|A New Approach to Understanding the Occurrence and Volume of Natural Gas Hydrate in the Northern Gulf of Mexico Using Petroleum Industry Well Logs
||Last Reviewed 12/11/2014
The overarching objective of the project is to significantly increase our understanding of the occurrence, volume, and fine scale distribution of natural gas hydrate in the northern Gulf of Mexico using petroleum industry and Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) well logs.
The Ohio State University, Columbus, OH 43210
A large quantity of natural gas hydrate certainly occurs within the sediments of the northern Gulf of Mexico; however, the total amount and distribution of gas hydrate across the basin is relatively unconstrained (Boswell et al. 2012). Gas hydrate forms in the gas hydrate stability zone (GHSZ), which is the interval between the seafloor and the sediment depth at which gas hydrate becomes too warm to be stable (gas hydrate stability depends on temperature, pressure, and salinity). A thin GHSZ originates in Gulf of Mexico sediments at the seafloor in water column depths of ~500 m and thickens as the water column increases (Milkov & Sassen, 2001).
Gas hydrate accumulations have historically not been sufficiently mapped by exploration seismic, though some new approaches seem promising (e.g., McConnell & Zhang, 2005; Shedd et al., 2012). Thus, most current knowledge of sub-seafloor natural gas hydrate in the Gulf of Mexico comes from hydrate-focused drilling cruises, particularly the Gulf of Mexico Gas Hydrate Joint Industry Project Legs 1and 2, and from models of organic matter deposition and methanogenesis in the Gulf of Mexico basin (Frye, 2008).
The focus of this project is to significantly advance understanding of the distribution and volume of natural gas hydrate from the log- to basin-scale in the northern Gulf of Mexico. To accomplish this, over 1700 industry well logs (obtained from the Bureau of Safety and Environmental Enforcement) from wells that penetrate the GHSZ will be analyzed for occurrence of natural gas hydrate in both sand and clay reservoirs. The industry well log analysis will be coupled with analysis and high resolution modeling of the sand and fracture gas hydrate reservoirs using well logs collected during the Gulf of Mexico Gas Hydrate Joint Industry Project Leg 2. Finally, researchers will use modeling results from the JIP Leg 2 wells and the industry analysis as inputs to a Monte Carlo simulation to formulate an estimate of the volume of natural gas hydrates in sand reservoirs and all sediment types in the Gulf of Mexico.
The project will significantly increase our knowledge of the nature and occurrence of deepwater gas hydrates and, in particular, the type of sediment in which gas hydrate forms. By assessing the in situ occurrence of gas hydrate in over 1700 industry wells, this research will directly identify methane hydrate resources, and may identify new potentially commercial hydrate-bearing sand reservoirs. In addition, approximately 200 of the 1700 industry wells were drilled at water column depths of 500–600 meters, which are most sensitive to warming temperatures at the ocean bottom or decreases in sea level. Understanding the distribution and concentration of hydrate in these shallow waters is important for understanding the response of gas hydrate over geologic time.
Accomplishments (most recent listed first)
- Project results to date were presented at the International Conference on Gas Hydrates in Beijing, China.
- Initial assessments were completed for OCS lease blocks Garden Banks, Green Canyon, Walker Ridge, Atwater Valley, and Mississippi Canyon.
- Researchers presented three posters and a paper at the Gordon Research Conference in March 2014.
- A paper entitled “Do Gas Hydrates Occur in Alaminos Canyon, Gulf of Mexico?” was presented at the Unconventional Resources Technology Conference in August 2013.
- Researchers completed assessments of the East Breaks and Keathley Canyon blocks in the Gulf of Mexico. Preliminary results indicate that 20 of 165 wells that were assessed in the East Breaks block may contain gas hydrates while only two of 48 assessed wells in Keathley Canyon showed indications of hydrates.
- Logging data from 46 wells in Alaminos Canyon were analyzed for the presence of gas hydrate. Twenty of the 46 wells analyzed were identified as likely to contain hydrate based on the resistivity log signature. Eleven of the 20 were located in AC 857.
- The depth of the GHSZ was calculated throughout the Gulf of Mexico using models obtained from the U.S. Bureau of Ocean Energy Management. Seafloor depths were cross-checked with bathymetry data to ensure GHSZ calculations were valid and wells above the P90 GHSZ cutoff were ordered.
- A resistivity model that incorporates the measured resistivity and seismic trace in JIP holes AC21-A and AC-21-B was developed.
- Eleven DVDs of raster image well log data were obtained from the Bureau of Safety and Environmental Enforcement.
Current Status (December 2014)
Researchers calculated hydrate saturation in fracture accumulations in JIP wells WR313 and GC955H using ANISBED models. The models indicated saturations ranged from 2–20 percent in the fractures. Digital well logs are currently being used to calculate hydrate saturations in sand reservoirs identified in industry wells from the GOM. The team has established and refined a new set of criteria to rank hydrate-bearing reservoirs. The ranking will clearly identify reservoirs with the highest potential based on their thickness and their increased resistivity above background levels. During the next quarter, the team will begin estimating methane volume in hydrates in the GOM using Monte Carlo models.
The development of formation resistivity models for JIP wells GC955-H and WR 313-G was delayed due to problems with proprietary code developed by Schlumberger. Researchers will utilize a new model, available at the University of Texas at Austin, to replace the Schlumberger code. When completed, the resistivity models will be used to estimate hydrate saturation in the sand reservoirs within the wells.
Project Start: October 1, 2012
Project End: September 30, 2015
Project Cost Information:
Phase 1 - DOE Contribution: $149,706, Performer Contribution: $52,500
Phase 2 - DOE Contribution: $136,506, Performer Contribution: $22,000
Planned Total Funding - DOE Contribution: $286,212, Performer Contribution: $74,500
NETL – Skip Pratt (firstname.lastname@example.org or 304-285-4396)
The Ohio State University – Ann Cook (email@example.com or 614-247-6085)
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