title: Physicochemical impacts associated with natural gas development on methanogenesis in deep sand aquifers.
abstract: The Minami-Kanto gas field, where gases are dissolved in formation water, is a potential analogue for a marine gas hydrate area because both areas are characterized by the accumulation of microbial methane in marine turbidite sand layers interbedded with mud layers. This study examined the physicochemical impacts associated with natural gas production and well drilling on the methanogenic activity and composition in this gas field. Twenty-four gas-associated formation water samples were collected from confined sand aquifers through production wells. The stable isotopic compositions of methane in the gases indicated their origin to be biogenic via the carbonate reduction pathway. Consistent with this classification, methanogenic activity measurements using radiotracers, culturing experiments and molecular analysis of formation water samples indicated the predominance of hydrogenotrophic methanogenesis. The cultivation of water samples amended only with methanogenic substrates resulted in significant increases in microbial cells along with high-yield methane production, indicating the restricted availability of substrates in the aquifers. Hydrogenotrophic methanogenic activity increased with increasing natural gas production from the corresponding wells, suggesting that the flux of substrates from organic-rich mudstones to adjacent sand aquifers is enhanced by the decrease in fluid pressure in sand layers associated with natural gas/water production. The transient predominance of methylotrophic methanogens, observed for a few years after well drilling, also suggested the stimulation of the methanogens by the exposure of unutilized organic matter through well drilling. These results provide an insight into the physicochemical impacts on the methanogenic activity in biogenic gas deposits including marine gas hydrates.
authors.affiliation: Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
authors.forename: Taiki
authors.initials: T
authors.lastname: Katayama
authors.affiliation: Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
authors.forename: Hideyoshi
authors.initials: H
authors.lastname: Yoshioka
authors.affiliation: Kanto Natural Gas Development Co., Ltd., Mobara, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Muramoto
authors.affiliation: Kanto Natural Gas Development Co., Ltd., Mobara, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Usami
authors.affiliation: Japan Oil, Gas and Metals National Corporation, Minato-ku, Tokyo, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Fujiwara
authors.affiliation: Fukushima Project Headquarters, National Institute of Radiological Sciences, Inage-ku, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoshida
authors.affiliation: Bioproduction Research Institute, AIST, Toyohira, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Kamagata
authors.affiliation: Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Sakata
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics / Q000302:isolation & purification; D005740:Gases; D060587:Groundwater / Q000737:chemistry; D008697:Methane / Q000378:metabolism*; D059206:Natural Gas; D061329:Oil and Gas Fields
chemical_list: D005740:Gases; D059206:Natural Gas; D008697:Methane
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