A Novel Axial-Torsional Isofrequency Impactor Improved Field Average ROP for Tight Shale Drilling
Authors: Sun Zhaowei , Mu Zongjie , Xi Wujun , Wang Lei , Wu Jiarui , Wu Xiaoguang , Huang Zhongwei 
Published: February 2025

Accessing petroleum and natural gas from deep unconventional reservoirs plays an important role in improving worldwide energy supply. However, directional well drilling into the unconventional reservoirs, especially tight shale, is accompanied by the higher friction and stick-slip vibration at the bit, which limits the rate of penetration (ROP) enhancement and thereby increasing the operation costs. The introduction of a novel axial-torsional isofrequency impact drilling (ATIID) technology, characterized by its joint action of rotary percussion drilling (RPD) and torsional oscillation impact (TOI) methodologies, has been instrumental in enhancing the on-bottom ROP in unconventional well drilling scenarios.

To effectively integrate this technology, an axial-torsional isofrequency impactor driven by the pulsed jet was developed, which involved the all-metal construction and be adept at penetrating into rocks within high temperature (&gt;300°C) and high pressure (&gt;180MPa) conditions. Moreover, the hydraulic hammers of this impactor could make the bottom bit-rock interaction process be subjected to the isofrequency impact loads in axial and torsional directions. For realizing the desired outcomes, a series of tests on drilling performance with ATIID technology were conducted. A comprehensive evaluation was undertaken to gauge the efficacy of the isofrequency impactor. This involved a real-scale impact drilling experiments on tight shale outcropped from Jimsar, Xinjiang, China, as well as a downhole field test in JHW wells factory at depth of 3966.14-5841.29m. Some engineering parameters, e.g., ROP, drilled depth, torque on bit and hook load, were employed as the critical indexes to assess the drilling capacity with ATIID technology.

The findings were promising. A significant observation from laboratory was that a growth of 11.4%-48.2% in average ROP was captured with isofrequency impactor as compared to the other drilling mode, i.e., rotary drilling, RPD, TOI drilling. Furthermore, the torque on bit showed a remarkable decline by employing the ATIID technology, which possessed with the minor fluctuation. This would be conductive to reduce the stick-slip vibration at the bit during drilling process. Downhole tests of the isofrequency impactor with 156.0-176.5h drilling period were conducted in cluster horizontal wells JHW6113 and JHW6114 of Jimsar shale oil field. The average ROP and drilled depth by the bit are 11.065m/h, 1832.5m, respectively. There was a marked improvement in the field ROP average when juxtaposed with the data of the offset wells JHW05831 and JHW05833 with rotary drilling technology, witnessing an increase of 12.5%-45.0%. This was in alignment with the ROP enhancement performance observed from laboratory. Another overarching insight was that the greater hook load and lower mechanical specific energy were obtained in our field test wells. Hence, this pioneering technology played a pivotal role in reducing friction and improving drilling efficiency, which is expected to pave the way for enhancing drilling capacity in unconventional oil excavation.