Abstract

The inevitable generation of the drill cuttings resulting from the oil and gas exploration and production activities has lately become one of the major global environmental concerns. Currently, due to the stringent international legislations imposed to mitigate the hazardous nature of these drill cuttings; the petroleum industry has been forced to treat the cuttings prior to their disposal. However, most of the prevalent treatment techniques employed are deemed to be unsustainable to tackle this problem.

The objective of this research thus, is principally focussed on exploring feasible techniques for treating drill cuttings into inert or non-hazardous waste form to be disposed of in suitable landfills or for potential reuse in construction industry. To this effect, two treatment techniques namely stabilisation/solidification (S/S) and pelletisation were adopted. Given the known difficulties of chlorides and oil treatment, the S/S technique was firstly applied to model cuttings spiked with these contaminants using low dosage binder systems; followed by its application to raw cuttings for the purpose of comparison. Petroleum drill cuttings from the North Sea and Red Sea areas were explored. A number of different binders, including a range of conventional viz. Portland cement as well as less-conventional viz. zeolite, microsilica, MgO and phosphate cements or waste binders viz. cement kiln dust, fly ash, blastfurnace slag and compost were employed in the S/S treatability study. A set of mechanical, chemical and microstructural examinations was conducted to evaluate the performance of the different binder mixes in treating the cuttings. On the other hand, the pelletisation technique was applied to thermally treated drill cuttings, which is produced in vast quantities in the UK yet destined to landfills; to produce a range of artificial aggregates using a laboratory scale disc pelletiser employing different binders at ambient temperatures. The optimum pelletisation procedures and parameters were studied in full-depth. The geometrical, mechanical and physical attributes as well as the chemical leachability of the produced aggregates were thoroughly evaluated.

The S/S results revealed that the UCS of the treated cuttings was successful in meeting the UK waste acceptance criteria of monolithic wastes, wherein some of treated mixes displayed their suitability to be used in construction industry. The leachability results showed the reduction of the oil and chloride concentrations in some of the treated cuttings to inert and stable non-reactive hazardous wastes respectively; compliant with the UK acceptance criteria. The thermally treated cuttings were successfully converted to a wide range of lightweight coarse aggregates (LWA). The produced LWA displayed mechanical properties comparable to those of natural aggregates as well as commercially available LWA ‘Lytag’, permitting their use in high-performance concrete. However, the chloride levels in the produced cuttings aggregates restricted their suitability to be only incorporated into un-reinforced concrete.

This research was thus successful in meeting the set objectives with various encouraging and significant outcomes.