The Barnett Shale Formation of North Texas and Oklahoma 

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Map Of The Barnett Shale Map  Oilfield Jobs In Texas

What Are Frac Tanks Used For?

barnett shale oil rig Rig site near Cleberne, TX   barnett shale oil rig worker Derrick Hand Working on Barnett Shale Rig

Horizontal or Directional Drilling For Gas In the Barnett Shale

In part due to the worldwide demand for energy and decreasing oil and  natural gas supplies, oil and gas companies are exploring areas previously passed over because they were believed to be unproductive. One such area that has been known about for years is the Barnett shale formation of North Texas and Oklahoma.

(Note: Some of the information in this article may now appear dated since it was written several years ago. Natural gas prices have fallen and drilling in the Barnett Shale has largely slowed down, yet is still ongoing. The original content of this article has been preserved to give an indication of what the play looked like in the beginning.)

What is The Barnett Shale?

The Barnett Shale is named after  early day settler John W. Barnett who homesteaded in San Saba County Texas where he named a local creek the Barnett Creek.  During the early 20th century during a geological mapping expedition a geologist noticed the black shale outcropping in Barnett Creek and named it the Barnett shale after the creek. In that area of the state the formation outcrops or touches the surface. It is in the seven to eight thousand foot deep range near Dallas.

What creates gas and condensate in the Barnett Shale is organic matter called kerogen that lies embedded in the shale. Through biogenic and thermogenic action, natural gas is given off. The Barnett Shale is rich in organic matter and some believe that biogenic action is still producing natural gas even now.  The Barnett Shale is known as a "tight" gas reservoir meaning that the gas is not easily extracted. The formation is a very hard shale and it was virtually impossible to produce gas in commercial quantities from this formation until recent improvements were made in fracturing technology and directional drilling. Large quantities of fresh water are used to frac the Barnett Shale. Surface water supplies may be depleted during this process.

How Old Is The Barnett Shale and How Large Is It?

It consists of Mississippian age (354-323 million years ago) sedimentary shale rocks and stretches  from Dallas to west  of Fort Worth and southward, covering at least 5,000 square miles in the Fort Worth Basin. The Barnett shale is also found as far West as Pecos County in West Texas. There have been exploratory wells drilled in Reeves County in the Barnett shale with mixed results but exploration continues there. (See map of Barnett Shale below)

How Much Gas Does The Barnett Shale Contain?

Oil and Gas Experts have suggested that it may be the largest onshore natural gas field in the US although new estimates from the newly discovered Marcellus Formation in Appalachia may equal the Barnett. The field is proven to have 2.5 trillion cu. ft  of natural gas and the figure could be higher as the boundaries of the Barnett Shale are pushed.  Besides natural gas condensate and  light oil  has  been found in lesser quantities and sufficient enough at today's prices to be commercially viable. Below is a chart showing the amount of natural gas production from the Barnett Shale.

Illustration of how much gas was produced since horizontal drilling in the Barnett Shale Began. (It is over 800 billion cu/ft per year now.)

What Is Horizontal Drilling?

Horizontal drilling is a technology whereby oil and gas companies can drill "sideways" at ninety degrees across a zone of rock such as the Barnett shale, allowing for hundreds of feet of profile to be exposed.  After the horizontal well bore is drilled it is cased, perforated and then "fraced". A frac job involves the pumping of super high pressure fluids into the formation to open up more fissures for gas to escape from. See the photo below of a Halliburton frac job in progress. Many high pressure pumps are used in stages to pump thousands of gallons of fluid into the formation, often along with a "proppant" or spherical type of glass or polymer bead to keep the fissures open.

horizontal drilling    halliburton frac job

How Does Horizontal Drilling Apply To The Barnett Shale?

The Barnett shale has been known to geologists and oil men for decades. When it was drilled through a small amount of natural gas would be encountered but because it was shale, a low porosity rock, it was never considered a reservoir of natural gas. When horizontal drilling was perfected a couple of decades, oil and gas companies such as Chesapeake, Devon, EOG and others, began taking a look at shale formations such as the Barnett shale. In 1981 Mitchell Energy, later acquired by Devon Energy, drilled the first well in the Barnett Shale and decided to try and produce it because of the amount of gas detected by the mudloggers. They set casing and did a small frac job and were able to produce a fair amount of vas for a vertical well. Although that well was not economically viable it focused attention on the Barnett shale. Over the years hydraulic fracturing techniques were perfected, as was horizontal drilling, and the gas boom was on. Now there are dozens of rigs drilling horizontal wells in the Barnett Shale for a variety of oil and gas companies.  See the You Tube Video below for an illustration of how horizontal drilling in the Barnett Shale is done.


