Drilling fluid loss model and loss dynamic behavior in fractured formations

In view of the lost circulation in fractured formations, a two-dimensional transient model for describing a power-law drilling fluid loss in an arbitrarily-oriented, compressible, permeable, rough-walled fracture was introduced. In this model, the mechanical fracture aperture and fracture tortuosity were considered to investigate the effect of fracture roughness on fluid loss dynamics. The governing equation of power-law fluid loss model was given and solved to analyze the fluid loss dynamics in fractured formations. The results show that the shear thinning behavior of power-law drilling fluid can result in high fluid loss rate at the initial stage of loss event; the fluid loss rate decreases as the fracture tortuosity increases, meanwhile, the effect of fracture tortuosity on fluid loss rate will decrease as the fracture aperture becomes larger; the larger the initial fracture aperture, fracture dip, fracture dimensions or fracture length, the higher the fluid loss rate will be; the fluid loss rate of rectangular fractures is much lower than that of square fractures; the higher the total leak-off coefficient, the higher the fluid loss rate will be; the fluid loss rate is the highest when the wellbore intersects the fracture at the center location; the fluid loss rate increases sharply as the differential pressure increases; the larger the normal stiffness of the fracture, the lower the mud loss rate will be.