulltekst i vitenarkiv Vis sammendrag

  Water-alternate-gas injections for improved recovery, slug-wise CO2 injections for permanent storage, and seasonal storage of natural gas and hydrogen are all processes that lead to cyclic flows of drainage and imbibition in the reservoir. Reservoir simulations of these processes need flow functions with hysteresis, which is typically implemented using correlations and hysteresis loop logic that could be inaccurate, especially for the description of higher-order scanning curves. Typically, measuring enough hysteresis-loop data from core-scale experiments is not feasible, and pore-scale simulation of these relations directly on micro-CT images is computationally demanding. The discrete-domain model (DDM) represents an efficient, physics-based, method to describe hysteresis. DDM divides the porous rock into a set of compartments where each compartment is described by a Helmholtz energy and a local saturation. These energy functions describe a rugged energy landscape where hysteresis occurs due to irreversible jumps across energy barriers separating the local energy minima. For pressure-controlled displacement, the evolution equations of the local saturations are uncoupled, while for saturation-controlled (or, rate-controlled) displacement they are coupled by global saturation constraints where capillary pressure is a Lagrange multiplier. The global coupling leads to fluid redistribution among compartments (cooperative behavior) and pressure fluctuations. Thus far, the DDM has only employed simple phenomenological energy functions. The objective of this work is to explore the applicability of the DDM on realistic data from rock samples. For that purpose, we simulate primary drainage, imbibition, and subsequent scanning loops, on segmented micro-CT images of Castlegate sandstone, using a level set model (LSM) for capillary-controlled displacement. The generated data is used to calculate the energy functions for different compartment architectures in the DDM. From the data we also explore how the interfacial area leads to differences in the energy between drainage and imbibition. We find that the DDM reproduces the capillary pressure curves from both the pressure- and saturation-controlled LSM simulations using the energy functions from the saturation-controlled case. A finer compartment division of the rock sample leads to more energy minima and smoother results. Using the same energy landscape for either drainage or imbibition on all processes (including scanning curves) leads to a slight deviation from the LSM results, whereas the case with different energy landscapes for drainage and imbibition shows excellent agreement. Hence, the DDM emerges as a suitable pore-to-core upscaling approach for hysteresis as its compartmental description is based on extensive properties.

• Jettestuen, Espen; Aursjø, Olav; Helland, Johan Olav; Vinningland, Jan Ludvig & Hiorth, Aksel (2024). Workflow for direct pore-scale simulation of relative permeability and capillary pressure curves with hysteresis at low capillary numbers. Fulltekst i vitenarkiv
• Pettersson, Per; Aursjø, Olav; Helland, Johan Olav & Jettestuen, Espen (2023). Optimization of offshore wind turbine positioning within bounded areas under uncertain wind conditions. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Jettestuen, Espen; Aursjø, Olav & Hiorth, Aksel (2019). Numerical Modelling of Wettability. Fulltekst i vitenarkiv
• Hetland, Bjarte; Shogin, Dmitry; Jettestuen, Espen; Aursjø, Olav & Hiorth, Aksel (2019). Micro scale simulation of polymer fluids. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Jettestuen, Espen; Aursjø, Olav & Hiorth, Aksel (2019). Influence of wettability on oil recovery during spontaneous imbibition. Fulltekst i vitenarkiv Vis sammendrag

  We show how the local pore space wettability correlates with the overall production of oil. Using a lattice Boltzmann model, we study how variations in wettability on the pore scale influence oil recovery during spontaneous imbibition for different geometries. On the pore scale, wettability will vary depending on mineralogy, ageing history, contacting fluids, etc. In our simulations, the local contact angle is given by the initial fluid configuration. Preliminary numerical results obtained using a sandpack geometry with high connectivity show that our approach yield oil production curves that qualitatively agree well with experimental spontaneous imbibition data. The simulation data also suggests that a homogeneous compared to a heterogeneous contact angle distribution with the same mean value has a significant effect on the recovery rate.

