Industry considers difficulty, cost of pursuing hydrates

Nankai Trough area, offshore of SE Japan, showing seismic 1996 survey lines, bottom seismic reflectors interpreted from seismic profiles, and the location of the MITI exploration well planned the be drilled in 1999 (Y. Tsuji et al - 1998). [30,446 bytes] Seismic stratigraphy of the exploration area in the Nankai Trough correlated with MITI wells and onshore geology (Y. Tsuji et al - 1998). [15,926 bytes] PART II: This is the second in a two-part series on the location, prevelance, and recovery

Resource for the 21st Century

Jan Krason
Geoexplorers International
PART II: This is the second in a two-part series on the location, prevelance, and recovery of methane hydrates under the world's oceans.

Japan National Oil Company's (JNOC) Nankai Trough Project re-ignited strong interest in the gas hydrates for several reasons:

  • They are a nuisance for offshore drilling, gas pipelines and processing facilities.
  • They may cause geotechnical and environmental hazards.
  • They will be explored for and tested as a potentially major competitor to conventional natural gas resources.
JNOC has opened up its methane hydrate projects program and is now sharing results with the public in a symposium entitled "International Symposium on Methane Hydrates - Resources in the Near Future?" In the symposium opening, Satoshi Tono confirmed JNOC's plan to drill a methane hydrate exploratory well this year in the Nankai Trough. The well will be drilled in ane area where a typical bottom-simulating reflector (BSR) has been observed on the seismic reflection profiles. The Pacific Ocean water depth of the proposed well site is 950 meters.

Tono emphasized that this will be the first well drilled in Japan's deepwater offshore to target methane hydrates. The project's R&D investigation will include basic properties of the methane hydrates, geological modeling and logging technology, seismic survey and processing, drilling and coring, production modeling and core testing technology.

Unlimited energy resource

Timothy S. Collett, in the keynote speech, stated that "several countries, including Japan, India, and most recently the United States, have launched ambitious national projects to further examine the resource potential of gas hydrates. These projects may help answer key questions on the properties of gas hydrate reservoirs, the design of the production systems, and, most importantly, the economics of gas hydrate production."

Methanol has been successfully used in production of gas from gas hydrates of the Messoyakh gas field at northwestern Siberia (Makogon, 1978, 1988, Krason and Finley, 1992). But recently, Collett and Ginsburg (1998) raised the question of whether, if at all, gas hydrates significantly contributed to gas production in the Messoyakh gas field? After brief geological and physical characteristics of gas hydrates of marine environments, Collett said that gas hydrates would not likely be an unlimited energy resource. He added that "in certain parts of the world characterized by unique economic and/or political motivations, gas hydrates may became a critical sustainable source of natural gas within the foreseeable future."

Resource assessment

The methane hydrates resources assessment was discussed by 11 presenters. Special attention was focused on the Nankai Trough, but, five other papers were devoted to special factors, such as the methodology, and basin analysis that have to be considered and well understood for more factual therefore, less speculative, assessment of gas hydrates. Tsuji et al (1998) and his co-authors report that for Nankai Trough potential reserves have been assessed by:

  • Krason (1992) and Matsumoto (1995) as (0.42. ~ 4.2) by 1012 cu mtr and (0.8 ~ 8.0) by 1012 cu mtr, respectively. The figures in parenthesis are assumed thicknesses for methane hydrate zone - the first figure represents 1 meter and the latter 10 meters.
  • According to Satoh et al. (1996) estimation resources of natural gas in the hydrates and associated free gas in the Nankai Trough offshore Shikoku region can be 2.7 by 1012 cu mtr and 1.6 by 1012 cu mtr, respectively. All cited estimations were calculated for an area approximately 35,000 sq km. In this area, the base of gas hydrates zone, interpreted from the presence of bottom seismic reflector (BSR), occurs in the range of 250-300 meters below the sea floor.

Nankai Trough priority

Yoshihiro Tsuji, a keynote presenter, made it clear that the wildcat MITI "Nankai Trough Project" scheduled for drilling in late 1999 will explore both methane hydrates as unconventional and Miocene prospect as conventional hydrocarbon reservoirs. Tsuji pointed out that the projected well would be located only about 50 km from the industrial belt along the Pacific coast. This belt is the biggest consumer of petroleum products in Japan.

Tsuji et al (1998) described the stratigraphy of the surrounding area of wildcat drilling. The area is characterized by fore-arc and accretional Cenozoic sediments consisting of alternating sandstone and siltstone with associated conglomerates and tuff. The widespread presence of BSRs in Nankai Trough has been also confirmed in the latest seismic survey (Satoh et al, 1996). Using BSR and considering other geological and geochemical indicators, the presence of gas hydrates is anticipated.

Tsuji's et al paper (1998) includes many details of the MITI Nankai Trough wildcat drilling project. The well will be drilled at 950 meters water depth, and its total planned depth should be 2,800 meters. Mikio Satoh et al (1998) considered marine natural gas hydrates as one of the largest prospective hydrocarbon resources around Japan. JNOC's Nankai Trough project is considered the most promising area for the discovery of viable amounts of gas. Eight other areas were also identified with gas hydrates.

