Numerical Investigation of Hydrate Production Characteristics in a Fractured Reservoir via Depressurization: Assessing the Influence of Fractures

The natural gas hydrate reservoir is known for its low permeability, leading to a suboptimal gas production rate, thus impeding its commercial viability. While reservoirs with high permeability fractures exhibit greater seepage capacity, their influence on hydrate dissociation characteristics remains unclear. The present study introduces a coupled thermo-hydrochemical numerical model to simulate the exploitation of the fractured hydrate reservoir through depressurization using a vertical well. The impact of the fracture on hydrate dissociation is characterized as a "double-edged sword", termed the "fracture end effect", with inhibition and promotion at the fracture end near/far from the well, respectively, resulting from the heterogeneous pressure gradient distribution within and adjacent to the fracture. A relatively high-pressure and high-temperature region is noted at the near end of the fracture due to thermal compensation from the distant reservoir through the fracture, potentially reducing the risk of ice and hydrate reformation around the wellbore during exploitation. Furthermore, the presence of the horizontal fracture can notably enhance the cumulative gas production and the gas-to-water ratio, especially in long-term production using a vertical well, thereby yielding superior production economic benefits for the fractured reservoir.