Estudo de composição de pasta de cimento contendo cinza de casca do arroz para aplicação em poços com elevadas temperaturas

Abstract

The cement when subjected to high temperature has an effect known as retrogression effect of compressive strenght, where the hydrated product is converted into phases like Hydrate α-dicalcium silicate (α-C2SH or Ca2 (HSiO4) OH), which has a crystalline structure, high density, high permeability and low mechanical resistance to compression. In the petroleum industry, it is common to use the addition of 35 to 40% by weight of cement (BWOC) of silica flour in the cement binder formulation to minimize the effects of the retrogression phenomenon. The objective in this work is to assess the behavior of the rice hull ash (RHA) as an alternative to silica flour in the fight against retrogression. The RHA is a residue derived from the burning of rice hull that has, on average, 92% of silica in its composition, being a promising alternative, national raw materials and low cost. To evaluate this product cement slurries was formulated containing 30 or 40% BWOC of RHA. The density of the formulations was varied until they were achieved free water parameters and consistence similar to those described in the standard NBR 9831 and API spec 10, respectively. The formulations with properties similar to those of a standard cement paste (normative) were subjected to compressive strength retrogression test (CS) of hydrated slurries under bottom hole static conditions (BHST temperature) and hydrated slurries in high conditions temperature (300 ° C). It was used the XRD techniques and TGA /DSC/ DTA to follow the chemical evolution of the process. The results obtained were compared with a cement paste reference density 15.8 lb/gal and containing 35.0% BWOC of silica flour, commercial additive for combating compressive strength retrogression. Formulations containing 30.0% of the RHA had an average retrogression of 60% in CS, whereas the formulations containing 40.0% CCA obtained about 5% retrogression. Using the RHA as an additive for combating the CS retrogression was possible to obtain better performance than the commercial additive (silica flour) and lower values of density 15.8 lb/gal, that is, with less binder, lower cost, greater efficiency, and higher yield.