Abstract

KADUKU, T.; DARAMOLA, M.O.; OBAZU, F.O.  and  IYUKE, S.E.. Synthesis of sodium silicate from South African coal fly ash and its use as an extender in oil well cement applications. J. S. Afr. Inst. Min. Metall. [online]. 2015, vol.115, n.12, pp.1175-1182. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2015/v115n12a5.

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 (SiO₂) was extracted from the CFA and used to synthesize CFA-derived sodium silicate (CFA-Na₂SiO₃), a typical OWC slurry extender. The physico-chemical properties of the CFA-Na₂SiO₃were compared to those of a commercial sodium silicate (com-Na₂SiO₃) 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% CaCl₂ by weight of water (BWOW) were prepared and extended using the CFA-Na₂SiO₃and the com-Na₂SiO₃at compositions ranging from 0.25-2.5% by weight of cement (BWOC). Rheological properties of the slurries were evaluated using American Petroleum Institute procedures and compared. The physico-chemical properties of the CFA-Na₂SiO₃are consistent with those of com-Na₂SiO₃, indicating the purity of the CFA-Na₂SiO₃. A comparative study of the OWC slurries indicated that the slurries extended with CFA-Na₂SiO₃have slightly lower densities, lower viscosities, and higher compressive strength than those extended with com-Na₂SiO₃. This indicates that CFA-Na₂SiO₃slurries would be easier to pump and preferable where early strength development is critical. This report could be instrumental in providing a way for the beneficiation of South African CFA in the petroleum, oil, and gas industry.

Keywords : oil well cementing; coal fly ash; sodium silicate; compressive strength.

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