Goal
The primary goal of this research is to visualize gas hydrate within sediment pore spaces under in situ condition 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 the development of the experimental system necessary to accommodate hydrate-bearing samples under in-situ conditions within an existing micro XCT system. Development will consist of the design, build and testing of 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 which will hold a small (~1/4 inch diameter by 3 inch long) sample under in situ conditions and which will allow visualization of hydrate formation and dissociation experiments within the vessel using the micro XCT (X-ray transparent cell). 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 optimizing for image quality. Following system testing, Micro XCT analysis for synthesized hydrate-bearing sediments will be performed to confirm the capability of the system to allow hydrate formation and confirm 3D visualization of hydrate accumulated within the pore space.

Specific activities will be focused around the following 3 areas:
1) Pressure vessel and experimental system design and build A pressure vessel will be prepared that includes the following characteristics: 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 ¼ 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 pressure up to 5000 psi and a temperature of -10 to +25 C. The specific design of the vessel will be a collaboration between NETL researchers and the manufacturer of the micro XCT scanner to assure appropriate compatibility.

Figure 1. Micro CT scanner (Xradia Micro XCT-400) installed in NETL at 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 that provides 3D observations of hydrate within the sediment matrix at the pore scale that is of sufficient resolution to quantitatively analyze the hydrate/sediment sample. Calibration methods to determine the densities of the sample components will be established and image processing techniques identifying and thresholding hydrate will be developed.

3) Visualization of synthesized hydrate during formation and dissociation Upon the completion of experimental system / pressure vessel development and system parameter optimization, methane hydrate will be formed and dissociated in packed sediments and 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 improve understanding of 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. Thresholded 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
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 is 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 .