DE-FC26-06NT42960

Goal
The goal of this project is to improve the understanding of regional differences in gas hydrate systems from three perspectives: as an energy resource, as a geohazard, and as a long-term influence on global climate.

Performers
Rice University
University of Texas, Austin, TX
University of Oklahoma, Stillwater, Oklahoma

Background
Heterogeneity in the distribution of gas hydrate accumulations impacts all aspects of research into gas hydrate natural systems. The challenge is to delineate, understand, and appreciate these differences at the regional scale, where differences in in-situ concentrations are relevant to the importance of gas hydrate as a resource, geohazard, and factor in the carbon cycle. Some of the key questions that remain unanswered are:

• Why do regional heterogeneities in gas hydrate distribution occur?
• How can we detect them remotely?
• Where are concentrated gas hydrate accumulations likely to be found?
• How will heterogeneities affect strategies for production of natural gas from hydrates?
• How would different distributions respond to temperature perturbations?

Potential Impacts
This project will result in enhanced understanding of:

• the processes controlling the behavior of the marine hydrate system,
• the potential viability of proposed methodologies for the production of natural gas from methane hydrates and,
• improved safety practices during offshore drilling through a better understanding of seafloor and wellbore stability in the presence of hydrates.

The work may also result in advanced methodologies for remote quantification of hydrate accumulation through novel techniques for evaluation of geophysical imaging.

Accomplishments
Phase 1 of this study was brief in duration and focused on the full development of a revised statement of work for subsequent project phases that incorporated advances and new data produced since the applicant’s proposal was received. The development occurred through detailed planning and discussion with NETL personnel as well as through cooperation with other ongoing NETL funded research projects. In addition, the performers reviewed and selected the appropriate data sets for use in this study. This component of the effort was completed in March 2007. The performer provided a detailed plan for conducting activities under the project. Following provision of this information, a formal statement of project objectives and associated budget was negotiated between Rice and DOE to carry out the Phases 2 – 5 of the project.

Phase 2 of the project initialized in June 2007. Work under the remaining project phases (2-5) involves sustained efforts within five specific research areas over the course of the project. The value of the work under each area will be evaluated at the end of each year long phase before being continued to subsequent phases. Phase 2 was completed in July 2008 and Phase 3 was completed in July 2009 by which time Phase 4 was initialized. Phase 4 is scheduled to end July 2010. Results of the effort under Phase 2 and 3 include the following:

Carbon Inputs and Outputs to Gas Hydrate Systems

• Determined the amount of iodine in sediment and pore waters down boreholes at 10 locations, including 3 with gas hydrate from several gas hydrate systems (Blake Ridge, Peru Margin, Gulf of Mexico, Japan Sea), clearly showing that iodine accumulates in marine sediment as a function of organic carbon input over time.
• Examined carbon, sulfur and metal chemistry across the SMT at sites in the Japan Sea and the Peru Trench to assess whether sulfate profiles can be used to determine the upward flux of methane. Assumption appears valid in the Sea of Japan, but only after all carbon fluxes are accounted for. In particular, an upward flux of bicarbonate and carbonate precipitation impact geochemical interpretations across the SMT.

