The efficient and economical application of a cement slurry programme for sandstone and carbonate reservoirs. A case study of the Zubair, Mauddud, and Mishrif formations in a supergiant oilfield, in southern Iraq

This study was accomplished in oil drilling wells located in the Mishrif and Mauddud carbonate formations and in the Zubair sandstone formation to ensure safer, efficient, and economical cementing operations, a better bond between the cement, casing, and formation, and a better isolation between the zones. Moreover, it was also undertaken to obtain competitive cement at the shoe. The study developed a cement slurry programme of 1.55 lead and 1.9 SG tail slurry for both the primary and secondary stages in well WQ1-XX0, as well as a new programme for the wells that would follow (the same primary stage, and 1.45 and 1.75 SG for the secondary stage), so as to improve the casing and cementing stability and reduce costs. The results indicated that well problems were gradually reduced in wells WQ1-XX1 and WQ1-XX2 and were entirely eradicated in well WQ1-XX3. The reduction in cement cost was 62% (from 0.756 to 0.47 barrels per metre), and the cement shows good bonding at the top of productive formations (Mishrif, Mauddud, and Zubair). The problems and costs in the Zubair sandstone and Mauddud carbonate formations were higher than in the Mishrif formation, and the programme adopted would prove to overcome them all. The lightweight high-performance slurry, with a specific gravity of 1.45, achieved the objectives of liner cementing in the Mishrif wells without involving any losses.