The mechanism of breathing effect and intelligent recognition method considering wellbore-formation coupling during drilling in deepwater

The development of deepwater oil and gas resources has become increasingly vital to meeting rising global energy demands. However, the narrow safe drilling window and complex stress environment in deepwater wells introduce significant technical challenges. One such issue is the formation breathing effect, a process involving the alternate loss and return of drilling fluid due to fracture opening and closing, which may be misinterpreted as well influx or loss, potentially leading to well control incidents. To better understand and manage this phenomenon, a specialized experimental apparatus was designed to simulate the breathing effect. A comprehensive coupled flow model was developed, accounting for unsteady wellbore flow, fracture deformation, fluid compressibility, flow resistance, and equivalent damage radius. A numerical method was proposed to solve the model and applied to field case studies. The results provided insight into the dynamic characteristics of the breathing effect. Based on these findings, a pattern recognition-based identification method was established, significantly enhancing detection accuracy. This research offers important technical support for the accurate identification and effective management of formation breathing during deepwater drilling operations, contributing to improved safety and efficiency in offshore resource development.