Lost Circulation Material (LCM)
The seepage loss or vugular loss of drilling fluid occurs due to high permeability formation, cavernous zones, or coarse beds of gravel. These losses seize once the solid particles in the mud system block the pore throats. In shallow unconsolidated sands or gravel beds, increasing the viscosity of mud also helps to stop or restrict the losses. If the loss rate is not controlled through these means, coarse, fibrous material is used, which is called 'Lost Circulation Materials' or LCM. Lost circulation treatment is most effective when LCM is mixed in batches of approximately 100 bbls. These LCM pills with a high concentration of coarse material are pumped into the well and placed opposite to the thief zones to stop or reduce the rate of drilling fluid loss.