Numerical simulation of thermal consolidation induced by a heat source in a clayey rock formation towards well plug and abandonment

Resumo

At the end of a well’s lifespan, proper plug and abandonment (P&&A) procedures are crucial to preventenvironmental contamination due to fluid leakage. To this end, effective sealing barriers must beestablished. The conventional method for the creation of a barrier is the injection of cement forming aplug. However, under specific conditions, natural rock formations such as clay-rich sedimentary rocks(shales) and salt rocks can close around the casing and form an impermeable seal, potentially serving asan effective barrier. Some clayey rocks (shales) are strong candidates due to their low permeability,ductility, creep behavior and self-healing capacity. To accelerate the closure of the barrier, certainactivation techniques, including pressure reduction, heating, and chemical stimulation can be adopted.There are studies that address the formation of barriers by considering creep properties as the main andsole mechanism for rock movement over time through creep constitutive models. Another appropriateapproach for clayey rocks is to consider the mobility generated by thermal consolidation, in whichthermal stimulation causing well heating leads to deformation both in the solid skeleton of the rock andin the fluids within its pores.This study aims to improve the modeling of thermal-consolidation in shale formations considering theuse of a heat source inside the well. This has been achieved, firstly, by replicating an analytical solutionavailable in the literature for displacement, pore-pressure and temperature changes caused by a pointheat source inside a clayey rock formation. Secondly, a corresponding finite element model was built inABAQUS to benchmark the analytical solution. Finally, an additional model of a well scenario with avolumetric equivalent heat source was simulated.Among several relevant parameters for studying the model&s sensitivity considering their expectedvariability in the field and their impact on material behavior in the context of Pamp;&A, the first version ofthis study selected permeability to be varied between 10⁻¹⁷ and 10⁻²¹ m² (about 10 -2 and 10 -6 mD). It wasobserved that the lower the permeability, the higher the pore pressure increase. Additionally, the timerequired to reach the maximum pore pressure value also increases as permeability decreases. Thedeveloped model provides insights into the formation’s integrity and deformation, contributing to amore reliable prediction of the sealing performance during well P&&A.