Natural Gas Hydrates: Future of Energy resource

Natural Gas Hydrates: Future of Energy resource

Introduction: Gas-hydrates is a crystalline form of methane encaged within the water molecule which looks like ice and is formed at high pressure and low temperature in the environment in continental margins (generally continental shelf and slope of the ocean) and permafrost regions such as the Krishna-Godavari basin, Hikurangi Margin, Blake ridge, and the Arctic, Tibet, etc. At standard pressure and temperature 1m³ of gas hydrate can produce 164 m³ methane gas and 0.8 m³ water. It has also been estimated that less than one-fourth of the world’s total Gas Hydrate extraction can meet the world’s energy demand for about more than two centuries.  Thus, Gas hydrates have attracted the attention of the whole scientific community because of their wide occurrences, potential as a future energy resource, role in climatic change and sub-marine landslide, etc. Being the emerging field of research, a lot of Research and Development (R&D) works are going on throughout the world both scientifically and technologically for taping the resource potential of gas hydrates without affecting the environment and for the efficient gas collecting and storing plants on the commercial scale.

Image Source: USGS Gas Hydrate Project.

Figure 1: Worldwide occurrence of Natural Gas Hydrates at different stages of R&D work.

There are generally three types of Gas Hydrates structures and are Structure-I, Structure-II and Structure-H. The S-I type of Gas hydrates are very common in the worldwide context which consists of mainly 46 water molecules, methane, and a small part of ethane along with a trace amount of Carbon dioxide gas and their origin is of biogenic nature. Similarly, The S-II type of Gas hydrates are less common and are made up of 136 water molecules with propane, iso-butane, and pentane like higher carbon molecules and generally made with a thermogenic origin. Finally, S-H type of Gas hydrates consist of 34 molecules of water along with methane and no hexane or cycloheptane like large Carbon molecules and are rarely found on Earth such as on the Gulf of Mexico.

Image Source: ONGC-India            

Figure 2: Ice-like crystalline natural gas hydrates recovered from the oil/gas pipeline.

Importance of Natural Gas Hydrates: These are the naturally occurring huge potential source of energy (~10¹⁸ m³ of Methane gas as estimated by Milkov, 2004) which has been found on the shallow depth, generally, less than 500 meters below the seafloor in marine and 1200 meters below the surface in a permafrost environment. From the map in figure 1, we can say that these Gas Hydrate reserves are available to almost all the continents and if the extraction mechanism/technology will be built within this decade than the production and use of conventional and non-renewable energy sources such as petroleum oil/gas, coal etc. can be reduced and the price of fuel will be lowered globally. In the meantime, the demand for high energy can be maintained by the supply of gases from the Natural Gas hydrates and the free gas obtained below the gas hydrates reservoir. The current consumption rate of Global fossil fuel is given in Figure 3, indicates that our energy demand is increasing at an exponential rate and will also increase more in the coming days. Thus, for the energy security of the world, Gas hydrates will be one of the important options for the forthcoming years and generations.

Figure 3: Trend of energy consumption since 1900 in a global way.

Data source: Vaclav Smil, Energy Transitions: Global and National Perspectives & BP Statistical Review of World Energy (2017)

Current research on Gas Hydrate Exploration and Extraction: Currently, USA, Canada, China, Japan, India, New Zealand, South Korea, and a few other countries of European Union are actively involving the exploration as well as production and storage of Gas Hydrates via their scientific expedition series such as International Ocean Drilling Projects (IODP-372, 375), National Gas Hydrate Production (NGHP-1, 2), USGS Gas Hydrate projects, etc. The main research topics on the recent scenario are;

·         Assessment of nature and occurrence of Natural Gas Hydrates over the different marine and permafrost regions of the world, where the stability of Gas Hydrates been observed.

·         Economical, technically feasible and environmentally friendly method of extracting natural gas from the obtained gas hydrates at different experimental drilling expeditions.

·         Identification of the role of Gas Hydrates on the sea-floor instability, carbon sequestration, and on the carbon cycle like geo-hazards because of the melting of gas hydrates from Global warming.

To precisely explain the above topics, a team of Geologists, Geophysicists, Petroleum engineers, Chemical engineers and other Geoscientists are separately and jointly doing research to find the best possible methods and technologies. Initially, the geological study of the probable gas hydrate occurring basins are to be done based on the available information and evidence of trace gas or the solid-gas hydrate on the oil/gas transferring pipelines on the seafloor. Then, geophysical seismic reflection-2D/3D methods and well-log analysis are done. After that, proper identification of the extension, saturation, and approximate volume of Gas Hydrate in a particular location is done based on the subsequent experimental drilling, well-log data collection. Also, physical, chemical, biological, and geological analysis of the acquired Gas Hydrate samples (core analysis) is to be done. All of these R&D works are currently going on at different laboratories and data centers of the Academy and Industry.

Environmental impacts of Natural Gas Hydrates: Although the understanding has not been cleared scientifically, it has been estimated that the gas hydrates melt due to increasing global warming at its stability region and hence the subsurface formation becomes unstable leading to sea-floor instability and sub-marine landslides along with the slow slip events (i.e. very small range earthquakes). Similarly, it has been observed the natural release of methane gas into the marine climate is making the oceanic water more acidic and the amount of carbon on the atmosphere is increasing which may add the greenhouse effect leading to further global warming and climate change. But, all the methane released from the gas hydrates are not exposed to the atmosphere, most of the methane gets broken down by oceanic bacteria to settle down into sediments. Similarly, it has also been predicted that increasing water level at the ocean may somehow counteract the increasing oceanic water temperature so that gas hydrate melting can be resisted. All of these assumptions and predictions are under the process of investigation and verification by scientific community.

Key Findings: The key findings from the different research works and experimental expeditions are starting to come and most of the research topics are still under study. Japan and China had already done their production test in 2015. It has also been estimated that China will complete its initial preparation work for commercial gas hydrate production by 2020 (Zhongfun Tan, 2016). The technique of breaking gas hydrates to recover natural gas is either fluid injection or the depressurization through which gas hydrates decompose to eject methane gas. This ejected gas will then be collected in the storage chamber and will be distributed via a pipeline system to the required locations.

Conclusion: It has been clear that the energy demand and its consumption are increasing at an almost exponential rate. The conventional sources of energy, coal/gas/oil are depleting fatly. In this situation, Natural Gas hydrates, if explored and extracted economically and if become commercially viable then we can say that from the starting or from the mid of the 2030s the era of gas hydrates would likely initiate. Currently, the gas hydrate mining technology is still in the sampling stage, not a trial mining stage (Zhongfu Tan, 2016). Although the gas hydrates are not completely clean energy, in comparison to conventional coal/oil/gas, it is less carbon releasing better alternative energy resources for the coming generation!!!