Numerical Simulation on Production Trials by Using Depressurization for Typical Marine Hydrate Reservoirs: Well Type and Formation Dip

Natural gas hydrate has huge reserves and is widely distributed in marine environment. Its commercial development is of great significance for alleviating the contradiction between energy supply and demand. As an efficient research method, numerical simulation can provide valuable insights for the design and optimization of hydrate development. However, most of the current production models simplify the reservoir as a two-dimensional (2D) horizontal layered model, often ignoring the impact of formation dip angle. To improve the accuracy of production prediction and provide theoretical support for the optimization of production well design, two three-dimensional (3D) geological models with different dip angles based on the geological data from two typical sites are constructed. The vertical well, horizontal well and multilateral wells are deployed in these reservoirs with different permeabilities to perform production trial, and the sensitivity analysis of dip angles is also carried out. The short-term production behaviors in high and low permeability reservoirs with different dip angles are exhibited. The simulation results show that 1) the gas and water production behaviors for different well types in the two typical reservoirs show obviously different variation laws when the short-term depressurization is conducted in the inclined formation; 2) the inclined formation will reduce the gas production and increase the water extraction, and the phenomena becomes pronounced as the dip angle increases, particularly in the low-permeability reservoirs; 3) and the impact of formation dip on hydrate recovery does not change significantly with the variation of well type.