Source of Oil
Well, silly, it comes from oil wells, of course! Sorry, that was just too easy to pass up (and in some respects the best answer out there)! Really now, where does oil come from?
The truth is, no one is completely certain how oil originated, migrated and accumulated.
Prevailing wisdom, based on over a hundred years of production history, has it that crude oil was formed from layers of dead organisms lying on the sea floor for millions of years. Over time, sand, clay, and limestone layers covered the rich organic sediments, which are typically fine-grained shales, choking out oxygen and allowing bacteria to break down the organisms.
As the organic-rich sediment was covered with more and more layers of earth, the weight of the overburden caused pressure and heat to transform the organic material into one of the various phases of hydrocarbon (natural gas, crude oil, or bitumen – see oil definition discussion). Scientists call this organic-rich sediment layer the source rock, as it is where oil is created.
It is estimated that it took millions of years to convert the organic matter into the quantities of hydrocarbon produced in the oil fields of today (see oil accumulation, and oil location discussions). As a result, oil is considered a finite resource. As the oil fields around the world are identified, and oil increasingly produced, the earth’s oil generating machine cannot keep pace, and the world’s overall oil balance declines.
Another novel theory for oil’s origin suggests that it is an inorganic product originating deep in the earth, between the mantle and the crust. Miles below the earth’s surface, it is theorized, the interaction of a now mobile, inorganic methane and high temperature pockets takes place and results in the condensing of crude oil.
An intriguing aspect of this theory is that oil is constantly being generated in numerous places around the world, and at rates that can continue to sustain our current way of life. So now, according to some, oil is not a limited resource after all.
It should be noted that this inorganic theory is held by a minority of industry professionals. The oil discoveries and development plans throughout the world have been based on the organic theory of hydrocarbon origination and a declining inventory. Seems to me like conventional wisdom wins the day.
So, where does crude oil come from? You decide and let me know!