• Golestan, Mohammad Hossein; Aursjø, Olav & Berg, Carl Fredrik (2018). Lattice-Boltzmann Simulation of Osmosis Effect During Low-Salinity Waterflooding. Fulltekst i vitenarkiv
• Hiorth, Aksel; Nødland, Oddbjørn Mathias; Stavland, Arne; Jettestuen, Espen; Aursjø, Olav & Vinningland, Jan Ludvig [Vis alle 9 forfattere av denne artikkelen] (2018). Simulation Tools for Predicting IOR Potential on the Norwegian Continental Shelf. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Aursjø, Olav; Jettestuen, Espen; Madland, Merete Vadla & Hiorth, Aksel (2018). Insight into core scale oil release from pore scale simulations. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Aursjø, Olav; Jettestuen, Espen & Hiorth, Aksel (2018). Digital EOR from pore to core. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Aursjø, Olav; Jettestuen, Espen; Madland, Merete Vadla & Hiorth, Aksel (2018). Effects of nucleation on mineral dissolution and precipitation predicted from reactive pore scale simulations. Fulltekst i vitenarkiv
• Jettestuen, Espen; Aursjø, Olav; Vinningland, Jan Ludvig; Skartlien, Roar & Hiorth, Aksel (2017). Pore scale simulation of electro-chemically induced wettability changes. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Jettestuen, Espen; Aursjø, Olav; Madland, Merete Vadla & Hiorth, Aksel (2017). Mineral Dissolution and Precipitation Rate Laws Predicted from Reactive Pore Scale Simulations. Fulltekst i vitenarkiv
• Jettestuen, Espen; Aursjø, Olav; Vinningland, Jan Ludvig; Skartlien, Roar & Hiorth, Aksel (2017). Pore scale simulation of electro-chemical induced wettability changes in three dimensional pore scale geometries. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Bogale, Nigussie; Larsen, Alf Inge; Havnen, Jorunn; Jettestuen, Espen & Aursjø, Olav [Vis alle 10 forfattere av denne artikkelen] (2016). A computer model for non-invasive heart diagnostics. Fulltekst i vitenarkiv
• Vinningland, Jan Ludvig; Jettestuen, Espen; Hiorth, Aksel; Madland, Merete Vadla; Aursjø, Olav & Skartlien, Roar [Vis alle 8 forfattere av denne artikkelen] (2016). Pore scale simulation and non-Newtonian flow. Fulltekst i vitenarkiv
• Nermoen, Anders; Korsnes, Reidar Inge; Aursjø, Olav; Madland, Merete Vadla; Kjørslevik, T.A. Carlsen & Østensen, Geir (2015). “When time comes into play: How does stress and temperature conditions affect rock-fluid chemistry and mechanical deformation”. Fulltekst i vitenarkiv
• Aursjø, Olav & Pride, Steven R (2011). A Two‐Phase Lattice Boltzmann Model Allowing Controlled Mixing Between Phases. Fulltekst i vitenarkiv
• Knudsen, Henning Arendt; Aursjø, Olav; Løvoll, Grunde & Måløy, Knut Jørgen (2008). TWO-PHASE FLOW IN POROUS MEDIA UNDER SEISMIC STIMULATION STUDIED BY NETWORK MODELS. Fulltekst i vitenarkiv
• Aursjø, Olav; Knudsen, Henning Arendt; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2008). TWO-PHASE FLOW IN POROUS MEDIA UNDER SEISMIC STIMULATION: A LATTICE BOLTZMANN STUDY. Fulltekst i vitenarkiv
• Aursjø, Olav; Hiorth, Aksel; Khrulenko, Alexey A. & Nødland, Oddbjørn Mathias (2022). Polymer flooding : Simulation Upscaling Workflow. Universitetet i Stavanger. doi: https:/orcid.org/0000-0002-1951-4998. Fulltekst i vitenarkiv
• Lohne, Arild; Stavland, Arne; Åsen, Siv Marie; Aursjø, Olav & Hiorth, Aksel (2022). Recommended polymer workflow: Interpretation and parameter identification. Universitetet i Stavanger. doi: 10.31265/usps.202. Fulltekst i vitenarkiv Vis sammendrag

  Injecting a polymer solution into a porous medium significantly increases the modeling complexity, compared to model a polymer bulk solution. Even if the polymer solution is injected at a constant rate into the porous medium, the polymers experience different flow regimes in each pore and pore throat. The main challenge is to assign a macroscopic porous media “viscosity” to the fluid which can be used in Darcy law to get the correct relationship between the injection rate and pressure drop. One can achieve this by simply tabulating experimental results (e.g., injection rate vs pressure drop). The challenge with the tabulated approach is that it requires a huge experimental database to tabulate all kind of possible situations that might occur in a reservoir (e.g., changing temperature, salinity, flooding history, permeability, porosity, wettability etc.). The approach presented in this report is to model the mechanisms and describe them in terms of mathematical models. The mathematical model contains a limited number of parameters that needs to be determined experimentally. Once these parameters are determined, there is in principle no need to perform additional experiments.

• Jettestuen, Espen; Aursjø, Olav; Vinningland, Jan Ludvig; Hiorth, Aksel & Lohne, Arild (2022). Smart Water flooding : Part 2 : Important input parameters for modeling and upscaling workflow. Universitetet i Stavanger. doi: 10.31265/usps.200. Fulltekst i vitenarkiv Vis sammendrag

  This document presents some guidelines on how to conduct numerical investigations of the physicochemical effects of Smart Water flooding on different length scales. The National IOR Centre of Norway (NIORC) has developed several simulation tools. The objective of this report is to describe how three NIORC-developed simulation tools BADChIMP, IORCoreSim, and IORSim, can be used to investigate Smart Water effects on different length scales. We present which input parameters are needed by the simulation tools, and we discuss which processes these tools are suited to study. When working with different length scales, one of the challenges is how to upscale results obtained from smaller scales, i.e., pore and core scale experiments or simulations, to the field scale. Here, three relevant questions are: 1) how far do the Smart Water effects propagate into a reservoir? 2) What is the effect of reservoir temperature on Smart Water behavior? 3) How is the oil release, observed on core scale, related to the oil production from a field? This document targets research scientists planning to perform either pore scale simulations, core scale simulations, or field scale simulations for Smart Water studies. The technical level of the document is targeting an industry engineer.

