A comparison of electrocoagulation and chemical coagulation treatment effectiveness on frac flowback and produced water
Date
2015
Authors
Hutcherson, John Ryan, author
Carlson, Ken, advisor
Omur-Ozbek, Pinar, committee member
Stednick, John, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Development and production of tight shale for crude oil and natural gas is increasing rapidly throughout the United States and especially in the Wattenberg field of Northern Colorado. Hydraulic fracturing is used to stimulate the shale formation, which allows previously trapped oil and gas to flow to the surface. According to Goodwin (2013), approximately 2.8 million gallons of water are required to hydraulically fracture a horizontal well. Freshwater makes up the vast majority of water used to create these fracturing fluids with a small portion coming from recycling of previously used fracturing fluid. In a semi-arid climate such as Northern Colorado, there are multiple demands for freshwater, often exceeding the supply. Once a well is fractured, water flows back to the surface along with the targeted oil and gas. This fluid is typically referred to as flowback or produced water. In some areas around the United States as much as 10 barrels of water flows to the surface for every barrel of oil recovered. For the purposes of this research, flowback is defined as water that flows to the surface within the first 30 days after fracturing. After fracturing, up to 71% of the water (produced water) used to fracture the well flows back to the surface along with oil and gas, with approximately 27% flowing back in the first 30 days (Bai et al, 2013). The flowback and produced water is currently being disposed of either by deep underground injection or in evaporation ponds. There has been very little effort to capture, recycle, and reuse this flowback or produced water as it has traditionally been considered a waste product. Due to the limited freshwater supply in Colorado, recycling and reuse should be explored in greater detail and with a sense of urgency. The ultimate goal for the oil and gas industry should be to recycle and reuse 100% of flowback and produced water in the creation of hydraulic fracturing fluid for other production wells, creating a closed-loop system. Before flowback and produced water can be reused, treatment of the water is required. Treatment for reuse typically consists of removal of solids, organic compounds, and some inorganic ions. Historically, chemicals have been the dominant method used for coagulation to remove solids, as they are readily available and in many cases can be cheaper than other methods. Electrocoagulation (EC) is now also being considered as a produced water treatment method. EC involves running electric current across metal plates (sacrificial anodes) in a solution, which creates an in situ coagulant dose (Emamjomeh and Sivakumar 2008). There is a time component to water quality changes over the life of a well. Early flowback typically has higher concentration of aluminum, solids, and total organic carbon (TOC) as it is influenced mostly by the makeup of the fracturing fluid. At some point around the 30-day mark, a transition in water quality begins. The formation or connate water seems to have a greater influence on water quality than does the fracturing fluid. Treatment seems to correlate to the changing water quality, as treatment is less effective on the early flowback compared to produced water. TOC and low ionic strength may be the reason early flowback is more difficult to treat. Also, chemical coagulation (CC) is more effective than EC at removing TOC and aluminum in early flowback water compared to EC, while EC is more effective at removing iron. However, both treatments are effective after day 27.
Description
Rights Access
Subject
electrocoagulation
oil and gas
water treatment
flowback
chemical coagulation
produced water