The drilling operation cost represents 25% of the total oilfield exploitation cost. Drilling fluids represent 15 to 18% of the total cost of well petroleum drilling operations. The main drilling fluids problem is the loss into fractures and vugs. Mitigation of severe lost circulation is a main challenge while drilling in fractured formations where conventional lost circulation materials (LCM) will not cure these losses. Therefore, specialized fracture seal material (FSM) is required when drilling fractured formations. In this study, a promising FSM made from shredded waste car tyres was tested at laboratory for its ability to seal artificially fractured cores under High Temperature High Pressure (HT-HP) conditions similar to wellbore conditions. For this purpose, the conventional 500 ml HT-HP filtration cell was modified to accommodate a fractured core plug of length and diameter equal to 38.1 mm (1.5 inch) instead of the ceramic disc. Moreover, the cell outlet channel located below the fractured plug was increased from 1.0 mm diameter to 5.0 mm, easily allow the passage of the FSM in none effective fracture seal tests. Using the modified HT-HP filtration cell, shredded waste car tyres proved its ability to perfectly seal the artificially made fracture in the test core samples at overbalance pressures up to 900 psi and temperatures up to 80°C. The optimum mud composition was fresh water, 7% by weight bentonite, 7% shredded waste car tyres (a mixture ranging between 2.3 mm and less than 0.45 mm granule sizes) in weight bases. In addition to its great ability to seal fractured formation, the shredded waste car tyres material is cheap and locally available in commercially quantities. Additionally, the utilization of waste car tyres in drilling operations and other industrial applications can protect the environment from many hazards.

Key words: HT-HP filtration, Fracture seal, shredded waste car tyres, drilling fluid, fractured core plug.