Gas Hydrates as Potential Resource of Energy and Pathfinders for Conventional Type Hydrocarbon Deposits
KRASON, JAN, Geoexplorers International, Inc., Denver, CO
Solid compounds of water and gaseous hydrocarbons are known as gas hydrates, clathrates, or cryohydrates. They occur naturally in offshore and terrestrial environments, in the areas where temperature is at least seasonally low (i.e. close to or below freezing), bathymetric, geostatic, ice, or permafrost pressure is sufficiently high, and the source of hydrocarbons is available. These factors (regional and local geological conditions of 21 locations grouped into 13 study regions worldwide offshore and one in permafrost environments with proven, reported, and inferred presence of gas hydrates) have been recently researched by Geoexplorers International, Inc.
As a result of Geoexplorers International's (among others) very extensive research, potential gas resources have been assessed. Although the resultant potential resource estimates are not of high accuracy, they are the most accurate available yet.
Thus, considering the volume of hydrate (1-m-thick interval of sediment with 50% of the pore space occupied by hydrates) and depending on the thickness and lateral extension assigned to the hydrate zone defined by the bottom simulating reflector (BSR), the estimated potential reserves of gas in place for the studied regions amounts to 730 tcf. Using the same data base for the same regions, in 10-m-thick hydrate zone the amount of gas in place is estimated at 5200 tcf. In most of the study regions, gas hydrate-bearing zone is much thicker and often reaches up to several hundred meters (e.g. 650 m in the western margin of the Gulf of Mexico). However, the amount of gas derived from 10 or more m-thick zone of hydrate is not proportional to the multiplier because the thickness of the zone typically refers to the layer of hydrated sediment that causes the BSR.
Then, considering the fact that the regions studied constitute only
about 10% of the continental margins of the world, conservative estimations from Geoexplorers International suggest that the world's total gas hydrates may contain 7000 to 50,000 tcf of natural gas.
Although at this time exploitation of gas trapped in the hydrate zone and below is not economically viable, because estimated reserves are enormous, they should be seriously considered as potential energy resource. Smaller, but less dispersed massive gas hydrate deposits associated with fault zones may be the first offshore gas resource to become economic.
This research, particularly of the Messoyakh gas field, has proved that the presence of gas hydrates provides very useful information in exploration for conventional oil and gas deposits. Gas hydrates indicate ongoing hydrocarbon generation in the sediments. Hydrates are valuable to assess the present heat flow and thermal history of a region. Since gas hydrates exist only under a very limited range of pressure and temperature, deviation in patterns of their occurrence can be related to changes in pore water chemistry, hydrocarbon composition, or pressure and temperature gradient anomalies.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)