New PDC Bit with Hollowed Cutters: with Increased ROP and Longer Service Life

Abstract

A novel design of PDC bit with hollowed cutters is presented that uses the principle of hydraulic lubricating and water jetting mechanism to improve ROP. Engineering results show its advantage compared to solid fixed cutters which are commonly used in today’s drilling industry. The structure of the new PDC bit is as follows: each cutter contains a specific fluid channel, which is tailor made; the bit body contains many fluid channels; Compared with the existing conventional PDC bit, the main distinctive features are: the cutters are hollowed, each cutter contains a fluid channel in the centre of itself; and the bit body has fluid passages which are communicating with each hollowed cutter, allowing the drilling fluid flows from the inside of the bit to the outside of each cutter. The failures of a PDC bit are mostly due to premature wear or cracks of compound cutters; the wear or cracks are due to mechanical and thermal effects. To improve the service life of cutters can effectively increase the life of the drill bit. According to thermal stress analysis, the position where the frictional heat concentrated is in the centre of the cutter, which will result in the generation and expansion of thermal cracks, which in turn leads to failure of the cutter and loss of ROP. Therefore, the cutter with fluid passage will improve the way of thermal concentration and expansion, thereby prolonging the life of the drill bit, reducing the number of trips, improving single run drilling footage, therefore the drilling efficiency is increased. During the drilling operation, the rock cuttings cannot flow out timely, and may accumulate on the drill bit, which is commonly referred to as mud balling. The presence of mud balling will reduce the cutting capability of the drill bit and decrease the ROP. The new PDC bit with hollowed cutters has self-cooling and self-cleaning functions to mitigate the thermal effect, while the pressurized flow from the micro-hole of the cutter has the effect of water jetting, which in turn increases the ROP. The novelty of the new PDC bit is in the capability to solve the issues of low ROP and short service life of today’s tough drilling conditions, to meet the requirement of a single trip to complete the total depth.