AN EXPERIMENTAL STUDY ON THE EFFECT OF ADDITIVES ON CASING-CEMENT BONDING STRENGTH

Abstract

Well integrity is a critical concern in the petroleum industry, as compromised integrity can lead to severe consequences, including loss of life, equipment failure, hydrocarbon leakage, and environmental pollution. Studies reveal that a significant percentage of oil and gas wells in the United States exhibit sustained casing pressure (SCP) or casing vent flow (CVF) during their operational lifespan, with occurrences ranging from 0.3% to 26.5% in key states like Pennsylvania, Colorado, and New Mexico. These findings highlight the importance of effective cementing practices to ensure well safety, prevent fluid migration, and maintain zonal isolation throughout a well’s lifecycle. Cementing operations play a pivotal role in securing wellbore integrity by providing structural support and preventing the migration of formation fluids. However, the complex nature of wellbore cementing necessitates a deeper understanding of the factors influencing bonding strength and compressive strength performance under various environmental and operational conditions.This thesis presents an experimental study investigating the effect of various additives on the bonding strength between casing and cement, using API Class G cement as the base material. The study explores six additives: microblock, silica flour, fly ash, iron powder, iron oxide, and gilsonite, each incorporated at specified percentages. Cement samples were cured for both 1 and 3 days at room temperature and at elevated temperatures of 75°C, reflecting real-world operational scenarios. The research evaluates the interplay between Unconfined Compressive Strength (UCS) and Interfacial Bonding Shear Strength (IBSS), two critical metrics that govern cement’s mechanical behavior and its ability to maintain bonding integrity with casing. UCS tests were performed on cubic cement molds to assess the compressive strength, while IBSS measurements were carried out to determine the bonding strength at the cement-casing interface under various curing conditions and durations. The results of this study provide insights into the additive-specific trade-offs between compressive strength and bonding performance. Some additives, such as fly ash, demonstrated superior UCS but at the expense of reduced IBSS, suggesting strong structural support but weaker bonding under certain conditions. In contrast, additives like microblock offered a balanced performance between UCS and IBSS, highlighting their potential for maintaining both strength and bonding integrity. The study underscores that high compressive strength does not always translate to strong bonding, necessitating careful additive selection to meet the specific requirements of wellbore operations. Additionally, the research explores the post-debonding characteristics of each cement recipe, providing valuable information on displacement behavior and force loss after debonding.