Fracking the Eagle Ford Shale:
Big Oil and Bad Air on the Texas Prairie
by InsideClimate News, the Center for Public Integrity and The Weather Channel
Amine unit: removes H2S and CO2 from natural gas
Compressor unit/compressor station: used to pressurize natural gas so it can be moved through pipelines.
Dehydrator: removes water from natural gas
Drill rig: a machine that contains the equipment to drill the wellbore—the hole in the ground that goes into the shale formation.
Drilling mud or drilling fluid: a mixture of a liquid base (water, oil or synthetic chemicals), clays and chemicals, used to lubricate and cool the drill bit as it creates the wellbore. The mud also transports the drill cuttings to the surface and helps control pressure within the well. Compressed air may be used instead of mud.
Flare: used to burn off excess gases. Flaring is a form of air pollution control, but less effective than capturing the gas in pipelines. It can be used as a safety device, to prevent the buildup of dangerous gases.
Flaring also produces pollutants such as soot and dioxins. Sustained flaring of the associated natural gas from oil wells aggravates climate change and wastes the methane that could be used as an energy source.
Flowback: the mixture of drilling mud, fracking fluids, produced water, oil, gas, salts, heavy metals, and natural gas liquids that comes out of a well after fracking. Flowback contains toxic compounds that must be treated or disposed of.
Frac tanks, or flowback holding tanks: open or closed-top tanks used to hold the liquids from flowback. May be used in place of open pits.
Frac pumps: used to pump fracking fluids into the well
Fracking or frac'ing: See Hydraulic fracturing. Fracking occurs during the well completion phase, when the well is prepped for sustained production.
Fracking fluid: Composed of mostly water, with small percentages of proppants and chemicals. The chemicals used are a mixture of benign products (guar gum) and toxic compounds (carcinogens like benzene). Some of the chemicals are harmful at concentrations of parts per million or parts per billion when released into the water or air. Many types of fracking fluids are used, with proprietary compositions, and the technology is constantly evolving. Although the chemicals make up a tiny fraction of the fracking fluids (sometimes less than 1 percent), the overall volumes are so high that a single well often requires tens of thousands of gallons of chemicals.
Generators: usually powered by diesel. Needed to provide electricity for lights, hydraulic pumps, etc. because most well pads are in remote locations off the grid. Once a well is in the production phase, electricity is often routed to the well pad, and the generators are removed.
Green completions, or reduced emissions completions (RECs): techniques and equipment used to reduce VOC emissions by up to 95% by capturing the gases from flowback.
Heater treater: removes water, liquid hydrocarbons and other impurities from natural gas.
Horizontal or directional drilling: an advanced drilling method where the wellbore is first drilled vertically, then gradually turned until it's sandwiched within the shale layer. A horizontal well can go on for more than a mile within the shale.
Hydraulic fracturing: an oil and gas stimulation method first introduced commercially in the 1940s, when water and sand were pumped underground to free up tightly-bound oil and gas. The process has a evolved a lot since then. For increased efficiency, companies experimented by pumping down brine, diesel, and mixtures of chemicals.
The type of fracking used today—high volume hydraulic fracturing—is quite different from the 1940's technique: there's a lot more pressure, greater use of chemicals and much higher amounts of fracking fluids, up to millions of gallons per well. That's because many wells are created via horizontal drilling, and the deeper, longer wells require more liquids to fracture. The combination of high-volume fracking and horizontal drilling is responsible for the recent shale boom.
The words fracking or fracturing, as used in this series, refers to the modern high-volume hydraulic fracturing technique used in the Eagle Ford and other shale plays.
Natural gas liquids: a mix of hydrocarbons present in natural gas and oil wells. These compounds, which include ethane, propane, butane, pentane and hexane, are used as feedstock in chemical plants and refineries. The larger hydrocarbons in natural gas liquids (mostly pentanes and above) are collectively referred to as condensate.
Natural gas wells: wells that extract the raw natural gas that comes out of the ground, which contains methane (the target compound) and sometimes includes various impurities: water, carbon dioxide, VOCs, H2S, natural gas liquids and condensate. The relative amounts of these impurities varies by formation and well. "Sour" wells have higher levels of H2S. Gas wells are considered "dry" if they contain only methane, or only methane and water without the other impurities.
Oil wells: wells that produce oil and natural gas liquids. Most oil wells in the Eagle Ford contain oil, gas and natural gas liquids. Operators will decide what to do with each type of product depending on market forces. Natural gas liquids are used in petrochemical plants and refineries. Due to the low price of natural gas, some operators will burn off (flare) the associated gas from oil wells because it's cheaper than building pipelines to collect the gas.
Open (waste) pits: used to hold liquids during flowback. Some operators are switching from pits to frac tanks, which emit fewer pollutants.
Produced water: naturally-occurring water from the shale formation that flows out of the well after fracking. Produced water contains salts, heavy metals, leached minerals, dissolved solids, naturally-occurring radiation and other toxic compounds.
Proppants: used to hold open fissures opened by fracking in the shale. Proppants may consist of sand, ground up walnut shells, ceramic beads or other similarly-sized particles.
Shale: a type of sedimentary rock. Because oil and gas are tightly bound within the shale, operators almost always need hydraulic fracturing or another stimulation method to increase the shale's permeability so oil and gas can flow out of the well.
Trucks: used to deliver drilling and fracking equipment, water, drilling mud, and fracking fluid chemicals to and from the well pad. The number of trucks on a pad depends on what's going on—during fracking, there may be hundreds of trucks traveling to and from a pad.
Well pad: a central location for the wells and equipment. A well pad may be several acres in size. Operators often place multiple wells on a single well pad.