Lab investigations of percussion drilling: from single impact to full scale fluid hammer

Lack of fundamental understandings of the physical mechanisms involved in percussion drilling limits hammer development and performance control. In this study, a series of lab investigations have been designed and executed. The tests are divided into two categories: single impact tests with an indentor and full scale fluid hammer tests under field conditions. Both Berea sandstone and Mancos shale samples are used. For each impact test, three impacts are sequentially loaded at the same location to investigate rock response to repetitive loadings. After each impact, crater depth and width are measured. Various pressure differences across the rock-indentor interface are used to investigate the pressure effect on rock penetration. For hammer drilling tests, an industrial fluid hammer is used to drill Berea sandstone and Mancos shale under both underbalanced and overbalanced conditions. Cuttings are collected and analyzed after the tests. The data and findings from the tests advance the understandings of the rock physics involved in percussive drilling. They also serve to calibrate a dynamic numerical model developed for percussion drilling.