Single Cutter Impact Tests Investigate Deep-Well Hammer-Drilling Performance

摘要

The use of a percussion hammer can provide highpenetration rates through hard rocks when air drilling. Thework of this paper was partly sponsored by the USDepartment of Energy to develop hammer drilling techniquesfor drilling deep hard rocks, using real drilling muds.Unfortunately, development is complicated becauseunderstanding rock breakage and cuttings removal under thedynamic loading conditions of hammer drilling is difficult.Historically, empirical relations have been used to relatehammer blow energy and blow rate with drilling.This paper presents results of carefully measuredsingle cutter impact-as well as high rate and 'static'-rockindentation tests under high borehole pressure conditions,using real drilling muds. The results include cutter force-displacementand crater volumes for both first stress wave(initial impact) and long time (quasi static) rock indentations.From this, specific energy for rock breakage (I.e. the energy toexcavate a unit volume of rock) can be calculated.The specific energy values measured in these singlecutter impact tests show the rock destruction efficiency thatcan be achieved by impact loading. They are compared withspecific energies measured during full scale hammer androtary drilling experiments, under relatively similarconditions.For a given rock type, impact stress, cutterconfiguration, wellbore pressure, and mud type are shown tobe critical parameters. A key observation is that most of therock breakage occurs during the first stress-wave, and forhigher impact stresses above the dynamic confined indentationstrength, relatively little additional rock breakage seems tooccur.