Dawsonh4,
My other fellow posters are much more informed about the generator end of this.
My interest is in the driver end. Your desire to use this energy is laudable, but given that people have been drilling gas wells for 100 years and no one does it this way, kind of tells you there is an issue, mainly it costs too much.
Well fluids are a mixture of gas, saturated water vapour, free water and liquid hydrocarbons. These do not go through high speed axial turbines very well.
Is your 7,000 psi a flowing well head pressure or reservoir pressure or what?
Either way, there is a practical limit on pressure ratio to get to your 800 psi, i.e. too much expansion of the gas. I'm not sure about axial turbines for drives, but in compressors (reverse of turbines), there is a max pressure ratio of about 2.1 So 7000 to 800 in one go is just too much.
Well head equipment is there to control and reduce pressures to that which makes the rest of the system much cheaper to build. Your device may work when flowing, but not when the well is shut in / starting up / controlling flow or pressure, so anything else is extra cost to the equipment already there. High pressure equipment costs a lot of money.
The amount of pressure energy in a gas well is actually quite small, so the generation and money you can get from this generation won't pay for the equipment, especially when, as you say, the pressure declines over a relatively short time.
But the key issue is the extra fluids which come up the well pipe wrecking your turbine. Also as you drop pressure, you drop temperature and even more water and liquids drop out. Turbo expanders are used in CPFs to lower temperature, drop out liquids and then the end of the expander connects to a compressor which pumps the gas pressure back up, just not to the same level or it needs a bit of help from a motor. But this is downstream of filters, separators etc which remove all free sand, dirt and liquids. If you have to stick a separator onto each well head before the turbine that's even more money.
Lots of people have tried to do this and not succeeded.
This lot
make a good unit for liquid pipelines, but no one so far has succeeded in getting sufficiently large amounts of power out of the hundreds if not thousands of gas pressure let down stations across the world where high pressure gas in transmission lines is let down to lower distribution pressures to make it worthwhile to install the equipment.
Especially at well heads, you can't mess around with the equipment - failure leads to catastrophic damage.
Whilst doing a quick search I cam accross this form 2009 -
A key paragraph is below and then silence - never happened.
"The idea is not completely new. US companies experimented with turbo expanders in the 1980s and Mercer said a handful of similar efforts have already been set up in Europe. "But this isn't a cheap way to generate electricity. The reason it hasn't really taken off is that it's expensive." "
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
