Advanced Lightweight Thixotropic Cement Slurry (ALWTC) First Time Worldwide Application in a Primary Cementing Across Natural Fractured Limestones

Abstract

Lost circulation while cementing intermediate sections across the Umm er Radhuma (UER) Formation, a naturally fractured limestone formation in UAE, is technically challenging and has financial impacts, including nonproductive time and remedial operational expenses. All fields in UAE encounter severe lost circulation while drilling UER Formation and cementing this section using lightweight slurries to isolate the zone and mitigate losses is a paramount task which requires several post-top jobs to provide zonal isolation of the casing. ALWTC technology was developed in the UAE as a lost circulation solution to reduce and mitigate losses across vugular and naturally fractured formations during drilling. But wells having the same or more complex loss scenarios during primary cementing where standard lost circulation materials and conventional lightweight slurries are used, have limitations. The ALWTC solution was evaluated and modified to be applied with the same lightweight technology currently used in primary cementing but enhanced with a specific thixotropic agent. An identified risk is the fast gel development (thixotropic behavior), a high risk that can compromise the cement placement in primary cementing, especially in jobs where large volumes are used. Smooth execution with well-coordinated events and best practices were deployed to ensure excellent execution without any health, safety, and environment or service quality incidents. During the first job, partial to full returns were observed, achieving cement to surface, which was our target. On one top job, only 5 to 6 bbl. of slurry were pumped, compared to 300 to 400 bbl. before. This saved 3 days of rig time and USD 25,000 of additional cost and services for the operator; additional jobs performed with similar performance. It was concluded that ALWTC is possible and suitable for primary cementing jobs across vugular and naturally fractured limestone formations. Cement evaluations also showed remarkable results across the UER and Simsima formations, compared to the normal slurry design that was being used before. ALWTC is a technology developed locally in the UAE for UAE cementing challenges across vugular and/or naturally fractured limestone formations. This technology has immense potential in the Middle East where losses across limestone formations are some of the biggest challenges and cementing to provide the required zonal isolation is a must.