Experimental Study of Conglomerate-Breaking Characteristics of Axe-Shaped PDC Cutter

ABSTRACT: Conventional PDC cutters are prone to get broken when drilling through conglomerate formations and soft-hard interbedded heterogeneous layers, leading to serious fatigue wear, short bit life, and small bit footage. Compared to the conventional PDC cutter, axe-shaped PDC cutter can dig out gravel and pebbles through crushing and shearing, which significantly reduces energy consumption for rock-breaking. Thus, this paper proposed to study effects of axe-shaped PDC cutter cutting parameters on rock-breaking characteristics of conglomerates. Using PDC cutter cutting equipment, the research quantitatively revealed the effects of cutting depth, back rake angle, and cutting speed on the cutting force, cutting size distribution, and the groove morphological characteristics of axe-shaped PDC cutter. Also, mechanical modeling was used to describe the mechanical dynamics of the axeshaped PDC cutter in the cutting process. Then, an axe-shaped PDC bit was designed and manufactured, for the purpose of field application. According to the testing data, the cutting force of the axe-shaped PDC cutter increases with increasing back rake angle and increasing cutting depth. The larger the cutting angle, the more complicated the relationship between the cutting force amplitude and the cutting depth, from linear relation to quadratic and cubic functions. Meanwhile, the mechanical specific energy for rock-breaking remains at a small level in a cutting angle range of 10 to 20 °. Compared with the conventional PDC bit, the bit footage of PDC bit with ASP-cutter increased by 399m and the average ROP increased by 24.22%. These findings are expected to provide theoretical guidance on the rock-breaking characteristics of axe-shaped PDC cutter, especially for the drilling process in conglomerate formation. INTRODUCTION Since PDC bit was introduced into the oil and gas drilling industries in 1970s by GENERAL Electric of the United States, it has been widely used in drilling soft to medium-hard formations with high rock-breaking efficiency and long service life (Yang and Guo 2018). However, in the drilling process of conglomerates and other heterogeneous layers (e.g. soft-hard interbedded layers), conventional PDC cutters are easily to get broken and prone to crack, leading to premature failure of drill bit, low drilling efficiency and high drilling cost (He et al. 2021; Zeng et al. 2021).