The Newark East, Barnett Shale, Field is one of the most active drilling targets in the past decade. The initial development of the field was centered in southeast Wise County. Activity has expanded to the north in Montague County, to the east in Denton County and to the south in Tarrant County and now is present in 16 counties in North Texas.
The success of the Barnett Shale is in large part a result of the use of stimulation technology. While the volume of gas–in-place is large in the Barnett Shale (estimated to be over 27 trillion cubic feet), recovery of the gas is difficult because of the low permeability of the shale. The Barnett Shale must be stimulated – treated to increase permeability – in order for the field to be economic.
In order to be able to produce gas at volumes that are economical, reservoirs with low permeability must be treated. One method of treatment to increase permeability is fracture treatment or “fracing,” which increases the available surface area by creating fractures that are “propped up” or held open by the propping agents in the frac fluid.
Hydraulic fracturing is used in the Barnett Shale. Hydraulic fracturing consists of pumping into the formation very large volumes of fresh water that generally has been treated with a friction reducer, biocides, scale inhibitor, and surfactants, and contains sand as the propping agent. The water treating fluid maximizes the horizontal length of the fracture while minimizing the vertical fracture height. The fractures, which are held open by the sand, result in increased surface area, which further results in increases in the desorption of the gas from the shale and increases in the mobility of the gas. The result is more efficient recovery of a larger volume of the gas-in-place.
In 1997, the first slick water frac (or light sand frac) was performed and found to be very successful in stimulating the Barnett Shale. Slick water fracing of a vertical well completion can use over 1.2 million gallons (28,000 barrels) of water, while the fracturing of a horizontal well completion can use over 3.5 million gallons (over 83,000 barrels) of water. In addition, the wells may be re-fractured multiple times after producing for several years.
Increasing water use due to growing population, drought, and Barnett Shale development has heightened concerns about water availability in North-Central Texas. In January of 2007, the Texas Water Development Board (TWDB) published a study of a 19-county area in North Texas that includes the Barnett Shale development area. This report, “Northern Trinity/Woodbine Aquifer Groundwater Availability Model, Assessment of Groundwater Use in the Northern Trinity Aquifer Due to Urban Growth and Barnett Shale Development,” includes estimates of water used in Barnett Shale development. This report can be found at http://rio.twdb.state.tx.us/RWPG/rpgm_rpts/0604830613_BarnetShale.pdf.
The TWDB report states that approximately 89% of the total water supply for the region for all purposes (municipal, agricultural, electric power generation, industrial, and mining) is provided by surface water sources, while groundwater is used for the remainder of the total demand (about 140,000 acre-feet per year1). The amount of water from all sources that is used for Barnett Shale development has been a relatively small (less than 1 percent), although growing, percentage of the total water use from all sources and for all purposes in the counties with Barnett Shale development.
The TWDB report estimates that, out of the total water used in 2005 for Barnett Shale development, approximately 60 percent was groundwater from the Trinity and Woodbine Aquifers. The report further estimates that groundwater used for Barnett Shale development accounted for approximately 3 percent of all groundwater used in the entire study area in 2005. However, the ratio of groundwater to surface water used in specific areas varies greatly. For example, groundwater provides as much as 85 percent of the total water supply for Cooke County. In general, groundwater provides for a greater percent of total supply in rural counties and a smaller proportion of total use in more urban counties. Therefore, increased groundwater use for any purpose will have a greater impact on rural areas in the study area.
The TWDB report makes predictions of future water needs for all purposes, including Barnett Shale development. The low estimate for Barnett Shale development predicts a decrease of about 2,000 acre-feet by the year 2025 and the high estimate predicts an increase from an estimated 7,200 acre-feet in 2005 to about 10,000 to 25,000 acre-feet per year by 2025, which corresponds to a estimated potential increase in groundwater used from 3% in 2005 to 7 to 13 percent in 2025. As with the development of any estimate of future conditions, the TWDB and its contractors used educated assumptions to develop reasonable low and high estimates in light of the unpredictability of the natural gas market, which would drive future drilling activity in the area.
Recognizing the concerns with water use in the area, over the past few years several companies have applied for, and the Commission has approved, recycling projects in the Barnett Shale to reduce the amount of fresh water used in Barnett Shale development activities. While no authorizations have been issued to date, Commission staff anticipates water recycling projects will be explored in South Texas and East Texas, as a result of development in the Eagle Ford Shale and the Haynesville Shale, respectively.
The following authorizations have been issued by the Commission and are currently active:
The following water recycling pilot projects have been previously approved but are no longer being pursued: