| 1. |
- Basirat, Farzad, et al.
(författare)
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Pore-scale modeling of wettability effects on CO2–brine displacement during geological storage
- 2017
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Ingår i: Advances in Water Resources. - : Elsevier. - 0309-1708 .- 1872-9657. ; 109, s. 181-195
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Tidskriftsartikel (refereegranskat)abstract
- Wetting properties of reservoir rocks and caprocks can vary significantly, and they strongly influence geological storage of carbon dioxide in deep saline aquifers, during which CO2 is supposed to displace the resident brine and to become permanently trapped. Fundamental understanding of the effect of wettability on CO2-brine displacement is thus important for improving storage efficiency and security. In this study, we investigate the influence of wetting properties on two-phase flow of CO2 and brine at the pore scale. A numerical model based on the phase field method is implemented to simulate the two-phase flow of CO2-brine in a realistic pore geometry. Our focus is to study the pore-scale fluid-fluid displacement mechanisms under different wetting conditions and to quantify the effect of wettability on macroscopic parameters such as residual brine saturation, capillary pressure, relative permeability, and specific interfacial area. Our simulation results confirm that both the trapped wetting phase saturation and the normalized interfacial area increase with decreasing contact angle. However, the wetting condition does not appear to influence the CO2 breakthrough time and saturation. We also show that the macroscopic capillary pressures based on the pressure difference between inlet and outlet can differ significantly from the phase averaging capillary pressures for all contact angles when the capillary number is high ( log Ca > -5). This indicates that the inlet-outlet pressure difference may not be a good measure of the continuum-scale capillary pressure. In addition, the results show that the relative permeability of CO2 can be significantly lower in strongly water-wet conditions than in the intermediate-wet conditions.
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| 2. |
- Joodaki, Saba, et al.
(författare)
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Model analysis of CO2 residual trapping from single-well push pull test based on hydraulic withdrawal tests : Heletz, residual trapping experiment I
- 2020
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 97
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Tidskriftsartikel (refereegranskat)abstract
- Residual or capillary trapping is one of the key trapping mechanisms for geological storage of CO2. Yet, very few studies so far have attempted to estimate the residual trapping and the related characteristic parameter, residual saturation, in situ. At Heletz, a pilot CO2 injection site in Israel a single-well push-pull experiment to estimate residual gas saturation in situ was carried out during autumn 2016. The main characterization method was hydraulic withdrawal tests. The residually trapped zone was also created by means of fluid withdrawal, by first injecting CO2 and then withdrawing fluids leaving behind the immobile residual CO2. This paper presents the first model interpretation of the experimental results. Numerical modeling with TOUGH2/ECO2N was carried out to model the entire test sequence, the focus being in matching the collected pressure, temperature and flow data as well as observations of gas content in the borehole. The experimental results could be well fitted with the model that also is in agreement with previously collected petro-physical data. The results indicate a somewhat lower residual gas saturation than that measured in the laboratory, the estimated maximum residual saturation from the field experiment being 10% and the corresponding value from the core 20%. The results also indicate that most of the CO2 entered the upper reservoir layer, thus actually giving an estimate of the effective residual trapping in that layer. Overall, pressure response gave a clear signal and was an effective method in getting an estimate of the effective residual trapping in the interval tested.
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| 3. |
- Joodaki, Saba, et al.
(författare)
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Model analysis of CO2 residual trapping from single-well push pull test - Heletz, Residual Trapping Experiment II
- 2020
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Ingår i: International Journal of Greenhouse Gas Control. - : ELSEVIER SCI LTD. - 1750-5836 .- 1878-0148. ; 101
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Tidskriftsartikel (refereegranskat)abstract
- Residual or capillary trapping is one of the key trapping mechanisms for CO2 geological storage. At the Heletz, Israel, pilot injection site, two dedicated field experiments have been carried out to characterize it in-situ. This paper presents the model analyses of the second of these tests, the Residual Trapping Experiment II (RTE II). In the experiment hydraulic, tracer and thermal tests before and after the generation of the residually trapped zone are used to quantify residual saturation. The creation of the residually trapped zone is based on injection of CO2-saturated-water following injection of free-phase supercritical CO2. For the modeling, both a radial-symmetric model with homogeneous layer properties and 3D model with stochastically heterogeneous properties were used. Extensive parameter sensitivity studies were carried out and various well-geometry related fluid injection/withdrawal scenarios were considered. In terms of the best estimate for the maximum residual saturation, this experiment, like the previous RTE I experiment, gave the best agreement with a residual gas saturation of 0.1, this value being somewhat lower than the core-measured value of 0.2. Overall, the pressure response provided a very robust signal enabling to distinguish different values of residual saturation as well as the extent of sections where gas blocking for water flow could have occurred. Analysis of the tracer data indicated the presence of phenomena such as gas-blocking water flow, the importance of multi-layer and channelized flow and transport, and the importance of taking into account the processes in the actual injection/production well also.
