Wednesday, January 30, 2013

A Trip to the (Booming) Eagle Ford Shale Petroleum Fields

Here's something a little different. The geology I normally am involved with has little to no economic benefit. There are no resources extracted from studying the origin of ancient landscapes or how the Grand Canyon was carved. I recently visited San Antonio, Texas where right now, a modern-day oil boom is underway to the southeast of that proud city. New technology has allowed petroleum companies to drive their drills 11,000 feet beneath the desert floor to a rock unit known as the Eagle Ford Shale. I recently got to visit a friend who owns a small ranch in Karnes County, right in the middle of this bonanza. I took some pictures while on Joe Orr's ranch. First though, a little background. The oil "play" is shown in the graphic below
Texas and the area where the Eagle Ford Shale play occurs
The Eagle Ford Shale is a mix of sandstone and limestone that records a transgression of the sea about 94 to 89 million years ago (Cenomanian/Turonian is the stage). Below is a paleogeographic map showing the setting during Eagle Ford time. Eagle Ford strata are overlain disconformably by the Austin Chalk.

Paleogeography about 95 million years ago. Map by Ron Blakey, Colorado Plateau Geosystems
Regionally, the Eagle Ford shale consists of two depositional units: a lower transgressive unit dominated by dark shale, and an upper regressive unit consisting of shale, limestone, and siltstone.  Eagle Ford microfacies exhibit distinctive sedimentological aspects and have source rock characteristics that vary systematically within a sequence stratigraphic framework. The transgressive rocks have optimum oil source potential, whereas the overlying regressive shales are gas-prone. Transgressive Eagle Ford strata represent poorly oxygenated low-energy, marine environments. In contrast, overlying regressive Eagle Ford rocks accumulated in higher energy, well-oxygenated, shallow marine environments.

Production has soared recently in the Eagle Ford Shale!

The gas flares at night have been captured in this stunning night time photograph (Image courtesy of Scientific American)

Lastly, the major determinant on who gets to play in the voluminous oil money game, depends on the depth of the shale beneath your land. In the graphic below, black represents the surface outcrop pattern of the Eagle Ford. The unit then dips to the southeast and is just beneath the surface in San Antonio. It gets progressively deeper and at about 11,000 to 12,000 feet, the shale produces liquid oil when fracked. Deeper positions yield wet gas and eventually dry gas. All of this geology might be confusing to cattle ranchers but when big oil comes a knockin' the royalty checks start rockin'.
Graphic courtesy of the Energy Information Administration
Now for a tour of the Orr Ranch!

EOG Resources stands for Enron Oil and Gas. It was spun off of the main company before it went down the tubes.

This is the thornbrush desert of south central Texas. There is lots and olots of prickly pear cactus and many species of mesquite.

The Orr Ranch used to be a cattle spread with occasional deer hunting as well. Here is a hunting blind constructed on the ranch.

The old barn on the Orr Ranch. The original ranch house was damaged in a storm and water leaked through the roof so it does not exist anymore.

Here is our gracious host, Joe Orr. His great great grandfather was William G. Butler and he first established his ranch here in the 1850's. Originally at about 75,000 acres, Joe currently has about 1,600 acres on two parcels. Joe is standing in front of a 30 foot deep trench that was the site of a uranium mine during the Cold War. South Texas was the site of much uranium mining, which was dug during the Cold War. See how the uranium was formed here.

Just around the corner we got our first glimpse of one of the wells on the ranch. All of the oil infrastructure you see on this blog has been here for only two years or less.

The necessary warnings to any visitors who happen to chance by

Pipelines are going in everywhere and they serve to connect the various wells into gathering stations, where tanks get filed with crude oil. Then  trucks come by and pick up the crude for refining in Corpus Christi.

A pump-jack at work on the Orr Ranch. This design has not changed very much in all the years of oil drilling. A short history of the pump-jack can be found here.

And another! All told there are 16 wells on Joe's land with another nine slated for instillation sometime soon. Joe is still in a kind of shock about the whole affair. Like myself, he worked for many years as an international guide with 10 years working for Mt. Travel/Sobek in Copper Canyon, Mexico. He really did not have ranching in his blood and inherited the land from his mother when she passed away. The the oil people came knocking about three years ago. It turns out that this relatively small piece of real estate was ideally suited for drilling in the Eagle Ford Shale. What made it possible was the development of fracking technology, whereby extreme pressures are injected into shale rocks releasing the trapped oil. Everyone knew there was oil in the Eagle Ford for decades - there just wasn't any way to get it out. An extensive discussion of the pros and cons of fracking can be found here.

Our "tour group" consisted of Leah M. Joe O., and Helen R.. I took the picture.

This is the Wilson County Courthouse built in the 1880's. Texas has some really beautiful courthouses but this one has some structural problems and is essentially out of commission. However, perhaps the nearby oil boom will allow for the rehabilitation of this historic building. Joe is certainly helping many worthy causes with his new found wealth. There is always a silver lining in any story, if only we know how to find it.


  1. I don't suppose you monitor this site any longer, but I wanted to mention that like Orr (whom I have never met) I too am a gg grandson of W.G. Butler. Unlike Orr, I am as poor as a road-side melon vendor,but it hardly bothers me. Many years back, some of the Butler land was leased out for Uranium mining. My Great Aunt & Uncle were made quite wealthy from their leases - but not happier. Anyway, your blog was very interesting, and I enjoyed it very much! Thanks.

  2. John - So glad to hear from another great-great-grandson of Wm. Butler. We remember Joe but all of the Butler clan who who made this possible. Joe's legacy is helping many fine organizations. Thank you.


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