Scientific drilling at a submarine mud volcano shows that geofluid migration stimulates methanogenesis in the deep biosphere.

Geological CO2 sequestration in unmineable subsurface oil/gas fields and coal formations has been proposed as a means of reducing anthropogenic greenhouse gasses in the atmosphere. However, the feasibility of injecting CO2 into subsurface depends upon a variety of geological and economic conditions, and the ecological consequences are largely unpredictable. In this study, we developed a new flow-through-type reactor system to examine potential geophysical, geochemical and microbiological impacts associated with CO2 injection by simulating in-situ pressure (0–100 MPa) and temperature (0–70°C) conditions. Using the reactor system, anaerobic artificial fluid and CO2 (flow rate: 0.002 and 0.00001 ml/min, respectively) were continuously supplemented into a column comprised of bituminous coal and sand under a pore pressure of 40 MPa (confined pressure: 41 MPa) at 40°C for 56 days. 16S rRNA gene analysis of the bacterial components showed distinct spatial separation of the predominant taxa in the coal and sand over the course of the experiment. Cultivation experiments using sub-sampled fluids revealed that some microbes survived, or were metabolically active, under CO2-rich conditions. However, no methanogens were activated during the experiment, even though hydrogenotrophic and methylotrophic methanogens were obtained from conventional batch-type cultivation at 20°C. During the reactor experiment, the acetate and methanol concentration in the fluids increased while the δ13Cacetate, H2 and CO2 concentrations decreased, indicating the occurrence of homo-acetogenesis. 16S rRNA genes of homo-acetogenic spore-forming bacteria related to the genus Sporomusa were consistently detected from the sandstone after the reactor experiment. Our results suggest that the injection of CO2 into a natural coal-sand formation preferentially stimulates homo-acetogenesis rather than methanogenesis, and that this process is accompanied by biogenic CO2 conversion to acetate.

Until now, identification of three‐dimensional non‐convex (concave) blocks has not been accomplished. However, a direct body concept, which is introduced here, can deal with both convex and concave blocks in the same process in connection with detection of individual blocks and computation of physical quantities. Thus, the dilemma in the generalization of identifying three‐dimensional multi‐block systems has been eliminated. The directed body concept used in geometrical identification problems makes it possible to build a novel automatic identification system for three‐dimensional multi‐block systems. This new system eliminates the time‐consuming work on geometrical identification, and copes with a variety of applications in multi‐body systems, such as rock masses.

We report the permeability of ~1.9 km deep coal-bearing formation samples retrieved at Site C0020 during Integrated Ocean Drilling Program Expedition 337 off the Shimokita Peninsula, Japan. The flow-through permeability test was conducted by a triaxial consolidation permeability test device. The intrinsic permeability of lignite coal samples is 3.80 × 10 -20 m 2 and 3.61 × 10 -20 m 2 at 1919.57 and 1922.95 meters below seafloor (mbsf), respectively. In contrast, a sample from a sand layer interbedded with the coal layer at 1925.38 mbsf is unconsolidated and too soft to conduct permeability tests. The sand size fraction (>75 µm) is 88.5 wt%, and the estimated porosity is 40.5%.

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Japan aims to reduce its greenhouse gas emissions by 80% by 2050 as a countermeasure against global warming. As part of its policy, by 2030, the Japanese government plans to put into action carbon dioxide (CO2) capture and storage (CCS) initiatives. On the other hand, site surveys for deep saline aquifers (DSA) in Japan are underway. This paper shows the potential for CO 2 storage using self-sealing of CO2 hydrate as a breakthrough to increase site options and the possible amounts of CO2 to be stored around Japan. In particular, the potential oceanic regions and the possible CO 2 amounts are estimated.

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