Experimental Study on the Characteristics of Mixed Tool Cutting Conglomerate with Stinger and Conventional PDC Cutter

Abstract

ABSTRACT The stinger cutter is a novel type of polycrystalline diamond compact cutter, which breaks rock by ploughing actions. Compared with the conventional cutter, the Stinger cutter can effectively reduce the fluctuation and size of cutting force and improve the rock breaking efficiency. However, the stinger cutter has lower bottom hole coverage and is often used in combination with the conventional cutter. In this paper, we conducted a series of mixed tool cutting conglomerate experiments with the conventional and stinger cutter. The influence of cutter spacing of stinger cutters and height difference between the stinger and conventional cutters on cutting force, the distribution characteristics of cuttings and cutting groove shape characteristics were investigated. The experimental results show that the mechanical specific energy (MSE) decreases first and then increases with the increase of cutter spacing. When the cutter spacing of stinger cutters is 18mm, the MSE reaches the minimum value. Furthermore, minimum value of MSE is also obtained when the cutter height difference is 0.5 mm. The average cutting force increases with the increase of cutter spacing. The results of this paper are expected to provide a theoretical basis for the design of hybrid PDC bit suitable for conglomerate formation drilling. INTRODUCTION Polycrystalline diamond compact (PDC) bits have been widely used in the petroleum industry for drilling soft and moderately firm forma-tions due to their high rate of penetration (ROP) and long duration life. However, when drilling in the conglomerate or soft-hard interbedded formations, the conventional PDC cutter has always suffered some dam-ages, such as chipping, fracturing and severe wearing et al, which would reduce ROP and increase drilling cost. As the world largest conglomerate oilfield, Xinjiang Mahu Oil field is rich in oil and gas resources (Wang et al.,2021). Mahu area is a large-scale reserve block explored and developed by Xinjiang Oilfield Company in recent two years, and has made continuous breakthroughs in oil and gas exploration of Triassic Baikouquan Formation. The proved oil geological reserves of Baikouquan reservoir in Ma 131 and Ma 18 well areas are more than 100 million tons. It is an ultra-deep and ultra-low permeability tight glutenite reservoir with complex lithology (Zhu et al.,2021). A total of 227 kinds of rocks have been identified, including 153 kinds of gravel, 58 kinds of sand and 16 kinds of mud (Hang et al.,2020; Jia et al.,2021). In addition, the reservoir has a large difference in particle size, diverse mineral structure, strong heterogeneity and poor drilling ability. Taking Ma 18 well block of Mahu oilfield as an example, the conventional PDC bit has serious wear and collapse, the average penetration rate is about 1 ∼ 3 m / h, the single footage of the bit is short. Furthermore, the damaged cutter are mainly concentrated on the shoulder of the bit with the largest linear velocity (Wang et al.,2020). Therefore, it is the primary goal to solve the problems of serious cutter collapse and difficult footage of PDC bit in drilling conglomerate formation.