Evaluation of failure criteria under dynamic loading of the wellbore with strain rates between 10−6 and 100 /s

Abstract

Dynamic loading is very common during drilling, mining, hydraulic fracturing, and tunnel excavation. This could compromise the long-term stability and integrity of the underground constructions. Under dynamic loading, rocks usually behave differently compared to static loading. Whether the static failure criteria can be used to evaluate structure failure under dynamic loading is a question that has not been answered yet. In this paper, the triaxial compression strength data under different strain rates (between 10−6 and 100/s) for four types of rock (Bedford limestone, Bukit Timah granite, Laurentian granite, and Dry silica sand) have been used to evaluate six different failure criteria. Two methods have been implemented to obtain rock cohesion and internal friction angle, which are the grid search algorithm and the Mohr failure line method. The results show that the grid search algorithm guarantees the best performance of the failure criteria, providing the best-fit rock parameters. The more practical method of the Mohr failure line can also generate reasonable predictions if a safety factor of 1.1 is considered. Both methods show that Modified Lade is the failure criterion that provides the best performance in predicting rock failure under dynamic loading. In the petroleum industry, most of the activities causing dynamic loading of the wellbore are characterized by a magnitude of strain rate lower than 100/s (even lower than 10−3/s). Consequently, this work shows that it is reasonable to assume that the commonly used static failure criteria, especially Modified Lade, could be selected to analyze wellbore stability under dynamic loading conditions effectively.