Scientific results of the Second Gas Hydrate Drilling Expedition in the Ulleung Basin (UBGH2)

doi:10.1016/j.marpetgeo.2013.07.007

Marine and Petroleum Geology

Volume 47, November 2013, Pages 1-20

https://doi.org/10.1016/j.marpetgeo.2013.07.007 Get rights and content

Abstract

As a part of Korean National Gas Hydrate Program, the Second Ulleung Basin Gas Hydrate Drilling Expedition (UBGH2) was conducted from 9 July to 30 September, 2010 in the Ulleung Basin, East Sea, offshore Korea using the D/V Fugro Synergy. The UBGH2 was performed to understand the distribution of gas hydrates as required for a resource assessment and to find potential candidate sites suitable for a future offshore production test, especially targeting gas hydrate-bearing sand bodies in the basin. The UBGH2 sites were distributed across most of the basin and were selected to target mainly sand-rich turbidite deposits. The 84-day long expedition consisted of two phases. The first phase included logging-while-drilling/measurements-while-drilling (LWD/MWD) operations at 13 sites. During the second phase, sediment cores were collected from 18 holes at 10 of the 13 LWD/MWD sites. Wireline logging (WL) and vertical seismic profile (VSP) data were also acquired after coring operations at two of these 10 sites. In addition, seafloor visual observation, methane sensing, as well as push-coring and sampling using a Remotely Operated Vehicle (ROV) were conducted during both phases of the expedition. Recovered gas hydrates occurred either as pore-filling medium associated with discrete turbidite sand layers, or as fracture-filling veins and nodules in muddy sediments. Gas analyses indicated that the methane within the sampled gas hydrates is primarily of biogenic origin.

This paper provides a summary of the operational and scientific results of the UBGH2 expedition as described in 24 papers that make up this special issue of the Journal of Marine and Petroleum Geology.

Introduction

Gas hydrates are an ice-like crystalline substance composed of water and natural gas (mainly methane). It is stable and naturally occurring at low temperature and high pressure conditions found in deep-water or onshore permafrost regions (e.g., Kvenvolden, 1993, Sloan and Koh, 2008). Because gas hydrate contains a large amount of methane and occur globally on most marine continental margins and northern permafrost regions, it is considered to be a potential energy resource (e.g., Kvenvolden, 1993), as well as a possible agent of global climate change (e.g., MacDonald, 1990; Sassen et al., 2001). Gas hydrates may in some cases also represent a significant drilling and production hazard (e.g., MacDonald, 1990, Paull et al., 2000, Hovland and Gudmestad, 2001).

Identifying domestic energy resource within Korea which would reduce the dependence on imported energy is in the national interests of Korea. To secure new energy resources for the future, the “10-year Korean National Gas Hydrate Program” was launched in 2005 with the support of the Ministry of Knowledge Economy (MKE). This program has been conducted under the management of Gas Hydrate Research and Development Organization (GHDO) with the participation of a research consortium governed by the Korea Institute of Geoscience and Mineral Resources (KIGAM), the Korea National Oil Corporation (KNOC) and the Korea Gas Corporation (KOGAS). The GHDO program has undertaken seismic surveying programs and drilling for the identification of gas hydrate occurrences, the assessment of gas hydrate resources in the Ulleung Basin, and the development of appropriate production technologies. As a part of this national program, significant amounts of geophysical data including 2D and 3D seismic data, and sediment samples were collected. In addition, two gas hydrate drilling expeditions were performed in the Ulleung Basin in 2007 and 2010.

