Characteristic Analysis of Flow Field and Cuttings Removal of Straight-Swirling Integrated Jet During Tubing Cleaning

Shale gas is a significant alternative resource to conventional gas. During the development of shale gas in Changning, the energy attenuation of the extracted shale gas leads to insufficient water discharge from the stratum. This ultimately leads to the gradual accumulation of sand from the stratum, which then clogs up both the tubing and casing over time, resulting in reduced or even halted productivity of horizontal wells. To improve the productivity of aging shale gas wells in Changning, a straight-swirling integrated jet (SSIJ) tool is designed. Computational fluid dynamics (CFD) method is utilized to investigate the velocity field and cuttings removal characteristics of the SSIJ tool, with comparisons made against the convergent-divergent jet (CDJ) tool. The findings suggest that: 1) Compared to the CDJ tool, the SSIJ tool's jet exhibits higher axial and tangential velocity extremes, stronger cavitation initiation capacity and cavitation erosion effect. 2) The SSIJ tool shows a greater cuttings-carrying capacity. However, this ability decreases with larger cuttings sizes, and increasing the viscosity of the liquid can greatly enhance the tool's cuttings-carrying efficiency. This research offers valuable insights for the design and optimization of downhole tubing and casing cleaning tools. 1. INTRODUCTION Shale gas production has experienced a significant increase in the last ten years, largely due to advancements in horizontal drilling and hydraulic fracturing technologies(Dong et al., 2024). Shale gas accounts for a substantial share of China's natural gas production, with an estimated annual production of 30×109 m3 by 2025. The Changning shale gas field, situated at the southwest edge of the southern Sichuan Basin, has proven reserves amounting to 440×109 m3. In 2020, it reached a production capacity of 5×109 m3/a for shale gas (Ailin et al., 2020; Ma, 2021; Zou et al., 2016). However, while extracting shale gas in Changning, sedimentation may occur at the bottom of the well (Liu, 2019). When fracturing bridge blockage are milled, this can result in the accumulation of cuttings at the bottom of the well, showed in Fig.1. This situation has the potential to cause tubing and casing blockage, leading to decreased production or even complete shutdown of the gas well. Therefore, it is important to promptly remove the sand buildup in the tubing and casing during production.