Geological reservoir characterization is essential for accurate evaluation of gas production performance from gas hydrate reservoirs. Particularly, the understanding of reservoir architecture and heterogeneity is of great importance since these are considered as major controls on fluid hydrodynamic and thermodynamic conditions. This study deals with well log and three-dimensional (3-D) vertical seismic profile (VSP) data acquired from the Hydrate-01 Stratigraphic Test Well within the 7-11-12 prospect, Prudhoe Bay Unit, Alaska North Slope and reports on the results of geological/geophysical evaluation related to the geological structure and reservoir properties of the 7-11-12 prospect. The structural trends of the target reservoirs, based on well correlations, are mostly consistent with the predrill prediction using the surface seismic data, and infer the existence of subseismic faults cutting through the Hydrate-01 well. The 3-D VSP data confirm a down-to-the-east normal fault that offsets the reservoir units across the Hydrate-01 well, which is concordant with the well identification of the same fault, and indicate a northeast-dipping relay structure associated with the overstepping normal faults. The edge enhancement attribute associated with discontinuity generated from the 3-D VSP data shows small faults/fractures, possibly as part of a complex fault network within the imaged normal fault system. These results reveal that the 3-D VSP data provide detailed structural information that is not present from the surface seismic data. The Hydrate-01 well log data confirm the occurrence of gas hydrate at high saturation in the two targeted sand units (B1 and D1 sands), and the comparison to a nearby preexisting well (7-11-12 well) shows the same general trend in gas hydrate saturation as a map of seismic impedance generated from surface seismic data. The well log data also suggest that the base of gas hydrate occurrence in the Hydrate-01 and 7-11-12 wells is almost aligned at the same depth in both of the targeted B1 and D1 sand reservoirs. Especially for the D1 sand in the Hydrate-01 well, the resistivity logs show a sharp transition from high gas hydrate saturation to fully water-saturated within the D1 sand, suggesting a common gas hydrate/water contact. The results of this study will be used to construct the geological models needed for reservoir simulation studies and they can provide important insights into the geological factors that control the occurrence of gas hydrate on the Alaska North Slope.

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There are many hazards caused by debris flows and landslides all over the world, and especially in Japan, every year. In June 1999 and August 2005 in Hiroshima prefecture and in July 2009 in Yamaguchi prefecture there were many large hazards of debris flows and landslides owing to torrential downpours. Through the survey of these hazards it seems that there is biodeterioration of the mechanical structures of the ground in the hillsides caused by eutrophication (nutrient enrichment) originating in the transition of ground ecosystems in hillside slopes. The eutrophication promotes microbial activities that deteriorate the mechanical structures of the ground in the hillside slopes. Microorganisms promote the weathering of rocks to soils and cause aggregation of soils by their enzymes. Aggregated structures of soils wet the ground to decrease resistance to landslides. It seems that microbial activities accelerate the occurrence of debris flows. This paper involves the investigation of the above-mentioned relationships between debris flows and mechanical deterioration of the ground due to eutrophication of ground ecosystems in hillside slopes. It was found that the values of the eutrophication indexes are low in the stable slopes and high in the unstable slopes. The values of the stability of ground formation are high in the stable slopes and low in the unstable slopes. Many microorganisms are found in the unstable slopes.

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