Thermochemical Upgrading of Calcium Bentonite for Drilling Fluid Applications
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The rheological properties of bentonite suspensions depend on the chemical composition and the contained dominant element, such as calcium (Ca), potassium (K), and sodium (Na). Na-bentonite type is the one used in drilling fluids, because it has good dispersion stability, high swelling capacity, and outstanding rheological properties. Ca-bentonite generally has bad rheological performance; however, it can be activated by sodium to be used in drilling fluids, since there are huge unutilized Ca-bentonite resources. Many previous attempts of activation of Ca-bentonite were not feasible, upgrading required addition of many extra additives or sometimes mixed with commercial Na-bentonite toimprove its properties. In this paper, a process of integrated beneficiation method is designed to efficiently remove the nonclay impurities and produce pure Ca-bentonite. An upgraded Ca-bentonite was produced using a combined thermochemical treatment in a wet process by adding 4 wt % of soda ash (Na2CO3) while heating and stirring. The new thermal treatment optimized and described in this study greatly improved the sodium activation and ions exchange process and improved bentonite properties. The thermochemically upgraded Ca-bentonite outperformed the rheological properties of the commercial bentonite. And when tested in a typical drilling fluid formulation at high temperature, the investigations showed an identical behavior of the commercial drilling grade bentonite. Moreover, the results obtained showed that the thermochemically upgraded Ca-bentonite has higher yield point/plastic viscosity (YP/PV) ratio than commercial Na-bentonite when mixed with the drilling fluid additives. Higher YP/PV ratio is expected to enhance the hole cleaning and prevent most of the drilling problems.
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