Observing Pore-Scale Gas Hydrate Morphology and its Acoustic Response to the Host Sediments

Abstract

Quantification of seafloor methane hydrates using seismo-acoustic remote sensing methods requires knowledge of the links between the pore-scale distribution of hydrate and elastic wave properties, especially P- and S-wave velocity. Hence, we combined laboratory high-resolution X-ray CT imaging and joint acoustical-TDR (Time Domain Reflectometry) observations during synthetic methane hydrate formation in quartz sands (grain size 0.425 – 0.85 mm). The distribution of the hydrate inside the sand pores was seen to vary with increasing hydrate saturation between 0 to 97%, from “bridging” to “floating” and back again to “bridging” morphologies. P-wave velocity (Vp) and S-wave velocity (Vs) increased rapidly when the dominant hydrate morphology was bridging (i.e. hydrate bonds and bridges sand grains), but they increased relatively slowly when floating hydrate was dominant (i.e. hydrate floated in the pore fluid with few connections to sand grains). We compared the results to five velocity models and found that the Weighted Equation and Biot-Gassmann-Lee models accurately described the evolution of hydrate saturation.

AAPG Datapages/Search and Discovery Article #90348 © 2019 AAPG Asia Pacific Region Geosciences Technology Workshop, Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand, April 15-17, 2019