Abstract: The main lithology of the igneous rocks under the Permian in Malang sag is basalt with the characteristics of strong abrasion resistance, low drillability and low drilling rate. This paper tests the drillability of the cores from the field, develops rock drillability model, computes the drillability grade of cone bit and PDC bit and optimizes the bit according to the bit structural features. The results indicate that in light of the basalt strata under Permian, using recommended bit has increased the mechanical drilling rate by 50% compared with other bits, shortened the drilling cycle, and attained the aim of excellent and fast drilling.

Key words: Santanghu basin, Malang sag, basalt, drillability, bit optimization