With the boom in oil and gas drilling over the last 100 years, there are many oil wells that have been depleted of oil. But these wells are drilled many thousands of feet in the ground, where the temperatures are far higher. So, these seemingly empty holes are not really empty at all, and there is an abundance of energy for the taking.
Geothermal energy is energy from the Earth. Sometimes it’s just using the shallow ground as a heat sink or source for a residential heat pump. In place like Iceland, which is located near a volcanic hot spot, it might be to generate high pressure steam and electricity. Iceland also uses the energy to heat over 90% of the homes. But the temperature of ground at the bottom of the oil wells is not that hot.
Despite this, work is underway to use the heat. In many places where the wells are close to a town, water is pumped through the well and back up, heating it enough so that it can be used for heating homes and businesses. Over 90% of the energy in the water can used for this purpose, but the temperature is too low to generate electricity using conventional steam power plant technology.
Instead, an Organic Rankine Cycle (ORC) is used. An ORC is the same as a regular steam power plant cycle, but instead of water as the working fluid, an organic refrigerant is used. The efficiency of a steam cycle is around 30-35% because of the high temperatures achieved in the boiler. In an ORC, the efficiencies are typically between 5 and 10% because of the lower temperatures. Remember though the heat for an ORC is free and completely renewable from the Earth for millions of years into the future.
A project funded by the US Department of Energy is now underway in Nevada to try this. Transitional Energy is hoping to tap 3-5 wells at the end of their lives to generate about 1 MW of clean energy. So, when someone says used up oil wells are worthless, tell them there is plenty of energy available if you just know how to get to it. – Steve Terry, DTC HVAC & Refrigeration Instructor
