Autonomous downhole tool

A system comprising:

• a well penetrating a subsurface;
• a tubing disposed in the well for transport of a fluid stream between the subsurface region and a surface region;
• and
• a downhole tool disposed in the well and further down the well than a bottom end of the tubing, the downhole tool comprising a plurality of turbine wheels that are each movable separately to each of a first position in which the turbine wheel is retracted inside a tool body, a second position in which the turbine wheel is oriented to produce mechanical energy from the fluid stream, and a third position in which the turbine wheel is oriented to roll along an inner surface of the well.

A method comprising:

• deploying a downhole tool into a well and leaving the downhole tool in the well with an axial axis of a tool body of the downhole tool aligned with a fluid flow direction in the well;
• transporting a fluid stream between the well and a surface region along the fluid flow direction;
• positioning the downhole tool in a first mode at one or more times during transporting the fluid stream by moving a plurality of turbine wheels of the downhole tool relative to the tool body and into a position and an orientation in which the fluid stream passes through the turbine wheels;
• and
• positioning the downhole tool in a second mode at one or more times during transporting the fluid stream by moving the plurality of turbine wheels of the downhole tool relative to the tool body and into a position and an orientation in which the downhole tool is transportable along the well by rolling of the turbine wheels.