Numerical Models for Quantification of Hydrate and Free Gas Accumulations

• Progressed the development of the numerical models for hydrate and free gas accumulation to increase the fundamental understand of the accumulation phenomena.
• Developed a numerical model for the simulation of the accumulation of hydrate and free gas over geological time and length scales in one dimension and initiated efforts to move to two spatial dimensions.
• Initiated simulations to delineate basic modes of gas hydrate distribution in marine sediment, including systems with no gas hydrate, gas hydrate without underlying free gas, and gas hydrate with underlying free gas below the gas hydrate stability zone, for various methane sources.
• Developed combinations of dimensionless variables, particularly the Peclet number and Damkohler number, such that the dependence of average hydrate saturation on numerous parameters can be summarized using two contour maps, one for a biogenic source and one for upward flux from a deeper source. Model presents a unified picture of hydrate accumulations that can be used to understand well-characterized gas hydrate systems or to predict steadystate average hydrate saturation and distribution at locations for which seismic or core data are not available.
• Demonstrated continuous change of SH and Sv over a long spatial distance (~300 m) is possible, indicating that a gradual change of acoustic properties may induce weak BSR or even no BSR.
• Determined, through numerical simulations, that the ratio of sediment absolute permeability to the sedimentation rate was the key dimensionless group controlling overpressure generation. The effect of overpressure, in turn, limits the amount (thickness) of free gas that can accumulate below the GHSZ.
• Developed numerical and analytical models for inferring gas hydrate saturation in marine sediments from pore water sulfate profiles. Results from these models are in agreement with gas hydrate saturations estimated from resistivity logs/chloride data at several sites along Cascadia Margin.
• A dimensionless, two-dimensional (2-D) model was developed to simulate gas hydrate and free gas accumulation in marine sediments over geologic timescales. Development of a 2-D model allows incorporation of lithologic heterogeneity and lateral fluid flow in the system. Focused fluid flow through a vertical fracture network and/or high permeability sand layers affecting regional and local hydrate accumulation and saturation can be elucidated with the help of this 2-D model. Currently, relatively simple systems with fracture systems and/or dipping sand layers are simulated, whereas realistic geologic settings are characterized by much more heterogeneous stratigraphy in terms of fracture networks, multiple sand layers embedded within shaley layers and combination of fracture systems and sand layers. These preliminary results, however, serve as a starting point and demonstrate that the numerical model can be used to simulate systems with considerable heterogeneity to realize the natural gas hydrate systems more precisely.
• The simulator of geological scale accumulation of hydrate and free gas has been extended to 2-D and example simulations of heterogeneous systems are demonstrated.

Analysis of Production Strategy

• Successfully completed initial evaluation of production simulator by evaluating the scenarios established under the DOE-NETL code comparison study.
• Initiated evaluation for the potential use of warm water aquifer injection for the purpose of hydrate production. Determined that for warm water injection, production well pressure, injection temperature and pressure play an important role in the production of gas from hydrate deposits.
• Methane production was simulated for different injection pressures, injection temperatures and production pressures for 3000 days and total production of gas was compared for these parameters. Testing has shown that depressurization alone is effective in dipping unconfined reservoirs, but gas production rate is much slower than that for warm water injection. As the injection point of the warm water moves down the reservoir, the start of the high gas recovery phase gets delayed, but the time for completion of gas recovery becomes shorter. The cost of wells and warm water must be optimized along with the gas production to determine the optimal strategy for producing hydrate reservoirs. Future work will entail pore scale modeling that will be used to find relative permeability of the wetting phase (water) and the non-wetting phase (gas) for different hydrate saturation. The results will be incorporated in the present simulator and production simulation will be done for production strategies of gas hydrates.

Seafloor and Borehole Stability

• Initiated compilation of published geomechanical, fluid flow properties and data for multi-phase flow in hydrate systems and for strength in low-to-moderate hydrate saturation in fine grained materials.
• Initiated collaboration with MIT, GATech, the USGS,and LBNL to evaluate what technology exists to fill existing data gaps in the complied information.
• Initiated integration of sediment properties work (Task 8), the geologic hydrate accumulation work (Task 6), the hydrate production work (Task 7) and the DOE sponsored JIP hydrate work in the Gulf of Mexico to develop forward models of hydrate accumulation to test the JIP predictions and to provide accurate and realistic sediment models for our hydrate production models.
• Measured permeability of samples to evaluate new techniques for getting permeability anisotropy and for getting robust permeability data from logging measurements.
• Began integrating the sediment properties work with the geologic hydrate accumulation modeling (Task 6) by looking at how permeability and permeability anisotropy can be characterized over geologic time-scales and then incorporated in accumulation models.
• Developed a safe drilling program that will maximize our understanding of hydrate in the Gulf of Mexico and proved data for modeling these accumulations.
• Measured permeability to evaluate new techniques for estimating permeability anisotropy and getting robust permeability data from logging measurements.
• Assessed sediment stability in hydrate systems through two different approaches. In the first, infinite slope stability analysis is being used in the geologic accumulation models (Task 6). This is the first step in trying to address the evolution of geohazards related to hydrate systems. This technique is computationally inexpensive, applicable in geologic and reservoir models, and provides a quick look at stability to identify locations for detailed stability analysis. The second stability analysis evaluates fracture genesis in fine-grained sediments to assess the condition for failure (fracture) and how that relates to fracture-hosted hydrate.
• Developed of a review paper on physical properties of hydrate bearing sediments (Waite et al., in review) that integrates numerous DOE and other studies defining the state of knowledge on sediment-hydrate properties and the key data gaps (primarily data on low hydrate saturation in sediments). Another advancement on this front has been the development of the fracture genesis model. This model will provide complementary data for other DOE studies looking at geomechanical properties and fractures in hydrate systems and how they relate to the presence of free gas within the hydrate stability region.

