The rheological, mineralogical and chemical characteristic of the original and the Na2CO3-activated Tunisian swelling clay (Aleg Formation) and their utilization as drilling mud

Abstract Clay deposits of the Aleg formation (Jebel Romana of the northern Chotts range, southern-east Tunisia) were sampled and investigated for their, mineralogical, chemical, rheological, and physical characteristics to develop their potential use as drilling mud. X-ray diffraction revealed a predominance of smectite (≥ 90%) with minor amounts of kaolinite and illite. Calcite, quartz and gypsum were also detected. Results show that the main oxides in the samples were SiO2, Al2O3, and Fe2O3, whereas the other oxides were present only in small quantities. However, the relatively high Na2O and MgO content is also one of the favorable points considered in terms of swelling and viscosity features. Standard tests show that the rheological behavior of the clay suspensions is unsuitable for preparing drilling muds. Therefore, the activation of these clays was performed using the most popular Na2CO3 in a wet condition. The drilling muds qualities of the Upper Cretaceous smectite-rich clay from Jebel Romana, significantly improved with additive sodium carbonate. The Ca-montmorillonite was completely converted into Na-montmorillonite after addition of 3% Na2CO3. The activation of the Aleg clay with soda influenced the viscosities, swelling indices and specific surface area. The optimum conditions for the preparation of high quality materials for drilling mud were investigated by studying the effects of clay minerals percentage, Na2CO3 concentration, activation time and temperature. Commercial bentonite samples imported from Algeria (A.G) were also included as reference materials. The optimum parameters for activation can be achieved under the operating conditions of 3% Na2CO3 concentration, 60 min activation time, 75 °C heating temperature and clay concentration of 75 g/l. Under these conditions, the rheological and physical properties including apparent viscosity, surface area and swelling index showed a maximum values. Therefore, by alkali activation, it is possible to upgrade smectite from Jebel Romana to meet the minimum API viscosity (15 cp); mud yield value (90 barrels/sh.ton) and swelling index (22 ml) standards. In addition, the apparent viscosity and mud yield efficiency was obtained around pH 10, as 18 cp, 101.93 (barrels/sh.ton), respectively. So, to achieve higher quality, optimization needs to be carried out in the formulation of batches or in the processing conditions. The utilization of these clays, after their upgrading and activation, can represent a value-added to the Tunisian economy by preventing the importation of bentonite.