This thesis develops a geological ensemble-reduction workflow for efficient uncertainty quantification (UQ) in Carbon Capture and Storage (CCS). Using early-time full-physics (FP) injection-rate data and distance-based clustering, representative models are selected to preserve ensemble percentile bounds (P10–P50-P90) within ≤5% relative RMSE. Applied to two 108-member ensembles, injection-rate uncertainty distributions were accurately reconstructed using only 6 and 9 representative models (∼7–10% of the total simulation cost). Early FP rates (≤10 days) proved strongly predictive of long-term behavior and key geological controls. Distance-based generalized sensitivity analysis (dGSA) effectively identified influential parameters governing reservoir response variability at only ~1.3% of the full simulation cost. The approach provides a transparent, low-cost framework for CCS reservoir UQ, enabling robust risk and performance assessment with order-of-magnitude computational savings.

This thesis explores whether vertical stratigraphic cross flow from the A zone to the C1 zone of the Upper Slochteren Member can occur without wellbore crossflow, and under what conditions such recharge is plausible. The study focuses on the B-well in the L-field, Dutch offshore North Sea, where production resumed after a shut-in period, and pressure behavior suggested possible recharge. Four different basecase models were constructed using Rapid Reservoir Modeling (RRM), each representing a different degree of vertical connectivity across the B zone. These models were then transferred to Computer Modeling Group (CMG) software, where dynamic multiphase simulations were performed to assess gas flow between the zones of the Upper Slochteren Member.
The results show that stratigraphic recharge from A to C1 is possible, but highly sensitive to the inter- nal architecture of the B zone. Increased vertical connectivity across the B zone consistently show earlier pressure communication and higher gas fluxes into the C1 zone. Sensitivity analyses were conducted on porosity, vertical permeability, and gas relative permeability to test their influence on flow behavior. These parameters affected not only the rate of gas migration, but also the degree of pressure redistribution across the model, which influences the gas rates even further. Capillary pressure and water saturation were also found to control gas mobility, particularly in low-permeability or heterolithic intervals. The findings do not fully support the hypothesis that stratigraphic recharge explains the observed pressure response in the reservoir, but suggest it may account for part of it. Additionally, the results emphasize the importance of considering vertical heterogeneity and capillary forces when evaluating near-wellbore connectivity.

This report aims to find the underlying cause of pressure fluctuations in five Icelandic geothermal wells. These fluctuations affect the productivity of the power plant; making it relevant to understand their causes and mitigation measures. Based on the available data we concluded that the fluctuations do not originate in the reservoir or surface infrastructure but in the well bore. We then proceeded to follow two hypotheses to explain fluctuations within the well bore. The first one, we called Internal Flow Instability. It describes oscillating behavior as a result of Ledinegg instability, where small instabilities in momentum balance become amplified along the well. To further explore this theory we built a 1D numerical model for two-phase flow. We plotted the characteristic curve (i.e. the relation between pressure drop and flow rate) for an example stable and unstable well. Our results show that the operating condition of the stable well lies in the stable region of the curve, and vice versa. The curves do predict the stability of the wells, correctly but do not give an explanation for the instability.
The second hypothesis examined in this report is the Multiple Feed Zones theory. This hypothesis investigates how different feed zones supplying fluids of different enthalpies mix within a well bore; focusing on the interactions between two phase flow in the well bore and single phase flow from the feed zones. A STARS model was developed to test whether single-phase flow could exist above a two-phase region in the well bore, and the simulations confirmed that this is feasible. To further investigate the mechanism, we applied the model from Matsumoto et al. (2020). This model was used as a proof of concept to demonstrate that interactions between multiple feed zones with different enthalpies can produce the type of fluctuations observed in the wells. While the simulated fluctuations do not match the observed frequency, the results support that, under the modelled conditions, the Multiple Feed Zones theory could provide an explanation for the pressure oscillations observed in the wells.

This study quantifies the impact of mesoscale geological heterogeneity on CO2 storage behavior, using the Pano flood-tidal delta as a case study. A hierarchical workflow was employed, progressing m simple to complex static modeling (L1 to L4) based on outcrop interpretation, followed by flow diagnostics analysis. The results reveal a non-linear relationship between model complexity and system behavior. The mesoscale architecture (L2) primarily controls early CO2 breakthrough risk, whereas the sub-lobe scale heterogeneity (L3) is crucial for reliably predicting long-term storage performance and sweep efficiency.
A key insight from this work is that the level of model complexity systematically biases the simulated flow narrative. Consequently, there is no single ”correct” model; instead, the choice of complexity inherently pre-selects which aspects of storage behavior (e.g., early risk vs. long-term efficiency) will be most accurately represented. This provides a decision-making framework for CO2 storage projects, demonstrating that distinct optimal levels of model complexity exist for specific engineering objectives, such as using L2 for risk identification and L3 for performance prediction—thereby guiding more effective and intentional model deployment.

Revealing an optimal geothermal development strategy attempt with long-term sustainability (upcoming 100 years) based on a real 3D model derived from seismic data is considered one of the main contributions of this research study. The heat extraction and thermal recharge of the reservoir must be in balance to extend the productive lifetime of the Koekoekspolder field system. Based on the best results obtained among different unconventional thermal development approaches, the best locations for the new production wells or extra geothermal doublets as well as the timing, injection temperatures, and rate at which the doublets operate are determined. The best strategy to develop the Koekoekspolder field can be achieved by several steps such as understanding the reservoir properties such as the sedimentary facies, porosity, and permeability distribution by analyzing the literature studies and the static model that simulates the Slochteren formation using Petrel software based on the seismic and log data available followed by a dynamic model that mimics the flow of the hot aquifer inside the reservoir using Eclipse 300 software. Both static and dynamic models must be calibrated by the accessible production data to decrease inaccuracy. The thermal boundaries that are taken into consideration for the koekoekspolder field are not mere confining layers. The workflow of this research study ensures a high degree of realism in terms of the input data and output information of the thermal model of the Koekoekspolder field. The best locations for the new production wells or extra geothermal doublets are determined based on the best simulation results obtained from this research study which fulfill the future energy demand increment. The procedures used in this research study give clear guidance on how the Koekoekspolder field or any other geothermal field can be sustainably developed using a robust history-matched model that has reliable predictions. The low-enthalpy deep geothermal system of the koekoekspolder field is optimized and developed using different types and scenarios of operational strategies for doublets which allow adequate periods for operational thermal recharge. This study takes into consideration different thermal parameters that are not common to achieve enhanced predictions. Moreover, it illustrates the importance and benefits of considering reservoir boundary conditions. Finding suitable sustainable geothermal field development for the Koekoekspolder field can be achieved by new well-studied techniques that can ensure adequate thermal recharge periods. The results of this research study show that the energy demand can be fulfilled with low investment costs to increase the profit of the field owner. Long-term (around 1 century) sustainable development of geothermal fields such as Koekoekspolder and the new technology in this research study can partially contribute to achieving the geothermal master plan objectives in the Netherlands as well as enhancing low and high-enthalpy geothermal field development worldwide.