Research and Application of ROP Enhancing Technology with Axial-Torsional Coupled Percussion in Tight Shale Drilling
Authors: Sun Zhaowei , Wu Xiaoguang , Wang Zikang , Huang Zhongwei , Mu Zongjie , Wang Xiangyang , Popov Yury 
Published: August 2024

ABSTRACT:
This paper focus on the rate of penetration (ROP) enhancing method in tight shale drilling operations. The axial-torsional coupled percussive drilling (ATCPD) is a promising technique for improving ROP in unconventional resource excavation. To determine the ROP enhancement performance of ATCPD, we conducted a series drilling tests on tight shale. Different drilling modes, i.e., rotary drilling, axial percussive drilling, and torsional percussive drilling, were compared with ATCPD, with respect to rock drilling capability. Results show that ROP and penetration depth are increased by 44.07%-119.88%, 39.64%-121.00%, respectively, under the ATCPD mode as compared to those under the other drilling modes. Rock breaking torque with minor fluctuation is generated by this coupled percussion method, which is conductive to reducing the stick-slip vibration of bit and increasing drilling efficiency. As a result, we developed a novel ATCPD impactor and the field test was conducted in horizontal well JHW61-31 of the Jimsar shale oil field. ATCPD technology shows the merits in enhancing ROP in downhole tight shale drilling operations, which are expected to provide guidance for ROP enhancing technology development for unconventional tight oil field.

1. INSTRUCTION
Unconventional drilling for tight shale by means of advanced rock-breaking method is an important global issue to optimal drilling efficiency and reduce well conduction cost. However, the rate of penetration (ROP) enhancement in unconventional drilling, e.g. long-horizontal well, are limited by stick-slip vibration and backing pressure phenomenon of the bit. Percussive drilling is an important technical method for increasing ROP as it meets the demand for efficient drilling in unconventional reservoir by using bit impact crushing on bottom rock. Since 1950s and 1960s, many of the researchers carried out experimental studies on the principle of percussive drilling and single well field tests, laying the research foundation for the formation of the theoretical system of percussive drilling (Fu et al., 2014). Maurer (1966) classified rock breaking under axial percussion into five stages. Hustrulid (1971), Chiang and Elias. (2000) explained the mechanism of percussive drilling bit-rock interface through a stress wave transfer model. The percussive drilling theory was further developed. France and Weber (2004) created a test platform for the resonance hammer drilling model and discovered that the dynamic behavior of the system would result in the transition from periodicity to chaos. Han et al. (2005) defined four basic processes of percussive drilling based on previous studies, as follows: The bit penetrate the formation by the percussion; The rock receives the percussive excitation of the drill bit, and stress propagates in the internal structure; The impact force reaches the strength of the rock structure, resulting in fracture and disintegration; The broken cuttings return to the annulus.