Compatibility study of commercially available chemical additives to oil well cement applied in ADNOC oilfields

In the oil and gas industry, oil well cementing is considered as one of the most important stages among all of the drilling and well completions operations. Cement additives are typically used to modify the behavior of oil-well cement and to control its fluidity under the aggressive well conditions. In this study, a comparative study is conducted between two kinds of lignosulfonates in order to evaluate their retardation effectiveness for seven concentrations by monitoring the cement hydration via isothermal calorimetry. The results show major differences between their performances due to their variation in chemical characteristics. Furthermore, the compatibility issue is investigated for a commercially available lignosulfonate and an NSF condensate by means of zeta potential and adsorption isotherms. Based on the obtained results the optimum dosages are proposed for different five cement/additives. The study continues with investigation regarding the effect of the optimum dosages on cement hydration. Additive solutions at 0.1% and 0.2% each by weight of cement (bwoc) with a ratio of (1:1) are also studied. The mechanisms accompanying this process are better understood by studying the morphology of cement/additives systems using environmental scanning electron microscopy. The results show clearly that NSF exhibits a retardation behavior on cement hydration due to their physical adsorption on cement surface especially C3A phase. In addition, rheological measurements show that lignosulfonate is more effective than NSF due to cement incompatibility and dispersion mechanisms. The effect of those additives formulations on oil well cement mechanical properties is further investigated. This study provides recommendations for applying the most effective and economic additive dosages in drilling and well-completion operations as well as enhancing the well-cementing quality.