This article is mainly based on the paper by Chong (2015) and Oellrich (2004).
Global energy fulfilment has always been vital to support a country’s development progress. But every years, the needs for energy is expected to increase significantly as human society grows. In the reference case of International Energy Outool by U.S. Energy Information Administration in 2016, total world consumption of marketed energy will expands from 549 quadrillion British thermal units (Btu) in 2012 to 629 quadrillion Btu in 2020, and 815 quadrillion Btu in 2040, a surprisingly 48% increase from 2012 to 2040.Eventhough the world is expecting more energy can be harnessed from renewable energies, energies from carbon based source such as oil, gas, and coal are still projected to fill the largest porsion of world’s energy demand in the coming years. Amongst these 3 carbon based energy sources, natural gas is poised to increase at the highest rate (1,7% per year) as compared to two others. Consumption of natural gas worldwide is projected to increase from 120 Trillion cubic feet (Tcf) in 2012 to 203 Tcf in 2040. Today, most of natural gas reserves and production comes from conventional sources, but with increasing natural gas demands in the coming years makes unconventional source could have a significant portion in the future. Those unconventional source could be tight gas, shale gas, coal bed methane, and gas hydrates. about 500. Things that make natural gas hydrates more interesting is because of its large quantities, natural gas hydrates have far greater amount and reserves than both conventional source and unconventional source of gas combined (Fig 1.).
Gas hydrates belong to a general class of unclusion compounds known as clathrates, a compound of molecular cage structure which made of host molecules encapsulating guest molecules. Natural gas clathrates owe their existence to the ability of H2O molecules to assemble using hydrogen bonding and form polyhedral cavities. Gas hydrates are formed under certain sets of high pressure and low temperature conditions, outside of which the gas and water species typically remain in separate phases. There are two types of structure of gas hydrates, structure I and structure II. Structure I consists of 2 small cages made up by 12 pentagonal surfaces called “512” and 6 larger cages of again 12 pentagonal and two hexagonal surfaces called “51262, structure II consists of 16 small cages made up by 12 pentagonal surfaces called “512” and 8 larger cages of again 12 pentagonal and 4 hexagonal surfaces called “51264” (Fig 3.) Hydrates in nature.
Gas hydrates are fundamentally different from the other unconventional natural gas sources. Gas molecules in the hydrate reservoir are trapped within cages formed by water molecules by van der Waals forces in molecular level. Therefore, in addition to creating conduits for gas flow, techniques to recover methane from gas hydrates involve dissociating the natural gas hydrates in situ. Three most commonly proposed and studied techniques in dissociating methane hydrate are thermal stimulation, depressurization and inhibitor injection.
This section will provide the overview on several significant field trials on gas production from hydrate reservoir.
Ignik Sikumi field trials
ConocoPhilips and researchers from the University of Bergen have collaborated on laboratory studies on hydrate production through – exchange. Notably, a patent has been awarded to the group on developing MRI method to monitor the – exchange process in hydrates, as discussed in Section 4. Further conclusions have been similar to those outlined previously: fugacity/chemical potential provides the driving force for the reaction although mass transfer limitations dominate the overall conversion. The first field trial of methane hydrate production using has been completed successfully in the Ignik Sikumi Gas Hydrate Field in Alaska North Slope in 2012. Researchers from ConocoPhilips, with partnership from the Japan Oil, Gas & Metals National Corp. (JOGMEC), injected approximately 210,000 standard cubic feet of flue gas (23% – 77% mixture) into the targeted hydrate bearing formation. Of the total injected volume of gas (167.3 MSCF of and 48.6 MSCF of ), approximately 70% of the injected nitrogen was recovered. In contrast, only 40% of the injected carbon dioxide was recovered during the production period, inferring the occurrence of replacement reaction which leave sequestered in the formation. A total of 855 MSCF of methane was produced over the total production period, including a six weeks sustained flow back of gas. The analysis of field test data has shown that – exchange did take place in solid phase.
Messoyakha Gas Field
The Messoyakha Gas Field in the Arctic on the border of West Siberia has been producing gas since 1969. The geology of the field has been identified to consist of unseparated gas hydrate and free gas layers. It has been claimed that the field has a cumulative gas production of 12.9 x thus far, with 5.4 xobtained via hydrate decomposition using the method of depressurization. However, the reported amount of water produced from this reservoir is at least 3 orders of magnitude lower than what is expected to be produced during hydrate decomposition. Collett and Ginsburghave questioned whether the gas production from this gas field was originated from the hydrate layer. Nonetheless, the proven existence of significant amounts of gas hydrates in this gas field makes it a very useful test site to study the potential hydrate production techniques and geological research.
Prospects and Challenges in NGH research
Gas production from methane hydrates has to be evaluated because many impact that caused by this. It Must be highlighted because CH4 is 21 times more potent than CO2 according to the assigned global warming potential (GWP) over 100 years.( IPCC,2007). Many company ignore this fact, because hydrate bearing sediment is valuable to conduct on a larger scale even in situ condition. Better understanding about mechanical properties of hydrate in nature is important. Geophysics researcher reported that methane hydrate is 20 times stronger than ice at the same condition and strain rate. (Durham WB, Kirby SH, Stern LA, Zhang W.,2003)
Except of technical studies, another challange is optimal exploitation that concern about environmental risk and policy instrument because this exploitation can causing the increase in greenhouse emissions due to carbon fuel consumption as well as any possible submarine landslides that might occur (Döpke and Requate,2014)
Chong, Z.R., et al. 2015. Review of natural gas hydrates as an energy resource: Prospects and challenges. Applied Energy. Elsevier.
Oellrich, L.R. 2004. Natural Gas Hydrates and their Potential for Future Energy Supply. ASME Heat and Mass Transfer Conference. Kalpakkam. (Page 70-78)