This paper reports the key findings of a multidisciplinary study established by the E&P Forum to examine the environmental effects of drill cuttings with different oil concentrations resulting from treatment with solvent extraction and thermal processes. The study examined the physical characteristics of the cuttings, deposition on the seabed and the impacts on the seabed fauna and on fish.
Concentration of oil on cuttings ranged from 15.8% for unprocessed cuttings to less than 1% for thermally treated cuttings. The removal of oil resulted in dry, dispersive cuttings which would be deposited in lesser amounts over a greater area compared to unprocessed cuttings.
Environmental effects were greatest for untreated cuttings. Solvent extracted cuttings showed some effect but there was evidence of recovery of the benthic fauna within the timescales of the study (8 months). For most of the experiments, there was little difference between the thermally treated cuttings and the controls. There was evidence of a threshold for effects at a concentration of oil in sediment of approximately 1000 ppm. Model predictions of cuttings deposition showed that the area of seabed affected by oil concentrations in sediment greater than 1000 ppm was small for both solvent extracted and thermally treated cuttings.
Both solvent extracted and thermal processing of oily cuttings, and the subsequent discharge of the treated cuttings, appears to result in negligible or short term environmental effects.