Contamination of cement slurries with oil based mud and its components in cementing operations

•The oil based mud does not hinder the hydration of cement slurries but can destroy the cement skeleton.•The “galactoid structure” is the primary cause of rheological variations for the contaminated slurries.•Emulsion is the greatest impact factor in the components.

Contamination will happen due to incompatibility during drilling fluid and cement slurry mixing. Therefore, this paper tests the effects of oil based mud (OBM) and its components on the performances of cement slurries, such as fluidity, thickening time, compressive strength, bonding strength, porosity, and permeability. This study combines the Ultrasonic Cement Analyzer (UCA), X-Ray Diffraction (XRD), Thermogravimetry (TG), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) to explore OBM contamination in cement slurries. The results demonstrate that the changes in the rheological properties of mixed cement slurries are caused by the free water of the cement slurries effect from the O/W or O/W/O galactoid structures. The presence of OBM does not hinder the hydration of cement slurries. This finding is the main reason for contamination by OBM such that the many holes in the cement stone and the lubrication effect of the oil phase lead to a reduction in strength and an increase in the porosity.