How do hydrocarbons migrate through granite and other intrusive rocks?

[eventob]

I've read some places that people discover hydrocarbons in intrusive and metamorphic rocks? For instance in Vietnam and Venezuela.

Why is this? Is it due to migration from sedimentary reservoirs (for instance if a granite intrudes a sedimentary rock)?

 

[klimatos]

I've read some places that people discover hydrocarbons in intrusive and metamorphic rocks? For instance in Vietnam and Venezuela.

Why is this? Is it due to migration from sedimentary reservoirs (for instance if a granite intrudes a sedimentary rock)?

Yes, that is one way in which contamination can take place. You can also add exposure to ground water, exposure to air, contamination with body oils in handling, contamination by packaging or shipping materials, contamination from display materials, . . . the list is endless. Generally speaking, any rock sample that is more than a few seconds out of matrix may be assumed to be environmentally contaminated.

 

[Ophiolite]

eventob is not talking about contamination, he is asking about full blown, producing hydrocarbon reservoirs in igneous rock.

This is not commonplace, but it most certainly occurs. You mention Vietnam: here the production is from fractured granite basement. It would be more correct to say the oil has migrated there from source rocks rather from other reservoirs.

In other locations the production is from granite wash, the coarse, minimally weathered material eroded from an adjacent granite.

The presence of oil in igneous rocks has been known for over 3/4 of a century. For example:

Oil in dolerite dykes and amygdales in lavas. (Haughton,S.H. et al Results into an investigation into the possible presence of oil in Karroo rocks in parts of the Union of South Africa, Geol.Survey Mem. 45, Union of South Africa, Dept. Of Mines. 1953)

Oil droplets and tar filled geodes in Columbia Plateau basalts. (Felts, W.M. occurrence of oil and gas and its relation to possible source beds in continental Tertiary of Intermountain region. Am. Assoc. Petroleum Geologist Bull. V38, 1954)

A wider range of examples can be found in Powers, S. “Symposium on occurrence of petroleum in igneous and metamorphic rocks.” . Am. Assoc. Petroleum Geologist Mem. 1 1932, and in van Tuyl, F.M. et al “occurrence of oil in crystalline rocks in Colorado.” . Am. Assoc. Petroleum Geologist Bull. v 16. 1932.

More recently there is a useful compilation of instances here:
Stephen R. Schutter, “Occurrences of hydrocarbons in and around igneous rocks” Geological Society, London, Special Publications; 2003; v. 214; p. 35-68;
Abstract
Data on the occurrence of hydrocarbons in and around igneous rocks show them to be global in extent, occurring in over 100 countries worldwide. While this list is not exhaustive, it is possibly the first of its kind to be published, and will serve as a useful source of reference for those wishing to embark on further study.

 

[GeoHamster]

Another great reference for these types of curious reservoirs:

Petford & McCaffrey (2003), Hydrocarbons in crystalline rocks, Geological Society of London, Special Publication 214

http://books.google.com/books?id=9i...&resnum=1&ved=0CCoQ6AEwAA#v=onepage&q&f=false

 

[razrah]

Ophiolite, since you are talking like the geologist, can I ask you some question. How is the hydrocarbon from the source rock migrated through the fractured granite basement or igneous body? is it the source rock location below the basement granite in the subsurface? As what I know (correct me if I was wrong) the basement granite always form at the bottom and then followed by the reservoir. is that the oil migrated downward? I'm very interested to see your explanation. thanks

 

[RockKnocker]

There are several scenarios where oil is found in igneous rocks, both as a reservoir and as a trapping layer. In the near past, there was thought that the rocks of the Columbia River Basalts could trap underlying hydrocarbons which formed in the older Eocene continental sediments over which the CRB's flowed. There are many similar occurrences of smaller extent world wide.

There are other situations where crystalline rocks could be thrust over younger sediments, and form a trap structure. This could very well be the case in Vietnam and Venezuela which the OP speaks of. In the US, this could be the case in some of the over thrust belt of Wyoming, particularly near Pinedale. But I'm not certain of this.

The last case which was popular by Russian and Soviet geologist, and latter by the physicist Thomas Gold, is that some hydrocarbons are the result of exhalations of hydrocarbon rich gasses from the upper mantle into shield rocks. Parralel to this is another hypothesis that extremophiles deep in the crust are responsible for much of the Earth's hydrocarbons.

A drill site in the Swedish shield, far removed laterally and much deeper than any younger sediments produced a exceptionally minor amount of oil ( on the order of 50 US gallons). Some have used this event to suggest that this proves the occurrences of oil deposits not explainable by standard model of decomposition of terrestrial organic matter in Phanerozoic sedimentary basins. Others contend that this oil is drilling oil, and the result of poor record keeping at the drill site.

Thomas Gold's book "The deep hot biosphere" is a good read. But remember that no occurrence of oil, coal or natural gas has been found that is not easily explained by more common models. If Gold was correct, I would suggest that old shield rocks (so there is ample time for accumulation) with structures compatible with formation of a reservoir ( such as the Michigan dome) where much geologic exploration as a course of industry has occurred ( such as the iron stone belts of the world) would have produced oil. This has not been the case.

 

[darksociety]

Ophiolite, since you are talking like the geologist, can I ask you some question. How is the hydrocarbon from the source rock migrated through the fractured granite basement or igneous body? is it the source rock location below the basement granite in the subsurface? As what I know (correct me if I was wrong) the basement granite always form at the bottom and then followed by the reservoir. is that the oil migrated downward? I'm very interested to see your explanation. thanks

Assuming a biogenic source, the structual framework of the study is important. If there is an unconformity, for example, between the granitic basement and the overlying source, sedimentary rock, hydrocarbons will find some way to exploit it if the conditions are right. Another scenario might entail brittle faulting configurations, or shear zones.