Pore-Scale Fluid Dynamics Resolved in Pressure Fluctuations at the Darcy Scale

Complex pore-scale dynamics have been observed during multiphase flow through porous rocks. These dynamics are not incorporated in large scale models for the migration and trapping of subsurface fluids such as CO2 or hydrogen. We show that fluctuations in pressure measured at the core-scale (centimeters) can reflect fluid displacements at the pore-scale (millimeters). The spectral characteristics of pressure data are shown to depend on the flow dynamics, the size of the rock sample, and the heterogeneity of the pore space. These results show that pressure data, transformed into the time-frequency domain using wavelets, provides information about flow dynamics, across scales, that are otherwise challenging to acquire. Understanding the flow of fluid in porous rocks is crucial for the safe, long-term, storage of CO2 and hydrogen. Complex fluid flow has been observed in small pores. However, imaging limitations prevent direct observation of such dynamics in larger samples. As such, small-scale flow remains a considerable source of uncertainty for predicting the underground storage or movement of fluid. In the absence of suitable imaging techniques, we demonstrate how flow dynamics at smaller scales can be explored by analyzing pressure data and its fluctuations using mathematical techniques. We apply this approach to larger samples and discover that pressure fluctuations contain useful information about flow dynamics, sample size, and rock composition that are often otherwise unavailable. Pore-scale dynamics can be linked to pressure fluctuations measured across the coreThe spectral signature of the pressure fluctuations can be used to classify the dominant flow regimeBy exploring the spectral signature of pressure fluctuations at the larger scale, we are able to infer the underlying pore-scale dynamics