Cement isolation is considered by some a critical component of effective well completions in horizontal, multi-stage, hydraulically stimulated oil and gas wells. Virtually every new unconventional well includes multiple cement jobs which cost tens to hundreds of thousands of dollars each. As cluster spacing gets tighter, the importance of high-quality cementing becomes even more pronounced, or does it? This paper explores the various diagnostic techniques used to measure cement isolation, including ultrasonic imaging, optical fiber, radioactive tracer, and downhole pressure gauges on sleeve completion assemblies. The paper ties these diagnostic techniques back to well performance for both new completions and refracs.
The study examines multiple US basins and reveals that the necessity of high-quality cement isolation is potentially related to the size of the annulus being cemented. Smaller annuli are more difficult to cement due to higher Equivalent Circulating Densities (ECDs) caused by friction, but well performance may be less impacted by poor cement in these scenarios because the large pressure drop in the annulus during stimulation contains much of the stimulation in and around the intended interval. However, this does not mean that poor cementing in smaller annuli can be overlooked, as it can still have an impact on well performance.
The paper presents case studies that evaluate the importance of cement isolation in both new completions and refracs with various annulus sizes and well spacings. The findings are applicable to cemented laterals completed with multi-stage stimulations in oil and gas reservoirs as well as in enhanced geothermal applications, where effective fracture uniformity is one key to performance.
Overall, this paper provides valuable insights into the importance of cement isolation in horizontal, multi-stage, hydraulically stimulated oil and gas wells. It emphasizes the need for accurate diagnostic techniques to measure cement isolation and the importance of high-quality cementing to ensure optimal well performance.