Abstract: Geothermal energy may be recovered through an underground well drilled to a depth approaching the earth's magma by circulation of injected heat transfer fluids flowing along separate parallel paths within closed loops extending into the well. One or more of the injected fluids may be conducted by a heat transfer portion of the loop establishing a lower heat absorbing zone within the well exposed to superheating conditions at ultra-deep depths. Circulation of the fluid within said heat transfer portion may be prolonged to efficiently absorb heat and heat loss may be minimized by heat exchange relationships between the parallel flow paths above the lower heat absorbing zone.

Abstract: Two or more independently expansible packer devices mounted on the mandrel of a free piston plunger assembly are axially separated by intermediate spacer sleeves through which the packer devices are keyed to the mandrel. Flow-conducting gaps between arcuate segments of the packer devices extend at an angle to the axis of the mandrel to impart rotation to the plunger assembly during axial reciprocation.