Analysis of mudcake structures formed under simulated borehole conditions

Tiny pieces of filter cake were shock-frozen and broken while immersed in coolant. The specimens were studied with scanning electron microscopy (SEM) in both freeze-dried and frozen-hydrated stages. These techniques were used to show that the original structure of the filter cake is preserved. The investigation covered filter cakes of four different drilling fluids with respect to fluid loss data and thermal and chemical degradation. Honeycomb structures of bentonite containing drilling fluids were also found in the resultant filter cakes. The investigation showed that gel strength of the drilling fluid exerts a considerable influence on dynamic filter-cake structures.