THM coupled analysis of cement sheath integrity considering well loading history

Abstract

The cement sheath is the heart of any oil or gas well for providing zonal isolation and well integrity during the life of a well. Loads induced by well construction operations and borehole pressure and temperature changes may lead to the ultimate failure of cement sheath. This paper quantifies the potential of cement failure under mechanically and thermally induced stress during the life-of-well using a coupled thermal–hydrological–mechanical (THM) modeling approach. A staged finite-element procedure is presented considering sequential stress and displacement development during each stage of the well life, including drilling, casing, cementing, completion, production, and injection. The staged model quantifies the stress states and state variables, e.g., plastic strain, damage, and debonding at cement/rock or cement/casing interface, in each well stage from simultaneous action of in-situ stress, pore pressure, temperature, casing pressure, and cement hardening/shrinkage. Thus, it eliminates the need to guess the initial stress and strain state before modeling a specific stage. Moreover, coupled THM capabilities of the model ensure the full consideration of the interaction between these influential factors.