Synthesis of sodium silicate from South African coal fly ash and its use as an extender in oil well cement applications

摘要

In this work, the use of sodium silicate derived from South African coal fly ash (CFA) in oil well cement (OWC) applications is reported. Silica (SiO_2) was extracted from the CFA and used to synthesize CFA-derived sodium silicate (CFA-Na_2SiO_3), a typical OWC slurry extender. The physico-chemical properties of the CFA-Na_2SiO_3 were compared to those of a commercial sodium silicate (com-Na_2SiO_3) using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. OWC slurries with varying proportions of cement, distilled water, and 2% CaCl_2 by weight of water (BWOW) were prepared and extended using the CFA-Na_2SiO_3 and the com-Na_2SiO_3 at compositions ranging from 0.25-2.5% by weight of cement (BW0C). Rheologicai properties of the slurries were evaluated using American Petroleum Institute procedures and compared. The physico-chemical properties of the CFA-Na_2SiO_3 are consistent with those of com-Na_2SiO_3, indicating the purity of the CFA-Na_2SiO_3. A comparative study of the OWC slurries indicated that the slurries extended with CFA-Na_2SiO_3 have slightly lower densities, lower viscosities, and higher compressive strength than those extended with com-Na_2SiO_3. This indicates that CFA-Na_2SiO_3 slurries would be easier to pump and preferable where early strength development is critical. This report could be instrumental in providing a way for the benefidation of South African CFA in the petroleum, oil, and gas industry.