Goal
The primary goal of this research is to visualize gas hydrate within sediment pore spaces under in situ conditions using a high-resolution micro-XCT scanner.

Performers
Yongkoo Seol ? NETL Office of Research & Development
Eilis Rosenbaum ? NETL Office of Research & Development
Jongho Cha- Oak Ridge Institute for Science and Education

Location
National Energy Technology Laboratory - Morgantown, West Virginia

Description
The initial phase of this research will focus on developing the experimental system needed to accommodate hydrate-bearing samples under in-situ conditions within an existing micro-XCT (X-ray transparent cell) system. Development will consist of designing, building, and testing the two main components needed to perform hydrate formation and dissociation experiments: (1) a micro-XCT compatible pressure vessel and (2) an experimental system providing controls on in situ pressure and temperature conditions, liquid /gas flow injection and collection, and data logging.

A pressure vessel will be developed that will hold a small (~1/4 inch diameter by 3 inch long) sample under in situ conditions and allow visualization of hydrate formation and dissociation experiments within the vessel using the micro-XCT. The experimental control system will provide and maintain the appropriate pressure and temperature required for hydrate stability as well as capabilities to control injection into and flow out of the pressure vessel.

Preliminary testing of the system will be performed with analogues mimicking hydrate with a focus on image quality optimization. Following system testing, researchers will perform micro-XCT analysis on synthesized hydrate-bearing sediments to confirm the ability of the system to form hydrate and confirm 3-D visualization of hydrate accumulation within the pore space.

Specific activities will be focused around the following 3 areas:

1. Pressure vessel and experimental system design and construction
   A pressure vessel will be prepared that includes the following elements: a top stainless steel end cap, a vessel body made of beryllium for best X-ray transparency, and a bottom connection for the micro-XCT scanner sample base. The vessel body will be designed to contain 1/4 inch diameter by 3 inch long samples. The vessel will be equipped with ports for fluid injection and pressure/temperature monitoring, and confining pressure capability. The vessel will be designed for pressures up to 5000 psi and temperatures from -10 to +25 C. The vessel design will be a collaborative effort between NETL researchers and the manufacturer of the micro-XCT scanner to ensure appropriate compatibility.

   
   Figure 1. Micro-CT scanner (Xradia Micro-XCT-400) installed at NETL in Morgantown, WV

2. System parameter optimization
   The X-ray CT system parameters (beam strength, filter, resolution, dimension of view-of-interest, etc.) will be optimized to obtain data on 3-D observations of hydrate within the sediment matrix at the pore scale that is of sufficient resolution to quantitatively analyze the hydrate/sediment sample. Researchers will establish calibration methods to determine the densities of the sample components and develop image processing techniques for identifying hydrates and their threshold properties.
3. Visualization of synthesized hydrate during formation and dissociation
   Upon the completion of the experimental system/pressure vessel development and system parameter optimization, methane hydrate will be formed and dissociated in packed sediments. Micro-XCT scans will be performed to confirm the capability to visualize hydrate within the pore space during the hydrate formation and dissociation processes.

   
   Figure 2. CT scanning image showing gas migration pathways (in red) through fine grain sediment core (in gray)

Impacts
Real-time imaging of phase change and gas migration during hydrate formation and dissociation and subsequent numerical simulations supported by CT-based 3-D distribution maps will help provide insight into the impact of hydrate on gas migration, well bore stability, and sea floor hazards that could occur during development and production from hydrate reservoirs.

Accomplishments

• Initial system testing has demonstrated the ability to visually identify a hydrate analog in the pore spaces of a sand medium.
• Preliminary results indicate that, with image manipulation and appropriate density standards, the system can be used to differentiate between water and hydrate in pore spaces.

  
Figure 3. Threshold micro CT images: Left: Epoxy (pink) in the pore spaces of the glass beads (purple), Right: partially water-saturated sand packs showing water blobs in blue

Current Status (March 2013)
Acquisition of the Beryllium core holder and recirculation system (with P/T control) is expected by early April 2013. Micro-XCT scanning with plastic analogues (polyethylene, n-vinyl carbazole, acrylic acid) is ongoing and being performed to establish the image processing procedure. Higher resolution scans of the simulated samples will be performed to optimize system parameters as a proof-of-concept and in preparation for creating and imaging laboratory formed methane hydrate in the specialized pressure vessel.

Cost Information:
DOE Contribution: FY2012: ~$120,000

Contact Information:
NETL?ORD: Yongkoo Seol (Yongkoo.Seol@netl.doe.gov or 304-285-2029)

Additional Information
In addition to the information provided above, a listing of any available project related publications and presentations, as well as a listing of funded students, will be included in the Methane Hydrate Program Bibliography.