[Paper Review] Permeability, compressibility, and friction coefficient measurements under confining pressure and strain, Leg 190, Nankai Trough

S. Bourlange, Laurence Jouniaux+1 more|arXiv (Cornell University)|Oct 20, 2006

Rock Mechanics and Modeling17 references16 citations

TL;DR

This study measures permeability, compressibility, and friction coefficient of Nankai Trough sediments under confining pressure and strain using triaxial testing. Results show permeability decreases with effective pressure up to 1.5 MPa, stabilizes at 1–4×10⁻¹⁹ m² above 1.5 MPa, and increases only under low effective pressure during failure, with friction coefficients of ~0.4 on slickenlined fractures.

ABSTRACT

Permeability measured on three samples in a triaxial cell under effective confining pressure from 0.2 to 2.5 MPa ranges from 10E-18 to 10E-19m2. Overall, results indicate that permeability decreases with effective confining pressure up to 1.5 MPa; however, measurements at low effec-tive pressure are too dispersed to yield a precise general relationship between permeability and pressure. When the effective pressure is increased from 1.5 to 2.5 MPa, permeability is roughly constant (~1-4 x 10E-19 m2). Samples deformed in the triaxial cell developed slickenlined fractures, and permeability measurements were performed before and after failure. A permeability increase is observed when the sample fails under low effective confining pressure (0.2 MPa), but not under effective pressure corresponding to the overburden stress. Under isotropic stress conditions, permeability decrease related to fracture closure occurs at a relatively high effective pressure of ~1.5 MPa. Coefficients of friction on the fractures formed in the triaxial cell are ~0.4.

Motivation & Objective

• To quantify the permeability response of Nankai Trough sediments to varying effective confining pressures and strain conditions.
• To assess changes in compressibility and friction coefficient during triaxial deformation and failure.
• To evaluate the influence of fracture development on fluid transport properties under different stress regimes.
• To determine the relationship between effective pressure and permeability evolution in subduction zone sediments.
• To measure the coefficient of friction on experimentally formed slickenlined fractures under controlled stress conditions.

Proposed method

• Conducted triaxial compression tests on three sediment samples from Leg 190 of the Ocean Drilling Program.
• Applied effective confining pressures ranging from 0.2 to 2.5 MPa to simulate in-situ stress conditions.
• Performed permeability measurements before and after sample failure to assess dynamic changes in fluid flow properties.
• Used strain-controlled deformation to induce localized fracturing and record frictional behavior on slickenlined surfaces.
• Measured compressibility through volumetric strain response under increasing effective pressure.
• Calculated the coefficient of friction from shear stress and normal stress data obtained during failure events.

Experimental results

Research questions

• RQ1 How does permeability of Nankai Trough sediments vary with increasing effective confining pressure?
• RQ2 What is the effect of sample failure on permeability under low versus high effective pressure conditions?
• RQ3 At what effective pressure does fracture closure significantly reduce permeability?
• RQ4 What is the coefficient of friction on experimentally induced slickenlined fractures in these sediments?
• RQ5 How does compressibility of the sediments correlate with effective pressure and deformation state?

Key findings

• Permeability ranged from 10⁻¹⁸ to 10⁻¹⁹ m² under effective confining pressures of 0.2–2.5 MPa.
• Permeability decreased with increasing effective pressure up to approximately 1.5 MPa, after which it stabilized at 1–4×10⁻¹⁹ m².
• A significant permeability increase was observed only under low effective pressure (0.2 MPa) during failure, indicating strain-weakening behavior at low overburden stress.
• Fracture closure under isotropic stress reduced permeability at a relatively high effective pressure of ~1.5 MPa.
• The coefficient of friction on slickenlined fractures formed during triaxial deformation was consistently ~0.4.
• Permeability measurements at low effective pressure were highly dispersed, preventing a precise general relationship between permeability and pressure at these conditions.