Influência da cinza da casca de arroz em pastas de cimento para fases iniciais de poços de petróleo offshore, uma alternativa sustentável e econômica

Abstract

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 RHA as source of amorphous or crystalline silica, and in the formulation of cement slurries, both for civil construction and 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 the 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 destined 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 (Compressive Resistance, UCA, Thickening Time, Sedimentation test, Rheology) in order to verify the feasibility of using ash for low temperature oil wells. Tests showed that the use of ash provided hydrated product with 96.8% of the standard slurry resistance (Portland cement + 2% bentonite), as well as improved stability and rheology of the slurry containing RHA in relation to those without ash. Replacement of 50% of RHA reduced the percentage of free water in the paste by 5.6%, compared to 0% RHA. The formulation containing 50% RHA showed adequate resistance gain profile, with a pumpability time of 23h (50Bc). Sedimentation test proved that the addition of RHA increases the stability of the paste, reducing the top drawn and avoiding decantation of the paste. RHA is a sustainable alternative for applications in low temperature environments, such as early stages of marine oil wells, considerably reducing cement consumption (15% by weight in relation to standard paste), thus contributing to the reduction in emissions of CO2 in the atmosphere due to cement production. Finally, RHA proved to be extremely economically viable. Compared to standard formulation, the use of 50% ash reduced the cost of the barrel by 15.6%, which represents savings of U$ 7.49 for each barrel (bbl).