Observations of bubbles in natural seep flares at MC 118 and GC 600 using in situ quantitative imaging

Abstract

This paper reports the results of quantitative imaging using a stereoscopic, high‐speed camera system at two natural gas seep sites in the northern Gulf of Mexico during the Gulf Integrated Spill Research G07 cruise in July 2014. The cruise was conducted on the E/V Nautilus using the ROV Hercules for in situ observation of the seeps as surrogates for the behavior of hydrocarbon bubbles in subsea blowouts. The seeps originated between 890 and 1190 m depth in Mississippi Canyon block 118 and Green Canyon block 600. The imaging system provided qualitative assessment of bubble behavior (e.g., breakup and coalescence) and verified the formation of clathrate hydrate skins on all bubbles above 1.3 m altitude. Quantitative image analysis yielded the bubble size distributions, rise velocity, total gas flux, and void fraction, with most measurements conducted from the seafloor to an altitude of 200 m. Bubble size distributions fit well to lognormal distributions, with median bubble sizes between 3 and 4.5 mm. Measurements of rise velocity fluctuated between two ranges: fast‐rising bubbles following helical‐type trajectories and bubbles rising about 40% slower following a zig‐zag pattern. Rise speed was uncorrelated with hydrate formation, and bubbles following both speeds were observed at both sites. Ship‐mounted multibeam sonar provided the flare rise heights, which corresponded closely with the boundary of the hydrate stability zone for the measured gas compositions. The evolution of bubble size with height agreed well with mass transfer rates predicted by equations for dirty bubbles.

How Do Oil, Gas, and Water Interact Near a Subsea Blowout?

“…Hydrate formation is pressure-and temperature-dependent, and has recently been studied in high-pressure laboratory facilities (Warzinski et al, 2014) and at natural seeps (B. . In the latter study, in situ high-speed imagery of seep bubbles near 1,000 m depth confirmed the formation of hydrate skins on gas bubbles from natural seeps in the field, and field measurements indicate that mass transfer rates vary between rates for clean and dirty bubbles (Rehder et al, 2009;B. Wang et al, 2016).…”

Using Carbon Isotope Fractionation to Constrain the Extent of Methane Dissolution Into the Water Column Surrounding a Natural Hydrocarbon Gas Seep in the Northern Gulf of Mexico

“…The gas samples were collected at the seafloor in dives H1405 and H1406, along with a 200‐m altitude sample in dive H1407. The bubble size distribution at the seafloor was measured using a stereoscopic imaging system (Wang & Socolofsky, ), following the same procedure as in the Gulf Integrated Spill Response Consortium research cruise G07 (Wang et al, ). The TAMOC model simulated 1,000 randomly generated bubbles based on a lognormal distribution that best fit the water column bubble size measurements (Figure ).…”

Xenon Hydrate as an Analog of Methane Hydrate in Geologic Systems Out of Thermodynamic Equilibrium

“…Slow diffusion through interfacial hydrate significantly impacts how gas is transported through the water column or within sediments. The phenomena of hydrate‐crusted gas bubbles in the water column (Warzinski et al, ; Wang et al, ; Waite et al, ) or crustal gas pockets in the sediment (Chen et al, ; Lei & Santamarina, ; Meyer, Flemings, & DiCarlo ; Meyer, Flemings, DiCarlo, et al, ; Sahoo, Marín‐Moreno, et al, ; Sahoo, Madhusudhan, et al, ) have been widely observed and allude to the prolonged coexistence of gas, liquid, and hydrate phases (three‐phase coexistence) that is not predicted by the equilibrium‐phase diagram (Fu et al, ). Although the three‐phase configuration across the interface is out of equilibrium, the two boundaries of the growing hydrate layer can independently approach local equilibria with the phase it contacts (gas or liquid).…”