GeologyRocks

It's a fair question - but everything does add up Oil is formed by the burial of organic matter. By checking the chemical signature of oil it has exactly that of life. You can also pick up some oil shale (try the kimmeridgian clay in the uk) and heat it up - you'll get oil exactly like (i.e. down to the molecular structure) sold on the markets.

To understand how we've used so much oil, let's walk through the formation process:

• organic matter gets deposited
• the sediment+organic matter is buried to a depth suitable for hydrocarbon generation (around 120°)
• it stays there for a long time (millions of years)
• the hydrocarbon generated then undergo migration from this source sediment. There are two migration phases: primary - which is from the source rock to the adjacent rocks, and secondary - which is long distance (kms) away from the source rock

Up to now we have 100% of hydrocarbons generated left in the crust. What has to happen for the hydrocarbons to be left in the rocks is that trap needs to form. A trap is a structural or stratigraphic configuration that literally traps the hydrocarbons. This needs to be both a spatial and temporal trap; i.e. the right place at the right time otherwise there's nothing to trap.

This is why there isn't that much - most of it leaks away and is not trapped. What we see today is simply that hydrocarbon that was generated, migrated and trapped. It is not all that was generated. Of course some hydrocarbons that were generated my have been lost as the trap was breached by tectonic activity. Hydrocarbons are lot like fossils - to be preserved is extremely fortuituous.

I plan to write a tutorial on hydrocarbon formation, but as ever time is my enemy :) 

Hope that helps.

That makes sense. Oil is just one of the ways hydrocarbons are left from millions of years of decaying bio-matter. It is not so much that things die and form oil but rather hydrocarbons. If there is a void big enough and made of the right rock then we get Oil. If not, leeching and other ways give us hydrocarbon is smaller amounts in different forms. Shale(the right kind?) and Coal I am assuming could be another form of hydrocarbon. Maybe a rock with trace amounts of hydrocarbons?

 

Make a sense.

Thank You very much

Grajek 

Anyone knows any low cost and effective methods of hydrocarbon detection, both surface and subsurface? 

I wish I did - I'd make billions!

I agree that most of the oil and gas that has formed due to burial of organic mater (be it coal or shale, indeed) has already escaped through earth crust or still is. I believe this is estimated to be up to 90% of what is being or has been formed. Therefore it is also true that most oil 'polution' in the ocean is from natural soures (http://tomnelson.blogspot.com/2008/07/oil-seepage-from-ocean-floor-accounts.html).

If you are implying though that we will not find more oil and that the famous 'Peak Oil' has been reached I disagree. Most reservoirs are being produced to 30% to 40% of what oil is in place. With more expensive techniques this remaining oil could also largely be produced. Furthermore new technology and higher oil price has recently opened up the Shale Gas volumes.

I still believe in the popular metaphor used when discussing peak oil: "the Stone age did not end because we ran out of stones". 

We'll find something new, but not because the hydrocarbons are depleted.