Sample collection
Medical x-ray CT imaging and image analysis
Sample preparation for x-ray microtomography, imaging and image analysis
Flow simulations for permeability, CO2 diffusivity, and apparent thermal conductivity
Dimensionless numbers
Percolation threshold analysis
Drainage experiment
The XRD analyses were performed on both bulk powder samples and clay fraction separated from the sample. The nest material was crushed using mortar and pestle to obtain a fine powder. The powder samples were analyzed using an PANalytical X-Pert Pro, using Cu Kα radiation at 40 kV and 40 mA. The samples were scanned over a sampling range of 2.5 to 70°2θ with a step size of 0.0066 and a scan speed of 0.023°2θ per second. For each nest, triplicate samples were used for bulk analyses and duplicate samples for separated clay fraction analyses with and without chemical treatment. As the clay particles (<2 μm in size) generally do not show clear diffraction patterns in bulk samples with random orientation, the clay fraction was separated from the bulk sample upon dispersion of the powder using an ultrasonic bath. Centrifugation of the samples at 1000 rpm for 2 min was used to separate the heavier fraction, whereas the clay was left in suspension. The clay suspended fluid was then put on glass rounds, the clay was allowed to settle, and the material was left to dry to generate oriented mounts for XRD analysis. The air-dried clay fraction samples and glycol-solvated clay fraction samples were used to identify different clays present in the samples. Moreover, some clay fractions were treated with 1 N HCl to confirm the absence of chlorite in the samples.
The diffraction analyses on the bulk samples of both nests show peaks of quartz (45); however, the Guinea sample also shows the presence of kaolinite and hematite (fig. S1). The XRD analysis on the separated clay fraction shows peaks of kaolinite and smectite in the Senegal sample and peaks of kaolinite and illite in the Guinea samples. The integrated intensities of the characteristic peaks were used for quantification of the relative mineral abundance in the samples. Separated fractions of different minerals are reported in table S1.