Filter cake formation and particle invasion: A comparative study of OBM and WBM in wellbore applications

Drilling fluids are central to energy production, enabling the extraction of hydrocarbons—currently a significant component of the global energy supply. Their importance extends beyond conventional fossil fuel extraction, playing an important role in geothermal energy development, carbon capture and storage projects. This experimental study compares the filtration behavior of an oil-based mud (OBM) and two water-based mud (WBM) formulations, one with filtration control agents and one without, under static and dynamic filtration conditions. Static tests show that OBM achieves lower initial spurt loss, indicating superior early fluid loss control. Under dynamic conditions, increasing cross-flow velocity delays filter cake formation for all fluids, resulting in greater early fluid invasion and spurt loss, with the effect more pronounced in the more viscous drilling fluids. Through X-ray computed tomography, this study shows that OBM produces a thicker, but slightly less dense, external filter cake. Higher cross-flow velocities yield thinner, more porous cakes, facilitating deeper particle penetration. Although OBM maintains a lower filtrate flux, it is more sensitive to velocity changes than the WBMs. These findings underscore the influence of mud composition, viscosity, and flow conditions on filtration performance and particle invasion. Specifically, the study reveals that higher viscosities and filtration additives can enhance particle transport into the substrate, and decrease early fluid invasion under dynamic conditions.