The Second Ulleung Basin Gas Hydrate Drilling Expedition (UBGH2) was successfully completed in 2010 by using the D/V Fugro Synergy. KNOC managed all field operations, logistics, and associated project contracts. KIGAM was responsible for the analysis of logging-while-drilling/measurement-while-drilling (LWD/MWD) acquired data onboard and all shore-based analyses of the recovered cores. The UBGH2 expedition was operated by KNOC with the scientific program in support of the expedition being led by KIGAM in collaboration with KOGAS, Hanyang University, Korea Ocean Research and Development Institute (KORDI; presently Korea Institute of Ocean Science and Technology (KOFST)) and Korea Advanced Institute of Science and Technology (KAIST), and with additional scientific contributions from the U.S. Geological Survey (USGS), Geological Survey of Canada (GSC) and Oregon State University (OSU). Fugro Well Services Ltd (FWS) was the main contractor who supplied the drillship and other services such as coring, wireline logging (WL), vertical seismic profiling (VSP), remotely operated vehicle (ROV) operations, and together with Geotek Ltd the onboard ship laboratories. For field investigation, Fugro GeoConsulting Inc., Fugro Alluvial Offshore Ltd. (FAOL), Fugro Engineers B.V., Fugro Survey Pte Ltd. and Geotek Ltd. were subcontracted by FWS. The LWD/MWD and WL/VSP tools were supplied by Schlumberger and FAOL, respectively. During the UBGH2, dedicated gas hydrate coring, drilling, downhole logging and ROV operation were conducted. The gas hydrate production test is planned to be conducted in 2015 at one of three potential areas where gas hydrate-bearing sand reservoirs were identified based on results of the UBGH2. Characterization of potential gas hydrate reservoirs is being conducted to select a site for the proposed future gas hydrate production test.

Section snippets

Earlier investigations

In the Ulleung Basin, exploration conventional oil and gas was mostly conducted along the southern continental shelf area until late 1980s. Since the early 1990s, there have been extensive research surveys in the deep-water area by KIGAM and KORDI. These surveys and studies were mainly focused on the geological mapping, tectonic history, sediment stratigraphy and paleoenvironment of the East Sea of Korea. In 2008, an additional phase of conventional oil and gas exploration in the Ulleung Basin

UBGH2 objectives

Previous studies in the Ulleung Basin indicated that gas hydrate occurs widespread and in potentially significant amounts for suitable for exploitation. However, the presence of gas hydrate-bearing sediments was confirmed at only a few sites during UBGH1. Limited scientific information on the nature of gas hydrate-bearing structures also made it difficult to assess the gas hydrate resource potential in the basin. Thus, the primary objectives of the UBGH2 were to confirm the occurrence of gas

UBGH2 scientific results and implications

UBGH2 provided the data and information needed to characterize the (1) geologic and sedimentologic record of the Ulleung Basin, (2) to verify the origin of gas and water included within the confirmed gas hydrate occurrences, (3) to understand the lithologic control on the distribution of gas hydrate in the basin, and (4) to further assess the in-place gas hydrate resource in the Ulleung Basin.

Initial scientific results obtained from UBGH2 were presented at scientific conferences, including Bahk

Components of the Ulleung Basin gas hydrate petroleum system

In view, gas hydrates in the Ulleung Basin occur under a wide range of geologic conditions. The geologic controls on the occurrence of gas hydrate as discovered during UBGH2 have been reviewed in the following section of this report as components of the Ulleung Basin gas hydrate petroleum system. In a gas hydrate petroleum system, the individual factors that contribute to the formation of a gas hydrate accumulation can be identified and assessed; the most important include (1) gas hydrate

Future research and direction

With the successful completion of the UBGH2, the primary goals of the expedition were sufficiently accomplished. A production test in the Ulleung Basin is planned to be performed in 2015. The targets are the gas hydrate-bearing sand reservoirs, which were found at three sites during the UBGH2. These gas hydrate-bearing sand reservoirs have been carefully characterized. At Site UBGH2-6, one of the potential sites for the production test, 200 km² of 3D seismic data were additionally acquired in

Acknowledgments

The authors wish to thank those that contributed to the success of the Second Gas Hydrate Drilling Expedition in the Ulleung Basin (UBGH2). Notably we wish to thank the co-chief scientists, the captains, crew and shipboard scientific party of the D/V Fugro Synergy. We also wish to acknowledge the support of the Gas Hydrate Research and Development Organization (GHDO) of the Ministry of Trade, Industry and Energy (MOTIE), Republic of Korea. Special appreciation is extended to Korea Institute of

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