Conventional visions of geothermal energy consist of tapping shallow hot zones with multiple lateral wells where fluids are passed through the formation. But the true potential of geothermal energy is so much greater.
Ideally, the best way to harness geothermal energy is to drill down 20 miles, fill the well with heavy drilling mud and then add pressure to the well. Over time, this pressure will expand the dimensions of the hole as the rock this deep is both hot and elastic, like hot glass. Relatively quickly, the bottom of the hole will expand into a cavern with a sufficiently large surface area to transmit an almost unlimited amount of heat to the heavy mud in the hole. Ultimately, the only real limitation of the energy that can be harnessed will be defined by the diameter of the hole and the limitations of fluid transport. Consequently, any such attempt to harness geothermal energy in this manner should begin with a relatively large diameter hole.
Drilling a large diameter hole using conventional approaches add great expense to the drilling process. For this reason, it is imperative that an alternate approach be used. Ideally, any such drilling attempt should use a core drilling approach. Consider the following depiction.
A Large-diameter, > 24 inches, dual-walled drill pipe is used that has between the concentric, electrically conductive pipes, a material that serves as an electrical insulator, a thermal insulator, and a buoyancy provider. Along the great length of an ultra-deep well are placed electrical powered pumps that push the drilling mud down the outside of the pipe. At the bottom of this drill pipe is a drilling head that has the same dimensions as the drill pipe with a large internal diameter and larger external diameter so that it can be described as a few-inch-thick-walled large-diameter pipe. It is only designed to cut a narrow ring through the formation.
This drill head section has teeth along its inner wall that can grab a core of the formation drilled and snap it off like a stalagmite. The circulation of drilling mud proceeds from the outside of the drill pipe, past the cutting face of the drill head and up the inside of the drill pipe. When a core section is snapped off, it is flushed up the pipe to the surface in one piece. This approach thus only requires the pulverization of less than 10% of the hole while also delivering to scientist a far more informative piece of information about the nature of the deep crust.
The cutting face of the drilling annulus could use a combination of roller bits, electrically powered needle guns, and sonic generators, thus cutting through formations far more quickly and with far less need to replace the bit compared to conventional drilling approaches. Furthermore, once the hole gets deep, the hardness of the formation decreases due to temperatures. It may very well turn out that the bottom half of an ultra-deep well is as simple as drilling through sandstone.
Another important consideration is the implications for the mining world. It may turn out that the most precious elements exist in ten or even hundred-fold concentrations at greater depths such that harvesting them in this manner is more cost-effective and vastly less energy intensive than open pit or even underground mining. And then there is the scientific potential of discovering exotic crystal structures that may exist like a silicon diamond equivalent.
Perhaps the most important points needing emphasis is the financial implications of deep-source geothermal energy. The conventional cost of just drilling an oil well is about $100/ft or $10 million for 20-mile deep well. Logically, the use of a needle gun or sonic bit combined with soft deep rock might conceivably drop this cost by half or more. The recoverable heat capacity would be at least $1M/day or as great as $10M/day making such hole worth from $4-$40 billion and this value does not encompass the value of its non-intrusive environmental impact. Also, such a hole does not include the complications of flowing fluid through rock as in conventional geothermal wells.
Lastly, there is the element of time. Decarbonizing the grid using renewable energy will not only be inconceivably expensive, it will take the better part of this century. In contrast, 120,000 wells a year are being drilled. It is entirely plausible that the entire electrical grid of the world could be decarbonized in a decade while reducing the cost of electricity tenfold.
It is likely that pursuing this approach to future electricity will meet strong resistance as it will reduce the fossil fuel industry to just transportation needs short term. It will also eradicate both the renewable energy and the nuclear industry. It is also likely to be resisted by those who think that requiring millions of laborers to provide energy is somehow better than having an energy resource requiring almost no labor. However, the indisputable reality is that, short of some fanciful star trek-like energy option, deep-source geothermal energy has no peer. It is the only logical way to power a future for the world and the sooner we start a discussion, the sooner we can quit wasting time and enormous funds and fantastic levels of human toil pursuing vastly inferior concepts.