Ryo Matsumoto

In 1995, Japan launched a national project to assess methane hydrates as future gas resources, which successfully identified and recovered hydrate-cemented sandy sediments from Pleistocene turbidite units at the Nankai Trough. Extensive geological and geophysical exploration over 20 years reveals a wide distribution of hydrate-induced BSR at the eastern Nankai Trough. The amounts of hydrates in sandy sediments are estimated to be 17 to 39 vol.% based on low salinity anomalies of squeezed pore waters. Hydrate amounts equivalent to 6 to 7 vol.% of sediment volume extend from the seafloor to the base of gas hydrate stability (BGHS). A probabilistic approach to assess amounts of hydrates based on 2D/3D seismic profiles, LWD geophysical parameters, and geochemical analysis of cores provides an approximation of the amounts of resources in place at 40 tcf of methane gas in the entire BSR area (4,687 km²) and at 20 tcf in the hydrate concentrated zone (767 km²) of the eastern Nankai Trough. An integrated academic, industrial, and national program carried out since 2004 identifies another type of hydrate in the eastern margin of the Sea of Japan. Japan Sea hydrates occur as massive aggregates in a chimney-like acoustic blanking zone of a few 100 m across and 100-120 m thick (gas chimney) in Pleistocene hemipelagic sediments. MBES and SBP surveys confirm 1,742 gas chimneys along the eastern margin of the Sea of Japan and around Hokkaido Island. Amounts of hydrates estimated from combined elastic wave velocity Vp and low salinity anomalies are 35 to 74 vol.% of the volume of the gas chimney structure. BSRs in hydrate-bearing gas chimneys exhibit a sharp pull-up structure within the gas chimneys, reflecting high Vp. Assuming that the Vp of massive hydrate is 3.7 km/sec and Vp of the host sediments in gas chimneys is same as Vp of the sediments around gas chimneys, the amounts of hydrates in the gas chimneys are calculated to be 15 to 65 vol.% of chimney volume. High Vp anomalies of hydrate-bearing sediments is also applied to hydrates estimate at the Nankai trough.

Due to the current energy crisis caused by global warming and geopolitical events, evaluating the energy potential of marine gas hydrates around the Japan Islands has become an urgent issue. Based on open and public reports, a critical overview is provided of the current status of the exploration of gas hydrates in the eastern Nankai Trough and along the eastern margin of the Japan Sea. In 2001, an exploration and resource assessment of gas hydrates in the eastern Nankai Trough was launched as a national project. In the late 20^th century, hydrate-induced BSRs had been widely recognized on the fore-arc basins and slopes of the accretionary wedges of the Nankai Trough. Integrated geological and geophysical exploration reveals that the hydrates of the eastern Nankai Trough occur in the interstitial pore space of sand layers (pore filling type) of the Early Pleistocene turbidite units of 100 to 200 m in thickness above the BSR-BGHS. Hydrate exploration in the Japan Sea entered the National project in 2012, following academic efforts over the preceding 10 years, confirming 1,742 columnar-shaped gas chimney structures (generally a few hundred meters across and roughly 100 m deep) in which a few centimeters to nearly 50 m of thick massive hydrate deposits occur in the Middle Pleistocene silty host sediments. Japan Sea hydrates are considered to have grown in the host sediments, displacing clayey particles (particle displacement type). Gas chimney structures are the main conduits for the migration of deep-seated methane, associated with sea floor methane seeps, chemosynthetic communities, and methane-derived authigenic carbonates. A high concentration of massive hydrate is related to enhanced maturation and accumulation of hydrocarbon deposits under the high heat flow of the Japan Sea basin. Additionally, glacial eustasy of the closed Japan Sea basin facilitated efficient recycling of methane to accumulate massive hydrates.

沖縄本島南部に広く分布する島尻層群とそれを覆う知念層の関係については，長い時間間隙/陸上不整合説と同時異相/整合説の2つが提示されてきた．新たに出現した大規模露頭の精査により島尻層群最上部の新里層を時間間隙なく厚い砂質スランプ層が覆い，これが知念層基底を成すことが分かった．境界付近にはドロマイト・コンクリーションが多産することも明らかになった．ドロマイトの同位体組成は両層の境界付近で堆積盆が少なくとも250 m浅化したことを示す．広域的浅海化によりスランプが発生，同時に島尻層群のメタンハイドレートが分解してメタン・フラックスが強くなりメタン由来ドロマイト・コンクリーションの生成が進んだと考えられる．

