Can Heating Induce Borehole Closure?

Xiyang Xie,Sigurd Bakheim,Tron G Kristiansen,Erling Fjær,Jørn F Stenebråten,Andreas Bauer,Alexandre Lavrov

doi:10.1007/s00603-020-02238-5

Xiyang Xie, Sigurd Bakheim + Show 5 more

Open Access

https://doi.org/10.1007/s00603-020-02238-5

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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.

Highlights

In petroleum engineering, plug and abandonment (P&A), as the last operation of a well, aims to isolate the wellbore permanently
It turned out that no hydraulic barrier was formed by borehole heating despite the evidence for thermally induced rock failure; the annulus permeability measurements did not indicate any measurable reduction in permeability throughout the test
The current study mainly focuses on how the thermal pressurization can induce borehole failure and trigger the borehole closure

Summary

Introduction

Plug and abandonment (P&A), as the last operation of a well, aims to isolate the wellbore permanently. 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. If an effective barrier exists in the casing annulus, the P&A standard, for example, NORSOK D-010 (Norsok 2013), only requires setting a cement plug inside the casing without cutting and pulling, which can save operation cost and time. This study aims to reveal whether heating a cased borehole can induce such an effective barrier in the casing annulus

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