Natural-gas hydrates have been encountered beneath the permafrost and considered a drilling hazard by the oil and gas industry for years. Drilling engineers working in Russia, Canada and the USA have documented numerous problems, including drilling kicks and uncontrolled gas releases, in arctic regions. Information has been generated in laboratory studies pertaining to the extent, volume, chemistry and phase behavior of gas hydrates. Scientists studying hydrates as a potential energy source agree that the resource potential is great--on the North Slope of Alaska alone, it has been estimated at 590 TCF. However, little information has been obtained from physical samples taken from actual hydrate-bearing rocks. This gas-hydrate project is a cost-shared partnership between Maurer Technology, Anadarko Petroleum, Noble Corporation, and the U.S. Department of Energy's Methane Hydrate R&D program. The purpose of the project is to build on previous and ongoing R&D in the area of onshore hydrate deposition to identify, quantify and predict production potential for hydrates located on the North Slope of Alaska. The project team drilled and continuously cored the Hot Ice No. 1 well on Anadarko-leased acreage beginning in FY 2003 and completed in 2004. An on-site core analysis laboratory was built and used for determining physical characteristics of hydrates and surrounding rock. After the well was logged, a 3D vertical seismic profile (VSP) was recorded to calibrate the shallow geologic section with seismic data and to investigate techniques to better resolve lateral subsurface variations of potential hydrate-bearing strata. Paulsson Geophysical Services, Inc. deployed their 80 level 3C clamped borehole seismic receiver array in the wellbore to record samples every 25 ft. Seismic vibrators were successively positioned at 1185 different surface positions in a circular pattern around the wellbore. This technique generated a 3D image of the subsurface. Correlations were generated of these seismic data with cores, logging, and other well data. Unfortunately, the Hot Ice No. 1 well did not encounter hydrates in the reservoir sands, although brine-saturated sands containing minor amounts of methane were encountered within the hydrate stability zone (HSZ). Synthetic seismograms created from well log data were in agreement with reflectivity data measured by the 3D VSP survey. Modeled synthetic seismograms indicated a detectable seismic response would be expected in the presence of hydrate-bearing sands. Such a response was detected in the 3D VSP data at locations up-dip to the west of the Hot Ice No. 1 wellbore. Results of this project suggest that the presence of hydrate-bearing strata may not be related as simply to HSZ thickness as previously thought. Geological complications of reservoir facies distribution within fluvial-deltaic environments will require sophisticated detection technologies to assess the locations of recoverable volumes of methane contained in hydrates. High-resolution surface seismic data and more rigorous well log data analysis offer the best near-term potential. The hydrate resource potential is huge, but better tools are needed to accurately assess their location, distribution and economic recoverability.
