Measuring Very Low Residual Oil Contents on Cuttings: A Challenging Approach of the Zero OPF Discharge Option.

Abstract

Abstract The discharge of waste containing OPF (Organic Phase Fluid including Low Toxicity Fluids and esters) such as drilling cuttings will gradually be banned from a number of regions throughout the world. In the North Sea, by the end of year 2000, dumping into the sea of OPF drilling cuttings will definitely be prohibited. Nevertheless, as wells are becoming more and more sophisticated, the use of OPF as drilling fluid is actually the only viable option to succeed. For the time being, cuttings re-injection and ship-to-shore appear to be the most probable options, but they involve a significant increase in operating cost, unless R&D efforts on new separation treatments enable cuttings to be cleaned to an extremely low residual oil content. If a major breakthrough that could decrease the final residual oil content to around 0.5% or less (0.5 g of oil by 100 g of dry cuttings) can be envisaged, what will be the position of the authorities regarding cuttings discharge? Is "zero %" OPF content on cuttings before discharge reasonable and achievable? But first of all, is such a very low content measurable with precision on the rig site? This paper provides answers regarding the sensitive problems of measuring a very low oil content on a mineral substratum. A comprehensive study has been performed aiming at comparing the performances of 2 different methods used in the oil industry: direct distillation with visual reading, and distillation/pyrolysis followed by an evaluation of the Total Organic Carbon (TOC) by a Flame Ionization Detector (FID). The conclusion is that the distinction has to be made between TOC and residual oil content (ROC). The method based on thermal extraction with control of the temperature slope, enables the determination of the different origins of the organic matter and clearly demonstrate the need for criteria: even Water Base Mud (WBM) cuttings can contain organic matter (from 0 to 3%), such as kerogen, that should not be taken into consideration when evaluating oil content by thermal methods. The authors hope that the presented results could help to define a set of standard procedures to evaluate the residual oil content on cuttings.