Do you own a SUV?

Chuck52 · Sep 22, 2005

Sneaky,

How about a lecture on the sources and differences in the natural gas products....I'm so confused!

I know there are gas wells in addition to petroleum wells, and I assume some wells produce both, though it may not be economical to collect both from the same well? Is propane derived from cracking petroleum, or is it isolated from the mixture of gases in natural gas? Is natural gas mainly methane, and is that why it can be possible to add bio-derived methane to a natural gas supply? Lastly, is the new-to-me theory of carbon cycle derived petroleum similar to cold fusion and magnetic water softeners, or is it possible in your view?

Semi-science-literate people want to know.

Chuck

sneaky_pete · Sep 22, 2005

( How about a lecture on the sources and differences in the natural gas products....I'm so confused!)

OK, I'll try, although someone like Skypup knows much more about the actual chemistry than I do.

Petroleum liquids and gases consist of a wide spectrum of hydrocarbon-chain molecules. Vastly simplified, these can range from near solids like tar, to heavy, medium, and light crude oil, to gas condensate, and many different constituents in natural gas - principally methane, ethane, propane, and butane. The relative concentrations or percentages of these hydrocarbons in any given reservoir (oil and/or gas field) depends on the thermal history and depth of burial and the timing of when the hydrocarbons migrated into the reservoir. But the important thing is, more than one phase of hydrocarbons almost always exist together in the same reservoir. In other words, yes, many fields produce both oil and natural gas, as well as water. Gravity and hydrodynamic pressure (among other things) will segregate the phases over time, so that it is common (but not universal) to have a field with water on the bottom, oil on top of that, and gas on top of the oil.

The source of all these products is the same in any given sedimentary basin, usually organic shales. Again, what makes the difference between them is the relative amount of "cooking" by the heat and pressure of burial and other tectonic events nearby. All of the gas and oil products are related and many coexist at the same time in the same reservoir. In this regard, the earth itself is a large (but very slow) refinery, breaking down and segregating the various hydrocarbon constituents of crude oil over time.

So, oil and gas are not mutually exclusive substances, but just different densities of the same basic petroleum material.

Crude oil is refined (distilled and/or hydro-cracked) into more distinct useful fractions like lube (motor) oil, diesel, fuel oil, kerosene, jet fuel, gasoline, and etc. Most crude oil has gas fractions in it too, but these are mostly seperated at the well head. Some Propane and other useful gases come from crude oil.

Similarly, raw natural gas must be processed to take out the water, C02, and H2S, and then to seperate it into Methane (what we call natural gas, or CH4) Ethane, Propane, and Butane. The bulk of our Propane comes from this kind of gas processing. Ethane, Propane, and Butane are just the heavier, longer-chain gas molecules that are stripped out of the raw mixed gas from the well.

Again greatly simplified, the rest is just acronyms: LP is Liquid Propane, LPG is liquid Propane and/or liquid Butane, LNG is Liquified Natural Gas (Methane). It is convenient, cheap, and relatively safe to store and transport these gases as liquids and then allow them to vaporize as needed to burn them.

( I know there are gas wells in addition to petroleum wells, and I assume some wells produce both, though it may not be economical to collect both from the same well?)

Depending on the design of the well, it is fairly easy and common to produce both oil and gas from one well, from different portions of the same reservoir, or from different vertical reservoirs in the same well. Usually, you will run a steel tubing string inside the well casing, and pump oil up the inside of the tubing and let gas rise by gravity in the annulus between the tubing and the casing.

( Is propane derived from cracking petroleum, or is it isolated from the mixture of gases in natural gas?)

Both, as explained above. Mostly the second way.

( Is natural gas mainly methane)

Yes; raw natural gas at the wellhead is about 80% Methane. The natural gas you buy and heat your house with (or the power company burns to generate electricity) is more like 99% Methane.

( and is that why it can be possible to add bio-derived methane to a natural gas supply?)

Yes, a Methane molecule is a Methane molecule, no matter where it comes from.

( Lastly, is the new-to-me theory of carbon cycle derived petroleum similar to cold fusion and magnetic water softeners, or is it possible in your view?)

