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The Eagle Ford Cafe

A Tale Of Two Oils, Cooked In the Same Kitchen

Here are two distinctly different crude oils, both cooked in the same late, Cretaceous Period kitchen that is some 90-120 million years old, give or take. The kitchen is located in the Eagle Ford shale of South Texas; its productive limits range in depths from 7,000 feet to 10,000 feet below the surface. Oil properties of the Eagle Ford vary greatly with gravities between 41 and 55 API, sulfur 0.6 t0 1.4 PBV, viscosities between 0.2 to 0.7 cp and gas to oil ratios all over the map.

Eagle Ford oil, on the right, above, came directly from the kitchen just a few days ago; it is 49 gravity API, has 0.6% BV sulfur, is very light and looks, smells and tastes like gasoline. If you take a big whiff it will give you a headache. It will burn easily.

The Eagle Ford oil on the left, in the first photo (taken in my cantina at home), was cooked at the same geological time, 100 million years ago, give or take, but escaped its place of origin and wandered around for 45-55 million years looking for a place to call home. Its expulsion from the source bed, and subsequent migration, exposed it to lower temperatures, less overburden pressure, and a great deal of contact with sea water that oxygenated the oil, or weathered it, altered its gas oil ratios and disbursed most high-end volatiles.

The Eagle Ford oil on the left is much lower, 21 API gravity, is more viscosus and its sulfur content is still very sweet at 0.4 PBV. It is deep, dark green and smells wonderful; In spite of that, Ms. Catherine will not put a little behind her ears now and then, like Channel No. 5. I took this dark green oil on the left out of its home just a few days ago also.

The oil on the right is good for making gasoline, little else. The oil on the left is an excellent lubricant oil and is hightly sought-after. It makes good diesel and can be blended with the other stuff, to make the other stuff seem better than it is.

Geology is really cool. To be able to understand depositional environments, source rocks, migration and oil traps (homes), one needs to set linear, two dimensional concepts aside, create mind-images that are multi-dimensional and invision events that occured at a snail's pace, spaced out over millions and millions of years.

Think of great oceans bounded by high mountains that covered Texas, receded back and forth leaving sediments behind that piled one on top the other over long periods of time. Those sediments had different characteristics, (permeability and porosity), they disappeared, reappeared, formed beaches, river channels, big holes, giant humps, and all the weight of this sediment loading over the years caused the earth great upheaval.

The Eagle Ford time of the Cratecous Period was a period when mudstones, rich in organics, drained onto the sea floor from northern reaches. Sea water above this mudstone became carbonate limestone over millions of years, mudstone because dense shale under overburden pressure and heat and... oil was made from those organic goodies embedded in the shale.

More sediments were stacked on top of old over geolgical time, slumppling, sloughing and faulting occured as the great sea

(Gulf of Mexico) finally receeded to its current location. This faulting, above, created a great deal of sediment compartmentalization and, sometimes, created structural traps for migrated oil to call home. A lot of Eagle Ford oil that was expulsed from the kitchen migrated up these faults.

The dark green oil sample on the left, above, migrated vertically up fault planes 6,000-7,000 feet and leaked out into Eocene (40 MM years old) sandstones with tremenous porosity and permeability and became trapped, unable to migrate anymore. I found where this oil resided over vast areas in South Central Texas and I squeezed as much of the stuff out of the ground as I could.

Souce beds, or oil (and gas) kitchens supplied all sediments in the world's producing basins. The Wolfcamp and Spraberry, for instance, are the source beds for shallow Greyburg, San Andreas, Canyon formations in the Permian Basin.

So, in my example, same oil, same kitchen. Some of that oil stayed in the kitchen and continued to cook in the crock pot, some of that oil escaped and took a different journey over its existence to shallower traps. Its long, arduous travels simply altered its properties.


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