Abstract: Assessment of Natural Gas Hydrate Resources -- Proposed Methodology

COLLETT, TIMOTHY S

The 1995 National Assessment of United States Oil and Gas Resources, conducted by the U.S. Geological Survey, has focused on assessing the undiscovered conventional and unconventional resources of crude oil and natural gas in the United States. This assessment includes for the first time a systematic resource appraisal of the in-place natural gas hydrate resources of the United States onshore and offshore regions. The primary objectives of our national gas hydrate resource assessment are to document the geologic parameters that control the occurrence of gas hydrates and to assess the volume of natural gas stored within the gas hydrate accumulations of the United States. This appraisal of gas hydrates is based on a play-analysis scheme, which was conducted on a province-by-province basis. In a play analysis method, prospects (potential hydrocarbon accumulations) are grouped according to their geologic characteristics into plays. The geologic settings of the hydrocarbon accumulations in the play are then modeled. Probabilities are assigned to the geologic attributes of the model necessary for generation and accumulation of hydrocarbons. In this appraisal method, geologists make judgments about the geologic factors necessary for the formation of a hydrocarbon accumulation and quantitatively assess the geologic factors that determine its size.

In this assessment, 11 gas-hydrate plays were identified within four offshore and one onshore gas hydrate provinces. The offshore gas hydrate provinces assessed lie within the U.S. Exclusive Economic Zone adjacent to the lower 48 States and Alaska. The only onshore province assessed was the North Slope of Alaska. In-place gas resources within the gas hydrates of the United States are estimated to range from about 3,200 to 19,000 trillion cubic meters of gas (113,000 to 676,000 trillion cubic feet), at the 0.95 and 0.05 probability levels, respectively. Although this range of values shows a high degree of uncertainty, it does indicate the potential for enormous quantities of gas stored as gas hydrates. The mean in-place value for the entire United States is calculated to be about 9,000 trillion cubic meters of gas (320,000 trillion cubic feet).

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria