The Schlumberger Losseal group of reinforced composite-mat pills reduced nonproductive time by mitigating the risk of lost circulation during drilling and cementing operations. Lost-circulation problems can occur during primary-cementing operations, resulting in unpredictable downhole conditions, ineffective mud removal, and/or poor zonal isolation. These issues can lead to time-consuming remedial cement jobs. The Losseal system combines fibers and solids into a specifically engineered, flexible-fiber additive pill, which uses synergy between the physical characteristics of fibers and solids to plug fractures that can cause partial or total circulation losses during drilling or cementing operations. The system creates an impermeable grid, which is strong enough to withstand pressure from mud density increases, as well as additional pressure from future drilling or cementing operations.