Quantification of synthetic-based drilling mud olefins in crude oil and oiled sediment by liquid column silver nitrate and gas chromatography

Abstract

Synthetic-based drilling muds (SBMs) are complex mixtures of man-made fluids used during the drilling of oil and gas wells. SBM-derived chemicals can enter the environment through failed wells and routine or poor disposal practices, where they can persist and thereby warrant measurement. SBMs are commonly formulated with linear and methyl branched α- and internal-olefins mostly in the C14 to C20 carbon range, which are not native to crude oils. Thus, SBM-derived olefins can provide a basis to recognize the impact of these drilling wastes in the environment. However, the presence of abundant native hydrocarbons in oils and sediments can hinder the detection of trace level SBM-derived olefins by conventional organic sample preparation and analytical methods. Silver ion chromatography using silver nitrate (AgNO3) impregnated silica gel can serve to physically separate olefins from saturated aliphatic hydrocarbons native in crude oils, which can subsequently be analyzed and measured by conventional one-dimensional gas chromatography-flame ionization detection (GC-FID). In this study, SBM-derived olefins are measured in crude oils from the Deepwater Horizon oil spill and in their laboratory mixtures to a detection limit of approximately 5000 µg/g (0.5 wt%). In oiled sediment, SBM-derived olefins were reliably detected at concentrations as low as 1 µg/g-dry. An application of this method is demonstrated through analysis of crude oils and oil-contaminated seafloor sediment from the Taylor Energy oil spill site in the northern Gulf of Mexico where SBM was historically used and discharged.