Study on Rock Burst Behavior and Tendency Identification of Surrounding Rocks in Hard and Brittle Formations of Deep and Ultra-deep Wells

Abstract

The phenomenon of the continuous collapse or the instantaneous block-falling incidents during the drilling of deep wells cannot be sufficiently explained by traditional wellbore instability theory. This phenomenon is similar to rock bursts that often occur during tunnel excavations and other engineering projects. This paper focuses on hard/brittle formations such as limestone, dolomite, and shale, which represent the most frequently collapsed formations while drilling a borehole. Based on rock burst theory and the results of the rock mechanics experiments, combined with rock failure model and other intuitive conditions, rock bursts are divided into three categories: weak, medium, and strong bursts. We establish the calculation models of strength brittleness index R and elastic energy index W based on rock uniaxial compressive strength and determine the interval values of these indexes for rock burst identification. We also propose a set of comprehensive identification methods for rock burst tendency and the classification of surrounding rocks in hard and brittle formations during the drilling of deep wells. The findings of this work provide a solid foundation for the research of wellbore instability prevention and control based on the classification of hard/brittle formations.