Assessment methodology

Ryo Matsumoto (1998) using data from Nankai Trough and from the Blake Ridge ODP Leg 164, at the US Carolinas offshore, suggests a way to estimate methane hydrate from the chloride and oxygen isotopic anomalies. Interrelated tests include:

  • Geophysical surveys and identification of BSRs
  • Research-oriented drilling and sampling and analysis of rocks, fluids, and gas
  • Geochemical investigations.
With reference to the resource assessment methodology, Amos Nur lecturing on the rock physics approach characterizing gas hydrate reservoirs, emphasized the importance of estimating the amount of gas hydrates from remote measurements. He concluded: "The exact amount and state of the hydrates can be obtained only from seismic reflection data." If the latter can be proven, exploration for and assessment of methane hydrate resources would be very simple.

Dominique Grauls stated that despite the uncertainty on this evaluation, the presence of hydrates in deep offshore zones appear to be increasingly confirmed by very recent seismic surveys. He concluded: "The trapping potential of hydrates with seafloor depth constitutes an encouraging factor for the hydrocarbon exploration in the ultra deep offshore areas."

The basin analysis methodology for geological evaluation of confirmed and suspected gas hydrate localities has been applied to the Nankai Trough and other 12 very large regions (Ciesnik and Krason, 1989, Finley and Krason, 1989, Krason, 1992, Krason, 1998). This author emphasized the primary importance of understanding the geological environments controlling gas hydrate occurrences. The basin analysis methodology, scope and the format of reporting set by Geoexplorers International, Inc. are very well suited to projects having similar objectives to those established by JNOC.

Contest

Because of their geotechnical nuisance, the petroleum industry is well aware that hydrates will block pipelines or gas chokes, can cause offshore blowouts, create drilling instability, platform instability and other inter-related problems. Considering the potentially immense gas reserves trapped in and under naturally formed hydrates. The Japanese Government and JNOC's interest in and exploration for methane gas as an energy resources for the near future, raised worldwide attention. This created an impetus of widely expanded new research of gas hydrates by numerous universities and various research organizations.

Some scientists also indirectly question the consideration of gas hydrates for any interrelated environmental hazards. The Shell Gas Hydrate Team mentioned the above skeptical opinion especially with reference to the methane hydrates assessed resources. Nevertheless, according to M. J. Mintz (Shell Research), "Shell is committed to the ongoing development of technology that will enable continued discovery, production and supply of various low cost fuel/energy sources to meet societal needs. While the technology for production of natural gas from hydrate deposits is but one of a suite of technologies being explored today, a breakthrough in this area could insure the availability of large volumes of low cost natural gas well into the 22nd century."

V. S. Yakushev, representing RAO Gazprom, Russia, stated that "gas production from submarine hydrates has very far and foggy prospects." But, Yakushev's conclusion can be contested by his own statement admitting that "practically, there were not special exploration works in Russia for hydrates, so this interest has decreased strongly from the middle 1980s."

Mud volcanoes?

M. Hovland (1998), posed the question asking whether there were commercial deposits of methane hydrates in ocean sediments?" Considering a very small percentage of gas in the gas hydrates and free gas estimated for ODP's (Ocean Drilling Programs) Leg 146 in the Eastern Pacific Ocean (Cascadia) and Leg 164 in the Western Atlantic Ocean (Blake Plateau), his answer is negative. But, judging from recent findings in the deep portion of the Gulf of Mexico and in the Caspian Sea, perhaps the most promising locations for higher-grade gas hydrate deposits are those where mud volcanoes exist on the ocean floor.

JNOC's commitment and the above highlighted efforts in exploration of its own gas resources prompted re-activation of the methane hydrate research and development program by the US Government. Such a program was sponsored and introduced on November 7, 1997, as Senate Bill S.1418. Among others, one US senator stated: "Despite their potential as an energy resource, methane hydrates have not received the attention they deserve. We are only beginning to understand the magnitude of this potential resource. The amount of methane sequestered in gas hydrates is enormous. Worldwide estimates range from 100,000 tcf to 270,000-million tcf. Locations of known methane hydrate deposits within the US include the Arctic, the seabed adjacent to northern California, the Gulf of Mexico, and the Eastern Seaboard."

"A conservative estimate of deposits under US jurisdiction is 2,700 tcf to 7,000,000 tcf of gas. A recent US Geological Survey analysis indicates the presence of over 500 tcf of methane at the Blake Ridge site off the coast of the Carolinas alone. When you consider that current US consumption is less than 25 tcf of natural gas per year, you begin to appreciate the magnitude of this energy resource.

Editors note: All 1998 cited references are included in the Proceedings of the Int'l Symposium on Methane Hydrates - Resources in the Near Future?; JNOC-TRC, Chiba City, Japan, October 20-22, 1998. A full list of references is available from the author, Jan Krason (Geoexplorers International, Inc.; 5701 East Evans Avenue, Suite 22; Denver, Colorado 80222; Tel: 303-759-2746).

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