The Current State of Researches Related to the Extraction of Methane from a Porous Medium Containing Hydrate
In the next few decades due to a depletion of traditional gas deposits, a question of using alternative sources of natural gas, such as gas hydrates deposits, might arise. Besides, there is a problem of existing greenhouse effect, which is constantly aggravated by increasing carbon dioxide emissions into the atmosphere. At the same time, carbon dioxide can replace methane in gas hydrates and remain in its stable hydrate state in the reservoir. Therefore, available deposits of hydrates are not only potential sources of energy, but also allow a sequestration (“burial”) of carbon dioxide with simultaneous extraction of methane. Several “classical” approaches to extract gas from its hydrate are discussed in the article: depressurization method (pressure reduction), thermal impact (temperature increase), and inhibitors’ use. Laboratory and practical experience of those approaches is reviewed, and their advantages and disadvantages are briefly described. Next, the most promising exchange method for simultaneous sequestration of the greenhouse gas and the production of energy is studied. The paper includes the results of this method’s use in the laboratory and the only practical application currently. The advantage of using a mixture of nitrogen and carbon dioxide for the exchange method was demonstrated, which significantly increases methane extraction degree from its hydrates, which was tested on the first well using this method. Comparing to previous studies reviewing this subject, additional studies related to methane exchange method in hydrates over the last two years were studied. The exchange method is acknowledged the most effective since it ensures a successful extraction of methane from gas hydrate deposits and a “burial” of greenhouse carbon dioxide. In this case, the highest percentage of methane extraction is observed when a mixture of carbon dioxide and nitrogen is injected into the formation. An additional advantage is the exchange can be combined with depressurization and thermal impact. The most promising for research and further application is the combined method for obtaining energy and disposing of the resulting greenhouse carbon dioxide gas. First, a hot mixture of carbon dioxide and nitrogen from combustion of methane on a power plant is pumped into the reservoir through the first well. Then, decomposition/exchange of methane hydrates occurs in the formation. Methane and associated products of its decomposition/exchange are extracted through the second well by depressurization method, and then the methane is cleaned and fed to the power plant for further combustion.