Identifications of Complex Fracture Geometry and Changing Drainage Radius in Tight Gas Reservoirs

Fracture geometries and drainage radius are essential parameters for developing a reasonable development plan for a single fractured well. However, owing to fracture hits, the complex fracture geometries bring challenges for parameter estimations. This paper establishes a well testing based model for a finite-conductivity fractured vertical well in radial composite reservoirs with dynamic supply and fracture networks. Based on the successive steady-state method, the point source function, pressure superposition principle, and boundary element method are used to solve the reservoir model, and the methods of discrete fracture and pressure superposition are used to solve the fracture model. By introducing the rate-normalized pseudopressure and material balance time, the variable fluid flux is equivalent to the constant fluid flux. The drainage radius value and fracture geometries are solved by fitting the log-log curves of pressure response, and case studies are performed. The results show that the drainage radius increases with the increase of production time and finally tends to a specific value, and it has an excellent exponential relationship with time. Also, the fracture geometries of the typical well are multiple-radial fracture networks. Through the study of dynamic drainage radius, the controlled reserves of single wells in unconventional gas reservoirs can be better determined, and it can also provide a theoretical basis for fracture evaluation, productivity prediction, and enhanced recovery study of the same type of tight gas reservoir.