InterPore2025

Quantifying Threshold Capillary Pressure in Sedimentary Matrix-Lamina Bedding Pairs using Pore-Scale Simulation

21 May 2025, 09:50

15m

Oral Presentation (MS06-A) Physics of multiphase flow in diverse porous media MS06-A

Speaker

Richard Larson (Stanford University)

Description

In multiphase flows near capillary equilibrium, such as the buoyant migration of fluids in the subsurface, small changes in the capillary pressure can play important roles in the dynamics of such systems. Capillary pressure variations are controlling factors for the migratory pathways of fluids such as those in petroleum, natural gas, geologic carbon sequestration, and geologic hydrogen storage. Typically, rock-fluid injection tests, such as core flooding, are used to characterize the capillary pressure behavior of rocks to be used for further analysis. In their absence, very generalized empirical approximations are used to estimate different capillary pressures of rocks. However, these simple approximations are only valid within certain assumptions originally formulated for unconsolidated sphere packings or soils.
When considering frequent and distinct variations in pore morphology, as in highly laminated geology, small variations of pore size distribution may not be adequately considered in capillary pressure approximations. Singular measures of average porosity, permeability, and/or pore size ignore potentially multimodal properties of rocks such as the capillary pressure of a contrasting lamina within a sedimentary rock matrix.
To study this, simplified, digital geometries containing regions of contrasting circle size distribution are generated to replicate a lamination in sedimentary rocks. Flow perpendicular to the layering is simulated using a lattice Boltzmann color gradient method for multiphase flow. CO2 drainage is simulated until breakthrough to the opposite side, and the time-variant saturation of the domains and regions, as well as the CO2 phase pressure, is calculated for various contrasts.
While the circle sizes, or grain sizes, of the fine-grained region are seen to be a dominant property for threshold capillary pressures, the capillary pressure curves may be influenced by the pattern matrix geometry; as such, descriptions of the influence of the matrix-lamina contrast are also discussed. Further, these sorts of findings attempt to show underlying patterns that could be used to estimate the capillary pressure characteristics of laminated architectures given some pore-level characteristics.