Rotary steerable drilling system and method with imbalanced force control

A drilling system includes a rotatable string for connecting with a bit for drilling a borehole, and an active stabilizer which includes a body having an outer surface for contacting a wall of the borehole, and a plurality of actuators connecting the body and the string and capable of driving the string to deviate away from a center of the borehole with a displacement to change a drilling direction. The drilling system further includes a module for measuring direction parameters including at least one of a declination angle and an azimuth angle of the borehole, a module for measuring imbalance parameters including at least one of a lateral force, a bending moment and a torque near the drill bit, and a controller including a calculator for calculating an adjustment needed for the displacement, based on the measured parameters and expected values of these parameters.