Geophysical Imaging of Gas Hydrate and Free Gas Accumulations

• Identified and initiated processing of a limited seismic dataset from the India (NGHP1) hydrate expedition. The identified seismic line has three inline wells all of which were drilled in 2001. The drilling was based on BSR signatures that appear to be similar at the well locations but the recovered hydrate concentration was found to be varying.
• Continued discussions with India NGHP program related to expanded collaboration with the Rice effort and the use of NGHP data in that effort.
• Initiated collaboration with National Institute of Oceanography (NIO), India to demonstrate geophysical imaging with multichannel seismic data from the Krishna-Godavari (K-G) basin in the Indian east coast.

Current Status (January 2010)
Phase 1 through 3 have been completed and Phase 4 work was initiated in July 2009 based on the finalized statement of work. The remaining project effort includes two one-year phases (Phases 4-5) which will consist of ongoing efforts in each of the research areas outlined in the Accomplishment section above. Accomplishments from work performed are also summarized in the Accomplishments section above and full detail can be found in the quarterly progress reports and the Topical Report for the project (links to project reports are provided in the Additional Information section below).

Project Start: October 1, 2006
Project End: July 16, 2011

Project Cost Information:
Phase 1 - DOE Contribution:     $3,624, Performer Contribution: $1,004
Phase 2 - DOE Contribution: $320,010, Performer Contribution: $114,613
Phase 3 - DOE Contribution: $331,135, Performer Contribution: $107,630
Phase 4 - DOE Contribution: $356,049, Performer Contribution: $110,489
Phase 5 - DOE Contribution: $259,335, Performer Contribution: $114,363
Planned Total Funding (if project continues through all project phases):
DOE Contribution: $1,270,153, Performer Contribution: $448,099

Contact Information:
NETL – John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
Rice University – Dr. George Hirasaki (gjh@rice.edu or 713-348-5416)

Additional Information
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].

Semi-Annual Report May - October, 2009 [PDF-2.04MB]

Semi-Annual Report November, 2008 - April, 2009 [PDF-1.95MB]

Quarterly Report July - October, 2008 [PDF-1.74MB]

2008 ICGH Paper - Relating Gas Hydrate Saturation to Depth of Sulfate-Methane Transition [PDF]

2008 ICGH Paper - Effect of Overpressure on Gas Hydrate Distribution [PDF]

2008 ICGH Paper - Production Strategies for Marine Hydrate Reservoirs [PDF]

Topical Report [PDF-3.92MB] - June, 2008

Quarterly Report [PDF-1.68MB] - January 1, 2008 - March 31, 2008

Quarterly Report [PDF-429KB] - October 1, 2007 - December 31, 2007

Quarterly Report [PDF-417KB] - July 1, 2007 - September 31, 2007

American Journal of Science Article [PDF-1.66MB] - June, 2007

Quarterly Report [PDF-395KB] - April 1, 2007 - June 30, 2007

Kick-off meeting presentation [PDF-701KB] - January 9, 2007