Desenvolvimento de pastas leves contendo nanossílica para aplicação em poços petrolíferos de alta temperatura com baixo gradiente de fratura

Abstract

The cement used in the drilling operation of high-temperature oil wells needs to be added with silica to avoid the process of retrogression of the mechanical resistance of the cementitious matrix that occurs from 110 °C, as it forms hydration products that are deleterious to the cement. In wells with a low fracture gradient, it is necessary to use light cement pastes to avoid rupture of the rock formation. For this, extender additives are used, such as sodium bentonite. However, its use implies a reduction in the compressive strength of the cement. In recent years, the addition of nanosilica in cement pastes has been widely studied. Promising results such as increased rheological parameters, reduced porosity and permeability, and increased compressive strength have been published in the literature. Based on the above, this work aimed to develop lightweight slurries containing nanosilica for application in oil wells with high temperatures and low fracture gradients. For this, slurries with densities of 12.5, 13.0, and 13.5 lb/gal, varying the nanosilica concentration, and reference slurries with sodium bentonite, containing 40% crystalline silica in all compositions. The slurries were characterized by rheological tests, stability, compressive strength, X-Ray Diffraction (XRD), Thermogravimetry (TG), and Scanning Electron Microscopy (SEM). The systems considered stable were selected and subjected to 41 °C and 14.7 Psi for 24 hours and 28 days, and also under 180 °C and 3000 Psi for 28 days. Based on the results obtained from rheology, it was possible to verify an increase in the values of the rheological parameters with the increment of the nanosilica concentration. In the stability and compressive strength tests, improvements were confirmed in the parameters with the increment of the nanosilica concentration. Finally, nanosilica showed promising results for application as an extender additive in oil wells’ cementing with high temperature and low fracture gradient.