Estimation of rock properties from seismic data is important for exploration and production activities in the petroleum industry. Considering the compressional velocity—the speed of propagating body waves in formations—and the quality factor (Q)—a measure of the frequency-selective energy losses of waves propagating through formations—both properties are usually estimated from multichannel seismic data. Velocity is estimated during multichannel processing of seismic reflection data in either the time or depth domain. In marine seismic acquisition, Q can be estimated from the following sources: Vertical Seismic Profile (VSP) surveys, where sources are located near the sea surface and geophones are distributed at depth along a borehole; and multichannel reflection data, where sources are also located near the sea surface and receivers are distributed either at the sea surface (conventional seismic survey with streamers) or on the sea floor (use of nodes or Ocean Bottom Cables (OBC)). The aforementioned acquisition devices, VSP, conventional streamers, nodes, and OBCs are much more expensive than single-channel acquisition with one receiver per shot due to the cost of operation. There are numerous old and new datasets from academia and the oil industry that have been acquired with single-channel acquisition devices. However, there is a paucity of work addressing the estimation of velocity and Q from this type of equipment. We investigate the estimation of Q and velocity from single-channel seismic data. Using the windowed discrete Fourier transform for a single seismic trace, we calculate the peak and dominant frequency that changes with time. In the geologic environment, higher frequencies are attenuated at shallow depths (time), while lower frequencies remain at deeper positions. From the rate at which higher frequencies are attenuated with time, we estimate the effective quality factor (Q_eff). However, when using Kirchhoff migration to process single-channel seismic data, events far from the vertical projection of the receiver contribute to the trace at a given time. Then, an underestimation of the effective quality factor occurs. To compensate for the effects of more distant events with lower-frequency content contaminating the shorter events, we propose a linear equation to correct the effective quality factor estimated from migrated seismic data. Effective Q and its correction are estimated in five single-channel seismic lines surveyed along the Joetsu Knoll, a SW-NE anticline structure on the eastern margin of the Sea of Japan. These results are linked to geomorphological and geological features and the velocity field. Joetsu Knoll is a known site of massive gas hydrates (GH), which occur in the first hundred metres of Neogene sediments and, together with gas chimneys, play an important role in seismic wave absorption. Q_eff estimated from migrated seismic data maintains the spatial relationship between high and low Q regions. The region of low Q, which is below 124 and has an average value of 57, occurs near the anticlinal hinge and tends to coincide with the region in which the Bottom Simulating Reflector (BSR) resides. The coexistence of GH and free gas coincides with the very low P velocity gradient of 0.225 s⁻¹. BSR occurrence, Q_eff and the geometry of the Joetsu anticline testify to progressive gas hydrate depletion northward along the dome.

To accelerate development and improve the quality of car navigation systems, we have built a system for automatic generation of evaluation courses. In general, the operation of car navigation systems is verified by driving tests using vehicles. The evaluation courses need to be designed so that inspection sites, such as underground parking lots, tunnels, etc., will be visited during the evaluation period. They should be circuits that include as many inspection sites as possible within a defined distance. However, as the number of the inspection sites increases, the number of courses that can be designed becomes enormous. This makes it difficult to create courses that meet all of the requirements. Hence engineers have spent a lot of time on evaluation course design. For this reason, automatic course generation has become essential for reducing man-hours. We believe that one of the effective approaches is to treat automatic evaluation course generation as a combinatorial optimization problem. In our formulation, inspection sites are grouped into clusters according to the required number of courses, and the shortest circuit is constructed in each cluster.Then, we treat the clustering and shortest circuit generation problems separately as a bi-level combinatorial optimization problem. In other words, the original problem is divided into smaller parts of the combinatorial optimization problems. We then propose a Markov chain Monte Carlo method for solving the bi-level optimization problem, and construct a system for automatic generation of evaluation courses. The proposed method significantly reduces course-design time compared to manual course construction.

This work aims to evaluate the best seismic attributes to use to identify the Bottom Simulating Reflector (BSR) of Umitaka Spur, a well-known gas hydrate area in Joetsu Basin, Japan. For this purpose, it uses 2D single-channel seismic data from cruises NT07-20 and NT08-09 provided by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The methodology used for the qualitative analysis of six seismic attributes to highlight the BSR was done using Schlumberger’s Petrel software. These attributes were Envelope, RMS Amplitude, Amplitude Volume Technique (tecVA), Relative Acoustic Impedance, Spectral Decomposition and Instantaneous Frequency. Thus, this study was fundamental to investigate gas hydrates occurrence through the seismic assessment of some geophysical property (amplitude and frequency) and the geological attributes that highlighted the faults of the complex local geology. The application of these attributes can be used in other areas providing an effective tool to enhance the recognition of BSR all over the world.

The present study deals with diagenesis and dolomitization modeling of Middle Miocene – Quaternary sedimentary sequence outcropped at Ras Banas Peninsula, Egyptian Red Sea Coast. This sequence is comprising successively overlapped clastics, carbonates, and evaporites attaining 254 m total thickness resting on the Pre-Cambrian basement rocks in the Peninsula. Diagenetic history and dolomitization were carefully investigated using several techniques including petrographic microscope, XRD, SEM, cathodoluminescence, atomic absorption, and isotopes of oxygen and carbon. The conspicuous phenomena is the pervasive dolomitization of directly pre- and post evaporite limestone components. These dolomites are mostly nonstochiometric, poorly to moderately ordered crystals. Based on all the results obtained from this study, the dolomitization processes of Ras Banas Peninsula are the result of complex geologic setting, paleo-climate changes, tectonic activity, and sea-level fluctuations. The proposed graphic model describes dolomitization mechanism which refers to mixed meteoric-hypersaline water environments.