The objective of this research is to improve understanding of the future production of methane from hydrate deposits in the Ulleung Basin (UB) in the Korean East Sea by numerically and experimentally investigating the challenging environment present there and elsewhere in the world.  

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA 94720

Methane hydrate in the UB is contained in seismic chimneys and in mud-confined layered sand/mud systems. The hydrate in the seismic chimneys is often veiny and hosted by fine material. Production of gas from these hydrate-bearing sediments is considered secondary to the layered sand/mud systems. A number of challenges require solutions for the production of gas from the sand/mud systems. These include understanding and controlling fines transport and the effect of hydrate dissociation and gas migration, the mechanical stability of the sediments. This work is part of a collaborative project that is partially funded by the Korea Institute of Geoscience and Mineral Resources (KIGAM) and NETL.
Both numerical studies and laboratory studies are included in this work. Objectives of numerical simulation studies include building the capabilities to be used in future collaborative work between KIGAM and LBNL in the planning of upcoming UB expeditions and in the design of future field tests. As part of this effort, LBNL will perform more realistic modeling of the near-wellbore zone in the thinly bedded mud/sand systems found in UB gas hydrate systems by leveraging recent LBNL work in the simulation of shale gas/shale oil systems to add non-Darcy flow, inertial effects, turbulent, and other physics of flow in very high-k and low-k porous media to TOUGH + HYDRATE / TOUGH+/HYDRATE (T+H/pT+H). To improve the reliability of the prediction of production behavior and wellbore stability in UB gas hydrate systems, the research team will incorporate the most complete geomechanical modeling capabilities into the coupled pT+H-ROCMECH simulator, implement a detailed, realistic representation of the wellbore itself, and further investigate the effect of hydrate dissociation on the reservoir and the stability of the well assembly. 
For gas production from hydrate, issues associated with these mud-confined layered sand/mud stratigraphies include permeable muds limiting the effectiveness of the seal, fines migration with fluids removal, reduction in sediment strength with hydrate dissociation and gas migration, and the possible lack of gas-flow pathways. Changes in mechanical properties of sediments could adversely affect the operation of vertical or horizontal wells. Laboratory experiments examining property changes will be performed to inform strategies for application of vertical wells and multi-stage horizontal wells in gas production in the UB. 

This work will inform KIGAM’s Production Technology Study, which will design optimal production schemes and evaluate the safety and stability of boreholes/wells and the stability of the reservoir during production. As such, it can help determine locations best suited to the upcoming third Ulleung Basin Gas Hydrate (UBGH) Drilling Expedition and the future production field test.
This effort will also improve understanding of the processes associated with the mechanical property changes of the sediments under the conditions present in the UB during natural gas production from hydrate-bearing sediments and will provide improved understanding and input into gas production strategies from interlayered sand/mud systems confined by somewhat shallow subsea muds. Similar systems are expected to be present in other locations worldwide.

• Added many improved capabilities to T+H allowing better simulation of UB-type hydrate deposits.
• Developed an in-house mechanics simulator (T+M (TOUGH+ROCMECH) (TAMU)).
• Performed a number of key simulations of gas production from UB sediments examining fluids flow, heat transfer, and geomechanics.
• Developed laboratory techniques to investigate particle transport and mechanical properties of sand/mud layered systems.
• Performed tests to examine behavior of UB-like hydrate deposits including particle transport and geomechanical behavior.

Efforts under the project are complete and a summary of project activities and findings can be found in the final scientific / technical report accessible from the Additional Information section below. Key findings resultant from project activities include:

• Under modeled conditions, displacement distances can be significant (from <0.4 m to ~1m) over the 14 day production period. The maximum displacements are above and below the production zone and will require engineering to address.
• Under extreme flow conditions while mechanically stable, some particle migration occurs. In our tests, this migration is measurable, but not geomechanically significant.
• There was no indication of hydraulic significance of particle migration in our tests.
• Consolidation of clays is time consuming. A few “simple” long-term (weeks) tests could provide some guidance.
• SAND MUST BE CONTROLLED or failure may be catastrophic.

$125,000 

KIGAM Contribution (separate agreement directly between LBNL and KIGAM): $150,000

NETL – Richard Baker, Project Manager (richard.baker@netl.doe.gov or (304-285-4714)
LBNL– Timothy J. Kneafsey, Principal Investigator (tjkneafsev@lbl.gov)

• Project Landing Page
• Final Project Scientific / Technical Report – November, 2018

Gas production test schematic

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Schematic diagram of the experimental setup

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packed mud/sand layer in molds prior to sample packing

CT image of packed sample after pressurization.

The packed mud/sand layered sample (a) Initial condition

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(b) After increasing the effective stress to 120 psi

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