Semianalytical model of complex fracture growth in vertical wells based on boundary element theory

Abstract

The recent developments in low-permeability oil and gas reservoir mining technology have led to the application of various forms of well fracturing models to determine the physical formation parameters and flow laws in porous media. However, most related studies have been aimed at conducting a pressure transient analysis after the formation of fractures, ignoring the pressure change characteristics during fracture formation. In this study, a fracture growth model based on vertical fractured wells was established and solved using the source function theory and boundary element method. The rationality of the model calculation method was verified by the superposition principle. The pressure change laws before and after fracture growth were analyzed, and the model was subjected to hydraulic fracturing experiments. The results showed that with the increase in the local pressure at the bottom of the well, main fractures, branch fractures, and microfractures were generated in three stages. When the fracture was formed, the pressure and pressure derivative curves fluctuated but gradually returned to a stable state under the fracture shape with the extension of the flow time. Moreover, from the main fracture to the microfracture stage, the pressure recovery time period was gradually shortened. The fitting results of the analysis model and fracturing experiment were found to be accurate, providing a theoretical support for analyzing the transient pressure changes during the formation of complex fractures. The different curve characteristics also provide a new reference basis for evaluating the fracture propagation behavior and predicting the fracture conductivity.