Geotechnical and geophysical properties of deep marine fine-grained sediments recovered during the second Ulleung Basin Gas Hydrate expedition, East Sea, Koreaby Hak-Sung Kim, Gye-Chun Cho, Joo Yong Lee, Se-Joon Kim

Marine and Petroleum Geology

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Year
2013
DOI
10.1016/j.marpetgeo.2013.05.009
Subject
Economic Geology / Geology / Geophysics / Oceanography / Stratigraphy

Text

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U 2, ce a esou a r t i c l e i n f o

Received in revised form 4 May 2013

Accepted 14 May 2013

Available online 30 May 2013 a b s t r a c t the sediment systems and gas hydrates. Gas hydrates function as pore-filling or load-bearing solids or cementation material among m (Kwon and Cho, the sediments are s hydrate-bearing ess if the gas hyydrates leads to a ins, a reduction of ess pore pressure rates, and a change e electrolyte confrom gas hydrates (Kwon et al., 2008). These geotechnical effects of gas hydrate dissociation can result in significant deformation or failure in gas hydrate-bearing sediments (Kwon and Cho, 2012; Kwon et al., 2010; Lee et al., 2010c; Sultan et al., 2004). Therefore, the geotechnical aspects of gas hydrate-bearing sediments are crucial with respect to safety issues in gas hydrate production.

Many studies have investigated sediments with or without natural gas hydrates in order to characterize the geotechnical and geophysical behavior of natural gas hydrate-bearing sediments * Corresponding author. Tel.: þ82 42 350 3622; fax: þ82 42 350 3610.

E-mail addresses: shield2000@kaist.ac.kr (H.-S. Kim), gyechun@kaist.ac.kr, gyechun@kaist.edu (G.-C. Cho), jyl@kigam.re.kr (J.Y. Lee), sjkim@kigam.re.kr (S.-J. Kim). 1 Tel.: þ82 42 350 3662; fax: þ82 42 350 7200. 2 Tel.: þ82 42 868 3219; fax: þ82 42 868 3417. 3

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Marine and Petroleum Geology 47 (2013) 56e65Tel.: þ82 42 868 3214; fax: þ82 42 868 3417.Gas hydrates are ice-like solid lattice compounds that are composed of hydrogen-bonded water cages that encapsulate guest molecules such as light hydrocarbons. Natural gas hydrates are found in both onshore permafrost sediments and offshore marine sediments. Because there is a large amount of natural gas hydrates present on Earth, hydrate reservoirs may be future sources of energy (Sloan, 1998).

The mechanical, chemical, and geophysical properties of deep marine gas hydrate-bearing sediments are distinct from those of general marine sediments due to the complex interactions between grains, while stiffening the entire sediment syste 2009). Therefore, the strength and stiffness of enhanced by gas hydrate formation. However, ga sediments lose their original strength and stiffn drates are dissociated. The dissociation of gas h loss of the load-bearing effect of gas hydrate gra the effective stress that results from the exc induced by the free gas emitted from the gas hyd in the sediment fabric due to a reduction of th centration induced by the fresh water released1. Introduction sediment particles (Dvorkin et al., 1999; Lee et al., 2010a; Yun et al., 2005, 2007). Gas hydrates share the effective stress with mineralKeywords:

Gas hydrate-bearing sediment

Geotechnical properties

Geophysical properties

Volume change0264-8172/$ e see front matter  2013 Elsevier Ltd. http://dx.doi.org/10.1016/j.marpetgeo.2013.05.009Korea. Conventional laboratory geotechnical engineering test methods were used to characterize the sediments from a geotechnical engineering perspective. The sediments were mostly uncompacted and classified as highly plastic silty soils according to the Unified Soil Classification System (USCS); they exhibited high compressibility when subjected to an increase in effective stress (or a decrease in pore water pressure), low hydraulic conductivities, and low coefficient of consolidation (or pressure diffusion).

It is expected that the application of a depressurization method for gas hydrate production at the investigated sites would cause a significant amount of settlement and compaction around the production hole. Because the shear wave velocity of gas hydrate-bearing sediments is much less sensitive to the stress state and is much higher than that of sediments without gas hydrates, it is possible to estimate the degree of hydrate saturation from shear wave velocity data measured in gas hydrate-bearing sediments.

In addition, the prior presence of gas hydrates in the sediments was verified through a comparison of water content, compressibility, and electrical resistivity of the sediments.  2013 Elsevier Ltd. All rights reserved.Article history:

Received 14 February 2013 marine sediments recovered during the second Ulleung Basin Gas Hydrate expedition (UBGH2), East Sea,This study investigates the geotechnical and geophysical properties of minimally disturbed fine-grainedGeotechnical and geophysical properties sediments recovered during the second expedition, East Sea, Korea

Hak-Sung Kim a,1, Gye-Chun Cho a,*, Joo Yong Lee b, aDepartment of Civil and Environmental Engineering, Korea Advanced Institute of Scien b Petroleum and Marine Resource Division, Korea Institute of Geoscience and Mineral RAll rights reserved.f deep marine fine-grained lleung Basin Gas Hydrate

Se-Joon Kimb,3 nd Technology (KAIST), Daejeon 305-701, Republic of Korea rces, Daejeon 305-350, Republic of Korea

SciVerse ScienceDirect leum Geology vier .com/locate/marpetgeo (Ryu et al., 2012), and the gas hydrate occurrences were identified within the depth interval of 110e155 mbsf (Fig. 2).

Most sediment samples recovered from the two sites were minimally disturbed (i.e. not remolded). The samples used in this study were 4e7 cm in length and sealed in plastic liners. The geotechnical index properties for each core sample were tested and several core samples were selected for one-dimensional consolidation tests in order to determine the compressibility, pressure diffusion, and geophysical properties of the sedimentary section at each site. 3.2. Geotechnical index tests

All 12 core samples were tested to determine their geotechnical index properties, including water content, Atterberg limit, specific gravity, and grain size distribution. The specific gravity (GS) was determined via water pycnometry (ASTM D 854). The water content (wc) is defined as wc ¼MW/MS∙100 (%), whereMW is the mass of water and MS is the mass of the solid particles; the wc was determined by drying a specimen at 80 C (ASTM D 2216).