Tailored Dependable Barrier Enables Operator to Flawlessly Complete True One Trip Ultra Slender Deepwater Well
Authors: Koch Ferreira Flávia , Fiorotti João , Brunherotto Leonardo , Cunha Marcelo , Paredes Jose Luis , Piedade Thiago , Peralta Rafael , Filho Geraldo 
Published: February 2022

Abstract
Drilling time and resources for casing and cementing the wellbore represent a significant cost in oil well construction. Therefore, slender wells have been targeted to be constructed with less phases and higher efficiency reducing costs by half. The objective of this paper is to present how a fit-for-purpose foam cement system contributed to delivering a dependable barrier for a True-One-Trip Ultra-Slender well, where a single barrier shall provide wellbore mechanical integrity and competent isolation from the reservoir to seabed. The methodology for this foam cement job involved, initially, hydraulic and thermal modeling, followed by lab testing, such as thickening time, compressive strength, and foam stability tests. The pumping schedule included 4 different tailored systems that were pumped to maximize probability of returns at the mudline. By using the constant-nitrogen-rate technique, the foam quality was optimized to help ensure slurry and foam stability at downhole conditions. Proper energized fluid selection and casing centralization were placed to guarantee a slurry system application with improved mud removal capacity and optimized standoff to avoid slurry contamination attributed to channeling.
During execution, no issues were observed until reaching the final depth. The open hole diameter was estimated based on volumetric determination by pumping a tracer and a scavenger slurry, to be visualized at the mudline. Based on that information, further volumes were fine tuned and pumped to ensure appropriated foam cement quality and density along the wellbore section. As one of the major objectives of the job, returns could be achieved at mudline and the final differential pressure was higher than expected, indicating a cement sheath in the annulus had extensive length. Cement job evaluation was performed after the job using sonic and ultrasonic tools to confirm the quality of the barrier placed in the annulus. Additionally, an advanced Cement Evaluation was executed and showed excellent isolation for the slurries placed in the well. The results from this unprecedented operation in Brazil have proven the features and benefits of using foamed cement in ultra-slender wells for specific challenges, such as: requirement of returns at mudline, application in long length zonal isolation operations, and the necessity of high-strength low-density solutions near the mudline. After this job, similar wells have been constructed in the same area, and the applied technique has continuously proven to be a dependable and sound solution for similar scenarios.
Based on the successful case history presented in this paper, the application of foam cement technology in ultra-slender wells represent an innovative and dependable solution for the actual and future high-efficiency wellbore geometries. By reducing the risks of having a single cement sheath in the entire well, it enables the oilwell industry to reduce time and risks during wellbore construction and helps enhance its productivity.