< p >有更多比其实质性的时代,但不是很多。< / p > < p >首先,一点背景。我们需要几个条件积累的石油或天然气:< / p > < ul > <李> < a href = " https://en.wikipedia.org/wiki/Kerogen " >干酪根< / >丰富的烃源岩,“熟”热成熟度。温度不足,或时间不足,未煮熟的;如果温度过高,或岩石很旧,挥发物都排放或破裂。我不知道任何关于奥陶系烃源岩比;最好的是侏罗纪时代。李李< / > < >迁移路径从源捕获配置,和时间发生。李李< / > < > < A href = " https://en.wikipedia.org/wiki/Structural_trap " > < / >结构或地层圈闭,如一个背斜,填充以来保存它的地质条件。李李< / > < >储集岩——多孔透水岩石。通常这是一种沉积岩,尽管碳氢化合物被发现在破碎花岗岩(例如在越南; this is rare). Only 'conventional' hydrocarbon deposits need all these conditions (sometimes called a 'petroleum system', such as you might find in the North Sea). 'Shale gas' is basically just a mature source rock — we can extract hydrocarbons from it by fracking, for example.
As you might guess from the list of conditions, there are lots of things that can destroy a hydrocarbon accumulation, or preclude its formation. For example, deep burial destroys porosity by diagenesis and compaction. Time increases the likelihood of trap leakage or thermal destruction of volatiles.
So, why no hydrocarbons in the (mostly Precambrian) Swedish-Norwegian shield? Maybe these are the top 3 reasons:
- These old rocks never had a good source rock: too old, too little life. A bad start.
- They are so old that any source would have been mature hundreds of millions of years ago.
- In any case, metamorphosis has destroyed any potential reservoirs, and a combination of tectonism, orogenesis, and exhumation has destroyed any traps.