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  • 1
    Online Resource
    Online Resource
    Capillarity and phase-mobility of a hydrocarbon gas–liquid system
    EDP Sciences ; 2021
    In:  Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles Vol. 76 ( 2021), p. 43-
    Details
    In: Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, EDP Sciences, Vol. 76 ( 2021), p. 43-
    Abstract: When oil fields fall during their lifetime below the bubble point gas comes out of solution. The key questions are at which saturation the gas becomes mobile (“critical gas saturation”) and what the gas mobility is, because mobile gas reduces the production of oil significantly. The traditional view is that the gas phase becomes mobile once gas bubbles grow or expand to a size where they connect and form a percolating path. For typical 3D porous media the saturation corresponding to this percolation limit is on the order of 20%. However, significant literature report on gas mobility below lower limits of percolation thresholds i.e. below 0.1%. A direct experimental insight for that is lacking because laboratory measurements are notoriously difficult since the formation of gas bubbles below the bubble point includes thermodynamic and kinetic aspects, and the pressure decline rates achievable in laboratory experiments are orders of magnitude higher than the decline rates in the field. Here we study the nucleation and transport of gas coming out of solution in-situ in 3D rock using X-ray computed micro tomography which allows direct visualization of the nucleation kinetics and connectivity of gas. We use either propane or a propane–decane mixture as model system and conduct pressure depletion in absence of flow finding that – consistent with the literature – observation of the bubble point in the porous medium is decreased and becomes pressure decline rate dependent because of the bubble nucleation kinetics. That occurs in single-component systems and in hydrocarbon mixtures. Pressure depletion in absence of flow results in critical gas saturations between 20 and 30% which is consistent with typical percolation thresholds in 3D porous structures. That does not explain experimentally observed critical gas saturations significantly below 20%. Also, the respective pore level fluid occupancy where pores are filled with either gas or liquid phase but not partially with both as in normal 2-phase immiscible systems rather diminishes connectivity of gas and liquid phases. This observation indicates that likely other mechanisms play a role in establishing gas mobility at saturations significantly below 20%. Experiments under flow conditions, where gas is injected near the bubble point suggest that diffusion may significantly contribute to the transport of gas and may even be the dominant transport mechanism at field relevant flow rates. The consequence of diffusive transport are compositional gradients where locally the composition is such gas nucleation may occur. That would lead to a disconnected but mobile gas distribution ahead of the convective front. Furthermore, diffusive exchange leads to ripening and anti-ripening effects which influences the distribution for which we see evidence in pressure depletion experiments but not so much at low rate gas injection. Respective relative permeability computed from the imaged fluid distributions using a lattice Boltzmann approach show distinctly different behavior between pressure depletion and flowing conditions. These findings suggest that capillarity in a gas–liquid hydrocarbon mixture is far more complex than in a 2-phase immiscible system. Capillarity is coupled to phase behavior thermodynamics and kinetics on a fast time scale and diffusion-dominated mechanisms such as ripening and anti-ripening effects at a slow time scale. While the consequences for the current experimental and field modelling approaches are not yet fully clear, this shows that more research is needed to fully understand these effects and their implications.
    Type of Medium: Online Resource
    ISSN: 1294-4475 , 1953-8189
    URL: Article
    DOI: 10.2516/ogst/2021025
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 2191926-4
    SSG: 19,1
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  • 2
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    Online Resource
    Determination of Critical Gas Saturation by Micro-CT
    Society of Petrophysicists and Well Log Analysts (SPWLA) ; 2020
    In:  Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description Vol. 61, No. 2 ( 2020-4-1), p. 133-150
    Details
    In: Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description, Society of Petrophysicists and Well Log Analysts (SPWLA), Vol. 61, No. 2 ( 2020-4-1), p. 133-150
    Type of Medium: Online Resource
    ISSN: 2641-4112
    URL: Issue
    URL: Journal
    URL: Article
    DOI: 10.30632/PJV61N2
    DOI: 10.30632/PJV
    DOI: 10.30632/PJV61N2-2020a1
    Language: Unknown
    Publisher: Society of Petrophysicists and Well Log Analysts (SPWLA)
    Publication Date: 2020
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  • 3
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    Online Resource
    Advanced Digital-SCAL Measurements of Gas Trapped in Sandstone
    Society of Petrophysicists and Well Log Analysts (SPWLA) ; 2023
    In:  Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description Vol. 64, No. 3 ( 2023-06-01), p. 368-383
    Details
    In: Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description, Society of Petrophysicists and Well Log Analysts (SPWLA), Vol. 64, No. 3 ( 2023-06-01), p. 368-383
    Abstract: Trapped gas saturation (Sgr) plays an important role in subsurface engineering, such as carbon capture and storage, H2 storage efficiency as well as the production of natural gas. Unfortunately, Sgr is notoriously difficult to measure in the laboratory or field. The conventional method of measurement—low-rate unsteady-state coreflooding—is often impacted by gas dissolution effects, resulting in large uncertainties of the measured Sgr. Moreover, it is not understood why this effect occurs, even for brines carefully pre-equilibrated with gas. To address this question, we used high-resolution X-ray computed tomography (micro-CT) imaging techniques to directly visualize the pore-scale processes during gas trapping. Consistent with previous studies, we find that for pre-equilibrated brine, the remaining gas saturation continually decreased with more (pre-equilibrated) brine injected and even after the brine injection was stopped, resulting in very low Sgr values (possibly even zero) at the pore-scale level. Furthermore, we were able to clearly observe the initial trapping of gas by the snap-off effect, followed by a further shrinkage of the gas clusters that had no connected pathway to the outside. Our experimental insights suggest that the effect is related to the effective phase behavior of gas inside the porous medium, which due to the geometric confinement, could be different from the phase behavior of bulk fluids. The underlying mechanism is likely linked to ripening dynamics, which involves a coupling between phase equilibrium and dissolution/partitioning of components, diffusive transport, and capillarity in the geometric confinement of the pore space.
    Type of Medium: Online Resource
    ISSN: 2641-4112
    URL: Issue
    URL: Journal
    URL: Article
    DOI: 10.30632/PJV64N3
    DOI: 10.30632/PJV
    DOI: 10.30632/PJV64N3-2023a4
    Language: Unknown
    Publisher: Society of Petrophysicists and Well Log Analysts (SPWLA)
    Publication Date: 2023
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