Application of the unstructured grids in the numerical simulation of fractured horizontal wells in ultra-low permeability gas reservoirs

• In view of the impermeable lithological boundary, a radial model is established.
• The impermeable lithological boundary is considered in fracturing horizontal wells.
• The vertical fractures can be accurately simulated using the unstructured grid.
• Intermittent open wells can effectively slow down the rate of the production decline.

Given the impermeable lithological boundary problem of the Sulige Gas Field in China, this study validates the dynamic characteristics of this reservoir through a radial model of the vertical well and proposes an unstructured grid refinement technology using a perpendicular bisector, while considering the horizontal well fracturing model. The vertical fractures and impermeable lithological boundary around the horizontal well can be accurately simulated using the unstructured grid refinement technology. This study also investigates the influence of stress sensitivity on the development indices of an ultra-low permeability gas reservoir. Results show that an impermeable lithological boundary in a horizontal well can effectively decrease the production rate of the working system of intermittent open wells. For ultra-low permeability gas reservoir with different stress sensitivities, important aspects, such as stabilization period, economic benefits, and ultimate recovery, should be considered in the early production allocation of gas wells.