For a long time I've been wondering about the amount of effort it takes to obtain energy, whether it's pumping oil, digging coal or manufacturing solar panels.
In this first post, I'll explore a simple concept: the Energy Return on Energy Invested (EROEI) of that icon of oil production, the pumpjack. To be more specific, I'll be looking into a Texas pumpjack: how many barrels does it produce in a day, and how much energy is needed to get that energy out?
I'm at this point only interested in the amount of energy required to make the pumpjack go up and down. Of course it took effort (skills, materials, energy) to discover the oil, drill the well and build infrastructure manufacture, but I'll leave that for another time.
Returns
So let's start with the returns. I'm brushing with broad strokes here. According to the Texas Railroad Commission, Texas produced 349 million barrels in 2009 from 157,807 wells. I'm assuming this is not counting the federal offshore fields. Further assuming that ALL Texas oil was produced using pumpjacks, and that there's one pumpjack per well, each pumpjack produced 2212 barrels in 2009--just over 6 barrels a day. Now, by taking the amount of energy released by burning a barrel of oil to be 6.1 GJ, a pumpjack produces 37 GJ worth of energy.
Investment
Now for the energy invested. I'm assuming from this thread that a typical pump jack uses a 40kW electrical motor, running 24/7. Assuming 100% efficiency (!!!) That's 60x60x24x40kWe = 3456 MJ or ~3.5 GJ.
EROEI
Simply dividing the former by the latter, the EROEI of a Texas pumpjack is slightly better than 10:1 IF the energy values of oil and electrical energy can be interchanged without loss.
Of course, crude oil is generally not used for heating or electricity production, and electricity is generally not used to drive a car (although that's changing), so this number can be deceptive--it merely gives an indication.
Conclusion: cut out the middle man?
Concluding this post --and this is me speculating--, it's interesting to note that a fossil-fueled/coal based power station never exceeds 50% efficiency, excluding transportation losses. Coal is by far the most common source of electricity, I'd guess.
That means at least 7 GJ worth of "coal energy" is needed to produce 37 GJ of "Texas crude energy" in one day. A combustion engine converts chemical into mechanical energy at an efficiency of ~33%, so only around 12 GJ of "Texas crude energy" gets released as mechanical energy by burning 7 GJ of coal, out of an initial 37 GJ.
Which almost means that (and I'm really taking this into the extreme), when you trade in your SUV for a small electric car that runs on coal-generated electricity, you can just as well leave the oil in the ground that would otherwise be used... A.k.a. cut out the middle man... But, as they say, your mileage may vary!
(P.S. Any comments, corrections, suggestions for better data and/or methodology are very welcome!)
