The production of shale and tight formation oil and gas has been increasing by leaps and bounds in the United States over the past few years. Just a decade ago, these same low permeable shale rocks were regarded as just source rocks for our conventional oil and gas fields. Thanks to horizontal well bores penetrating these very tight formations and multi-stage hydraulic fracturing of the shale in them, this resource is growing into a world-wide phenomenon.
While the frac fluids that are being pumped down holes are increasingly safer for the environment, these fluids are designed to dissolve tars and allow hydrocarbons to flow through fractures, enhancing recovery and making the produced water very dangerous to human health and the environment. The rapid increase in wells drilled, along with production, has led to mounting environmental concerns. There are numerous websites, such as Waterdefense.org, posting warnings such as:
“Natural Gas Exposed tells the stories of Americans whose lives have been devastated by gas drilling. All across the country, gas companies are poisoning water, tearing apart communities, and destroying the American dream for thousands of families who can’t protect their children from what comes out of the tap.”
Without hydraulic fracturing, the resource simply cannot be unlocked from these tight formations. Yet, governments continue to hold up development over this one issue even though reports of any problems are rare. In fact, a recent study funded by the Energy Institute at the University of Texas at Austin of shale gas development in the Barnett, Marcellus and Haynesville shales found no evidence of a direct link between hydraulic fracturing and groundwater contamination.
Still, environmental concerns persist. To address some of these concerns, and at the same time make shale production more efficient, nanotechnology research is promising solutions involving new proppants, enhanced membranes to contain and treat fracture fluids, and
unique, easily detectable tracers so that the movement of fracture fluids can be followed.
Water is the main ingredient used for hydraulic fracturing. Well stimulations can use between 2 and 10 million gallons (8 and 38 million litres) delivered under very high pressures to create fractures in the producing horizon. A small percentage of chemicals are added to the water and vary from play to play. Some of the typical additives and their common uses include: diluted acid (hydrochloric or muriatic) that helps dissolve minerals and initiate cracks in the rock (also used as a swimming pool cleaner); friction reducers such as mineral oil or polycrylamide, that reduce friction between the fluid and the pipe and are also used for water treatment, laxatives and candy; crosslinkers (borate salts) to maintain fluid viscosity, also used in laundry detergents, hand soaps and cosmetics – and the list goes on. One of the companies heavily involved in the fraccing business, Halliburton, has a complete list of additives regionalised on their website.
One of the most critical components of the fraccing process is the proppant, or the component used to keep the fractures open. Commonly used proppants include plastic-ceramic beads, sand, lightweight ceramics and sintered bauxite. “These proppants are either hard and heavy or soft and light,” says Dr. Andrew R. Barron, Welch Chair of Chemistry and Professor of Materials Science at Rice University, Houston, Texas. “The ideal proppant should be mono-dispersed, round, and high in strength with low fines to enhance flow through the fractures. It also needs to be light to optimise transportation.
“Fraccing with particles of different sizes, often the case when using sand as the proppant, can slow flowback,” Dr. Barron continues. “Nanotechnology research at Rice has developed a proppant with particles consistently the same shape (round) as well as being stronger and lighter than previously used proppants. This new proppant, OxBall©, is being used in the Barnett, Haynesville and Eagle Ford shale plays and tests results have been excellent. All wells stimulated with the OxBall showed better than 25% increase in production.”
While there is no evidence that the downhole fracturing process has ever contaminated ground water, the same cannot be said for the large volumes of produced frac water. These waters have been dumped or spread over unprotected surface areas and allowed to evaporate. Containment in surface pits has been problematic. “Pits lined with visqueen can leak allowing liquids to percolate into the ground water,” says Dr. Barron. “We have developed a felt and poly-asphalt system that has enhanced resistance to wear and corrosion using nano-alumina coatings on the frac fluid containing pits. Four pits have been constructed and proven a very effective containment system.”
Water Clean-up and Tracers
Hydraulic fracturing fluids are getting much safer and less toxic. “However, 25 to over 40% of these fluids return to the surface and, in addition to the fraccing fluids, may contain formation and heavy metals, while all contain organics and hydrocarbons making these fluids very dangerous,” according to Felipe Lembcke, CEO of Molecular Filtration, Inc. “This produced water needs to be treated on-site to reduce the carbon content to below the Environmental Protection Agency’s (EPA) standards.”
Waste water containing hydrocarbons can present a major pollution control problem to the industry. Filtration through traditional ceramic membranes that work on size exclusion requires a fairly high feed pressure of 4 to 8 bars and multiple layers that can become fouled by organics and cannot retain the small molecules such as xylene or benzene. “The nanofunctionalised membrane (the first organophobic ceramic membrane) requires less than a 2 bar feed pressure that will not become fouled by organics or show decay,” says Felipe. “The molecular forces in this membrane are so powerful that only water passes through. The cancer-causing small molecules like xylene and benzene are retained by the membrane along with all the other hydrocarbons, organics, bacteria and viruses. This is all accomplished without the use of chemicals.”
Fraccing has received much bad press about contaminating ground water and polluting drinking water. “One way to remove doubt from the public and government agencies is to introduce a unique tracer to your fraccing operation,” says Dr. Barron. “We can control the composition and design magnetic properties at the nano scale to manufacture non-toxic tracers that are easily detectable in ultra small quantities, water soluble, and not retained in the reservoir formation. The first customer field trials are in development and tests may soon begin in west Texas.”
Fraccing’s Future and Policies
Information and reports about hydraulic fracturing abound in the public domain; some are true and some are false. “In either case, the policy makers and regulators, both federal and state, must alleviate some of the fears, uncertainties and doubts of the communities in these shale regions being impacted by the way we produce hydrocarbons,” says Emil Peña, former Deputy Assistant Secretary for Oil and Gas at the US Department of Energy, industry veteran, and Executive Director of the National Corrosion Center, Rice University. “They must also balance the industry’s needs and rights to produce these natural resources in a safe and environmentally friendy manner.
“Water is our most precious resource and should never be wasted,” Emil Peña continues. “The nano-based technologies covered in this article are only the tip of the iceberg and if these and others are implemented in a responsible manner, the public will begin to feel a better comfort level through transparency. The role of the policy maker and regulator is to ensure that these measures are taken and reported by the industry. The Federal government through various agencies has started their own requirements on federal lands. The State of Texas was the first to pass and implement frac transparency laws and other producing states have followed and are also beginning to coordinate their efforts towards transparency.
“The challenges before us are twofold,” according to Emil. “Firstly, we must have common disclosure standards and not a patchwork of regulations that would impede industry progress. The second is a continuing and dynamic review of reporting requirements and technologies that are now being commercialised to better produce, while having minimal impact on the environment.
“While laws and regulations are needed, the companies have the true incentive, in part driven by the insurance industry, to produce our resources in a responsible manner,” says Emil. “When you are managing a producer’s risk better through superior knowledge, techniques, and technologies, the impacts to the producing regions can be minimised, lowering insurance rates and allowing our communities to rest a little easier.”