Economic Characteristics of Deepwater Natural Gas Hydrate

Natural gas hydrate (NGH) is unique among gas resources. In its natural state NGH is a pure, solid crystalline material formed by digenetic crystallization in permafrost regions and in marine sediments where temperature, pressure, and gas flux are suitable. NGH compresses methane and minor other gases by about 164 times (above 1 atm @ STP) within the crystal structure. Greater than 95% of the NGH resource is found sediments below seafloors that are deeper than 500 m in the open ocean. First order exploration objectives are concentrations of NGH occur generally in deepwater and ultra-deepwater host sandy turbidites within and near the base of the gas hydrate stability zone (GHSZ), the shallow sub-seafloor interval where the pressure and temperature conditions allow NGH concentrations to potentially form, and that have economic potential for production of its natural gas. Other types of NGH concentrations occur but are amenable to production using conventional methodology. NGH is stable within its sedimentary hosts and will only convert to its constituent gas and water phases relatively quickly if reservoir pressure-temperature conditions are artificially disturbed. Environmental change can induce conditions that may cause more NGH to form or dissociate, but relatively much more slowly. Induced dissociation has the potential to produce gas rapidly enough to support long-term natural gas production. NGH is potentially the largest of the three types of unconventional gas resources, with estimates of gas-in-place within producible reservoirs in excess of 40,000 Tcf.