Filter Cake

Property of Drilling Mud

When drilling, a thick layer of residue, called "filter cake", builds up when the fluid is pushed against a porous surface. Some liquid seeps through, leaving the solids in the mud behind which is what builds this filter cake. Filter cake has both positive and negative affects on drilling such as mitigating against losses (positive) and contributing to differential sticking (negative)

Since this cake can affect how smoothly drilling goes, it's tested for things like thickness, toughness, and how easily it lets liquids pass. Filter cake design and its ability to be removed is extremely important in the reservoir section as it can lead to reduced oil and gas production if incorrectly designed