A Proven Successful Case for Long-Term Zonal Isolation in a Water Injection Well Under Continuous High-Pressure Pumping Using Flexible Ultra-Lightweight Cement: A Case Study from Kurdistan, Northern Iraq

Abstract In the Khurmala field, Kurdistan, a challenging water injection well required the cementing of a 7″ liner while managing pre-existing formation losses. The primary objectives were to prevent further losses during cementing and ensure long-term zonal isolation, given the cement's continuous exposure to bottom-hole pressures of 3000 psi during water injectivity post-completion. A novel ultra-lightweight (ULW) flexible cement slurry with a density of 9.5 ppg was developed to maintain equivalent circulating density (ECD) below the fracture point. The slurry was designed to provide improved mechanical properties for sustained zonal isolation under high-pressure conditions. To meet the challenges of cementing a 7″ liner in the Khurmala field's loss-prone formation, a 9.5 ppg ULW flexible cement slurry was developed. The slurry was designed to maintain the ECD below the formation's fracture gradient, preventing losses. Mechanical properties, including Young's modulus and Poisson's ratio, were optimized using Cement Stress Analysis software and extensive lab working to ensure flexibility, minimize micro-annuli, and withstand high injection pressures. The slurry blend was engineered for homogenous particle distribution to achieve a compressive strength of 2000 psi, ensuring consistent mechanical performance. A spacer with bridging LCM was also designed to mitigate losses. Extensive laboratory testing was performed under simulated downhole conditions, confirming its ability to maintain zonal isolation and structural integrity under continuous high-pressure exposure. The cement mixing and pumping operations were carried out as planned, with no losses encountered during the job. Post-job cement bond log (CBL) results demonstrated exceptional zonal isolation and bond quality. The cement successfully maintained its integrity under continuous exposure of 3000 psi, confirming the effectiveness of the design and the field application of the ULW flexible cement slurry. The Ultra-light weight slurry and improved mechanical properties ensured safe cement placement without inducing losses and ultimately provided long-term well integrity. The key novelty of this work is the development and field application of a 9.5 ppg ultra-lightweight flexible cement slurry designed for long-term zonal isolation in water injection wells. The slurry's mechanical properties were tailored to withstand high-pressure conditions while ensuring long-term durability over extended time, even when exposed to compression, traction, and potential creation of micro-annuli. The approach provided an innovative solution to the challenges of cementing in weak formation, delivering both immediate operational success and sustained well integrity.