Characterization and surfactant-enhanced washing treatability of drilling fluids stored for more than 20 years

Drilling fluids represent a significant environmental hazard owing to the fact that they are frequently stored in open vessels without any treatment. The drilling fluids studied in this work have been stored for 20-30 years in open cesspits in the state of Tabasco (Mexico). The aim of this work was to characterize the drilling fluids produced in this region and to determine their treatability by means of surfactant-enhanced washing. Two anionic and two non-ionic surfactants (sodium lauryl ethersulfate SLES and sodium dodecylsulfate SDS, ethoxylated nonylphenol ENP and an unknown composition ethoxylated nonionic Surfynol 440 respectively) were employed for surfactant-enhanced washing assessments in the presence of a commercial dispersant. Drilling fluids were contaminated with 135,400 mg of total petroleum hydrocarbons (TPH)/kg soil, including seven polycyclic aromatic hydrocarbons (PAHs) from 1.18 to 57.28 mg/kg. TPH removal efficiencies as high as 55.7% were reached when washing drilling fluids with SDS (4%), followed by ENP 906 (1%), which showed a TPH removal of 52.2%, and ENP itself at a lower dose (0.1%). SLES and S440 gave removal of around 10-15% with the assessed doses.