Harvesting Natural Gas: Fracking

Paul Glanville, Principal Engineer at the Gas Technology Institute.

Fracking. Surely you’ve heard of this term, shorthand for hydraulic fracturing, a technique used in the development of oil and gas resources and most notably in the extraction of shale gas.  The term “fracking” also invokes the rapid development of U.S. shale gas plays, a welcome boost to many local economies in an otherwise difficult period, and similarly the surrounding controversy of its environmental impact, particularly its impact on water quality.  While my work focuses on energy efficiency for the built environment, I spent some time “upstream” with Tom Hayes, an Institute Engineer in the Exploration & Production group at the Gas Technology Institute, a not-for-profit R&D organization near Chicago, IL, to learn how engineers are tackling the engineering and environmental challenges with shale gas fracking.

Why we’re hearing about fracking in the news so much recently is that the U.S. has experienced something of a natural gas boom over the past 5 years, through technological improvements in fracking and horizontal drilling techniques.  While in the late 1990’s domestic gas supplies were projected to steadily decline and shortages were predicted as recently as 2007, with several liquefied natural gas (LNG) terminals to be built along the coastlines for importation, this recent boom has lead the U.S. Energy Information Administration to predict the U.S. will be a net exporter of natural gas by 2016.  Not unexpectedly this rapid development has had far reaching impacts throughout the energy industry, with the resource price as one indicator.  The price of crude oil and natural gas are typically linked as natural gas was historically developed as a by-product of oil production, with the last spike observed during the summer of 2008 when natural gas exceeded $13/MMBtu and crude oil topped $140/barrel.  While both prices have dropped considerably with the broader market since then, crude oil has returned to over $100/barrel from less than $40/barrel, while this shale gas boom has kept natural gas prices depressed, in steady decline since to $2/MMBtu at the time of writing.  In addition to financial indicators, there are other suggestions that this domestic boom might be more of a permanent feature of the U.S.’s domestic energy resource portfolio, as President Obama has noted this “supply of natural gas that can last America nearly 100 years”.

As with all resource development, with the extraction of shale gas come numerous challenges to minimize its environmental impact, the rapid nature of this boom compounded these challenges.  Put simply fracking is the injection of water under high pressures in deep wells to fracture gas bearing shale formations, so it is no surprise that its impact on water quality impact is critical.  With the large amount of water required for fracking operations, its reuse, treatment, and transportation are a “major operational component and cost of shale gas development going forward”, Tom notes. 

Initially, flowback water is directly reused in the development of a shale play from well to well, however the “reuse capacity” diminishes over the development as the produced water increases the salinity above an acceptable limit.  The salt content of produced water creates challenges in its treatment and disposal, as typical produced water has a salt content of 50 – 250 g/L of dissolved salts compared to 38 g/L for seawater.  Put into perspective, the salt output of a development area in a typical Pennsylvania county (roughly 1,000 wells) will produce more salt per year than the entire state uses for roads over a decade, with transport and treatment of brine on the order of $10 million per year per development area.  To aid in characterizing the produced water, Tom and his team have developed a lifecycle simulation tool that models the produced water and salt output of a given well and tracks the output of thousands of wells in a development area to identify when problems arise.  The team began by characterizing the produced waters from wells in the Marcellus Shale not only for salts, but also trace chemicals of concern for water quality including heavy metals, chlorinated hydrocarbons, and other species, developing a database of the chemical composition of produced water.  They followed up this monitoring by documenting and analyzing the produced water at field sites in real time, at wells in both the Marcellus and Barnett Shales.  Tom notes that over the life of a shale development area, the period when most of the flowback water can be reused is anywhere between 6 – 15 years, however after this “crossover point” when the volume of produced water exceeds the reuse capacity of the wells, this brine wastewater has to be dealt with otherwise.  Beyond direct reuse, this wastewater is either disposed of or treated. 

In one of the most active areas of the U.S., the portions of the Marcellus Shale in Pennsylvania, geology prevents many drillers from disposing of the wastewater through injection into Class II wells (regulated by the Clean Water Act), which are deeper than local conditions allow.  For this reason and also state regulations, much of the wastewater is shipped out of state to eastern Ohio for disposal.  This large cost of hauling wastewater can certainly add up, which on average 400-800 trucks are needed per well completion at a rough cost figure of $1/barrel-hour of truck transport (each development area is roughly 5,000 wells).  Additionally beyond the high cost of hauling wastewater, its disposal may also be problematic, as state regulators are investigating the potential link between deep well wastewater disposal in eastern Ohio and abnormal seismic activity. 

As an alternative this costly practice of the interstate hauling and deep well disposal of wastewater brine, Tom and his team are currently investigating several methods of wastewater concentration and treatment.  They have investigated methods that simply concentrate brines, reducing the brine volume from 10-20% up to 50-70%, reducing transportation costs, however if produced wastewater is treated instead of disposed, Tom notes, the impact of hauling is minimized – with reduced trucking emissions, road wear, and traffic.  Working with the University of Texas to apply their polydopamine coating technology to improve the fouling resistance of new ultra filtration reverse osmosis membranes, the team has reduced the energy requirements of the process by 35% and extended the membrane’s life by 2-3 times in laboratory studies.  In a two year program, they have also investigated improvements to electrodialysis techniques to handle high calcium brine streams to reduce treatment costs by 40%.  Both methods have been evaluated in the field at Barnett and Marcellus Shale drilling sites. 

For handling of wastewater streams with higher salt concentrations, Tom’s team has borrowed from the food, beverage, and sugar industries in their use of mechanical vapor recompression (MVR).  The effectiveness of MVR was demonstrated at a Devon Energy facility recently as a viable method of demineralizing produced water, cleaning it to the point that it can be discharged as surface water or to be treated further at public owned water treatment facilities.  A challenge for the engineering community, Tom notes, is the development of an effective hybrid treatment process that leverages the strengths of these and other treatment processes at an appropriate scale.  Centralized treatment is effective, however shale gas plays are geographically disperse presenting a logistical challenge.  Another remaining challenge for the engineering community is the cost-effective treatment and disposal of concentrated salts through thermal crystallization, with effective management of the naturally occurring radioactive species, ideally finding a secondary market for their use. 

With this boom in the domestic natural gas supply likely to continue over the next several years, engineers must develop this resource responsibly, with minimal impact to both public health and the environment.  With researchers like Tom Hayes leading this effort, the engineering community is on the right track. 

Note: For those in the industry seeking further information, research performed by Tom Hayes and his colleagues will be published in a series of short technical reports in the public domain through the Research Partnership to Secure Energy for America (RPSEA) website.