Can Heating Induce Borehole Closure?
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ORIGINAL PAPER
Can Heating Induce Borehole Closure? Xiyang Xie1 · Andreas Bauer3 · Jørn F. Stenebråten1 · Sigurd Bakheim1 · Alexandre Lavrov1 · Erling Fjær1,2 · Tron G. Kristiansen3 Received: 19 August 2019 / Accepted: 25 August 2020 © The Author(s) 2020
Abstract 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. Keywords Rock failure · Borehole closure · Plug and abandonment (P&A) · Thermal pressurization · Thermo-poroelastoplasticity · Shale rock
1 Introduction In petroleum engineering, plug and abandonment (P&A), as the last operation of a well, aims to isolate the wellbore permanently. Unsuccessful implementation of P&A may cause fluid leakage, which may escalate to an environmental crisis without proper countermeasures. A traditional P&A is challenging for its capital intensity and time consumption since the casing is to be cut and pulled and the cement plug is to be set across the borehole as a permanent barrier. Cement bond logging (CBL) indicates that the deformation of soft rock, shale or mudstone, can form a permanent barrier and * Xiyang Xie [email protected]; [email protected] 1
SINTEF Industry, Trondheim, Norway
2
Norwegian University of Science and Technology, Trondheim, Norway
3
Aker BP, Trondheim, Norway
isolate casing annulus hydraulically (Williams et al. 2009). If an effective barrier exists in the casing annulus, the P
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