Characterization of solids in produced water from wells fractured with recycled and fresh water
Date
2015
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Abstract
Water management is a central issue in oil and gas development. Hydraulic fracturing applied in unconventional tight oil and gas development requires large amounts of water, and the wastewater that results after production--containing high levels of organic and inorganic matter-- usually is disposed of through deep well injection. A new approach reuses this produced water as part of subsequent fracturing fluid, an alternative that could significantly reduce both fresh water demand and the cost associated with deep well injection. However, produced water must be treated prior to reuse, to remove most of the suspended solids and multivalent ions that would otherwise cause scale or clogging problems. Understanding the amount and composition of solids in produced water is crucial in achieving optimized treatment and reuse. This study targeted the characterization, both qualitatively and quantitatively, of the solids in produced water from oil and gas operations and the comparison of solids from wells fractured with fresh water and recycled water. Samples were collected from five wells at the Crow Creek and Chandler State pads in the Wattenberg field of Northern Colorado. Wells in the same pad were fractured either with fresh surface water only or with water blended with some portion of recycled produced water. Gravimetric analyses of dissolved and suspended solids were performed, and particle size distributions of suspended solids were measured. Suspended solids also were isolated and characterized with X-ray photoelectron spectroscopy (XPS). Gravimetric analyses showed that total dissolved solids (TDS) averaged about 24000 mg/L and 17000 mg/L for Crow Creek and Chandler State wells, respectively. Total suspended solids (TSS) concentrations were much lower, measuring 550 and 260 mg/L for the two pads. About 9 to25 percent of TDS was volatile and 88 to 99 percent of TSS was highly volatile. Particle sizes were high during first few days of production and then stabilized at about 400 nm and 900 nm for wells on the Crow Creek and Chandler State pads, respectively. At the Crow Creek pad, particle sizes were smaller and mono-distributed in produced water samples collected during the first week of production from the well fractured with recycled water, suggesting that the recycled water was more compatible with shale formation and that wells fractured with recycled water tend to clean out faster. XPS tests for isolated suspended solids showed the presence of major elements such as oxygen, carbon, and silicon, along with minor elements such as calcium, magnesium, zirconium, iron, and others. Core-level scanning confirmed that the isolated suspended solids were mainly composed of carbonate based minerals and metal oxides; several iron compounds with different valences were also found in the produced water samples.
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Subject
produced water
Wattenberg field
particle size
XPS
solid characterization