TECTONIC
TREMBLINGS

STORY: Thom Barker

Images of oil-soaked pelicans struggling in the gulf of mexico break my heart.

I feel a certain kinship with these magnificent birds having lived for three years on B-Say-Tah point on beautiful Echo Lake in southeastern Saskatchewan where a considerable flock spends its summers.

Adding outrage to my compassion is the callous behaviour of oil executives, in particular British Petroleum CEO Tony Hayward, who epitomizes the wanton selfishness and shortsighted greed of his industry. Unfortunately, there is not a person among us, certainly not me, who is not at least peripherally culpable.

But this is not a political column, so I will leave that at that. What is this gooey mess now floating about on the surface of the Atlantic? And how did it get in the ground in the first place?

Most people have a very basic understanding that organic matter plus heat over time equals fossil fuel.

“Fossil fuel” is actually a bit of a misnomer. Although coal, oil and gas technically fit the definition of “any preserved evidence of life from a past geological age,” they are not the kind of direct evidence provided by, say, the petrified bones of a dinosaur. Scientists, therefore, infer organic origin from the chemical structure of the hydrogen-carbon chains, which are only found among living things.

And although a perusal of the Internet may suggest there is a raging debate about the organic origin, the prevailing theory remains that hydrocarbon fuels were formed by the breakdown of organic matter, most importantly, plankton. Plankton are any drifting organisms, including plants (e.g., algae), animals (e.g., jelly fish), bacteria and archaea (a group of microbes that until recently were lumped together with bacteria). Other marine life and even terrestrial organisms may have contributed to the biomass, but not to any significant degree.

When plankton die, they settle to the bottom of the ocean where they are buried along with accumulating inorganic sediments, sand, silt, mud and carbonates deposited mainly by rivers. Anyone who has ever tried to swim to the bottom of a pool knows that at depth pressure increases. Scuba divers have an even greater appreciation for how this effect multiplies the deeper you go.

Multiply that again many-fold for the entire water column plus layer after layer of sediment and before long—geologically speaking—the pressure, along with other thermodynamic processes, starts to generate heat. When the temperature gets to somewhere between 50 and 70 degrees Celsius, the organic matter in the mixture starts to “cook,” for lack of a better term. If you’ve ever burned a steak, you have seen first hand how heat reorganizes hydrogen and carbon in organic material, carbohydrates to hydrocarbons.

Very oversimplified, I know, but now we’ve got oil, albeit trapped in sediment. In order for it to become concentrated in massive reservoirs, such as the Macondo deposit currently spewing into the Gulf, somehow it has to migrate through the rock.

It is somewhat difficult to grasp just how this could happen because of our preconceived notion that rock is solid and behaves as it does on the surface where we can see it, but try this rather simple thought experiment. Take a sponge saturated with water and put it in an equal sized container. As long as it just sits there, and is not acted upon by evaporation, water and sponge would remain interlocked. But place a barbell plate on top, the kind with a whole in the middle, again the same size as container and sponge, and what will happen? Put a smaller container over the plate’s hole and you’ve got a trap for the migrating water. What would happen if you then punched another hole in the top of the small container?

That is also why, once you drill an oil well and there is no rig to collect the crude, it continues to spew into the sea.

In nature, the sponge described in our thought experiment is a layer of porous rock such as sandstone or limestone. A subsequent layer of impermeable rock, for example salt or shale, provide the trap.

Over time, the Gulf of Mexico region has provided a perfect environment for the cooking and trapping of oil. Approximately 175 million years ago, as North America began separating from Africa and South America, the region went through a number of periods of varying sea levels. The reasons for that is another column, but during periods of low sea level, plankton thrived, depositing vast amounts of organic matter on the seafloor. During periods of high sea level that material was buried by sand, silt and limestone. At intermittent times levels be- came so low, evaporation of the seawater created large salt deposits.

A question often asked is why something that comes from formerly living organisms is so hazardous to currently living organisms. I don’t have a good answer that wouldn’t take up another two pages, but as the BP disaster drags on, it is clear we need to find better ways to quench our thirst for fuel.