Real‐Time Imaging Reveals Distinct Pore‐Scale Dynamics During Transient and Equilibrium Subsurface Multiphase Flow

Spurin, Catherine; Bultreys, Tom; Rücker, Maja; Garfi, Gaetano; Novák, Vladimír; Berg, Steffen; Blunt, Martin J.; Krevor, Samuel

doi:10.1029/2020wr028287

Cited by 27 publications

(42 citation statements)

References 43 publications

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“…Cascading displacement events involving multiple pores show a relaxation time scale around one second (Armstrong et al, 2014a). The time scale of pressure fluctuations observed in this work, in particular the periodic oscillations in Figures 2-4, are on the order of 1-20 min, which is also the time scale of periodic pressure fluctuations reported in recent studies (Spurin et al, 2020;Menke et al, 2021) see also the supporting information of (Spurin et al, 2020). The time scale of the saturation fluctuations is 30-60 min, which is similar as the characteristic time of traveling waves from Figure 6, which is still faster than the slow relaxation behavior observed in (Schlüter et al, 2017).…”

Section: Time Scale Of Fluctuationssupporting

confidence: 81%

“…Cascading displacement events involving multiple pores show a relaxation time scale around one second (Armstrong et al, 2014a). The time scale of pressure fluctuations observed in this work and related studies (Spurin et al, 2020;Menke et al, 2021) are on the order of 1-20 min and the saturation fluctuations and traveling saturation waves from Figure 6 are on the order of 30-60 min. That is still faster than the slow relaxation behavior observed in Schlüter et al (2017).…”

Section: Time Scale Of Fluctuationssupporting

confidence: 61%

“…In order to gain deeper insight into the cause for the oscillations, which have also been observed in several independent pore scale experiments (Spurin et al, 2020;Menke et al, 2021), in Figure 6 we show the saturation profiles for f w = 0.1, which has the longest oscillation period and the sampling rate of saturation would be sufficient to resolve both pressure and saturation. A closeup of the pressure data from Figure 2D showing pressure data in blue and saturation data (sampled at much lower frequency) in red.…”

Section: Analysis Of Capillary Fluctuations At the Darcy-scalementioning

confidence: 86%

“…Wettability heterogeneity may also impact the magnitude of fluctuations due to the associated energy dissipation (Murison et al, 2014). Also, fluctuations are stronger for a gas-liquid system and more often reported explicitly (Alkan and Müller, 2008;Reynolds and Krevor, 2015;Xu et al, 2015;Spurin et al, 2020), which suggests that viscosity ratio may be an important factor, which has been also reported in (Spurin et al, 2019).…”

Section: Introductionmentioning

confidence: 89%

“…The remaining question is what actually triggers the fluctuations in general and waves in particular. In the following sections, we will establish from pore scale fractional flow experiments conducted in a similar steady-state manner as the core flooding experiments in Figures 2-5 that periodic variations of pressure and saturation already occur on the oil-cluster scale and ultimately caused by pore scale displacement events (Berg et al, 2013(Berg et al, , 2014Spurin et al, 2020;Menke et al, 2021). The pressure and connectivity signature and 3D imaging of respective pore scale fluid distributions observed in the fractional flow micro-CT experiment suggest that pore scale displacement events are the underlying cause of fluctuations that are still visible in experiments commonly assumed at Darcy scale.…”

Section: Physical Interpretation Of the Wave Characteristics Of The Observed Fluctuationsmentioning

confidence: 99%

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The Origin of Non-thermal Fluctuations in Multiphase Flow in Porous Media

et al. 2021

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Core flooding experiments to determine multiphase flow in properties of rock such as relative permeability can show significant fluctuations in terms of pressure, saturation, and electrical conductivity. That is typically not considered in the Darcy scale interpretation but treated as noise. However, in recent years, flow regimes that exhibit spatio-temporal variations in pore scale occupancy related to fluid phase pressure changes have been identified. They are associated with topological changes in the fluid configurations caused by pore-scale instabilities such as snap-off. The common understanding of Darcy-scale flow regimes is that pore-scale phenomena and their signature should have averaged out at the scale of representative elementary volumes (REV) and above. In this work, it is demonstrated that pressure fluctuations observed in centimeter-scale experiments commonly considered Darcy-scale at fractional flow conditions, where wetting and non-wetting phases are co-injected into porous rock at small (<10−6) capillary numbers are ultimately caused by pore-scale processes, but there is also a Darcy-scale fractional flow theory aspect. We compare fluctuations in fractional flow experiments conducted on samples of few centimeters size with respective experiments and in-situ micro-CT imaging at pore-scale resolution using synchrotron-based X-ray computed micro-tomography. On that basis we can establish a systematic causality from pore to Darcy scale. At the pore scale, dynamic imaging allows to directly observe the associated breakup and coalescence processes of non-wetting phase clusters, which follow “trajectories” in a “phase diagram” defined by fractional flow and capillary number and can be used to categorize flow regimes. Connected pathway flow would be represented by a fixed point, whereas processes such as ganglion dynamics follow trajectories but are still overall capillary-dominated. That suggests that the origin of the pressure fluctuations observed in centimeter-sized fractional flow experiments are capillary effects. The energy scale of the pressure fluctuations corresponds to 105-106 times the thermal energy scale. This means the fluctuations are non-thermal. At the centimeter scale, there are non-monotonic and even oscillatory solutions permissible by the fractional flow theory, which allow the fluctuations to be visible and—depending on exact conditions—significant at centimeter scale, within the viscous limit of classical (Darcy scale) fractional flow theory. That also means that the phenomenon involves both capillary aspects from the pore or cluster scale and viscous aspects of fractional flow and occurs right at the transition, where the physical description concept changes from pore to Darcy scale.

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Section: Time Scale Of Fluctuationssupporting

confidence: 81%

“…Cascading displacement events involving multiple pores show a relaxation time scale around one second (Armstrong et al, 2014a). The time scale of pressure fluctuations observed in this work and related studies (Spurin et al, 2020;Menke et al, 2021) are on the order of 1-20 min and the saturation fluctuations and traveling saturation waves from Figure 6 are on the order of 30-60 min. That is still faster than the slow relaxation behavior observed in Schlüter et al (2017).…”

Section: Time Scale Of Fluctuationssupporting

confidence: 61%

Section: Analysis Of Capillary Fluctuations At the Darcy-scalementioning

confidence: 86%