A Decade of Challenges and Successes in Well Construction at Majnoon Oil Field – Southern Iraq

Abstract Majnoon Oil Field is situated in the southern region of Iraq and stands as one of the world's most prolific oil reserves. Its strategic importance lies in its contribution to meeting global energy demands. However, this field, once a battlefield, presents unique challenges and remarkable successes. Over 70 wells have been meticulously drilled and brought into production. Upon completion, the operator faces the critical task of ensuring well integrity, which hinges on the cement's performance against each section of the casing under scrutiny. There are two types of well designs with an S-shaped trajectory: slim design and fat design (also known as big-bore). These well designs traverse fourteen separate hydrocarbon-bearing zones, primarily consisting of carbonate and clastic reservoirs with a host of challenges: Lost Circulation: Caverns, vugs, and large fractures,Cement Level Drop: In the intermediate section,Differential Sticking: The UER formation poses challenges,Washout Sections: Several washout sections impact the efficiency of cement displacement.Sustained Casing Pressure (SCP): Gas influx from the Ghar formationShale Instability: The Shiranish formation Considering the challenges, multiple solutions were engineered from the initial design of cement slurries to the completion of the cement job. To combat lost circulation, a thixotropic and acid-soluble cement was tailored to remedy losses and prevent accidental sidetracking. The fluid parameters of the cement were optimized to minimize fluid loss (less than 10cc) in high-permeable zones. Additionally, shale stabilizers and anti-shrinkage additives were included to enhance the cement properties. A novel spacer system was introduced, enhancing displacement efficiency, and providing competent isolation in the intermediate sections. Furthermore, the integration of an expandable liner hanger with carefully tuned fluid properties in the production sections, along with computer-aided simulation for analyzing torque and drag limits, ensures the highest cement coverage around the liner. This approach aims to achieve a competent cement sheath and meet the criteria for zonal isolation acceptance.