Following the first attempt at producing gas from a naturally occurring methane hydrate (MH) deposit in the Daini–Atsumi Knoll in the eastern Nankai Trough area off Honshu Island, Japan in 2013, a second attempt was made in April to June of 2017 at a nearby location using two producer wells sequentially and applying the depressurization method. The operation in the first borehole (AT1-P3) continued for 12 days with a stable drawdown of around 7.5 MPa and 41 000 m3 of methane gas being produced despite intermittent sand-production events. The operation of the other borehole (AT1-P2) followed, with a total of 24 days of flow and 222 500 m3 of methane gas being produced without sand problems. However, the degree of drawdown was limited to 5 MPa because of a higher water production rate than expected in the second hole. The pressure and temperature sensors deployed in the two producers, along with the two monitoring holes drilled nearby, gathered reservoir response data and information about the long-term MH dissociation processes in the vicinity of the production holes in the temporal and spatial domains. Although the ratio of energy return to the input was considerably larger than that for the depressurization operation, some observations (e.g., the high contrast in the production rates between the two holes and the almost constant or slightly reduced gas production rates) were not predicted by the numerical models. This failure in prediction raises questions about the veracity of the reservoir characteristics modeled in the numerical simulations. This paper presents the operation summaries and data obtained with thought-experiment based-anticipated production behaviors and preliminary analysis of the obtained data as the comparison with expected behaviors. Detailed observations of gas and water production, as well as the pressure and temperature data recorded during the gas flow tests, indicate that the heterogeneous MH distribution within the reservoir was mainly responsible for the discrepancies observed between the anticipated and actual behaviors. Furthermore, the motion of the water that does not originate from MH dissociation introduces complexity, such as the occurrence of concentrated water-producing intervals and unexpected gas production responses to decreases in pressure, into the production behavior. The influence of heterogeneity should be clearly understood for the accurate prediction of gas production behavior based on MH reservoirs.

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The second offshore production of methane hydrate in the Nankai Trough and gas production behavior from a heterogeneous methane hydrate reservoir

Production behavior and numerical analysis for 2017 methane hydrate extraction test of Shenhu, South China Sea

Methane hydrates: A future clean energy resource

C1 chemistry, which is the catalytic transformation of C1 molecules including CO, CO2 , CH4 , CH3 OH, and HCOOH, plays an important role in providing energy and chemical supplies while meeting environmental requirements. Zeolites are highly efficient solid catalysts used in the chemical industry. The design and development of zeolite-based mono-, bi-, and multifunctional catalysts has led to a booming application of zeolite-based catalysts to C1 chemistry. Combining the advantages of zeolites and metallic catalytic species has promoted the catalytic production of various hydrocarbons (e.g., methane, light olefins, aromatics, and liquid fuels) and oxygenates (e.g., methanol, dimethyl ether, formic acid, and higher alcohols) from C1 molecules. The key zeolite descriptors that influence catalytic performance, such as framework topologies, nanoconfinement effects, Bronsted acidities, secondary-pore systems, particle sizes, extraframework cations and atoms, hydrophobicity and hydrophilicity, and proximity between acid and metallic sites are discussed to provide a deep understanding of the significance of zeolites to C1 chemistry. An outlook regarding challenges and opportunities for the conversion of C1 resources using zeolite-based catalysts to meet emerging energy and environmental demands is also presented.

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Applications of Zeolites to C1 Chemistry: Recent Advances, Challenges, and Opportunities

Numerical simulation of gas recovery from a low-permeability hydrate reservoir by depressurization

Marine methane hydrate in sands has huge potential as an unconventional gas resource; however, no field test of their production potential had been conducted. Here, we report the world’s first offshore methane hydrate production test conducted at the eastern Nankai Trough and show key findings toward future commercial production. Geological analysis indicates that hydrate saturation reaches 80% and permeability in the presence of hydrate ranges from 0.01 to 10 mdarcies. Permeable (1–10 mdarcies) highly hydrate-saturated layers enable depressurization-induced gas production of approximately 20,000 Sm3/D with water of 200 m3/D. Numerical analysis reveals that the dissociation zone expands laterally 25 m at the front after 6 days. Gas rate is expected to increase with time, owing to the expansion of the dissociation zone. It is found that permeable highly hydrate-saturated layers increase the gas–water ratio of the production fluid. The identification of such layers is critically important to increase the en...

Key Findings of the World’s First Offshore Methane Hydrate Production Test off the Coast of Japan: Toward Future Commercial Production

Sustainable gas production from methane hydrate reservoirs by the cyclic depressurization method

Gas hydrates are expected to be an energy resource in this century. Many countries, such as the United States, China, India, and Japan, have explored potential reservoirs and promising production m...

Koya Akamine

Papers

Key Findings of the World’s First Offshore Methane Hydrate Production Test off the Coast of Japan: Toward Future Commercial Production

Sustainable gas production from methane hydrate reservoirs by the cyclic depressurization method

Influence of Flow Properties on Gas Productivity in Gas-Hydrate Reservoirs: What Can We Learn from Offshore Production Tests?