Oil-based mud (OBM) cuttings are a waste generated during the process of oil well drilling. The drilled rocks are removed from deep within the drilled well and pumped to the surface. These ‘cuttings’ are a mixture of rocks, mud, water, and oil. Most drilling companies store this waste in open yards without specific treatment. The environmental regulations in Oman specify that cutting storage should involve isolation to prevent contamination of the surface and underground water. This has made OBM cutting waste an environmental problem with an associated cost for oil companies. OBM cuttings, being rich in calcium oxide, silicon oxide, and aluminum oxide, may be a suitable raw material in cement manufacture. Furthermore, the oil content may help to reduce fuel use during the calcination and clinkerisation process. In this research, OBM cutting waste was analysed and used as a constituent of raw meal in cement clinker production. Raw meal mixtures were prepared with increasing OBM content. The impact of adding OBM to the resultant clinker was investigated using analytical techniques such as XRF, XRD, SEM-EDX, and DSC-TGA, and burnability test.
OBM cuttings contain dolomite, which increases the rate of carbonate dissociation and, hence, contributes to lowering the calcination temperature. However, it also leads to a higher free lime content in the resultant clinker, which is a result of the presence of trace elements, such as barium. Clinker can be prepared by simply heating OBM cuttings at 1200 oC without any additives, with the resulting clinker containing belite and a very low free lime content and no alite. Clinker prepared using 12% and 55% OBM cuttings had very similar microstructures, chemical composition and properties to clinker prepared from the limestone normally used in cement production. However, the addition of OBM cutting to the raw meal led to acceptable higher free lime content in the resultant clinker. There are many reasons for this, including the role of trace elements, especially barium, in destabilizing alite, as demonstrated in this study.
The hydration behaviour of the prepared cement was studied by many techniques such as ICC, STA and mechanical properties. XRD plus SEM-EDX analysis of polished cross-sections enabled study of the major hydrate phases. SEM and optical microscopy of the clinker was undertaken to understand if there were any significant changes to the main phases which may influence the cement hydration behaviour. The degree of hydration was obtained and the main hydrated products such as C-S-H and CH were identified. Hydration behaviour was normal with no significant changes observed and no significant differences between the reference sample and industrial cement. Thus, OBM cuttings could be used in the manufacture of Portland cement clinker, providing a cost-effective, environmentally-friendly way to manage OBM cuttings derived from the oil drilling sector.
