Mud lift pump for dual drill string

Abstract

A mud lift pump for a dual drill string includes an energy input and an energy output in fluid communication with a fluid return flow passage in the dual drill string.

What is claimed is: 
     
         1 . A mud lift pump for a dual drill string, comprising:
 an energy input in communication with a power source in the dual drill string; and   an energy output in fluid communication with a fluid return flow passage in the dual drill string.   
     
     
         2 . The mud lift pump of  claim 1  wherein the dual drill string comprises nested conduits, the energy input accepts power from a fluid supply flow passage in an annular space between an outer pipe and an inner pipe, and the fluid return flow passage is in an interior of the inner pipe. 
     
     
         3 . The mud lift pump of  claim 2  further comprising a flow crossover, a motor disposed in a fluid discharge side of the flow crossover and a pump disposed in a fluid return side of the flow crossover, the motor and pump rotationally coupled to each other. 
     
     
         4 . The mud lift pump of  claim 2  wherein the pump is disposed in a segment of the nested conduit, the pump comprising a nozzle in fluid communication with the fluid supply flow passage and having an outlet disposed proximate an eductor disposed inside the inner pipe. 
     
     
         5 . The mud lift pump of  claim 2  wherein the pump comprises a first turbine rotatably in the annular space between the inner pipe and an outer pipe of a segment of the nested conduit and a second turbine rotatably inside the inner pipe. 
     
     
         6 . The mud lift pump of  claim 5  wherein the first turbine and the second turbine are rotationally magnetically coupled. 
     
     
         7 . The mud lift pump of  claim 6  wherein the inner pipe comprises a non-magnetic material. 
     
     
         8 . The mud lit pump of  claim 7  wherein the non-magnetic material is electrically non-conductive. 
     
     
         9 . The mud lift pump of  claim 1  wherein the energy input comprises an electric motor. 
     
     
         10 . A method for controlling pressure in a wellbore having a dual drill string therein, the method comprising:
 pumping fluid through a fluid supply passage in the dual drill string;   driving a pump energy input using power transmitted along the dual drill string;   discharging the pumped fluid into the wellbore;   imparting energy to fluid returned into a fluid return passage in the dual drill string from the wellbore using an energy output of the pump.   
     
     
         11 . The method of  claim 10  wherein the driving a pump energy input comprises passing the pumped fluid through a fluid-driven motor. 
     
     
         12 . The method of  claim 11  wherein the motor comprises at least one of a turbine and a positive displacement motor. 
     
     
         13 . The method of  claim 10  wherein the driving a pump energy input comprises discharging fluid from the fluid supply passage into a nozzle proximate an educator disposed in the fluid return passage. 
     
     
         14 . The method of  claim 13  wherein the imparting energy comprises increasing velocity of fluid in the fluid return passage by passing the returned fluid and fluid discharged from the nozzle through the educator. 
     
     
         15 . The method of  claim 10  wherein characteristics of the pump energy input, the pump energy output, a density of the pumped fluid and a flow rate of the pumped fluid are selected to provide a selected pressure in the wellbore. 
     
     
         16 . The method of  claim 15  wherein the selected pressure provides a selected equivalent circulating density of drilling fluid in a wellbore. 
     
     
         17 . The method of  claim 10  wherein the driving a pump energy input comprises rotating a first turbine, and the imparting energy comprises rotating a second turbine rotationally coupled to the first turbine. 
     
     
         18 . The method of  claim 10  wherein the driving a pump energy input comprises operating an electric motor using electric power transmitted along the dual drill string.