Introduction

Depleted oil fields in the Gulf of Suez (Egypt) can serve as geothermal reservoirs for power generation using a CO₂-Plume Geothermal (CPG) system, while geologically sequestering CO₂. NubiaStore is a research project that entails the injection of a substantial amount of CO₂ into the highly permeable brine-saturated Nubian Sandstone at Hamam Faraun Hotspring.

We are developing numerical models of two-phase flow processes for predicting the CO₂-plume migration at multiple length scales ranging from the Nano-meter scale using Synchrotron Radiation X‐ray Tomographic Microscopy (SRXTM) to reservoir-scale using the released subsurface field dataset. We are, currently, focusing on employing capillary pressure, relative permeability curves, and pore-scale displacement mechanisms to predict the extent of CO₂ plume migration at a representative geological scale.

Pore-Network Modeling

A quasi-static pore-network modelling has been used to simulate the equilibrium positions of fluid-fluid interfaces, and thus determine the capillary pressure and relative permeability curves. Three-dimensional images with a voxel size of 0.65 um² of a Nubian Sandstone rock sample have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we performed sequential primary drainage–main imbibition cycles of quasi-static invasion in order to quantify (1) the CO₂ and brine relative permeability curves, (2) the effect of initial wetting-phase saturation (i.e. the saturation at the point of reversal from drainage to imbibition) on the residual–trapping potential, and (3) study the relative permeability–saturation hysteresis. The results improve our understanding of the potential magnitude of capillary trapping in Nubian Sandstone, essential for future field-scale simulations. Further, an initial basin-scale assessment of CO₂ storage capacity, which incorporates capillary trapping, yields a range of 14-49 GtCO₂ in Nubian Sandstone, Gulf of Suez Basin.

Pore-Network Modeling: Quasi-static (Drainage and Imbibition) simulations of two-phase (scCO₂-Brine) in a natural rock sample (Nubian Sandstone, Egypt) to incorporate the effects of CO₂ trapping. © NubiaStore project.

Reservoir simulations

CO₂ Plume Geothermal systems (CPG) (Randolph and Saar, 2011a, b; Saar et al., 2012; Buscheck et al., 2013), involve the injection of CO₂ that comes from a CO₂ emitter, as a working fluid to extract heat and pressure energy (enthalpy) from naturally high-permeability sedimentary or stratigraphic basins. The injected CO₂ forms a large subsurface CO₂ plume that permanently sequesters CO₂ underground and absorbs heat from the geothermal reservoir. The CO₂ plume can be “tapped” for thermal and/or electric power production in a geothermal power system (Randolph and Saar, 2011a; Saar et al., 2012; Adams et al., 2014, 2015).

Reservoir simulation of scCO₂ injection into a brine-saturated Nubian Sandstone (the Gulf of Suez, Egypt). The CO₂ enters the reservoir through a vertical (or deviated) injection well. After moving through the geothermal reservoir, the heated CO₂ is produced from deviated production wells. © NubiaStore project.

Related Publications by the GEG Group

REFEREED PUBLICATIONS IN JOURNALS

PROCEEDINGS REFEREED

Other Publications (Journals and Conference Proceeding/Abstracts)

• Hefny M., Ebigbo A., Qin C.-Z., Adam B., and Saar M. O.: NubiaStore: A multidisciplinary investigation for implementing CPG in the Gulf of Suez (Egypt). Maturing Geothermal Energy for Saudi Arabia – Research Conference 2020: 27-29 January in KAUST, Thuwal, Kingdom of Saudi Arabia. [ePoster]
• Qin C.-Z., and Hefny M.: Quantitative Predictions of Two-Phase Flow Dynamics in Porous Media by the Pore-Network Modeling. AGU Fall Meeting 2019: 9-13 December 2019in San Francisco, California, USA. [Abstract]
• Hefny M., Qin C.-Z., Ebigbo A., Gostick J., Saar M. O., and Hammed M.: CO₂-Brine flow in Nubian Sandstone, Egypt: A Pore-Network Modeling using Computerized Tomography Imaging. European Geothermal Congress (EGC): 11-14 June 2019 in The Hague, The Netherlands. [Conference Proceeding]
• Qin C.-Z., Hefny M., and van Brummelen, E.H.: Quantitative Predictions of Two-Phase Flow Dynamics in Porous Media by the Pore-Network Modeling. 11 Annual Meeting – InterPore 2019, Minisymposia 9 Pore-scale modelling: 6-10 May 2019 in Valencia, Spain.[Abstract]
• Hefny M., Hammed M., Ebigbo A., and Saar M. O.: Petrophysical characterization of Nubian Sandstone reservoirs and their potential for geothermal applications; central Gulf of Suez, Egypt. 6th European Geothermal Workshop (EGW): 10-11 October 2018 in Strasbourg, France.

References

• Adams, B. M., Kuehn, T. H., Bielicki, J. M., Randolph, J. B., & Saar, M. O. (2014). “On the importance of the thermosiphon effect in CPG (CO₂ plume geothermal) power systems.”  Energy 69:409-418.
• Adams, B. M., Kuehn, T. H., Bielicki, J. M., Randolph, J. B., & Saar, M. O. (2015). “A comparison of electric power output of CO₂ plume geothermal (CPG) and brine geothermal systems for varying reservoir conditions.”  Applied Energy 140:365-377.
• Buscheck, T. A., Elliot, T. R., Celia, M. A., Chen, M., Sun, Y., Hao, Y., Lu, C., Wolery, T. J., & Aines, R. D. (2013). “Integrated geothermal-CO₂ reservoir systems: Reducing carbon intensity through sustainable energy production and secure CO₂ storage.”  Energy Procedia 37:6587-6594.
• Dezayes, C., Genter, A., Hooijkaas, G. R. (2005). “Deep-seated geology and fracture system of the EGS Soultz reservoir (France) based on recent 5km depth boreholes.” Proceedings of World Geothermal Congress, Antalya, Turkey.
• Gardes, R. A. (1995). Method of drilling multiple radial wells using multiple string downhole orientation. U.S. Patent No. 5,394,950.
• Gardes, R. A. (1998). Method and system for drilling underbalanced radial wells utilizing a dual string technique in a live well. U.S. Patent No. 5,720,356.
• Noble, J. B. (1992). Directional drilling apparatus and method. U.S. Patent No. 5,113,953.
• Randolph, J.B., & Saar, M. O. (2011a). ” Coupling carbon dioxide sequestration with geothermal energy capture in naturally permeable, porous geologic formations: Implications for CO₂­ sequestration.”  Energy Procedia 4:2206-2213.
• Randolph, J.B., & Saar, M. O. (2011b). “Combining geothermal energy capture with geologic carbon dioxide sequestration.”  Geophysical Research Letters 38 (10).
• Saar, M. O., Randolph, J. B., & Kuehn, T. H. (2012). Carbon dioxide-based geothermal energy generation systems and methods related thereto. U.S. Patent No. 8,316,955 (International patents pending).
• Spycher, N., Pruess, K. (2011). “A model for thermophysical properties of CO₂-brine mixtures at elevated temperatures and pressures.” Proceedings Thirty-Sixth Workshop on Geothermal Reservoir Engineering, Stanford Geothermal workshop, Stanford, CA.
• Welch, P., Boyle, P. (2009). “New Turbines to Enable Efficient Geothermal Power Plants.”  GRC Trans 33:765-772.