The Importance of Hydration Heat on Cement Strength Development for Deep Water Wells

Abstract

After placement of cement on conductor and surface casing, the temperature anomalies caused by the hydration of cement can be substantial. From volumetric considerations, it is known that the maximum temperature anomalies depend on the size of the casing-annulus gap and the cement/water ratio as well as on reaction kinetics. For deepwater wells, because of the low temperature and large annular gap, special attention should be paid to the hydration process of the cement to properly design and evaluate the cement treatment. Currently, there is no universally accepted way of defining temperature schedules for testing cement setting. Operators and field locations rely mostly on local experience, and API-proposed temperature schedules are not applicable conditions where setting time is important such as deep-water conditions. In an effort to better understand the dynamics involved with cement temperature during hydration, a numerical model was developed to predict the temperature evolution in the wellbore, cement and formation during the setting of cement. The model takes into account heat exchange with the formation and casing fluid (heating or cooling effect) as well as the heat generated during the hydration of the cement. The key parameters (formation thermal conductivity, cement thermal properties and annulus size) were assessed with the model. Based on the model, a study was completed to characterize temperature and cement strength development. And this in turn is essential to properly design conductor and surface casings in deepwater conditions, which represent the most critical sections for ensuring a competent cement hydraulic seal and support the casing. The results of the study allow to define compressive strength schedules that effectively mirror down-hole conditions and thus give reliable estimates of the necessary wait-on-cement time that could lead to substantial savings for deepwater drilling operations. Introduction When cement is mixed with water, an exothermic reaction occurs and a significant amount of heat is produced. This heat in typical wellbore geometry can produce an important temperature increase for the cement placed in the annulus. Based on that principle, field temperature logs following cementing operations have often been used for locating the top of the cement column behind the casing. Field measurements have shown that in some cases the temperature increases can be substantial1. Temperature increase of up to 50°F has been observed in some cases. Cement hydration and its related heat generation is highly dependent on temperature. The rate of heat generation during cement hydration increases with temperature and at low temperature hydration reaction can become extremely slow. Indeed the temperature in the annulus is one of the most important factors influencing the development of the cement compressive strength. Previous studies of cement hydration have primarily measured only the total amount of heat release over long periods of time2. However, cement hydration reactions are complicated and the rate of heat release is not constant.

Hindered Strength Development in Oil Well Cement due to Low Curing Temperature (Russian)

“…Скорость выделения тепла при гидратации сильно зависит от температуры: при низких температурах реакция гидратации может стать предельно медленной (Romero and Loizzo 2000). Скорость выделения тепла при гидратации сильно зависит от температуры: при низких температурах реакция гидратации может стать предельно медленной (Romero and Loizzo 2000).…”

West Africa Deepwater Wells Benefit from Low-Temperature Cements

“…15,16 Proper laboratory schedules and test procedures derived from these temperature simulations would realistically optimize the slurry formulation and reduce further wait-on-cement time. This effort is coupled with the accounting and simulation of the heat generated during the setting of the cement.…”

A Joint Industry Project To Assess Circulating Temperatures in Deepwater Wells

“…This can lead to substantial savings through a better estimation of the time necessary to wait on cement before releasing the casings. 1 The industry relies on three main methods for predicting temperature profiles in a well while circulating mud, placing cement, and waiting on cement.…”