The Barnett Shale is a formation that is approximately 5,000 square miles in North Texas beneath 18 different counties within the state. The play is known for being the first of its kind amongst shale plays when Mitchell Energy & Development first used new technology necessary to access shale gas successfully in the 1990s. In 2007, experts believed that the Barnett Shale would have the largest producing reserves of natural gas in the United Sates. Its peak production for natural gas was in 2012 when the average reached 5.74 Bcf/d. The shale is known to be very impermeable, being almost impossible to extract gas from the formation until hydraulic fracking was used effectively and efficiently on the formation. This, and with the use of horizontal drilling, increased production exponentially opening new underdeveloped areas up for commercial extracting.
The Barnett Shale was formed around 338 million years ago during the Mississippian period. During this time, shallow oceans allowed for this shale to originally form. The formation was named the Barnett Shale in the early 20th century after geologists had discovered organic, rich shale that was near to its neighboring stream, the Barnett Stream. Geologists decided to name it after the nearby stream for name and location convenience.
The Barnett was soon discovered in 1981 when the first well was completed and it utilized outdated techniques to extract the organic materials, the nitrogen foam fracturing technology. The first well did not produce any significant amount of gas to bring attention to this new formation. More wells were slowly implemented through the 1980s using various techniques such as gel fracturing. Even though the fracturing technique slowly increased production, nothing proved to be an economical viable way of extracting gas from the formation.
It wasn’t until 1997 when hydraulic fracturing techniques became a prominent way to extract hydrocarbons from this formation.
The technique allowed for cheaper well completion costs as well as increasing the natural gas production rates astronomically. This created a stir within the industry and many companies began acquiring land in North Texas.
Along with this, horizontal wells began increasing the price of natural gas within the early 2000s making the Barnett Shale even more economically sound. An amassing amount of wells were drilled within the Northern Texas area, in 2008 the tally reached 2,900 horizontal drilling wells and over 10,000 wells drilled.
Geologic Risk and Uncertainties
Many different companies use Core Logs to classify different parts of the shale into “Core” and “Non-Core” areas. Core areas are where most development take place as these places have thicker shale and uncertainty involved is significantly reduced. This reduction allows for well production to be drilled at lower gas prices than that of the Non-core areas. As of now, there are four main core areas and several non-core areas that still have the potential to be a core area.
Within the shale, the number of dry holes has significantly decreased due to 3D Seismic technology that allows for engineers to identify hazards, such as faults and cracks, before they drill wells. Faults create difficulty when drilling wells in shale, due to them relieving pressure from hydraulic fracturing and overall hindering the fracturing effectiveness. This drastically reduces the risk within the play.
From an environmental standpoint, there are many regulations and risk management challenges that face the Barnett Shale. With development of highly populated areas nearby, such as Dallas and Ft. Worth, there has been question on human health with regard to the development of the shale. The Texas Railroad Commission (TRC), local government, and the Environmental Protection Agency have all a say in the regulation of oil and gas facilities and development throughout Texas, including the Barnett.
There have been two cases of water well contamination filed by EPA against Range Resources. However, tests concluded by the Texas Railroad Commission proved that these contaminations came from a different shale play that the company did not complete their wells to, alleviating them of any lawsuits.
These government groups rely on rigorous and scientifically driven methods to evaluate the shale development with the help of advanced technologies. These new risks and challenges are constantly being updated and argued about to ensure the safety of future human development near the shale.
The traps that can be found throughout the Barnett are mainly stratigraphic. Sediments were deposited 25 million years ago from a basin flooding that was later entrapped in the pre-Barnett erosional unconformity. The organic material that comprises the shale is surrounded by low permeable and porosity matrix which minimizes the hydrocarbon expulsion. This results in the hydraulic fracking technique being used exclusively now in the Barnett.
