Quantitative Evaluation of Liquid Permeability in Cracked Oilwell Cement Sheaths

Abstract

Summary Understanding the consequences of cracking in oilwell cement sheaths is crucial to evaluating the leakage scenarios that can lead to sustained casing pressure. However, the theoretical equations commonly used to estimate flows and permeabilities tend to overestimate actual flow rates through cracks, primarily due to the omission of key factors such as crack tortuosity, surface roughness, and self-healing processes. Therefore, experimental methods are required to quantify the influence of these factors and define “empirical reduction factors.” Because each material exhibits its own unique effects on flow behavior, empirical reduction factors must be determined for each specific material, including oilwell cement. This paper presents a comprehensive procedure for systematically measuring flows, determining permeabilities, and evaluating self-healing processes in deliberately cracked cement specimens with controlled crack widths. The procedure considers pressure gradients and crack widths relevant to oilwell conditions aiming to contribute to the development of more accurate models and simulations for cemented oil wells.