2012-05-16 / Oil and Gas Report / Columns

Oil & Gas Report

Development of oil and gas drilling in Atascosa County
Leon Zabava

"The Somerset Field, in the northwest area of the county, was where the first drilling activity occurred in Atascosa County, in 1919," said local geologist, Arthur Troell, continuing, "The second field, developed in this county, was the Imogene Field, on the Mark Thompson Place, in 1943, on County Road 429, south of Pleasanton. That Thompson well was Edwards production. Humble Oil and Refining Company (Exxon now) was in the Imogene area and they mapped the surface geology of Atascosa County. They determined where the formations are and they sought the faults that intersected the county. It was the surface mapping, based on these faults, that led to the Mark Thompson Well #1, which was a discovery in the Edwards Limestone."

"Carrizo discoveries happened in the 1950s. That's the Carrizo Sand that we get our drinking water from here in Atascosa County. There was fresh oil on top of the Carrizo water, in certain places, on the faults and that accounted for another big wave of exploration in the county. Then we had some shallow production in the Escondido, but that was not as big. There was early production in the Edwards and Carrizo, in the Fashing area, in southeast Atascosa County."

The first Eagle Ford well drilled in Atascosa County was likely the Emma Tartt #16, in the Fashing area, in February of 2007. This was a vertical well, initially drilled into the Edwards in 2006, but later, a bridge plug was set to seal off the Edwards, to see what the Eagle Ford would produce. It came in at about 120 or so barrels a day and tapered off quickly and wasn't a viable well a couple of months later. This was an XTO (now XTO/Exxon) well. It was an example of why horizontal fracturing was necessary to complete wells efficiently in the Eagle Ford.

Troell said, "Everybody's always asking about the Eagle Ford and bringing up their concerns about the Carrizo Sands being fracked into. When you look at the position of the Carrizo related to where the Eagle Ford Shale is located, you find a great deal of distance between the two. Looking at charts, there's the Union #1 Downey Well, drilled on September 21, 1958, about six miles southeast of Pleasanton, just north of Jim Brite Road. This is where Humble Oil was trying to extend the production along that fault. At the Union #1, there's over 5,000 feet of interval between the base of the Carrizo and the top of the Eagle Ford. Most reasonable geologists will tell you that it's not likely for that to frac up that far through the interval section, then contaminate the water.

"We have reports from around the country of where they frac and they have Arthur TroellArthur Troellcontamination, but what they're not telling us is the details. For instance, where are the water sands relative to the formation they're fracing? So, we'd need to have that data to compare it. There have been no reports about that at all in the Eagle Ford wells," continuing, "Drillers are required to cement off the water sands. Drillers do take care and they're constantly inspected by Railroad Commission personnel out in the field. It's not to the driller's advantage to be losing fracing fluids anywhere. They want that to go where it's intended. This is all under the supervision of the Railroad Commission, and their rules, and they're on the sites all the time. One shouldn't extrapolate and try to assume conclusions from details derived from reports from other parts of the country."

"You hear all the talk about water and natural gas. There was an article, before, showing that, when they first drilled water wells in the town (Pleasanton) in the Queen City, they produced both natural gas and water (Pleasanton Express, Oct. 19, 2011, front page, Once upon a time...Natural gas a bonus). If you recall, a water well was drilled on the former Atascosa County Courthouse property, now Pleasanton City Hall location. Some wells produced both drinking water and natural gas. People would use a separator on wells like here in the City of Pleasanton, and produced the gas to burn their lights, cooking and heating. The reason for this occurrence is that the Queen City is imbedded sandstone, shale and lignite. Lignite is a type of coal that contained the natural gas that collected in the water sand. Also, fields like the Carrizo, discovered in the county in the 1950s, contained oil on top of the water. Carrizo Sand oil floats on water. If you get off the structure that produces the oil, you have no problem with the water. This is all a natural occurrence. Oil, water and natural gas in the subsurface is part of nature's work and a lot of people don't think about that."

"Oil comes out of organic matter that was deposited along with the sediments. It's not oil to begin with. What it takes is heat and pressure to convert that organic matter into oil and natural gas. The type of material that gives rise to natural gas is called humic matter which comes off land. Alright, so whereas, in the sediments that are deposited, like in the Queen City delta, here, this is ancient matter. In the modern Mississippi

Delta, today, where the precursors of coal called peat, accumulates and eventually, when buried, and through time, give rise to natural gas. That peat goes to lignite. Peat is deposited in swamps, and buried through time, millions of years, becomes deeper. Eventually, if you bury that material deep enough, with time, it becomes bituminous coal. The miner's up east have that gas and explosions because of natural gas."

Troell added, "In marine environments, when we get organic matter, called sapropelic material, originating from marine plants, such as the various algaes, and that material accumulates, it is converted, mostly, into oil. That is why, for example, in the Middle East countries such as Saudi Arabia, Kuwait and Iraq, the oil fields over there all come from marine beds. Their beginnings didn't have anything to do with land deposits."

The rock we're looking at here in the Eagle Ford Shale is, basically, a limestone. It's a marine deposit. It came from offshore marine deposits millions of years ago, therefore, that organic matter is sapropelic, that gives rise to oil. Now, if you bury it deep enough, the temperature and pressure can then convert that into natural gas, as you find, in the down dip of the Eagle Ford Shale. At shallow depths, you'll have oil and go a bit deeper and you'll have condensate and natural gas, and then, even deeper, it's pure natural gas.

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