The seal found in this shale is mainly carbonate shale due to high amounts of limestone throughout the shale from the Mississippian era. The Marble Falls Limestone and Chappel Limestone, above and below respectfully, entrap the shale both having low permeabilities likewise of the Barnett. However, this does not have as much of a significant impact since the Barnett is already low in permeability. The play itself is for the most part unconventional oppose to being conventional. Due to the huge play overall having low permeable results in high amounts of freshwater needed to complete these operations for fracking.
The source rock is a crucial part of any formation as this is where the hydrocarbons are formed and if heated enough will produce oil or gas. The Barnett is comprised of clay and quartz mainly along with dolomite and siderite. It is an organic-rich shale that has three separate classes: upper shale, middle limestone, and lower shale. The Shale is enriched with type II Oil that originate from marine-algal kerogen. There is also little to no migration due to the calcite faults that inhibit this from happening.
Reservoir rocks are known for storing fluids inside their pores in in which hydrocarbons can be stored. Moreover, geologists were first optimistic about the play from high radioactive measurements through gamma ray logs, this was due to high uranium content and the rest of the measurements coming from thorium and potassium that are present in the shale. Knowing the Barnett was Shale, they were able to do more test to find the low permeability within the area. The most productive part of the reservoir are places away from fractured areas.
Future & Current Assessment of Barnett Basin
Currently, there is still an estimated 40 trillion cubic feet of natural gas that is available in the shale, this makes the Barnett Shale the largest natural gas field in Texas and potentially in the United States. On average, the field still produces around 4.5 billion cubic feet a day making the shale a significant play still. According to the Texas Railroad Commission there are 235 current operators in the Barnett Shale as of 2012, however, only around 30 rigs are operational due to the low prices of natural gas in years past. This includes companies like Chesapeake Energy, Devon Energy, and EOG Resources.
The Barnett has proved its stability and reliability for dry gas, however, there are problems with dry gas. According to Ed Ireland, the executive director of the Barnett Shale Energy Education Council, most companies prefer liquid gas over dry gas due to the liquid gas having more elements in it for potentially more profits such as ethane, propane or butane. Dry gas has also shown to have steep declines in production after promising starts. The Barnett heavily relies on the price of natural gas since the cost of hydraulic fracturing is higher than other techniques.
Along with this, there are relatively no new wells being drilled throughout the shale. This is due to most wells being drilled from 2002 to 2008 before efficient hydraulic fracturing techniques were in place. Most companies assess old wells and see if fracturing is a viable option to extract the gas. Not only are companies fracturing old wells, but some are investing into the idea of refracturing wells which have shown promising success of even passing their initial production rates. This could be a huge impact in shale plays, especially in the Barnett as there is still around 2 to 3 times the amount of natural gas in the shale than what has been extracted.
Petroleum and Facility Engineering:
Many facilities are not running in the past year due to Covid-19 and prices of natural gas decreasing so much. There are few that operating; however, these rigs are producing at strong numbers. Enough to put the Barnett in the top 3 producing natural gas plays in the United States. When gas prices rise there will be many more rigs operating.
Another factor that goes into these operating wells is the cost of hydraulic fracking. Fracking is the main way most of the wells on this play are used to extract hydrocarbons. One way this is helped is through the engineering of proppants. Proppants are chemically modified or pure, fine sand that is used to keep the fractures popped open when a well is hydraulically fracked. This is a tedious process as if these proppants are mixed with unsanitary items then it may not be able to hold open the frack well which would be costly as this sand, along with water, is not cheap.
The initial cost of the well is relatively cheaper than it is compared to just the hydraulic fracking cost from the shear amount of water needed for the process. The cost for this process does not outweigh the need to extract the dry gas that is in the shale. Lots of other plays have seen more active rigs since, unlike the Barnett, are higher producers in oil. Most rigs on the Barnett are targeting to extract gas instead of oil.
- https://www.universalroyaltyco.com/resources/history-barnett-shale/#:~:text=The%20Barnett%20Shale%20was%20formed,limestone%20and%20an%20upper%20shale. History of Barnett Shale. Universal Royalty Company. https://www.universalroyaltyco.com/resources/history-barnett-shale/ accessed May 11, 2021.