Aggregate reserves of methane gas hydrates, which occur in seas and oceans, exceed considerably prospected conventional reserves of natural gas and are seen as the most powerful source of potential mineral energy resources. At present, only a part of these deposits concentrated along coastland of continents can be considered as potentially commercial reserves. Some of them have been comprehensively surveyed, and reliable data on reserves and mining conditions of development of deposits gathered already.
Despite the numerous state programs of large-scale prospecting for and development of gas hydrates in seas and oceans, which were adopted by leading countries and states rich in deposits of gas hydrates, apropos including Ukraine, a universal ‘technological clue’ to economically successful offshore production of methane hydrates has not been discovered to date.
On the one hand, this can be explained by the fact that field research is focused on the problems of prospecting for deposits of gas hydrates, as well as by lack of experimental and commercial trials to develop offshore deposits, whereas theoretical approaches, modeling and inventions at the stage of concepts prevail today. In the main, a resource base is being determined, and key stakeholders are in no haste to pump large investments into testing of imperfect technical solutions because risks are greater than expected benefits.
On the other hand, there is an abundance of conditions of bedding and properties of gas-hydrate layers and the environment: the depth and relief of a seabed, temperature and chemical aggressiveness of the bed environment, the place where deposits of gas hydrates are concentrated (on the surface or they occur deep in bed rocks), the structure and properties of the roof and sole of a layer in the rocks, particularly their thickness, availability or absence of released methane in contact with layers, composition and properties of a gas hydrate layer, among other things. This indicates expedience to create the technology of production, which is expressly designed for specific deposits, thereby resolving the problem of the efficient techniques of development.
Made by inventors from various countries, the analysis of the known techniques of production of methane of offshore gas hydrates can be conditionally broken down into two groups in terms of the amount of their impact on a layer: 1) the greater part of the techniques that has a local impact on the limited section of a gas hydrate deposit; and 2) the techniques that have a wide-ranging impact on the vast area of a surface or internal structure of a deposit. The second group is the most worthwhile because it enables simultaneous dissociation of the large amount of gas and is capable of securing the profitability of offshore gas production.
Today the second group includes a sufficiently efficient technique of the development of conventional deposits of natural gas that are overarched by the mass of a gas hydrate stratum whose dissociation starts with a change in pressure when pumping free gas out of a conventional deposit (it is under these conditions that the first commercial experiment for offshore production of methane hydrates was carried out). Unfortunately, few deposits, including both conventional gas-fields and gas hydrate strata, occur in nature. That is why the area of application of the above technique is severely limited.
The fracking technique to develop offshore gas hydrate strata, which is similar to shale-gas fracking when drilling horizontal long wells in a productive layer that are designed for hydraulic fracturing of a layer and gas extraction from vast areas, looks promising as well.
It must be noted that physical properties of gas hydrates differ considerably from other rocks that have ever been developed by fracking. There are reasonable doubts of the possibility for ensuring the efficient formation of fissures and maintaining continuously the system of fissures during fracking of a layer (water and gas are quickly turned back into gas hydrate). In addition, there is a flaw in this technique, namely the high risk of the sudden release of gas caused by the rapid decomposition of gas hydrate. It is clear that such technique requires a substantial improvement. Both solutions of the second group provide for the extraction of gas generated by wells and the availability of impenetrable rocks of the roof of a gas hydrate layer (i.e. isolation from the penetration of gas into a water area).
A group of researchers led by Prof. Gennadiy Gaiko of the Kiev Polytechnic Institute (KPI) have the intriguing concept that also provides for practice of a wide-ranging impact on the vast surface area or internal structure of a deposit. However, the main idea lies in the formation of the open system of fissures in rocks of the roof of a gas hydrate layer. Released gas flows out through the system to a branched gas-collecting blanket that screens the greater part of a deposit. Currently, the KPI researchers are working on 1) the techniques of washout, explosive destruction and fracking of rocks of the roof; 2) facilities designed for gas dissociation through depressurization, injection of a heat carrier or chemical reagent; 3) design and technology of assembling branched gas-collecting screens; 4) system of transportation of gas obtained from a gas-collecting screen through sea-bed pipelines in particular.
The system of screening development of gas hydrate deposits may well become the unique technique of production of methane hydrates that would require a broad synergy of efforts among concerned partners and investors. The KPI scientists invite all the parties concerned to cooperate on the project with them.
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