Successful primary cementing operations are critical to long-term well integrity and well completion. The operator's Block-9 contract area is situated in the Southeast portion of Iraq. Wells drilled in Block-9 are primarily within the Yamama limestone reservoir. The Yamama formation is composed of four compartments (YA, YB, YC, and YD). The main production reservoir area is the YA; high-permeability characteristics and pressure depletion effects in certain layers are prominent in this compartment. In some wells, the cement quality across permeable and depleted layers of the YA presents challenges attributed to high pressure differential, early cement hydration, and microdebonding at the casing-cement interface. To achieve acceptable zonal isolation across these high-permeability and depleted layers, a thorough understanding of the issues is necessary. The operator's philosophy and procedures for cementing production casing to better understand the proposed solutions are discussed.
Cementing practices adopted in Block-9 in the past are discussed in addition to their impact on cement quality, current practices, and plans to address future challenges. To overcome this critical well integrity related challenge, a multifaceted approach was adopted. Offset well records, cement recipes, job execution, cement evaluation logs, and challenges faced during testing and production were reviewed in detail and are highlighted. Understanding these technical challenges and the formation response to cement slurry and hydration processes were key to designing cement slurries and job execution in such deep wells. Primarily, the operator focused on attempting to control/manage the cement hydration process and fluid-loss control across the permeable zones.
The proposed suggestions included understanding the permeable carbonate zones, high differential pressures, cement recipe design, cement additive impact, spacer and mud properties, pumping rates, casing centralization, casing rotation during cementing, the cement setting process, and cement evaluation log interpretation.
Lessons learned from this review can assist other operators globally with addressing similar issues with permeable depleted carbonate reservoirs and compromised cement bonding.