How is methane hydrate formed in the ocean?
Innovative Mathematical Model Sheds Light on Methane Hydrate Distribution in Japan’s Nankai Trough
In a significant breakthrough, scientists have developed a new one-dimensional mathematical flow model that simulates the formation and distribution of methane hydrate deposits in the Nankai Trough, off the coast of Japan. This innovative approach, published in the journal Island Arc on September 19, 2023, offers valuable insights into the potential extraction of methane hydrates, a promising energy source, and the prevention of related geohazards.
Methane hydrate, a solid compound where methane becomes trapped within a crystal structure of water. Forms under specific high-pressure and low-temperature conditions typically found in continental margin sediments and permafrost regions. Recognized for its substantial energy potential, understanding the intricate mechanisms that govern methane hydrate reservoirs has become a critical research area.
Given the geological complexity and time-consuming formation process of these deposits, direct observation and evaluation have proved challenging. Addressing this, Associate Professor Hitoshi Tomaru and Chao Xu from Chiba University‘s Graduate School of Science and Engineering have refined an existing mathematical model from 2007, originally proposed by Liu and Fleming, to study methane hydrate saturation levels using numerical simulations.
Utilizing logging and geochemical data from the Kumano Forearc Basin in the Nankai Trough, known for its significant methane hydrate reserves, the researchers explored the distribution patterns and accumulation mechanisms of these hydrates. “Our goal was to discern the regularity of methane hydrate distribution and identify the controlling factors of its generation,” Dr. Tomaru explained.
Additionally, the improved model allowed the team to examine the effects of deep fluid supply and reservoir lithology on methane hydrate distribution. As a result, offering a clearer view of the impact of methane flux variations.
The research team conducted simulations under varying methane flux conditions—low, moderate, and high—to determine their influence on hydrate distribution. The observed patterns in the Nankai Trough correlated with scenarios involving relatively low methane flux. These findings align with previous studies. Which indicated that low methane flux leads to higher saturation near the base of the gas hydrate stability zone. Thus, whereas high flux increases saturation closer to the seafloor.
The simulations also considered the geological impact of factors. Such as the distribution of fractures and deep fissures in rock formations, which affect sediment stress conditions and flow regimes. Thus, by running simulations with typical permeability values for sand and mud, the researchers were able to understand how changes in permeability due to lithological units influence hydrate distribution, noting a significant increase in saturation within sand layers and a decrease in mud layers.
“Our simulation model circumvents the need for the intensive energy and labor usually required by traditional methods such as physical drilling or coring of the sea floor,” moreover, Dr. Tomaru stated. Furthermore, this novel approach stands to revolutionize how scientists and industry stakeholders assess the viability and risks associated with methane hydrate extraction. As a result, paving the way for sustainable energy solutions and informed management of oceanic resources.
