Functionalization of fly ash for the substitution of bentonite in drilling fluid

Abstract

Oil exploration activities have increased the demand for American Petroleum Institute (API-) grade drilling bentonite leading to a significant increase in the cost of naturally occurring bentonite and overall cost of the drilling operations. In this work, fly ash (FA) was functionalized to replace API-grade drilling bentonite for drilling of wells. Epichlorohydrin and aminopropyl triethoxysilane were used to functionalize the ultrafine-structured planetary ball-milled FA. The morphology, mineralogy, structure and specific surface area of the functionalized FA were determined by the field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry and Brunauer-Emmett-Teller analysis, respectively, to determine the efficacy of functionalized FA as a colloidal base in aqueous suspension. Fourier-transform infrared spectrometer and X-ray photoelectron spectroscopy analysis was used to confirm the grafting of alpha-glycol and amine functional group on FA surface and quantified by iodometric and acid-base titration method, respectively. The zeta potential and cation-exchange capacity of functionalized FA were found to be −47.1 to −68.1 mV in pH range 8–12 and ∼68.0 meq/100 g of functionalized FA, respectively, and were found comparable to API-grade drilling bentonite. Rheological behavior and filtration loss properties of the functionalized FA in aqueous suspension were determined and compared with the API-grade drilling bentonite yielding similar results. The performance of the functionalized FA-based drilling mud system involving tamarind gum and polyanionic cellulose was evaluated by determining the thermal stability, cuttings transportation ability, friction and shelf-life properties under the downhole condition at 75 °C and 100 psig and the results were compared against the existing drilling mud system, yielding the comparable performance. Finally, the functionalized FA was found to be cost-effective over API-grade bentonite.