Simplifications help in understanding the energy big picture.
BTU, British Thermal Unit, is the amount of WORK required to raise one pound of water one degree Fahrenheit.
BTU is a measure of work, so can be related to all other forms of work measurement.
1 BTU = 252 calories = 1055 joules = 1055 watt second
Energy sources, like oil and wood are rated in btu, with that number being potential btu. How efficiently the resource is used has no bearing on that number.
Using these type of calculations, it has been said that a barrel of oil is the equivalent of more than 10 years of human labor. That makes oil a very valuable and necessary resource for powering today's lifestyles. Oil is well worth fighting over.
Using those same calculations, purely work potential, a cord of wood holds the equivalent of about 47 years of human labor. Mostly we look for ways to quickly be rid of the excess, like piling it up and burning it out in the open.