The greatest limitation of the spallation process is its inability to
spall (or to consistently spall) many rocks encountered in petroleum d
rilling and mining operations. The New Mexico institute of Mining and
Technology has conducted a series of experiments to investigate the po
ssibility of expanding the use of the spallation process to the penetr
ation of rocks generally considered not to be spallable. The methods u
sed during this work were I) spalling at temperatures below that produ
ced by the stoichiometric burning of fuel oil and air, and 2) spalling
by alternately hearing and quenching the rock surfaces. No success wa
s experienced in spalling at the lower temperatures but initial rests
showed the alternate heating and chilling system to be successful part
icularly in penetrating travertine limestone. However, continued testi
ng indicated that, unless the rocks are extremely uniform in compositi
on, spalling will result in highly irregular holes or holes that canno
t be directionally controlled.