The economic production of natural gas from oceanic hydrate deposits will require new offshore drilling systems and methods. Also, the product of hydrate dissociation may be relatively low pressure, wet gas, especially where the excess pressure produced by hydrate dissociation can be equilibrated rapidly through high-porosity sediments. Natural gas derived from hydrate may result in low local production rates. The low production rate requires low-cost drilling methods to ensure economic viability. Recovering methane and economically transporting it pose a challenge to technologists and scientists. Ideas have been conceptualized and research has been initiated to address these challenges.
Methane hydrate will be commercially exploited only when the price of petroleum oil and conventional gas rises substantially. The apparent abundance of conventional hydrocarbon deposits and their relatively low prices are inhibiting research into various aspects of gas hydrate. Research and development activities in this field need to be sustained. Hydrate recovery will in all probability involve forced dissociation, which will involve significant demand for heat. Supplying and managing this heat and maintaining an artificial thermodynamic balance that allows the controlled dissociation of hydrate and the safe recovery of methane will probably prove the key to commercialization.
On the basis of calculations, depressurization was shown to be the most promising technique for class 1 type reservoirs (Moridis 2003). Depressurization has also been quoted by many researchers as the most economically viable option (Makogon 1997; Pooladi-Darvish 2004).
Methanol is approximately 3 times less expensive than ethylene glycol. One must pay particular attention to the amount of methanol necessary to treat the inlet gas. With increasing gas flow rates, the ethylene glycol injection process typically becomes a more viable option because the inhibitor is regenerated. The increased cost of utilizing methanol injection to treat larger gas volumes can be directly associated with the raw material makeup cost.
Most methane hydrate deposit locations were discovered serendipitously when scientists looked anew at existing seismic data. These initial efforts did not require
much expenditure. As the number of finds increased, knowledge about various aspects of oceanic hydrates also increased and scientists began realizing their immense potential as a fuel resource. The challenges of hydrate exploration and production and its probable impact on the global climate and the geological environment became clearer. Policymakers are gradually recognizing the long-term potential of marine methane hydrates as well. It appears, however, that the complexities and challenges for exploration of methane hydrates and their production from the hostile and difficult marine environment require considerable focused research and development efforts in various fields, for which adequate financial support is lacking. This is perhaps due to the perception that methane hydrate exploitation will be economically viable only when the price of conventional hydrocarbon and other fuels rises substantially.
On the other hand, many hydrate deposits are located on continental slopes not far from major markets in industrialized countries. Countries that have strong economic bases, or are witnessing high industrial growth rates, but have low energy resource potential, could potentially become energy-independent, an event that would affect international affairs, foreign policy, and other interrelations. The repercussions would extend to world trade, regional power equations, and the foreign currency balance of existing major importers when gas hydrate begins to be exploited. The realization that such a situation could come about has recently generated some interest in the field of gas hydrate research in many countries. It is expected that the prospect of energy self-reliance will catalyze some of these countries to initiate harvesting methane hydrates as soon as scientists and technologists come forward with dependable, safe, and cost-effective mechanisms to explore and exploit this resource.
Lack of suitable production technology was a major impediment in exploitation of this resource. However, the past 5 years has witnessed a dramatic improvement in drilling technologies for oil and gas in deepwater areas, where hydrate deposits occur. There has also been a distinct reduction in deepwater development costs. All these are positive factors for hydrate exploration and development. Much of the engineering required to exploit these deposits can be achieved by suitably adopting proven technology currently used in connection with exploitation of deepwater oil and gas reserves.
Three processes have been proposed for dissociation of methane hydrates: thermal stimulation, depressurization, and inhibitor injection. The obvious production approaches involve depressurization, heating, and their combinations. The depressurization method involves lowering the pressure inside the well and encouraging the methane hydrate to dissociate. The chemical inhibition method seeks to displace the natural gas hydrate equilibrium condition beyond the hydrate stability zone’s thermodynamic conditions through injection of a liquid inhibitor chemical adjacent to the hydrate. Of these three production methods, the depressurization combined with the thermal stimulation process appears to be the most practical for zones where free gas is trapped beneath the methane hydrates.
There are two gas hydrate reservoirs. They are Arctic hydrates and marine hydrates. Gas hydrates are found within and under permafrost in Arctic regions. They are also found within a few hundred meters of the seafloor on continental slopes and in deep seas and lakes.
The main cost here is only that of the pipeline used to transport the gas to the production platform. For subsea systems that do not produce to a fixed platform, a drilling template must be used that connects to a group of wells. Transportation of methane from the production site to the shore could be through submarine pipelines as is done for long-distance transportation of natural gas. However, submarine pipelines are expensive and the geological hazards of the continental slope make this option difficult.
The economic production of natural gas from oceanic hydrate deposits will require new offshore drilling systems and methods. Recovering methane and economically transporting it pose a challenge to technologists and scientists. Ideas have been conceptualized and research has been initiated to address these challenges.
On the basis of calculations, depressurization was shown to be the most promising technique for class 1 type reservoirs. Depressurization has also been quoted by many researchers as the most economically viable option. Methanol is approximately 3 times less expensive than ethylene glycol. One must pay particular attention to the amount of methanol necessary to treat the inlet gas. With increasing gas flow rates, the ethylene glycol injection process typically becomes a more viable option because the inhibitor is regenerated. The increased cost of utilizing methanol injection to treat larger gas volumes can be directly associated with the raw material makeup cost.