Porosity‐Permeability Relationships in Mudstone from Pore‐Scale Fluid Flow Simulations using the Lattice Boltzmann Method

Abstract

We model mudstone permeability during consolidation and grain rotation, and during fluid injection by simulating porous media flow using the lattice Boltzmann method. We define the mudstone structure using clay platelet thickness, aspect ratio, orientation, and pore widths. Over the representative range of clay platelet lengths (0.1–3 μm), aspect ratios (length/thickness = 20–50), and porosities (ϕ = 0.07–0.80) our permeability results match mudstone datasets well. Homogenous kaolinite and smectite models document a log linear decline in vertical permeability from 8.31 × 10−15–6.84 × 10−17 m2 at ϕ = 0.76–0.80 to 6.33 × 10−19–1.30 × 10−23 m2 at ϕ = 0.14–0.16, showing good correlation with experimental data (R2 = 0.42 and 0.56).We employ our methodology to predict the permeability of two natural mudstone samples composed of smectite, illite, and chlorite grains. Over ϕ = 0.32–0.58, the permeability trends of two models replicating the mineralogical composition of the natural mudstone samples match experimental datasets well (R2 = 0.78 and 0.74). We extend our methodology to evaluate how vertical permeability might evolve during microfracture network growth or macrofracture propagation upon fluid injection in compacted mudstone. Fluid injection results in a permeability increase from 1.02 × 10−20 m2 at ϕ = 0.07 to 2.07 × 10−16 m2 at ϕ = 0.29 for growth of a microfracture network, and from 1.02 × 10−20 m2 at ϕ = 0.07 to 1.23 × 10−16 m2 at ϕ = 0.32 for macrofracture propagation. Our results suggest that a distributed microfracture network results in greater permeability during fluid injection in compacted mudstones (ϕ = 0.07–0.32) in comparison to a wide macrofracture. Our modeling approach provides a simple means to estimate permeability during burial and compaction or fluid injection based on knowledge of porosity and mineralogy.

Permeability and elastic properties of rocks from the northern Hikurangi margin: Implications for slow-slip events

“…Permeabilities measured in boreholes are typically orders of magnitude higher than those measured in the laboratory due to the presence of fractures (Fig 4B lines M,T,B) (Neuzil, 2019), and numerical models of permeability in microfractured claystones agree with the mudstone porositypermeability in Fig 4B (Vora & Dugan, 2019). We also propose that the permeability of rocks in the Northern Hikurangi accretionary prism can be described by a Kozeny-Carman relation (dashed lines in Fig 4B ):…”

Permeability and Elastic Properties of Rocks From the Northern Hikurangi Margin: Implications for Slow‐Slip Events

“…We suggest that Equation 2 (Figure 4b) overestimate permeabilities in the Northern Hikurangi accretionary prism at depths >1 km because helium gas is not as efficient as seawater in activating swelling clays, whose expansion lowers the effective permeabilities (Villar et al, 2005); At burial depths >1-2 km, the porosity of clay-bearing sediments and mudrocks drops below 35% (Griffiths & Joshi, 1989;Magara, 1978;Skempton, 1969). Permeabilities measured in boreholes are typically orders of magnitude higher than those measured in the laboratory due to the presence of fractures (Figure 4b lines M,T,B) (Neuzil, 2019), and numerical models of permeability in microfractured claystones agree with the mudrocks porosity-permeability in Figure 4b (Vora & Dugan, 2019). Therefore, we propose that the permeability of mudrocks, similar to those the Northern Hikurangi accretionary prism, can be described by a Kozeny-Carman relation (dashed lines in Figure 4b):…”

Permeability and elastic properties of rocks from the northern Hikurangi margin: Implications for slow-slip events

“…We suggest that the permeabilities comprised between equations 1 and 2 (Fig. 4B MN,S) are proxies for rock permeabilities in the Northern Hikurangi accretionary prism at depths >1 km, because helium gas limits clay swelling, which would have lowered the measured permeabilities (Villar et al, 2005); At burial depths >1-2 km, the porosity of claybearing sediments, mudstones, siltstone, and shales drops below 35% (Griffiths & Joshi, 1989;Skempton, 1969;Magara, 1978); Permeabilities measured in boreholes are typically orders of magnitude higher than those measured in the laboratory due to the presence of fractures (Fig 4B lines M,T,B) (Neuzil, 2019), and numerical models of permeability in microfractured claystones agree with the mudstone porosity-permeability in fig 5B (Vora & Dugan, 2019). We also propose that the permeability of rocks in the Northern Hikurangi accretionary prism can be described by a Kozeny-Carman relation (dashed lines in Fig 4B ):…”