Temperature and fluid affect the rock properties is an unavoidable problem in drilling engineering. The objective of this study is to separate the effect of temperature and fluid medium on hard sandstone drilling parameters, which include the weight of bit (WOB), torque and mechanical specific energy (MSE). A series of rock drilling experiments was carried out. The results was very interesting that liquid nitrogen (LN2) cause the sandstone more difficult to drill than air and water, which is contrary to the view that the differential temperature between low temperature fluid and the rock enhance the rock failure. LN2 caused the average MSE to be increased by about 20.64%, water caused the average MSE to be reduced by about 42.66%, compared with dry drilling. From the results, it can be concluded that the temperature has no significant effect on hard sandstone drilling parameters and fluid medium type affect the parameters remarkably in the range of 20-300°C. This phenomena maybe attribute to that water caused the surface free energy of new cuttings surface reduced and LN2 caused the surface energy increased compared with air.

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