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doi:10.2204/iodp.proc.338.202.2015

Methods and materials

A total of 19 bulk cuttings and core samples (Table T1) were collected shipboard, sealed in storage bags, and stored at 4°C until they were prepared for MICP measurements at Core Laboratories (Houston, Texas). Bulk cuttings samples were selected from the >4 mm cuttings fraction, and each bulk cuttings sample contained at least 12 cm³ of material. Core samples were core pieces with a total volume exceeding 12 cm³. All samples were selected because they were mud or mudstone. No sand-bearing samples were collected or analyzed.

Mercury injection capillary pressure measurements

MICP measurements were performed at room temperature (20°C) using a Micromeritics AutoPore device. Before the measurements, samples were oven-dried at 115°C for at least 24 h to allow weight equilibrium (±0.001 g); this is the standard approach at Core Laboratories and is similar to the moisture and density drying technique of 100°C for 24 h (Blum, 1997). For the MICP measurements, each sample was immersed in mercury in a pressure-sealed chamber attached to a capillary stem with a cylindrical coaxial capacitor. The mercury pressure was increased incrementally from 0 to 380,000 kPa. Each pressure step forced mercury intrusion into sample pore spaces, and each pressure step was maintained until volume equilibrium was reached. Volume equilibrium was determined by the capacitance of the system. The volume of mercury injected at each pressure increment was determined by capacitance measurements. Pore volume was computed from the bulk sample volume determined by immersion in mercury, and porosity was determined following the method of Blum (1997). Details about MICP experimental set-up, experimental procedure, and interpretation of MICP results can be found in Amyx et al. (1960), Bear (1972), Peters (2012), and Purcell (1949).

The volume of mercury injected and the pore volume at each pressure were used to construct a pore size distribution for each sample. Mercury injection pressure (P_Hg) was converted to pore throat radius (r_p) using the Young-Laplace equation:

(1)

where σ_Hg is air-mercury interfacial tension (0.485 N/m) and θ_Hg is the mercury-sediment contact angle (140°) (Table T2). The median pore throat radius (r₅₀) was defined from the pore throat size distribution as the pore throat size at a mercury saturation equal to 0.5.

Mercury injection pressure (P_Hg) was converted to air-water capillary pressure (P_c) by:

(2)

where σ_aw is air-water interfacial tension (0.072 N/m) and θ_aw is the air-water contact angle (180°) (Table T2). Air-water capillary entry pressure (P_centry) was determined from the minimum mercury injection pressure at which the volume of injected mercury was nonzero. This corresponds to the mercury percolation threshold (Bear, 1972).

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