What Is A Shale Gas Play?

The term “play” is used in the oil and gas industry to refer to a geographic area which has been targeted for exploration due to favorable geoseismic survey results, well logs or production results from a new or “wildcat well” in the area. An area comes into play when it is generally recognized that there is an economic quantity of oil or gas to be found. Oil and gas companies will send out professional “land men”  who research property records at the local courthouses and after having located landowners who own the mineral rights in the play area, will offer them an oil and gas lease deal.  Competition for acreage usually increases based on how hot the play is in terms of production from discovery wells in the area. The more oil and  gas there is to be had, the higher the lease payments per acre are.

The size of an oil or gas play may be only a few hundred acres or as is the case with the Eagle Ford shale, Haynesville shale, Barnett shale and Marcellus shale, cover hundreds of thousands of acres over a wide region.

A shale gas play, such as the ones mentioned above, is simply a discovery of oil or gas in shale rock that is significant enough for oil and gas companies to launch a campaign of leasing and subsequent exploration. In the case of the Eagle Ford shale it is turning out to be both a shale gas play and and oil play.

What Is Shale Gas?

Shale is a sedimentary rock that is generally formed as particles of sediment settle out in calm water. Shale can be formed in shallow inland waters or deep ocean basins. Many of the shale formations in the United States, such as the Marcellus shale, were formed during the Devonian period, around 390 million years ago.

The rock found in the Eagle Ford shale, which is the focus of this blog, was formed in a marine environment during the Cretaceous period, approximately 145 to 65 million years ago. It was during the Cretaceous period, following the Jurassic period, that many of the worlds limestone formations were laid down. Cretaceous literally means “chalky”, taken from the German word for chalk,  Kreide. The Cretaceous period was a time of warm climate and high seas. During the Cretaceous period billions of tons of CO2 were “sequestered” by marine organisms and eventually returned to the earth in the form of sediments.

Shale rock is generally high in organic content. Once covered up by other sediments and buried over millions of years, heat and pressure begin to work on these sediments and oil and gas are formed. Some of the oil and gas may begin to migrate upwards, to layers of sandstone and porous limestone where it becomes trapped. These are considered conventional oil and gas reservoirs and shale is often the “source rock” or original source of the hydrocarbons. In some cases, as in the Eagle Ford shale play, a significant quantity of oil and gas remain in the shale rock. Natural gas and oil that occur in shale are called “unconventional”.  Now with new horizontal drilling and hydraulic fracturing methods it is possible to extract that oil and gas. “Unconventional” gas is quickly becoming the new norm.

The illustration below shows how South Texas looked during the Cretaceous. It was covered by shallow warm seas. It was during this period that the Eagle Ford shale was deposited.

Below is an illustration of what a shale formation looks like underground and how a horizontal well is drilled.

Shale gas, from rock formations such as the Marcellus shale, Haynesville shale, Barnett shale and now the Eagle Ford shale, is an important energy resource for the United States. Now thanks to these “discoveries” or moreover the advances in technology that make recovery of oil and gas from shale possible, we have over 100 years worth (and growing) of natural gas supply in North America. Hopefully our elected officials will wake up to this new reality and quit wasting our tax dollars on things like corn ethanol and “clean coal” and instead focus on converting our vehicles and power plants to use abundant natural gas.

Article by Nolan Hart

Here is a good book to get if you are considering leasing your land for oil and gas exploration. It’s not cheap but could save you thousands in the long run.