Impact of Well Cement Retarder Types Towards Improving Early Compressive Strength Development and Reducing Waiting-On-Cement Time

Well cementing retarders can be classified based on their chemical nature, such as lignosulfonates, inorganic compounds, organophosphates, and hydroxycarboxylic acid. In this paper, we evaluate the behavior of these retarders on the early compressive strength development of API Class G well cement during the first 24 hours. The scope includes a 15.8 lbm/galUS system with 35% by weight of cement (BWOC) silica flour, antifoam, and varied types of retarders with a constant type of dispersant. API 10A-compliant Class G cement is prepared with different retarders at varying dosages and a single type of dispersant to obtain a thickening time of 5 hours at a bottomhole circulating temperature of 110°C. This resulted in different retarder loadings to obtain the same thickening time where some retarders required lower dosages, while others required higher. These formulations were then evaluated for their early compressive strength development at a bottomhole static temperature of 130°C to establish the significance of retarder type. Testing shows that different types of retarders require different dosages ranging from 0.065 and 0.5 gal per sack of cement to achieve a similar thickening time of approximately 5 hours. This variation of concentration is influenced by the chemistry of the retarder, its retarding mechanism, and test conditions. Although the formulations all have a thickening time of around 5 hours, their respective time to reach 50 psi and 24-hour compressive strength vary significantly. This difference can be attributed to the nature of the additive and how it works in synergy with the dispersant to delay the setting time while providing substantial compressive strength development within 24 hours. The lowest-performing retarder provided a compressive strength of about 1,000 psi, while the best performing provided over 3,000 psi which is about a threefold difference. The time to reach 500 psi compressive strength was optimized to as early as 3 hours 35 mins, while the 2,000-psi mark could be achieved in as little as 5 hours 24 mins. Cement formulations require different amounts of retarders depending on their type and well conditions. A common misconception is that all retarders provide similar compressive strength development. This study demonstrates that certain retarder types offer significant advantages, including improved compressive strength within 24 hours and significant reduction on waiting-on-cement (WOC) time, improving overall rig efficiency.