Abstract
Several field observations by cement bond logs (a technique used to detect substance behind casing) indicate progressive borehole closure in soft rock such as shale. This study considers the problem of progressive borehole closure in an elasto-viscoplastic rock mass. The behavior of the rock mass is represented by a Bingham constitutive model. The borehole closure problem is solved using two numerical codes: an in-house (problem specific) MATLAB code and a commercial code (FLAC) with user-defined constitutive model capabilities. The MATLAB results are used as semi-analytical reference solution to verify the proper implementation of the Bingham constitutive model in FLAC. The simulation results using the two approaches are compared successfully in the paper. The Bingham constitutive model has application in formation sealing in ductile rocks in general, and in the Plug and Abandonment (P&A) operation as a particular application. Additional model functionality can be introduced in the FLAC simulations via the user-defined model, and more realistic scenarios can be simulated in future work.