Numerical simulation on combined production of hydrate and free gas from silty clay reservoir in the South China Sea by depressurization: Formation sealing

The co-extraction of hydrate and free gas through depressurization assisted by reservoir reformation in the South China Sea holds great promise for commercial development. Formation sealing, as one of reservoir reformation methods, demonstrates strong feasibility due to its benefits for enhancing depressurization and preventing water invasion. However, the application of this approach within a symbiotic system of hydrate and free gas has not been thoroughly evaluated. To reveal the mechanism behind increased yield and clarify the impact of various sealing factors, this study conducts numerical simulations based on a three-dimensional geological model constructed using survey data from site SHSC-4. The influences of sealed radius, sealed thickness, and permeability ratio before and after sealing on production are examined using orthogonal design. Additionally, the maximum percentage of gas contribution from hydrate dissociation (w) during co-extraction is calculated. The results show that: (1) Formation sealing can significantly enhances production potential; (2) Free gas serves as the primary gas source during the whole co-extraction, with the maximum w reaching approximately 20 %; (3) The optimal parameters of sealed layer by using a vertical well are as follows: a sealed radius of 150–200 m, a permeability ratio of 5000, and a sealed thickness of 0.50 m.