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| 4. |
- Joodaki, Saba, et al.
(författare)
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The effect of designing parameter of WAG injection on enhancement of CO2trapping in heterogeneous formations: A numerical study
- 2017
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Ingår i: Greenhouse Gases. - : Wiley. - 2152-3878. ; 7:6, s. 1008-1019
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Tidskriftsartikel (refereegranskat)abstract
- Dissolution and residual trapping of CO2 injected in saline aquifers can be influenced by injection strategies applied. In this study, we focus on the water-alternating-gas (WAG) strategy and investigate the importance of parameters needed to design an effective WAG injection sequence, including (i) CO2 and water injection rates, (ii) WAG ratio, and (iii) number of cycles. Using TOUGH2-ECO2N, we perform 3D numerical simulations of sequences of CO2 and water injection into a heterogeneous formation. Hysteresis in relative permeability and capillary pressure functions is considered based on the Land trapping model. Results show that to design a WAG injection in a high permeable formation, the WAG ratio and number of injection cycles are more important parameters than the CO2 and water injection rates. Increasing the total amount of water injection (i.e., decreasing the WAG ratio for given total amount of injected CO2) improves the CO2 dissolution and residual trapping. It is also shown that increasing the number of injection cycles has a negative effect on both residual and dissolution trapping as measured at the end of the injection sequence, because both the free-phase and the dissolved CO2 plumes in the one-cycle injection scenario reach farther distances and occupy larger reservoir volumes than in the multi-cycle injection. This result means that while water injection following the CO2 injection improves trapping in comparison with the CO2-only injection strategy, the WAG scheme with multiple cycles should not be chosen to enhance trapping for the scenario considered in this study.
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| 5. |
- Niemi, Auli, et al.
(författare)
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Chapter 4: Mathematical Modeling : Approaches for Model Solution
- 2017
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Ingår i: Geologicalstorage Of Co<sub>2</sub> In Deep Saline Formations. - Dordrecht : Springer Netherlands. - 9789402409949 - 9789402409963 ; , s. 129-185
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Bokkapitel (refereegranskat)abstract
- The governing equations and mathematical models describing CO2 spreading and trapping in saline aquifers and the related hydro-mechanical and chemical processes were described in Chapt.3. In this chapter, the focus is on methods for solving the relevant equations. The chapter gives an overview of the different approaches, from high-fidelity full-physics numerical models to more simplified analytical and semi-analytical solutions. Specific issues such as modeling coupled thermo-hydro-mechanical-chemical processes and modeling of small-scale processes, such as convective mixing and viscous fingering, are also addressed. Finally, illustrative examples of modeling real systems, with different types of modeling approaches, are presented.
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| 6. |
- Niemi, Auli, et al.
(författare)
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Characterizing CO2 residual trapping in-situ by means of single-well push-pull experiments at Heletz, Israel, pilot injection site : experimental procedures and results of the experiments
- 2020
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 101
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Tidskriftsartikel (refereegranskat)abstract
- Two dedicated field experiments have been carried out at the Heletz, Israel pilot CO2 injection site. The objective has been to quantify the CO2 residual trapping in-situ, based on two distinctly different methods. Both experiments are based on the principle of a combination of hydraulic, thermal and/or tracer tests before and after creating the residually trapped zone of CO2 and using the difference in the responses of these tests to estimate the in-situ residual trapping. In Residual Trapping Experiment I (RTE I), carried out in autumn 2016, the main characterization test before and after the creation of the residually trapped zone were hydraulic withdrawal tests. In this experiment, the residually trapped zone was also created by fluid withdrawal, by first injecting CO2, then withdrawing fluids until CO2 was at residual saturation. The second experiment, Residual Trapping Experiment II (RTE II), was carried out autumn 2017. In this experiment, the residually trapped CO2 zone was created by CO2 injection, followed by the injection of CO2-saturated water, to push away the mobile CO2 and leave the residually trapped CO2 behind. In this test, the main reference test carried out before and after creating the residually trapped zone was injection and recovery of gas partitioning tracer Krypton. This paper presents the experimental procedures and results of these experiments. A hydraulic withdrawal test as a characterization method was robust and gave a clear signal. Given the difficulties in injecting water optimally saturated with CO2, in order not to dissolve the residually trapped CO2 or to create situations with excess mobile gas, withdrawal test may also be a generally preferable hydraulic testing method, in comparison to injection. The limitation of any hydraulic test is that it only gives an averaged value over the test section. At Heletz additional information about CO2 distribution was obtained based on thermal measurements and by monitoring the pressure difference between the two sensors in the bolehole. The latter could be used to estimate the amount of mobile CO2 in the well test section. Tracer experiments with gas partitioning tracers can in principle give more detailed information of CO2 residual distribution in the reservoir than hydraulic tests can, but are also far more complicated to carry out, involving sophisticated and sensitive equipment. In the Heletz case the optimal injection of CO2-saturated water turned out to be difficult to achieve. Creating the zone of residual saturation by means of fluid withdrawal rather than by injecting CO2-saturated water seemed a more robust approach. Monitoring the gas contents in the test interval gave good guidance on the state of the system. Model interpretations of the two experiments to obtain values for CO2 residual saturation are presented in companion papers in this same Special Edition.