• Stavland, Arne; Åsen, Siv Marie; Lohne, Arild; Aursjø, Olav & Hiorth, Aksel (2022). Recommended polymer workflow : Lab (cm and m scale). Universitetet i Stavanger. ISSN 9788284390970. doi: 10.31265/usps.201. Fulltekst i vitenarkiv Vis sammendrag

  Polymer flooding is one of the most promising EOR methods (Smalley et al. 2018). It is well known and has been used successfully (Pye 1964; Standnes & Skjevrak 2014; Sheng et al. 2015). From a technical perspective we recommend that polymer flooding should be considered as a viable EOR method on the Norwegian Continental Shelf for the following reasons: 1. More oil can be produced with less water injected; this is particularly important for the NCS which are currently producing more water than oil 2. Polymers will increase the aerial sweep and improve the ultimate recovery, provided a proper injection strategy 3. Many polymer systems are available, and it should be possible to tailor their chemical composition to a wide range of reservoir conditions (temperature and salinity) 4. Polymer systems can be used to block water from short circuiting injection production wells 5. Polymer combined with low salinity injection water has many benefits: a lower polymer concentration can be used to reach target viscosity, less mechanical degradation, less adsorption, and a potential reduction in Sor due to a low salinity wettability effect. There are some hurdles when considering polymer flooding that needs to be considered: 1. Many polymer systems are not at the present considered as green chemicals; thus, reinjection of produced water is needed. However, results from polymer degradation studies in the IORCentre indicates that a. High molecular weight polymers are quickly degraded to low molecular weight. In case of accidental release to the ocean low molecular weight polymers are diluted and the lifetime of the spill might be quite short. According to Caulfield et al. (2002) HPAM is not toxic, and will not degrade to the more environmentally problematic acrylamide. b. In the DF report for environmental impact there are case studies using the DREAM model to predict the transport of chemical spills. This model is coupled with polymer (sun exposure) degradation data from the IORCentre to quantify the lifetime of polymer spills. This approach should be used for specific field cases to quantify the environmental risk factor. 2. Care must be taken to prepare the polymer solution offshore. Chokes and vales might be a challenge but can be mitigating according to the results from the large-scale testing done in the IORCentre (Stavland et al. 2021). None of the above-mentioned challenges are server enough to not consider polymer flooding. HPAM is neither toxic, nor bio-accumulable, or bio-persistent and the CO2 footprint from a polymer flood may be significantly less than a water flood (Dupuis et al. 2021). There are at least two contributing factors to this statement, which we will return in detail to in the next section i) during linear displacement polymer injection will produce more oil for the same amount of water injected, hence the lifetime of the field can be shortened ii) polymers increase the arial sweep reducing the need for wells.

• Nermoen, Anders; Giske, Nils Harald; Skadsem, Hans Joakim & Aursjø, Olav (2015). Implementing resistivity measurements into compaction and immiscible flow experiments for EOR. IRIS Internal Report, 2015/218. Fulltekst i vitenarkiv Vis sammendrag

  The main goal in this project has been to quantify the contributing oil recovery mechanism from pore volume reduction driven by compaction and from the displacement of immiscible fluids. For chalks, some of the surface-active ions such as sulfate trigger compaction that lead to enhanced oil recovery and a more effective reduction in oil saturation. The saturation is calculated from the ratio of the volume occupied by oil divided by the total volume. When compaction, triggered by sulfate injection occurs, this affects both the numerator and the denominator in the saturation dynamics. As such, a more precise estimate of oil/water saturation is required where compaction is properly accounted for such that a more precise EOR potential estimate can be obtained. As an analogue to chalks we wanted to do tests on a highly porous material and in the absence of dissolution/precipitation processes. The best analogue we identified was a pack of bi-porous glass beads in which the beads are porous themselves. Two experiments were performed with modified core holders where electrical resistance and axial strain were measured while injecting NaCl brine into the glass bead pack. Test 1 was performed at increasing confining pressures and temperatures in which axial strain, electrical resistance and hydraulic permeability were estimated. We found the resistivity and permeability to be highly sensitive to variations in porosity, and that the resistivity of NaCl solution was sensitive to temperature, as expected. Test 2 was performed at ambient temperature, while alternating flow with Marcol oil and NaCl brine at 20, 100 and 300 bar confining pressure. In this experiment the production of the fluid phase that is expelled by the injected phase phase was quantified together with the electrical resistance and permeability. Since the relation between absolute permeability and “absolute resistance” was known from Test 1, we could compare the observed permeability (of the injected phase) and electrical resistance as function of the immiscible saturation and porosity. The relative magnitude of compaction and immiscible fluid displacement on the oil/water production could be directly quantified from these experiments.

• Aursjø, Olav (2010). Two-Phase Flow in Porous Medium Stimulated by Oscillations. Det matematisk naturvitenskapelige fakultet. Fulltekst i vitenarkiv

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