Turning Waste drilling fluids into a new, sustainable soil resources for landscaping

Waste drilling fluids (WDF) is a complex mixture of different additives with different chemical and biologic properties, which have no biodegradability and seriously pollute the soil system without any disposal. After the later stage treatments, like landfill and solidification, waste drilling fluids also have potential detrimental to the environment and health. In this paper, a formula has been studied that can turn the waste water-based drilling fluids into an environment friendly soil. The treatment process can realize the harmless disposal and effective utilization of water-based drilling wastes. In the laboratory column study, by assessing the germination time and growth of ten kinds of plants which were grown on the high quality soil mixture with the waste drilling fluids (10:1, wt:wt), the Festuca arundinacea seed was selected to evaluate the quality of the soil. The formulas were used as a treatment agent mixing with drilling wastes collected from drilling well sites in Dagang, Tianjing, China with design of orthogonal experiment. The analysis was comprised of evaluation of heavy metals, chemical oxygen demand (COD), soluble salt content, and pH. The formula (20%coal + 10%solid sludge +5%chips) was proposed as a low-cost strategy to reduce leaching of toxic elements, and improve plant establishment. The concentrations of heavy metals in leachate solution exacting from the soil were lower than the EPA toxicity limit set by USEPA. The pH was approximately 7 ∼ 8. COD was less than 100 mg O2/L and the soluble salt content was less than 25 g/kg. In the Field application, the environment friendly formula developed in this study has been successfully applied to Dagang Oilfield. The treated waste drilling fluids are favorable to the growth of the plants (the soil organic matter is more than 30 g/kg, the porosity is more than 50%). The treatment process is easy to handle, low-cost ( < 100RMB/m3) and realizes a new, sustainable soil resources for landscaping.