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| 7. |
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| 8. |
- Tian, Liang, et al.
(författare)
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Gaussian Process Emulators for Quantifying Uncertainty in CO2 Spreading Predictions in Heterogeneous Media
- 2017
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Ingår i: Computers & Geosciences. - : Elsevier BV. - 0098-3004 .- 1873-7803.
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Tidskriftsartikel (refereegranskat)abstract
- We explore the use of Gaussian process emulators (GPE) in the numerical simulation of CO2 injection into a deep heterogeneous aquifer. The model domain is a two-dimensional, log-normally distributed stochastic permeability field. We first estimate the cumulative distribution functions (CDFs) of the CO2 breakthrough time and the total CO2 mass using a computationally expensive Monte Carlo (MC) simulation. We then show that we can accurately reproduce these CDF estimates with a GPE, using only a small fraction of the computational cost required by traditional MC simulation. In order to build a GPE that can predict the simulator output from a permeability field consisting of 1000s of values, we use a truncated Karhunen-Loève (K-L) expansion of the permeability field, which enables the application of the Bayesian functional regression approach. We perform a cross-validation exercise to give an insight of the optimization of the experiment design for selected scenarios: we find that it is sufficient to use 100s values for the size of the training set and that it is adequate to use as few as 15 K-L components. Our work demonstrates that GPE with truncated K-L expansion can be effectively applied to uncertainty analysis associated with modeling of multiphase flow and transport processes in heterogeneous media.
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| 9. |
- Yang, Zhibing, 1982-, et al.
(författare)
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Modeling of dense nonaqueous phase liquid entrapment and dissolution in variable aperture fractures
- 2009
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Ingår i: Proceedings of TOUGH2 Symposium 2009. - Lawrence Berkeley National Laboratory, Berkeley, California.
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Konferensbidrag (refereegranskat)abstract
- This study investigates dense non-aqueous phase liquid (DNAPL) entrapment and dissolution in single, variable-aperture fractures. Log-normally distributed aperture fields with local permeabilities following the cubic law are assumed. Special attention is given to the capillary pressure-liquid saturation function to account for the specific drainage and wetting characteristics of fractures. DNAPL migration and immobilization is modeled by using the iTOUGH2/T2VOC models, and dissolution is simulated using the TMVOC model. Multiple realizations with different sets of aperture statistics and fracture inclination angles are analyzed.The results suggest that the entrapment geometry of DNAPL in a heterogeneous fracture is highly sensitive to the aperture statistics. Larger correlation length or standard deviation produces a wider range of total entrapped DNAPL volume. Modeling of different fracture inclination angles reveals that gravity force plays an important role as well. Subsequent dissolution modeling shows that mass transfer will also be strongly influenced by the different DNAPL entrapment architectures corresponding to the different aperture correlation lengths and standard deviations.
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| 10. |
- Yang, Zhibing, 1982-, et al.
(författare)
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Two sides of a fault : Grain-scale analysis of pore pressure control on fault slip
- 2018
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Ingår i: Physical review. E. - : AMER PHYSICAL SOC. - 2470-0045 .- 2470-0053. ; 97:2
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Tidskriftsartikel (refereegranskat)abstract
- Pore fluid pressure in a fault zone can be altered by natural processes (e.g., mineral dehydration and thermal pressurization) and industrial operations involving subsurface fluid injection and extraction for the development of energy and water resources. However, the effect of pore pressure change on the stability and slip motion of a preexisting geologic fault remains poorly understood; yet, it is critical for the assessment of seismic hazard. Here, we develop a micromechanical model to investigate the effect of pore pressure on fault slip behavior. The model couples fluid flow on the network of pores with mechanical deformation of the skeleton of solid grains. Pore fluid exerts pressure force onto the grains, the motion of which is solved using the discrete element method. We conceptualize the fault zone as a gouge layer sandwiched between two blocks. We study fault stability in the presence of a pressure discontinuity across the gouge layer and compare it with the case of continuous )homogeneous) pore pressure. We focus on the onset of shear failure in the gouge layer and reproduce conditions where the failure plane is parallel to the fault. We show that when the pressure is discontinuous across the fault, the onset of slip occurs on the side with the higher pore pressure, and that this onset is controlled by the maximum pressure on both sides of the fault. The results shed new light on the use of the effective stress principle and the Coulomb failure criterion in evaluating the stability of a complex fault zone.
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