Apparatus and methods for producing electricity using geothermal energy
A geothermal power system is disclosed. The system comprises a downhole turbine configured to operate within a wellbore and a downhole electrical generator configured to be driven by the turbine. A channel facilitates flow of a working fluid through the turbine. The channel has a feed portion allowing the working fluid to flow in a direction away from the surface and a return portion allowing the working fluid to flow in a direction towards the surface. A surface structure is in fluid communication with the feed portion and the return portion to circulate the working fluid through the channel.
1 . A geothermal power system comprising:
a channel configured for containing a working fluid and directing the working fluid at least in part through a wellbore, wherein the channel is a continuous channel which comprises a feed portion configured to allow the working fluid to flow in a direction away from a surface of the wellbore and a return portion configured to allow the working fluid to flow in a direction towards the surface, wherein the feed portion and the return portion each include downhole portions installed in the wellbore, wherein the channel is a closed loop and the working fluid harvests thermal energy from a formation surrounding the wellbore;
a downhole liquid turbine disposed in the feed portion and configured to operate within the wellbore being driven by the working fluid contained within the channel;
a downhole electrical generator disposed in one of the downhole portions and configured to operate within the wellbore and to be driven by the turbine to generate electricity; and
an electrical cable for transmitting the electricity generated by the downhole electrical generator to the surface.
2 . The geothermal power system of claim 1 , wherein the downhole liquid turbine comprises an impulse turbine, a reaction turbine, or a Tesla turbine.
3 . The geothermal power system of claim 1 , wherein the downhole electrical generator is an axial flux generator.
4 . The geothermal power system of claim 1 , wherein the system comprises multiple turbines within the wellbore.
5 . The geothermal power system of claim 4 , wherein the system comprises multiple turbines and generators operating within a single thermal circuit to allow multiple reheat cycles between the turbine generator units.
6 . The geothermal power system of claim 1 , wherein the system is configured to be positioned in a horizontal well having a vertical section and a horizontal section, such that the downhole liquid turbine is configured to be positioned toward the bottom of the vertical section or in the horizontal section.
7 . The geothermal power system of claim 1 , wherein the system is configured to operate at a maximum downhole temperature of between 60° C. and 150° C.
8 . The geothermal power system of claim 1 , wherein the geothermal power system comprises two turbines positioned at the same overall measured depth in opposing channels connected to a single generator.
9 . The geothermal power system of claim 1 , wherein the feed portion is thermally insulated from the return portion such that feed flow does not begin to vaporize until after the downhole liquid turbine.
10 . The geothermal power system of claim 1 , wherein a cross-sectional area of the return portion is greater than a cross-sectional area of the feed portion.
11 . The geothermal power system of claim 1 , wherein the wellbore is within a depleted oil and gas formation and wherein the wellbore is resealed to prevent fluid and pressure communication between the wellbore and formation.
12 . The geothermal power system of claim 1 , wherein the feed portion is thermally insulated from the return portion up to 400 m before and after a location of the downhole liquid turbine.
13 . The geothermal power system of claim 1 further comprising a check valve in the feed portion or where the feed portion connects to the return portion to ensure that the working fluid flows towards the return portion.
14 . A method of generating electricity using the system of claim 1 , the method comprising:
directing the working fluid through the channel;
while the working fluid remains in a liquid phase, passing the working fluid through the downhole liquid turbine;
after passing the working fluid through the downhole liquid turbine, directing the working fluid toward and into the return portion, the working fluid transitioning to a gas phase after the downhole liquid turbine;
driving a downhole electrical generator from the downhole liquid turbine to generate electricity; and
transmitting the electricity to the surface.