Percussion Drilling: From Laboratory Tests To Dynamic Modeling

摘要

Percussion drilling has long been considered an effectivernapproach to breaking rock in the civil and mining industries. Arnlarge number of air hammers were introduced to oil and gasrnindustries in the 1980's. However, limited fundamentalrnunderstandings of the physical mechanisms involved inrnpercussion drilling hinder its acceptance and applications.rnIn a 2-year research effort, fundamental rock physics arerninvestigated through a series of lab tests, including single impactrntests and full-scale hammer drilling tests. For each impact test,rnthree impacts are sequentially loaded at the same rock locationrnto investigate rock response to repetitive loadings. Besidesrncrater depth and width, the displacement and force in the rodrnand the force in the rock are recorded at 100K Hz frequency.rnFor hammer drilling tests, an industrial fluid hammer is used torndrill Berea sandstone and Mancos shale under bothrnunderbalanced and overbalanced conditions. The bottom holernpressure varies from 3.5MPa to 20.7MPa while pore pressure isrncontrolled separately, varying from 0MPa to 24.2MPa. Duringrnthese tests, Rate of Penetration is recorded continuously fromrnone pressure condition to another. Cuttings are then screened,rncollected, and analyzed.rnThe lab data are then used to calibrate a 3D drillingrnsimulator developed specifically for percussion drilling. First arnstrain-softening rock material model is derived from matchingrnrock stress-strain curves in a series of rock mechanical tests.rnThen a stress history is specified as loading conditions based onrnthe stress and displacement data recorded in the impact rod.rnWith appropriate material model and boundary conditions, bothrnrock displacement and indentation geometries are well matched.rnFurther, the simulation reveals in detail how rock becomesrndefragmented when receives impact. These developmentsrnimprove the fundamental understandings of rock physicsrninvolved in hammer drilling. The 3D drilling simulator can alsornbe applied to investigate rock breakage and optimize operationsrnin field.