DOE/NETL Methane Hydrate Projects
 
Dynamic Behavior of Natural Seep Vents: Analysis of Field and Laboratory Observations and Modeling Last Reviewed November 2017

DE-FE0028895

Goal
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.

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

Background
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.

Impact
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.

Accomplishments (most recent listed first) 

  • Researchers completed the transfer of 24 TB of HPWT data from NETL to a new server at Texas A&M University.
  • 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.

Current Status (November 2017)
Researchers have completed the analysis of the 24 TB of HPWT data obtained from NETL. All of the video data for bubble experiments in the HPWT that were conducted in the HSZ have been analyzed. From the videos, the team identified the moment that hydrate skin coverage was completed for each bubble, as well as for key moments when hydrate dynamics changed.

Post-processing of the image data collected during the GISR seep cruises has been completed. All video data collected from a high-speed, stereoscopic image system deployed on the ROV Hercules during the two cruises have been analyzed to quantify bubble sizes and the rise velocities of individual bubbles. In addition, researchers have completed the development of analysis tools for the acoustic data collected during the G07 and G08 cruises. The analysis tools will be used to validate data by comparing the measured target strength from the EM 302 multibeam sonar data with the predicted target strength from the numerical model for a simulation of the seep.

During the next quarter, additional image data will be analyzed for bubble shrinkage rate during hydrate formation and dissociation. In addition, observed hydrate formation times will be compared with the time predicted in the model, a key step toward the validation of the hydrate formation mechanisms in the model.

Project Start: October 1, 2016
Project End: September 30, 2019

Project Cost Information:
Phase 1 – DOE Contribution: $144,311, Performer Contribution: $36,086
Phase 2 – DOE Contribution: $121,128, Performer Contribution: $30,374
Phase 3 – DOE Contribution: $ 96,094, Performer Contribution: $24,038
Planned Total Funding – DOE Contribution: $361,533, Performer Contribution: $90,498

Contact Information:
NETL – Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396)
Texas A&M Engineering Experiment Station – Scott Socolofsky (ssocolofsky@civil.tam.edu or 979-854-4517)

Additional Information:

Quarterly Research Performance Progress Report [PDF] July - September, 2017

Quarterly Research Performance Progress Report [PDF] April - June, 2017

Quarterly Research Performance Progress Report [PDF] January - March, 2017

Quarterly Research Performance Progress Report [PDF] October - December, 2016