Abstract
To achieve the secondary production in multistage fracturing wells of tight oil, milling tools are usually used to remove the multistage fracturing ball seats to achieve production with a large diameter in later. In this paper, first of all, the working mechanism of milling tools for multistage fracturing ball seats was studied and a mechanical analysis model of single abrasive grain was established. Then, an experimental system for milling tools was developed, and the experimental tests of the flat, the blade, and the slope milling tool were conducted in order. Besides, the morphology of chips and the surface morphology of the workpiece after the experiment were analyzed. Also, the working performance of milling tools was evaluated from the perspectives of working safety, working efficiency, and wear resistance of the milling tool. The results show that the torque of the milling tool increases nonlinearly with the increase in the cutting depth of the abrasive grain and increases linearly with the increase in the cutting width. Also, the chips are irregular particles and the size is mainly from 10 to 50 μm. So, the chips should be pumped up with a small pump pressure and a large displacement. Besides this, the cutting depths of the abrasive grains are from 216.20 to 635.47 μm and the bottom surface of the milling tool should be eccentric to avoid the zero point of cutting speed. Furthermore, the torque of the slope milling tool is 23.8% larger than that of the flat milling tool, which is also 30.4% smaller than that of the blade milling tool. Compared with the flat milling tool, the working efficiency of the blade milling tool improves by 79.9% and the slope milling tool improves by 111.1%. Also, the wear resistance of the blade milling tool decreases by 102.7%, while the slope milling tool declines by 32.6% when compared with the flat milling tool. Therefore, the slope milling tool has the characteristics of moderate torque, stable working conditions, the highest working efficiency, and fine wear resistance, which is preferably used to mill multistage fracturing ball seats. This study provides a theoretical basis and guidance for milling multistage fracturing ball seats on-site and realizing production with a large diameter in later stages of multistage fracturing wells.
Highlights
With the rapid development in exploration technology, unconventional oil and gas resources, such as tight gas, tight oil, and shale oil, have been successfully developed all over the world (Zhang et al 2016; Zhao and Hou 2017; Li et al.Edited by Xiu-Qiu Peng2019a, b; Qu et al 2019)
The material QT500-7 of multistage fracturing ball seats was milled by the experimental system for milling tools, and the morphology and microstructure of the chips from the experimental workpiece was analyzed
It shows that these abrasive grains of the milling tool are not on the same plane, which results in different stress conditions of each abrasive grain and different cutting depths
Summary
With the rapid development in exploration technology, unconventional oil and gas resources, such as tight gas, tight oil, and shale oil, have been successfully developed all over the world Che et al (2017) presented an experimental study of the cutter’s cutting performance and the rock’s failure behaviors on a newly developed linear rock cutting facility to investigate the influences of process parameters and the rock’s mechanical properties on chip formation and force responses. First of all, the mechanism analysis of the working process for cutting the metallic material of multistage fracturing ball seats by carbide abrasive grains on the milling tool was conducted, and the experimental equipment for different milling tools was developed. The experimental study on the working performance of different milling tools for multistage fracturing ball seat provides theoretical guidance for field construction, which is of great significance for removing wellbore blockages and achieving more production at the later stage of multistage fracturing wells
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