The current study shows that heating a cased borehole in low-permeability shale rock can induce plastic deformation, leading to the closure of the casing annulus and decreasing annulus connectivity. The thermally induced borehole closure is interesting for the field operation of plug and abandonment (P&A), as it potentially saves operation cost and time by avoiding cutting casing and cementing. Lab experiments and numerical simulations are implemented to investigate the thermally induced borehole closure. Pierre shale and a field shale are tested. The lab experiments are performed by heating the borehole wall in a 10-cm-OD hollow cylinder specimen. Here, a novel experimental setup is applied, allowing for measuring temperature and pore pressure at different radii inside the specimen. Both the experimental data and the post-test CT images of the rock samples indicate the rock failure by borehole heating, and under certain conditions, heating results in an annulus closure. The decrease of hydraulic conductivity through the casing annulus is observed, but this decrease is not enough to form the hydraulic-sealed annulus barrier, based on the results obtained so far. Lab-scale finite-element simulations aim to match the lab results to obtain poro-elastoplastic parameters. Then the field-scale simulations assess the formation of shale barriers by heating in field scenarios. Overall, (i) the lab experiments show that heating a borehole can increase the pore pressure in shale and hence induce rock failure; (ii) the numerical simulations match the experimental results reasonably well and indicate that the heating-induced borehole closure can sufficiently seal the casing annulus in the field-scale simulation.

中文翻译：

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加热会导致钻孔封闭吗？

目前的研究表明，加热低渗透页岩中的套管钻孔会引起塑性变形，导致套管环空闭合并降低环空连通性。热致钻孔闭合对于堵塞和废弃 (P&A) 的现场操作很有意义，因为它通过避免切割套管和固井来潜在地节省操作成本和时间。实施实验室实验和数值模拟以研究热致钻孔闭合。测试了皮埃尔页岩和油田页岩。实验室实验是通过加热 10 厘米外径空心圆柱体试样中的钻孔壁来进行的。在这里，应用了一种新颖的实验装置，可以测量试样内部不同半径的温度和孔隙压力。岩石样品的实验数据和测试后的 CT 图像都表明钻孔加热导致岩石破坏，并且在某些条件下，加热会导致环空闭合。观察到通过套管环空的水力传导率降低，但根据目前获得的结果，这种降低不足以形成液压密封的环空屏障。实验室规模的有限元模拟旨在匹配实验室结果以获得多孔弹塑性参数。然后，现场规模模拟评估了在现场场景中通过加热形成的页岩屏障。总体而言，(i) 实验室实验表明，加热钻孔会增加页岩中的孔隙压力，从而导致岩石破裂；