This paper is based on continuous cement job improvements carried out for deep HPHT wells over the last ten years by KOC and their cementing service providers. The particular challenges in these complex wells compelled us to place primary attention on well construction aspects while also considering long term well production. Because of narrow annuli, dense saline water in formation situation cannot be managed with other tools like ECP/Swellables etc. Our cement slurry is designed to be pumped in place without sacrificing its intrinsic qualities. It responds in a predictable manner and confirms by testing and simulation under relevant conditions including multiple producing layers with pressure variations.

KOC cementations described cover the deep wells in a depth range of 16,000 to 19,000 ft., with possible strength retrogression because of temperatures, narrow difference of pore and frac pressure, mud weight ranges of 19.5 to 20.0 ppg, three liner systems, and a seven string casing policy. Encountered difficulties have included inability to displace from the string, wet shoe track, hanger top leakage and poor quality cement sheath in the annulus.

Different combination of spacers and slurry weight have been tried. Many HPHT cement additives were trialed and eliminated and new ones introduced in order to achieve success. Extensive laboratory testing and software simulation was done to finalize slurry designs. Slurries were selected to meet both drilling and production requirements. This approach will be detailed in the paper including examples. This paper will explain the criteria of selecting the most suitable slurries that comply with best practices for successful HPHT cementing. It will detail slurry selection methods for a number of practical cases including: formation fluid influences, prevention of gas migration, slurry property changes with hydrostatic pressure variations, and influence of high percentage of non-cement materials in the slurry.

The subject matter of this paper is very important in deep HPHT wells slurry selection and placement. This case history is developed referencing the wells drilled in Kuwait, but the concepts will have significant relevance for application to similar wells in other regions.

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