Valorization of spent drilling fluid as mixing water in cementing oil, gas and geothermal wells

Recently, a new drilling fluid based on a 3D silica gel has been developed. Compared to conventional drilling fluids based on clays, the newly introduced “Si-Drill fluid” excels with superior hole-cleaning ability and lower cost. However, during its synthesis, which uses hydrochloric acid, a high concentration of chloride is generated, increasing the disposal cost for spent drilling fluid. Thus, in the spirit of circular economy, recycling of the Si-Drill fluid was evaluated, whereby the Si-Drill fluid functions as mixing water for oil well cement. The impact of Si-Drill as mixing water for common API Class G cement was tested regarding the three fundamental slurry properties—rheology, thickening time, and fluid loss. First, a Si-Drill fluid containing 2.5 wt% “SiO₂” was found to cause excessive thickening of the cement slurry, which was solved by dilution to 1.0% “SiO₂” content. Furthermore, commercially available cement additives were tested to control the critical slurry properties—namely, a dispersant, two retarders, and a fluid loss additive. The cement slurry prepared from 1.0% “SiO₂” Si-Drill fluid responded well to the additives, individually as well as in combination. By using the proper additive combinations, the slurry achieved all properties required in well cementing in the temperature range of 27 °C to 80 °C. The study concludes that diluted Si-Drill fluids can be used successfully in well cementing. Moreover, it also provides economic advantages over using plain water for slurry preparation because of lower costs for cement additives, and it contributes to a circular economy.