A Holistic Approach to Achieve a Successful Liner Cement in Gas Bearing Early Cretaceous Formations in South Iraq

Abstract

Obtaining a good cement bond is a continuous challenge, especially if the well being cemented is a high-pressure exploration gas well, and it is one of the very few gas wells drilled in the country. Poor adherence to the casing and the formation, channeling due to gas migration and microannulus are some of the main risks that could result in a poor cement job. Achieving zonal isolation and a good cement sheath protecting the 7-inch liner turned out to be an objective missed for the first two wells of the campaign, compromising the long-term supply of gas to the South region of Iraq. To solve the situation, it was necessary to implement something more than a mere cementing additive; it required a multifactor analysis with an experienced multidisciplinary team. A set of good drilling practices, proper drilling fluids, proven cementing techniques and new technology slurries were combined to improve the precious results. To obtain a sound cement quality log, the well engineering department teamed up with cementing experts, drilling fluids specialists, liner hanger company representatives and operations personnel. With effective meetings, proper risk assessment and visible leadership, the team generated a series of initiatives that included: drilling hydraulics optimization, mud weight selection, drilling practices re-definition, liner hanger procedure adjustments and cementing slurry design. As a result, the borehole caliper was significantly improved, the liner hanger allowed full rotation while cementing, cement returns were observed above the liner top after the job, no evidence of gas migration was observed and the CBL-VDL-USIT log showed a remarkable improvement in the two jobs where the engineering initiatives were applied. Being able to achieve a positive proof on cementing integrity, one of the most important acceptance criteria for the National Oil Company (NOC) regulation entity, enhanced the trust on the technical experts of the engineering team to deliver solutions of complex problems.