Fractured gas reservoir shut-in curve analysis and application

Due to the fluid leak-off effect in the reservoir, the bottomhole pressure decreases after the pumps are shut down. Analyzing the shut-in pressure decline curve of a fractured well is a common method for determining fracturing parameters. Although the G-function pressure decline analysis method briefly explains the pressure decline process, it is not accurate for calculating fracture parameters in fractured low-porosity gas reservoirs. This paper considers the influence of natural fractures on the leak-off coefficient and proposes an approach to evaluate fracture complexity by using the fluctuation characteristics of the construction pressure curve and the G-function characteristics during fracture closure. In this study, the pressure decline curve was segmented to determine fracture parameters, and a shut-in pressure decline analysis model for fractured low-porosity gas reservoirs was established. The fracture complexity is characterized by the fluctuation of the superposition derivative curve, and the approximate series is calculated to quantitatively evaluate fracture complexity. Field data from multiple wells were used to calculate the approximate series, thereby verifying its practicality. Results from actual case data show a positive correlation between fracture complexity and the approximate series. Additionally, this paper adopts a comprehensive filtering model to remove the noise caused by water hammer effects during the shut-in process, improving data quality and analysis accuracy. The feasibility and reliability of the model are validated using actual data from fractured wells in the Dabei Oilfield.