Thermal Properties of Pressure Core Samples Recovered From Nankai Trough Wells Before and After Methane Hydrate Dissociation

The thermal properties of methane hydrate (MH)-bearing sediments are necessary for developing gas production technologies (e.g., gas production rate prediction). The direct thermal property measurement of a general MH reservoir is difficult because it demands an advanced coring and measuring technology. Therefore, a good thermal property value estimation model for a system containing sediment grains, water, MH, and gas is necessary. In 2018, the pressure core samples were recovered from the AT-CW1 and AT-CW2 wells in Nankai Trough of Japan. Using a single-sided transient plane source method, we measure herein the thermal property values of those core samples and estimate their thermal conductivity by improving existing models. The measured thermal conductivity (lambda), specific heat (rho C-p), and thermal diffusivity (alpha) of the MH-bearing sediments before and after MH dissociation are obtained. The de Vries model agrees well with the measured thermal conductivity values before and after the MH dissociation. For the random distribution (geometric mean) model, the difference between the estimation values and the data after the MH dissociation increases as the gas saturation S-g & PRIME; increases. In the worst case, the distribution model shows an 87.6% error, while the de Vries model yields 5.2% of the same. We propose and use an estimation method of the thermal property values in an MH reservoir, which requires classical thermophysical models and well log data. The in-situ thermal property values can be estimated when the log data are highly accurate.

Automated summary

This study aims to develop a thermal property estimation model for determining the thermal properties of methane hydrate (MH)-bearing sediments, as direct measurement of thermal properties of general MH reservoirs is difficult. By improving existing models and using a single-sided transient plane source method, we measured the thermal property values of pressure core samples from the Nankai Trough of Japan and estimated their thermal conductivity. The de Vries model agreement well with the measured thermal conductivity values before and after MH dissociation, while the random distribution model shows increasing discrepancy as gas saturation increases.