2.3.1. Water-Saturated Sample Preparation

To simulate deep-marine sediments, a water-saturated fine sand (i.e., Ottawa F110 sand) sample was prepared. First, the sample was mixed with distilled water and packed into the cell by hand tamping. The cell was fully filled with moist sand and the porosity of the sample was 0.40. Then, the cell was slowly flushed with distilled water at pressure of ~0.5 MPa for several hours to remove remaining air bubbles. During the water flushing, a cooling process was initiated. After the completion of water flushing, the cell was pressurized to 5.5 MPa with distilled water and left for about 16 h to stabilize the temperature throughout the sample.

Our primary goal was to study the self-trapping effect induced by CO2 hydrates, and because of that, distilled water was used as pore water instead of saline water (it allows easier hydrate formation). However, this decision means that the electrical and geochemical behavior in this experiment was different from the real behavior in the marine sediments.
