The overall objective of this research is to develop a mechanistic model for dissolution of hydrate-coated methane bubbles from natural seeps that fully explains fundamental laboratory and field observations of methane bubbles within the gas hydrate stability zone of the oceans, to validate the model to data from the NETL High-Pressure Water Tunnel (HPWT) and the Gulf Integrated Spill Research Consortium (GISR) seep cruises, and to demonstrate the capability of the model to quantify bubble characteristics and concentration from M3 and EM 302 multibeam echosounder data collected during the GISR cruises.

Phase 1 will focus on laboratory and field data analysis and will achieve project Objective 1 to analyze existing data from the NETL HPWT and Objective 2 to synthesize data from the GISR natural seep cruises.

In Phase 2, the effort will be on project Objective 3 to refine and validate the seep model to predict the laboratory and field data obtained through Phase 1. The team will also collect new data to calibrate the backscatter response of the M3 multibeam echosounder, which will be needed in Phase 3 of the project.

Phase 3 will accomplish project Objective 4 to demonstrate the capability of the refined and validated seep model to interpret multibeam data and will perform the work to disseminate the results and data of the project to the public. Together, these objectives will meet the project goal of developing a validated natural seep model and demonstrating its skill in interpreting laboratory HPWT data and field data from natural seeps.

Texas A&M Engineering Experiment Station, College Station, TX 77845

Acoustic and in situ observations of methane and gas bubble flares from natural seeps in the oceans increasingly demonstrate that gas hydrate deposits in the sediments and leakage of bubbles into the water column are ubiquitous occurrences on the continental margins around the world, including the coastlines of the United States and the Arctic. Bubbles that enter the water column transport methane vertically upward, and it is important to develop models to predict their dissolution and fate to understand the input of methane to the ocean-atmosphere system from methane hydrate deposits. Models exist in the literature to predict the bubble dynamics in the water column, but they are limited in their ability to predict the formation time for hydrate skins that can coat bubbles in the deep ocean and to understand the appropriate mass transfer rates for hydrate-coated bubbles. This project seeks to address this gap by synthesizing insight from existing high-pressure laboratory and in situ field data to refine and validate an advanced computer model for methane bubble dynamics and to demonstrate the model performance using field acoustic data from the Gulf of Mexico. This work is important to clarify the processes by which gas hydrate deposits, an important reservoir of the global carbon budget, are maintained and evolve within the natural ocean environment.

The validated model will predict the evolution of hydrate-coated methane bubbles from the sea floor, including their rates of dissolution into the water column, to their point of maximum rise or the sea surface. This provides a holistic understanding of free methane gas in the ocean water column, which is important to predict dissolved methane input to the oceans from natural seeps, a key element of the global carbon cycle, and potential ventilation to the atmosphere, both under baseline conditions as well as in response to future climate scenarios.

Ultimately, the main outcome and benefit of this work will be to clarify the processes by which hydrate-coated methane bubbles rise and dissolve into the ocean water column, which is important to predict the fate of methane in the water column, to understand the global carbon cycle, and to understand how gas hydrate deposits are maintained and evolve within geologic and oceanic systems, both at present baselines and under climate-driven warming.

• Compared the model simulations with the EM-302 data measured during the GISR research cruises to validate model performance at field scale.
• Completed simulations of all experiments in the HPWT dataset using the TAMU oil spill Calculator (TAMOC) and quantified the model performance.
• Analyzed mass transfer rates for all measured data in the HPWT dataset. Mass transfer rates are about two times higher than theoretical rates for dirty bubbles and can be predicted analytically using a constant correction factor.
• Completed the experiments in the Offshore Technology Research Center (OTRC) to measure acoustic properties of bubble plumes with a calibrated M3 multibeam sonar.
• Passed Decision Point 2, which permits the experiment in the OTRC. Completed modifications to TAMOC, allowing it to be applied to the HPWT dataset.  
• Completed the evaluation of hydrate formation time for the NETL HPWT data.
• Completed the development of analysis tools for the HPWT data and the GISR acoustic data. 
• Researchers completed the transfer of 24 TB of HPWT data from NETL to a new server at TAMU.
   

Work under the project is fully completed and activities and results of the effort are contained in the project’s final scientific/technical report that is available from the link in the Additional Information section below. 

Phase 1: $144,311

Phase 2: $121,128

Phase 3: $ 96,094

Planned Total Funding – $361,533

Phase 1 – $36,086

Phase 2 – $30,374

Phase 3 – $24,038

Planned Total Funding – $90,498

NETL – Richard Baker (richard.baker@netl.doe.gov or 304-285-4714)
Texas A&M Engineering Experiment Station – Scott Socolofsky (ssocolofsky@civil.tam.edu or 979-854-4517)

Final Project Scientific /Technical Report [PDF] December 2020
   OSTI Identifier