A fluid treatment method includes positioning a tubing string in a non-vertical borehole section, and applying a sliding-sleeve-actuating fluid pressure within the tubing string's inner bore such that a first sliding sleeve moves from a position in which a first port is covered to another position in which the first port is exposed to the inner bore. The method further includes pumping fluid through the first port. The method also includes conveying first and second fluid conveyed sealing devices through the inner bore such that the first and second fluid conveyed sealing device seal against the seats of second and third sliding sleeves, respectively, thereby moving the second and third sliding sleeves to open port positions exposing second and third ports, respectively. The method also includes pumping fluid through the second and third ports to treat first and second portions of the formation, respectively.