Clathrates (Gas Hydrates) in Deep-Sea as Next Global Hydrocarbon Province

LOWRIE, ALLEN, Consultant, Picayune, MS, and MAX MICHAEL, Naval Research Labs, Washington, D.C.

Preliminary reconnaissance of ocean basins indicates that more hydrocarbons may be located in clathrates (gas hydrates) and trapped gases than hitherto found on all continents, including coal. Clathrates are medium- to high-pressure stabilized, icelike compounds. Natural gas clathrates are stabilized by higher than sea level, ambient pressure, and are stable in the cold, deep-ocean environment.

Location of clathrates on a regional scale would include using seismic reflection data. Bottom simulating reflections (BSR) are the most common indicators. The BSR reflections do indeed generally mimic the water bottom at a relatively uniform depth of some tenths of a second. Apparently, the strong acoustic impedance marking the lower clathrate/upper trapped gas reservoir contact creates the BSR.

Sea floor bathymetry determines the configuration of the clathrate. Clathrate serves as a trapping mechanism; clathrate and methane gas accumulated beneath it, depending on geometry, are the reservoir; the entire sediment section is the source.

Clathrates are commonly near or at the sea bottom, below 200-400 m water depth, under at least 20 to 50 atmospheres of pressure. Clathrates in the Arctic basin have been found to be up to 1700 m thick, and along continental shelves and slope of the Atlantic basin, up to 1100 m thick.

Exploration may proceed either by drilling vertically into the clathrate or drilling laterally along the flanks of the clathrate. Drilling into the clathrate involves the problem of rupturing the "seal" and permitting gas to escape. Indirect drilling under the flanks could permit "draining" the accumulated gases and then removing the gas within the clathrate.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)