Drill cuttings in the environment: possible ways to improve their properties

Purpose The disposal of drill cuttings (DCs) in landfills is one of the major impacts of oil extraction on the environment. The DC composition is predetermined by the type of drilling fluid and can include petroleum hydrocarbons (PHCs), salts, and metals. Designing effective approaches to DC recycling is a key problem. We propose the use of certain additives to reduce the toxicity of DC mixtures and improve properties to enable their utilization as artificial soils. Materials and methods Samples of DCs with different contents of PHCs (from 0 to 50 g kg −1 ) were taken from landfills and collectors, tested in mixtures with different additives (sand, shungite, diatomite, glauconite, peat, phosphogypsum, and cement). Physical and chemical characteristics of DCs and their mixtures with additives were analyzed. We conducted the leaching experiment by applying amounts of water equal to mean annual precipitation to both pure DCs and their mixtures and analyzed the composition of the leachates. Concentrations of PHCs, chlorides, and metals were measured using gas chromatography, ion liquid chromatography, and inductively coupled plasma mass spectrometry, respectively. We conducted bioassays involving pot experiments with terrestrial plants and aquatic tests on crustaceans and unicellular ciliates to evaluate the toxicity of mixtures. Results and discussion Sand was the best additive for diluting DCs and improving the structure of mixtures. Phosphogypsum additions caused an intensification of Sr leaching. Cement additions resulted in a dramatic pH increase in mixtures and triggered the formation of soluble Sr and Cu compounds. Additions of 13% peat resulted in the formation of soluble metal-organic complexes, while 5–10% peat additions increased oat and clover biomass. Diatomite was the most efficient additive to absorb PHCs. Mixtures with the PHC concentrations of 1.5–15 g kg −1 caused root and sprout elongation in oat, mustard, and barley. Shungite was efficient in reducing DC contamination levels at pH ≤ 8.5. Paramecium did not show any correlations with contaminants, but the activity of daphnids significantly depended on pH levels and PHC contents. Conclusions We were able to design soil-like mixtures to be organically integrated into the environment. DCs with PHC contents of ≤ 30 g kg −1 and Cl contents of ≤ 6 g kg −1 could be safely used in mixtures with ≤ 0.7 DC, ≥ 0.2 sand, and ≥ 0.04 diatomite (% v / v ) that form soil-like materials. DCs with high HCO 3 −