Evaluation of mudcake buildup and its mechanical properties

The use of drilling fluids while drilling for oil and gas is critical for successful drilling. The mud pressure is usually maintained higher than the formation’s pore pressure to stabilize the wellbore and prevent kicks. The difference in pressure between the wellbore and the formation drives part of the drilling mud to seep into the formation. For water-base mud, water and possibly solid particles are lost to the formation. Inappropriate fluid loss could be associated with costly problems. High fluid losses are costly in drilling, and might lead to formation damage which hinders the production stage. Fluid loss is associated with the buildup of a mudcake on the wellbore wall. Filtration and mudcake buildup were studied extensively over the past years, but are not fully understood yet. This is due to the complexity of the problem and the high number of affecting parameters. The first part of this study focuses on the mudcake buildup and the evolution of its properties with time. When fractures exist around the wellbore, fluid loss through the fractures results in the buildup of a mudcake on the fractures’ walls. The mudcake formation inside the fractures might affect the pressure distribution there. In fact, the mudcake might isolate the wellbore pressure from the fracture or from a part of it. And therefore, it might have a significant effect on the fracture propagation pressure and help in wellbore strengthening. The second part of this study investigates experimentally the mechanical properties controlling the sealing and pressure isolation ability of the mudcake.