Experimental and Numerical Investigations of Cement Bonding Properties at Elevated Temperatures—The Effect of Sample Cooling

Abstract

Well integrity is currently defined through the concept of well barriers, in which one or more barriers are used to prevent unwanted fluid flow. Many papers have highlighted that the casing–cement interfacial bonding is critical for well integrity, but many discrepancies between laboratory experiments and field data have been noticed. The use of finite element analysis is now established as an alternative to complex in situ tests, but these simulations are sensitive to the input parameters, which results in many discrepancies across published works. Currently, the cohesive zone material (CZM) method is considered to offer good results if the correct parameters are selected or experimentally determined. The novelty of this paper lies in the development of a better workflow that enables the simulation of three processes that are acting on the laboratory-scale casing–cement system: temperature changes, debonding, and post-debonding behavior. The aim of this paper is to fully understand the debonding process within laboratory-scale samples, and thus to eventually enable upscaling in the near future. The paper presents a new workflow generated using FEM that allows us to determine the contact stresses at the casing–cement interface during temperature changes at the moment of debonding and post-debonding. The results presented within this paper show that temperature samples tested according to the push-down setup will provide similar interfacial bonding shear strength values; however, post-debonding, there is a remaining frictional force slightly higher than that of the room-temperature samples. In this case, the results are within a 5% error of the average field data, which is slightly higher than in our previous experiments, where only room temperature data were considered. A major outcome of our paper is the demonstration of the existence of friction forces after debonding, which are a result of radial stresses induced during the debonding process.