Mud Cake forms along the borehole surface primarily due to which phenomenon?

• A. Increase in temperature
• B. Corrosion
• C. High clay swelling
• D. Loss of drilling fluids

Answer: (D)

Mud cake forms along the borehole wall mainly because drilling fluids are lost to the formation through filtration, leaving solids behind at the wall. As the mud is pumped under pressure, some of the liquid filtrate penetrates into the formation while the solids are deposited at the borehole surface, creating a filter cake. This buildup can help limit further filtration, but if it becomes too thick it can cause wellbore problems like differential sticking or increased filtration losses. Temperature rise, corrosion, or clay swelling aren’t the primary mechanism for forming the mud cake—the key factor is the loss of drilling fluids into the formation during filtration.