Eagle Ford Shale Drilling Effect On Carrizo Wilcox Aquifer

A sign indicating the beginning of the Carrizo Wilcox aquifer recharge zone, north of Stockdale in Wilson County where Eagle Ford shale drilling is occurring.

Drilling of the Eagle Ford shale may cause some depletion of the Carrizo Willcox aquifer, a vital source of fresh groundwater for much of South Texas. Many communities south of San Antonio get their water from the Carrizo Wilcox water sand. What is concerning some hydrologists is that each new Eagle Ford shale well requires at least three to seven million gallons of fresh water to drill and complete. Long used as a source of water for irrigation in South Texas, the Carrizo Wilcox aquifer has been depleted in some areas as much as 500 feet since the 1940’s.

In addition to potential oilfield water use in South Texas, a major system of wells and pipelines carrying water from the Carrizo Wilcox aquifer has been proposed to supply water hungry cities such as San Antonio.

Below is an excerpt of a paper about Eagle Ford shale water use on the AAPG website.

Below is a map showing major aquifers in Texas, and the Carrizo Wilcox aquifer. From the Texas Water Development Board

Conductivity, or how fast water moves underground in the Carrizo Wilcox aquifer ranges from .1′ day to 900′ day. Because of slow recharge rates, using Carrizo Wilcox aquifer water to frac Eagle Ford shale wells basically amounts to nothing more than water mining. Water is already being removed at a rate faster than which it recharges. A drop of water pumped out of a well in McMullen county may have taken over a hundred years or more to come from the recharge zone, much longer in some areas. A severe strain may be put on the Carrizo Wilcox aquifer as hundreds, then thousands of Eagle Ford shale wells are being completed using hydraulic fracturing. Some small towns could potentially see their municipal water supplies dry up or become brackish as levels fall.

On the positive side, once an Eagle Ford shale well is drilled and completed that is the end of the water usage.  Over the time that it takes to infill the Eagle Ford shale with wells, or space wells out for maximum production, there will be thousands of wells, each requiring several million gallons of water. Unlike some areas of the nation where water rights are a big deal, in South Texas there are no citizen’s groups or landowner’s associations up in arms yet. The same landowners that own the groundwater beneath their land also stand to benefit from Eagle Ford shale gas and oil royalties. 

Below is a map showing the existing water districts in the Eagle Ford shale play. It is a live link to a Texas Water Development Board report.

And who can blame some South Texas landowners for not worrying as much about  water issues. In much of South Texas a Carrizo Wilcox well costs over $50,000 to drill. The only way a landowner might be able to afford one is if it is drilled by an oil company. Oil and gas companies often turn water wells over to farmers and ranchers  after they were done with them.

How Much Water To Frac An Eagle Ford Shale Well?

According to Chesapeake Energy’s website, it takes somewhere around   250,000 gallons to drill a horizontal well in the Barnett shale, which is a similar shale formation. Another three to six million gallons of water are required to hydraulically fracture or “frac” the well.  Reports are that Eagle Ford shale wells are requiring about 6 million gallons each to frac.

What will happen to the Carrizo Wilcox aquifer and other water bearing zones such as the Queen City / Sparta sands  in South Texas as a result of Eagle Ford shale drilling?

Your humble blogger doesn’t have all the answers. However, this will not be the last you hear of what is about to become an very controversial issue in the coming years. Carrizo aquifer water will be one of the hotbed legal issues of the next decade in South Texas.  Our nation desperately needs domestic sources of oil and natural gas, yet we need water even more. Hopefully the Eagle Ford shale can be developed with minimal impact on the Carrizo Wilcox aquifer. Other sources of brackish groundwater in the region may be exploited for frac water instead of the Carrizo.  This is definitely a subject that needs to be examined, and quickly, so that ample groundwater remains in South Texas.

(Note: There have been concerns by some citizens groups about contamination of fresh water aquifers such as the Carrizo, yet little hard evidence has been shown proving that hydraulic fracturing has caused any damage to water sources. The process of fracking oil and gas wells has been done for over five decades in Texas and the Texas Railroad Commission (unlike some eastern states where horizontal drilling is new), has a lot of experience in regulating the process at each step of the game.  There is typically many thousands of feet separating water bearing formations and the Eagle Ford shale. A frac job done on a well that has been properly cemented and tested poses little hazard to water aquifers.)

Below is a map of the Carrizo Wilcox aquifer. The down-dip area of the formation is water bearing and it closely follows the Eagle

Ford shale gas and oil play area.

eagle ford shale water use carrizo aquifer

As Eagle Ford shale frac water from surface supplies becomes increasingly scarce due to a record breaking drought, more Carrizo Wilcox water wells will be drilled. Only time will tell how South Texas’ most important source of groundwater is affected. In an interesting side note, a small oil and gas exploration company, Jadela Oil, is experimenting with Eagle Ford shale frac jobs that utilize propane gel instead of water. See Propane Frac job

For a more updated article see Eagle Ford Shale Frac Water