On-Site Measurement of Hydrocarbons in Drill Cuttings

Portable infrared analysers, such as the InfraCal Analyzers from Wilks (USA), have been used worldwide for measuring offshore oil levels in produced water for over 45 years. They have the advantage over other analytical instruments in that the measurement can be performed by non-technical users and it is relatively unaffected by composition changes in the effluent. They also provide offshore users with the necessary ruggedness and reliability that is a key requirement.

In addition to their use for measuring oil content in produced water, portable IR analysers are ideal for both onshore and offshore oil content measurements in drill cuttings. If drill cuttings are to be disposed of via land application or overboard, there are limits on hydrocarbon levels depending on the disposal choice.

While water samples typically have hydrocarbon levels in the part per million (ppm) range, drill cuttings can be in the 1-10% range. Both the InfraCal TOG/TPH Analyzer Model HATR-T2 and the new InfraCal 2 Model ATR-SP are configured with horizontal ATR sample stages. Hexane, pentane or cyclohexane is used as the extraction solvent for oil in water levels from 0.3 to 1000 ppm range. The solvent is evaporated off and the infrared absorbance due to the residual oil film is measured.

 The same InfraCal Analyzers with an ATR sample stage can be used for the higher 1-10% range found in drill cuttings. The sample is diluted by using a solvent that does not have an infrared absorbance at the hydrocarbon wavelength such as tetrachloroethylene (perchloroethylene) or S-316 (dimer/trimer of chlorotrifluorethylene) and, therefore, does not require evaporation. The solvent dilution allows for the high percent range measurements with the same ATR sample stage used to measure the ppm levels.