The 8½-in. hole sections of two fields in Kuwait have historically presented drilling problems associated with swelling shales and differential sticking. This drilling problem was alleviated by changing from a water-based drilling mud (WBM) to an oil-based mud (OBM). The change from WBM to OBM significantly reduced drilling problems; however, zonal isolation in the sand and limestone sections suffered, causing poor cement-bond logs across the 7-in. production liners. This paper presents the case histories of several wells in which zonal isolation problems were overcome, and production liners were successfully cemented.
In an attempt to determine the nature of the cementing problems in these two fields, the authors thoroughly analyzed the wells and completion designs. They reviewed formation properties, hole condition, mud properties, slurry and spacer designs, openhole logs and cement bond logs (CBLs), and the placement techniques of the affected wells. This paper documents the conclusions of this study, as well as the products and processes that significantly improved the zonal isolation of the 8½-× 7-in. annulus. CBLs performed across the intervals of four wells drilled with OBMs and cemented with improved products and processes indicate significantly better bonding than previous logs. These wells are currently on production and are being observed for short-and long-term performance.