Determination of Polycyclic Aromatic Hydrocarbons in Drilling Muds and Reserve Pits by Isotope Dilution GC/MS with Selected Ion Monitoring

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Abstract
Shale cuttings, spent fluids, and drilling muds from natural gas exploration were analyzed for extractable hydrocarbons including polycyclic aromatic hydrocarbons (PAH) and alkylated-PAH. Complex mixtures of aliphatic hydrocarbons with carbon numbers from 10 to 32 were found in three phases coexisting in waste pits where extractable hydrocarbons were 45–990 mg/L in wastewater and 265–59 000 mg/kg in drilling muds/pit sediments. Over 20 members of 2–4 ring PAH and alkylated-PAH were isolated using chemical prefractionation and quantified by isotope dilution GC/MS with selected ion monitoring. Concentrations of total PAH assessed at three sites including a central waste storage site followed the trend: hydrocarbon film > oil-based muds > water-based muds > shale cuttings > = phase and ranged from 15mg/L for reserve pit water to > 24000mg/kg for oil-based drilling muds. Inhomogeneity of large reserve pits due to mechanical dispersion of wastes was illustrated using solution/sediment distribution ratios. Relative standard deviations with isotope dilution GC/MS determination of PAH were 1.9–27% and were generally 1.2 to 6-fold better than those using external calibration methods.