Compressional wave velocity measurements through sandy sediments containing methane hydrate

Abstract

An experimental apparatus was built to measure P-wave velocity (v P ) of sandy sediment during hydrate formation from brine and free methane gas. The influences of hydrate saturation, initial brine saturation, conversion ratio of water to hydrate, and grain size of sand upon v P were investigated. The experimental results demonstrate that v P strongly depends on both hydrate saturation and initial brine saturation, whereas the influence of the grain size of sand is unremarkable. During the formation of hydrate for different experimental runs at identical initial brine saturation, v P increases with the increase of hydrate saturation; while it decreases dramatically with the increase of initial brine saturation for a given hydrate saturation. The correlation between v P and conversion ratio of water into hydrate was studied, and it was found that the relation between v P and the conversion ratio of water to hydrate is approximately the same for different experimental runs, regardless of how big the differences in initial saturation of brine and the size of sand grain are. v P was calculated for four different hydrate distribution models. The results suggest that low conversion ratio of water to hydrate, hydrate mainly acts as a load component of a dry frame matrix, whereas at higher conversion ratio of water to hydrate it partly acts as a cement that coats grains at grain contacts, and thereby leads to a dramatic increase in v P . Compared with the hydrate saturation, the conversion ratio of water to hydrate has a large role in distributing hydrate in the pores of sediments.

Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X‐ray computed tomographic microscopy

“…For the same GH saturation, the predicted material properties, (in particular the seismic and electrical response and the permeation behavior) vary considerably with the chosen microstructural model. Experimentally observed seismic velocities suggest that the actually adopted microstructure in a fully water‐saturated regime changes with GH saturation [ Dai et al ., ; Konno et al ., ; Zhang et al ., ] ranging from a more pore‐filling situation toward a more load‐bearing case. While this general trend certainly is also observed in our tomographic experiments, some further details emerge.…”

Evaluation of Different CH4-CO2 Replacement Processes in Hydrate-Bearing Sediments by Measuring P-Wave Velocity

“…A schematic outline of the experimental apparatus for measuring P-wave velocity of hydrate-bearing sediment is shown in Figure 1 [16]. The main parts of the apparatus are a high-pressure reactor, an air bath, a gas filling system, and a data collection system.…”

“…In our previous work [16], we have described an apparatus for measuring V p of the hydrate bearing sediment and a series of V p datasets were obtained for different hydrate saturations. In this work, the stability of hydrate reservoirs during the replacement process of CH 4 with CO 2 is examined by measuring and analyzing the variation of V p .…”

Squirt flow due to interfacial water films in hydrate bearing sediments

“…Additionally, the recovery of unaltered natural GH samples is hampered due to their fast decomposition under ambient conditions. Therefore, various researchers have attempted to mimic the natural environment of GH-bearing sedimentary matrices in laboratory experiments (Berge et al, 1999;Ecker et al, 2000;Dvorkin et al, 2003;Yun et al, 2005;Spangenberg and Kulenkampff, 2006;Priest et al, 2006Priest et al, , 2009Best et al, 2010Best et al, , 2013Hu et al, 2010;Li et al, 2011;Zhang et al, 2011;Dai et al, 2012;Schicks et al, 2013). The results of this collective effort established a number of conceptual models for the role of GH embedded in its sedimentary matrix (Fig.…”