Investigation of gas hydrate potential of the Black Sea and modelling of gas production from a hypothetical Class 1 methane hydrate reservoir in the Black Sea conditions Sukru Merey * , Caglar Sinayuc Middle East Technical University, Department of Petroleum and Natural Gas Engineering, Ankara, Turkey article info Article history: Received 27 October 2015 Received in revised form 26 December 2015 Accepted 28 December 2015 Available online 31 December 2015 Keywords: CH 4 hydrate Black sea hydrate BSR Class 1 hydrates Hydrate modelling HydrateResSim abstract Gas hydrate deposits which are found in deep ocean sediments and in permafrost regions are supposed to be a fossil fuel reserve for the future. The Black Sea is also considered rich in terms of gas hydrates. It abundantly contains gas hydrates as methane (CH 4 ~80e99.9%) source. In this study, by using the liter- ature seismic and other data of the Black Sea such as salinity, porosity of the sediments, common gas type, temperature distribution and pressure gradient, it was estimated that up to 71.8 (median) standard trillion cubic meters (tcm) of CH 4 can be available in the Black Sea. Due to biogenic and thermogenic gas potential of the Black Sea, the composition of natural gas may also include ethane (C 2 H 6 ), propane (C 3 H 8 ) and other impurities. This is an indication of sI and sII types of hydrate potential in the Black Sea. Moreover, according to the seismic data, single and multiple bottom-simulating reflector (BSR) lines were observed in the literature. Therefore, there is a high potential of Class 1 hydrates (stable hydrate layer and an underlying free gas zone) in the Black Sea. In this study by using HydrateResSim numerical simulator, gas production potentials from a hypothetical Class 1 hydrate reservoir in the Black Sea conditions by depressurization (at different production pressures) and depressurization combined with wellbore heating were simulated. When the depressurization (production) pressure is lower, much more gas is produced but until certain value. If the depressurization pressure is very low, there is a risk of hydrate reformation and ice formation along the wellbore and/or inside the reservoir. Moreover, it was shown that wellbore heating might be necessary in order to avoid any hydrate reformation along the wellbore during the production. The effect of intrinsic permeability on gas production was also inves- tigated. It was observed that until 400 mD, there is no important effect of intrinsic permeability on gas production but below 400 mD, the gas production is quite low because of very low effective permeability with 65% hydrate saturation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Increased natural gas prices and advancement of technology have triggered the production of natural gas from unconventional natural gas reservoirs such as gas hydrate, shale gas, tight gas, and coalbed methane reserves. As seen in Fig. 1, gas hydrate reservoirs are found in all over the world in both permafrost and ocean sed- iments. It is known that even the most conservative estimates place the amount of gas contained within hydrate deposits at 2e10 times larger than the global estimates of conventional natural gas of 4.4  10 14 standard m 3 [Koh et al., 2012]. Although there are controversial initial methane in-place calculations in gas hydrates, it is obvious that there are huge methane (CH 4 ) hydrate reservoirs in the world [Moridis et al., 2005a; Koh et al., 2012; Sinayuc and Merey, 2015]. Gas hydrate, or clathrate, is a nonstoichiometric ice-like crys- talline composite that is established by water (host) and gas mol- ecules (guest). They form at low temperature and high pressure values. The formation of gas hydrate depends on the type of gas, temperature, pressure, gas saturation, and water salinity [Sloan and Koh, 2007]. Methane (CH 4 ), Ethane (C 2 H 6 ), propane (C 3 H 8 ), carbon dioxide (CO 2 ), hydrogen sulfide (H 2 S) and other gases can form their hydrates when the appropriate conditions are satisfied. In nature, CH 4 is the most common hydrate forming gas, which is good in terms of energy source. Moreover, 1 m 3 of hydrate contains * Corresponding author. E-mail address: merey@metu.edu.tr (S. Merey). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2015.12.048 1875-5100/© 2015 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering 29 (2016) 66e79