Waste Management of Cuttings, Drilling Fluids, Hydrofrac Water and Produced Water

Cuttings and Drilling Fluids/Muds

When a well is drilled, the ‘cuttings’ of drilled rock need to be removed from the well bore. The cuttings, the drilling fluid or mud (to lubricate the drill and help remove the cuttings), and water in the bore hole are brought to the surface where the cuttings are then separated from the fluid, which will be reused in the drilling process. The cuttings and remaining fluids are generally stored in a drilling pit. In New York State, there are specifications regarding the construction of these pits, including a requirement that all pits be lined with plastic to avoid polluted water in the pit entering the soil and shallow groundwater. Where groundwater is likely to be at or near the surface (e.g. wetlands and floodplains) further restrictions can be imposed on the placement of pits. (http://www.dec.ny.gov/docs/materials_minerals_pdf/dgeisv1ch9.pdf)

Drilling muds will be used in drilling in the Marcellus shale zone. According to the Oil and Gas Accountability Project, “drilling fluids or muds are made up of a base fluid (water, diesel or mineral oil, or a synthetic compound); weighting agents (most frequently barite is used); bentonite clay to help remove cuttings from the well and to form a filter cake on the walls of the hole; chrome lignosulfonates and lignites to keep the mud in a fluid state; and various additives that serve specific functions, such as biocides, diesel lubricants and chromate corrosion inhibitors….Drilling muds that circulate through the well and return to the surface may contain dissolved and suspended contaminants including cadmium, arsenic, and metals such as mercury, copper and lead; hydrocarbons; hydrogen sulfide and natural gas, as well as drilling mud additives, many of which contain potentially harmful chemicals (e.g., chromate, barite).” (http://www.earthworksaction.org/pubs/OGAPMarcellusShaleReport-6-12-08.pdf)

Drill cuttings consist of a mixture of the different types of rocks through which the well is bored. As horizontal drilling will occur through the Marcellus shale, the cuttings from this shale are likely to make up a substantial portion of the total cuttings. These cuttings may be acidic and have the potential to mobilize metals in the cuttings or the soil to which they will be potentially exposed. Additionally, the Marcellus shale contains naturally occurring radioactive materials (NORMs), including uranium. A 1999 investigation of NORMs in oil and gas wells found that the concentrations of NORMs on oil and gas production equipment and wastes pose no threat to the public health and the environment. (http://www.dec.ny.gov/docs/materials_minerals_pdf/normrpt.pdf). However, the Marcellus shale apparently was not included in the geological formations tested for this report. Therefore, it would seem prudent to test for NORMs in this rock, as well as the reactions it will undergo when exposed to fresh water in a lined pit.

Hydrofracing Fluids

Hydrofracing fluids are injected into wells under pressure in order to create cracks or fractures in the rock formation. These cracks accelerate gas flow out of the rock and into the well. Hydrofracing fluids are created by adding a proppant (such as sand) to water. The role of the proppant is to keep the cracks from resealing once the hydrofracing fluid is withdrawn from the well. In addition to the proppant, several types of chemicals are added to the hydrofracing fluid to serve a number of purposes. With respect to chemicals likely to be added to the hydrofracing fluids used to exploit the Marcellus shale, the following preliminary information was provided by Rick Kessy from Fortuna Energy. Also, the specific chemical loadings cited below may change as the Marcellus shale is developed.

• A friction reducer is added to reduce the friction pressure during pumping operations. A polyacrylamide (PAM) is typically used for this purpose at concentrations of 0.06% by weight in the frac fluid. PAMs are used as flocculating agents in waste water treatment plants and applied at times to soil surfaces to stabilize them.
• A surfactant is used to increase the recovery of injected water into a well. In the case of Fortuna Energy, the formulation of the surfactant used is proprietary to the company it hires for hydrofracing. However, that composition has been given to the New York State Department of Environmental Conservation. In general, surfactants are organic compounds that are soluble in both water and organic solvents. The surfactant used in this case is methanol based and is 0.085% by weight of the frac fluid, but is added only during the first half of the treatment.
• A biocide is used to inhibit the growth of organisms that could produce gases (H2S) that could contaminate the methane gas. The biocide being used is 2.2- Dibromo -3- nitrilopropionamide (DBNPA) at a rate of 0.00935% by weight in combination with polyethylene glycol (PEG) at a rate of 0.01871% by weight. DBNPA is a common biocide used in heating and cooling systems. PEG is used for many purposes, including medications. In this case, it is presumably aids in delivery of the biocide.
• Scale inhibitors are used to control the precipitation of carbonates and sulfates. Ethylene glycol and polyacrylate are currently being added to the first 10,00 gallons of frac fluids for this purpose, at rates by weight of 0.00705% and 0.009% respectively. Ethylene glycol is used to de-ice airport runways and aircraft. Polyacrylates are absorbent, and so are used for many purposes, including baby diapers.

After hydrofracing, the hydrofracing fluid is withdrawn from the well, and to the extent possible, from the formation. The Marcellus shale is of marine origin, which means it will contain high levels of salt, some of which will dissolve in the hydrofracing fluid. This is a major issue for disposing of the spent hydrofracing fluid. These fluids can be processed through a water treatment plant but they must be sufficiently diluted by other water entering the plant that discharged water will not be salty enough to disrupt freshwater ecosystems. This means that waste water treatment facilities will be limited in the volume of fracing fluids they can treat. Another component of fracing fluids addressed in waste water treatment plants is their biological oxygen demand (BOD). Fracing fluids have high BOD because they contain readily decomposable organic compounds, and so they cannot be directly released into surface waters. Waste water treatment systems are designed to treat water with high BOD (i.e. sewage).

As gas is pumped out of a well, water contained in the Marcellus shale formation may be withdrawn as well. This water is often called produced water. Marcellus Shale produced water will be salty, and may contain other chemical constituents as well. The volume of water produced is not expected to be great; one estimate is 42 gallons of water per million cubic feet (MMcf) of gas produced. At the end of the first year, a typical horizontal well in the Marcellus shale is not expected to produce more than 1 MMcf of gas per day; so produced water is not likely to exceed 300 gallons per week.