Influence of rice husk ash on cement slurry for early stages of offshore oil wells

The use of rice husk ash (RHA) in cementitious formulations has been widely studied in the literature in recent years. There are several applications for this by-product of the food industry. Some examples are the use of ash as a fertilizer, as a source of amorphous silica, as a source of pozzolanically active biomass and in the formulation of cement pastes for onshore oil wells, from medium to high temperature (50-200 ° C). However, little has been investigated about the use of RHA for low temperature systems, as is the case with the cementation processes of  initial phases of offshore wells, which generally occur at temperatures around 3-5 ° C. This study aims to analyze the influence of the addition of RHA in cement matrices designed for offshore operations that occur between 3-5 ° C. Cement pastes with a fixed density of 13.5 lb / gal (1.62 g / cm³), containing RHA (0%; 10%; 20%; 30%; 40% and 50%), were prepared and technological tests conducted (Long Time Curing RC , UCA, Thickening Time, Stability, Rheology) in order to verify the viability of using ash for low temperature oil wells. The tests showed that the use of ash provided hydrated product of resistance similar to a standard paste (13.5 lb / gal - 1.62 g / cm³ + 2% bentonite), as well as improving the properties and rheology of the paste in relation to the paste without addition. The addition of 50% ash reduced the percentage of free water in the paste, from 8.6% (0% RHA) to 3.00%. The formulation containing 50% RHA showed an adequate resistance gain profile, with a long setting time (> 45h). The stability test proved that the addition of RHA increases the stability of the paste. Finally, RHA presents itself as a sustainable alternative for applications in paste compositions for early stages of marine wells, considerably reducing the consumption of cement and, consequently, the emission of CO2 into the atmosphere.