| CPC E21B 21/08 (2013.01) [E21B 4/02 (2013.01); F03B 13/02 (2013.01); F04C 2/1071 (2013.01); F04C 13/008 (2013.01)] | 15 Claims |

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1. An equivalent circulating density (ECD) reduction tool for use in a subterranean well, the ECD reduction tool comprising:
a positive displacement fluid motor;
a fluid pump, the fluid pump comprising a fluid inlet and a fluid outlet disposed on respective opposite sides of an external flow restriction; and
a coupler connected between a rotor of the fluid motor and an impeller shaft of the fluid pump, in which the coupler is configured to transmit a rotary output of the fluid motor to the impeller shaft of the fluid pump, and in which the coupler comprises at least one port which permits fluid flow into a first flow passage of the impeller shaft.
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