Usually, a drilling engineering is complex and systematic. During drilling complex stratum, in addition to
excellent drilling fluid, drilling tools can select and use semi-core tube, imported high quality clamp spring and
spring seat; drill bit select and adopt 12-14 degree diamonds, in consideration of rock’s high drillablity and reducing
fragmentation volume of rock, the drill bit’s diamond use small particle size of diamonds. And to reduce core
shaken and broken, it is necessary to use drill bit with ladder matrix face; to reduce core wear by the drill bit, the
length of bit inner gage can be decreased; to avoid core erosion by mud flow, bottom spray bits should be used. On
occasion, according to mud flushing requirement, the outer diameter of bit should be increased.
Drilling operations should be carried out according to the following three measures, only through cooperating
together, high drilling efficiency and satisfactory construction results can be gained.
(1)Three of low drilling parameters: low rotate speed, low weight on bit, low pump output volume. Low rotate
speed and weight on bit is mainly in favour of reducing vibration. Low pump output volume need to be calculated
using plastic viscosity of mud and diameter and drilling tools, in order to avoid turbulent flow erosion of hole’s wall.
(2) If using bottom jet drill bit, the clearance of spring seat and inner matrix of drilling bit should be adjusted to
near zero.
(3) For completely loose, fine particle layer, to do appropriate dry drilling an extruding can ensure cores do not
fall off, force when a roundtrip drilling is over, sometime it is necessary to control roundtrip drilling footage.