The Economic Impact Of The Barnett Shale

The Barnett Shale Formation Of North Texas Is possibly the biggest economic boost to that area in history.  It has been estimated by the Fort Worth Chamber Of Commerce, that the impact of the Barnett shale on the economy of a five county area, including Tarrant, Johnson, Hood, Palo Pinto and Erath counties is equal to five Boeing jet manufacturing plants opening up.   The Barnett shale is productive in at least 17 counties. Far from a drop in the bucket, the natural gas contained in the Barnett shale will go a long way to powering America's future. Advocates of a natural gas powered United States, such as T. Boone Pickens, believe that there is enough natural gas in shale formations like the Barnett to last over 100 years.

Formerly economically depressed areas such as Cleberne, Texas and Weatherford, Texas are now boom towns. Thanks to high paying oilfield jobs and  landowners spending gas royalties, the local economies and tax base have drastically improved in counties where the Barnett shale is productive.  In 2006, the Barnett Shale was responsible for  creating 55,385 permanent new jobs, and is estimated to have  contributed $491 million in revenues to the state of Texas, and $228 million  to local governments. Economists estimate that by 2015 the Barnett Shale may be responsible for more than 108,000 total jobs in the areas where it is being heavily exploited. One drilling rig provides good paying jobs directly and indirectly for over 130 persons.

Impediments to Development  barnett shale homeowner protest     barnett shale cartoon  From the Comic Strip "BC"

The development of the full potential of the Barnett shale has come up headlong against the dense urban areas of the growing Dallas - Fort Worth Metroplex and protests are growing from homeowners and city governments worried about eyesores and noise from drilling rigs and pipeline construction. Lawsuits from neighborhood groups and individuals abound, especially ones from parties that do not own the mineral rights under their property.

 Environmental Concerns.  Due to the fact that it is a low porosity, low pressure gas formation it requires a serious "frac job" or fracturing of the rock formation, by a company  such as Halliburton to produce gas.  The fracturing  process requires massive amounts of water, which is injected under extreme pressure to fracture the rock and allow it to release gas.  This need for large amounts of water has put a strain on surface water supplies in the areas where Barnett shale  directional drilling is concentrated.   Despite these impediments rigs are working night and day at present and there is no end in sight to the wells being drilled despite the economic downturn and the resulting lower price of natural gas.  Drilling throughout this area has been intense, with directional drilling programs by companies such as Chesapeake running at full steam ahead and landmen rushing to grab up mineral rights in areas that were previously overlooked.

Main Players

Devon, EOG, XTO, Chief, Williams, Chesapeake and Quicksilver are all major players. The maps below show the heart  of the Barnett shale in Parker, Tarrant, Johnson, Hood, Palo Pinto and Erath counties  and top leaseholds.

Map Of The Barnett Shale. (From USGS) barnett shale map   Click Here For Full Sized Map Of The Barnett Shale

barnett shale play map     

How Long Will Drilling In The Barnett Shale Last?

In an interview with the American Association of Petroleum Geologists, Larry Brogdon, exploration manager for Four Sevens Oil Company, had this to say; "We will all be dead and folks will still be drilling Barnett wells," he said. "There are literally thousands of infill wells to be drilled in the core areas and operators will continue to push its limits."

Update: Depressed natural gas prices have led to a reduction in overall drilling in the Barnett Shale. Despite this, drilling continues in some parts of the play, especially the "Barnett Combo" which centers around Montague county, and which contains valuable liquids such as oil and condensate.

Helpful Links about shale gas drilling:    The Haynesville Shale  Oil Patch Bookstore    Marcellus Shale Formation



In an interesting side note, another shale formation, the Eagle Ford shale in South Texas, is proving to hold even more natural gas than the Barnett shale.  For more about the newly discovered Eagle Ford Shale click here: The Eagle Ford Shale Formation, Map and Info.  Bookmark and Share  

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