I think you might mean abiogenic (non-biologically-derived) petroleum? The traditional view of hydrocarbon generation by the decay of organic material is part of the Carbon cycle as it is understood and taught today. Some have proposed various theories of abiogenic petroleum generation, but these have yet to be proven successful by the drill bit. Not to say that they couldn't work, just that they have not been proven yet. One thing I like about geology as a science is that there are not many absolutes, and there is lots of room for new ideas. I had college professors who didn't believe in plate tectonics, yet today it is pretty universally accepted. We will have to come up with some new ideas and new technologies to make it through the rest of this century without some drastic upheaval.

( Semi-science-literate people want to know.

Chuck
)

They probably got more than they wanted! /forums/images/graemlins/blush.gif

Chuck52 · Sep 23, 2005

That was what I was looking for. Thanks! I was not aware, though I probably should have been, that commercial natural gas is essentially pure methane. I thought it to be a mixture of the lower hydrocarbons, essentially as it came from the well.

Abiogenic petroleum generation was indeed what I was referring to. I have worked with synthetic organic chemists who use very high temperature/pressure synthesis techniques and get some surprising results, so the idea that CO2, water and whatever else could be cooked by the heat and pressure near the mantle and could potentially yield hydrocarbon mixtures doesn't sound completely off the wall, but then neither did cold fusion when I first read about it. /forums/images/graemlins/blush.gif
The particular article about it that I read stated that many oil deposits are located in zones which have no obvious link to sources of the biomaterials which presumably were the raw products from which the petroleum was derived. I had no way to evaluate that claim.

Chuck

sneaky_pete · Sep 23, 2005

( I was not aware, though I probably should have been, that commercial natural gas is essentially pure methane. I thought it to be a mixture of the lower hydrocarbons, essentially as it came from the well.)

You can burn wellhead gas in your house (if you're very careful), people do it all the time - but Propane and Butane have very different burn rates and hence need larger orifice jet sizes in the burners of gas appliances, so if you have very much of these two in your Methane mix it could be a fire hazard for gas appliances.

( The particular article about it that I read stated that many oil deposits are located in zones which have no obvious link to sources of the biomaterials which presumably were the raw products from which the petroleum was derived. I had no way to evaluate that claim.)

The vast majority of petroleum (that we know about) has migrated away from where it was generated. Since petroleum is less dense than just about anything else in the earth, gravity tends to force it upwards and sideways over long periods of time. You must have at least three things for an oil or gas field to exist and be discovered: a source for the hydrocarbons, a reservoir to hold them in, and a trap or seal to reservoir to keep them from escaping. Geochemists can usually tell the source of petroleum by its composition.

Again, not to say that there isn't or couldn't be any abiogenic petroleum, but if there is, it hasn't been proven beyond reasonable doubt yet.

slowrev · Sep 23, 2005

Sort of amazing. We do not even know how oil was made, but we know how much is left ????

Ben

HGM · Sep 23, 2005

/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

sneaky_pete · Sep 23, 2005

( Sort of amazing. We do not even know how oil was made, but we know how much is left ????

Ben
)

"knowing" how much is left is in reality more of a WAG. Most predictions of how much is left must depend on statistics. For example, the average size of new discoveries has been getting smaller over time, therefore one could conclude that this trend will continue and extrapolate it out.

The other thing that makes remaining oil a very elastic number is economics. For example, there is a large resource of crude locked up in tar sands that is very expensive to process, so as long as the price of oil is below some threshold it will never be produced, but at sustained elevated prices it would be economic to produce. Same with things like wells that produce a lot of water with the oil - the water is expensive to lift, process, and dispose of, so every well that makes water eventually comes to point where you can't afford to handle the water even though it is still making some oil too. The higher the price of oil, the longer you can afford to make water and oil. Therefore, how much is remaining (is economically recoverable) is a very different number with $20 oil than it is with $60 oil.

MikePA · Sep 23, 2005

sneaky_pete, thanks for your well written and informative posts! /forums/images/graemlins/smile.gif

Boomerang1 · Sep 23, 2005

My two cents worth. We Americans can drive what we want, waste or save as much as we want and care about this planet as much or as little as we want. If I wish to leave my truck running for 24 hours straight, that's my business. If some one wishes to drive an all electric car, that's their business. Don't tell me what I should or should not do and I won't tell you want you should or should not do.

I have had people confront me about the type of vehicle I drive and they soon found out they picked the wrong person and walked away with their tail between their legs.

sneaky_pete · Sep 24, 2005

You're welcome, Mike. I'm trying to give up debating, arguing, or defending the oil industry, capitalism, and the environment and just post the facts when I have them.