Experimental study on the thermal characteristics of dry drilling of diamond coring bits

Abstract:

Dry drilling has little impact on the environment. In the absence of cooling medium， it can effectively solve the problem of borehole coring when drilling some water or drilling fluid reacts or produces new pollution， so this method is one of the important means of exoplanets sampling. However， exoplanets object drill bits were mostly alloy drill bits， which had certain limitations for drilling into hard rock formations. Diamond drilling is a relatively advanced rotary drilling technology， which is widely used in oil and gas exploration and geological exploration， and is a powerful tool for drilling hard rock formations. In this paper， the dry drilling tests of diamond drill bits were carried out for hard granite， and the influences of drilling parameters and bit types on the thermal characteristics during the drilling process is discussed. The results show that： （1）The heating rate of PDC drill bits is lower than that of conventional diamond coring bits， which is about 1/2 of that of impregnated diamond bits； （2）PDC coring bits can be a way for the dry drilling of granite under suitable process parameters；（3）The rotary speed has a great influence on the temperature rise of diamond bits in dry drilling， and it shows a nonlinear growth trend；（4）The cooling curves of drill bits in air show an exponential downward trend. During the cooling from 300°C to 100°C， the cooling rate≥60°C/min. The research results can provide a basis for the scientific design and rational use of dry drilling bits.

Key words:dry drilling;diamond drill bit;surface-set drill bit;impregnated drill bit;PDC drill bit;temperature rising rate;exoplanets sampling