With the continuous development of social science, various new energy sources are emerging. But for a long time, oil and natural gas are still the main energy sources of human society[1]. With the development of oil and gas to deeper layers, the number of deep wells, ultra-deep wells, complex structure wells and special craft wells is increasing[2]. Therefore, the stratum structure encountered during the drilling process is becoming more and more complex, and the difficulty of completion is increasing day by day. In complex strata which is high-pressure layers or lost layers, the traditional methods have little effect on the leakage and collapse accidents. However, the advantages of using SET technology to repair the local corrosion, perforation of the casing, and blocking the lost layer are obvious[3].
In the 1990s, SET technology gradually emerged. It is a technology that uses the cold plastic forming characteristics of metals and relies on external force to expand the inner diameter to the required value. After decades of development, it has achieved tremendous development in plugging, repairing casing, and optimizing the wellbore structure[4]. In recent years, a large number of scholars and engineers have conducted research on many aspects of the technologyThey mainly focused on the selection of materials, the optimization of the expansion cone, the collapse after expansion, the expansion force, etc., and achieved remarkable achievements[5–14]. In general, there are few studies on open hole wells, and these studies are mainly on casing damaged wells[15].
Due to the essential difference between open hole wells and casing wells, there are huge difference between the two in the process of applying SET. Although Halliburton, Weatherford and Baker Hughes and other companies have successfully applied some cases in Enventure,but due to the complexity of open hole wells,they still have broad research prospects.
In this paper, for the SET (152 mm × 8 mm) and 61/2 open-hole wells, it study the applicability criteria of the borehole and the influence of the expansion cone structure on the forming of SET. Based on experimental data,this paper established a dynamic three-dimensional model which considers friction and contact. This paper studies the influence of borehole size on the stress change and driving force during SET expansion.The influence of SET's residual stress and sealing capacity after expansion was also studied.In addition, the sensitive parameters of the expansion cone are analyzed.