Characterization and treatment of produced water from Wattenberg oil and gas wells fractured with slickwater and gel fluids
Date
2014
Authors
Sick, Bradley A., author
Carlson, Kenneth, advisor
Omur-Ozbek, Pinar, committee member
Bradley, Thomas, committee member
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Abstract
Treatment of produced water for reuse as a fracturing fluid is becoming an increasingly important aspect of water management surrounding the booming unconventional oil and gas industry. Understanding variation in water quality due to fracturing fluid and produced water age are fundamental to choosing an effective treatment strategy. This study involves the collection and analysis of produced water samples from three wells in the Wattenberg Field, located in northeast Colorado, over a 63-day study period (15 sampling events). One well was fractured with a cross-linked gel fluid, one with a slickwater fluid, and one with a hybrid of both fluids. Extensive water quality characterization was conducted on each sample to understand the impact of fracturing fluid type on temporal water quality trends. The greatest impact observed was that total organic carbon (TOC) concentrations were significantly higher in produced water samples from the wells fractured with the gel and hybrid fluids (943 to 1,735mg/L) compared to the well fractured with the slickwater fluid (222 to 440 mg/L). Total dissolved solids (TDS) concentrations, as well as many of the component inorganics that make up TDS, were fairly consistent among the three wells. TDS concentrations at each well increased with time from roughly 18,000 mg/L at day 1 to roughly 30,000 mg/L at day 63. Jar testing was conducted on collected samples to understand the variability in chemical coagulation/flocculation treatment due to type of fracturing fluid and well age. For the sampled wells, it was found that chemical coagulation can successfully reduce the turbidity of produced waters from wells fractured with both slickwater and gel fluids immediately after the start of production. The coagulant demand for produced waters from wells fractured with gel fluids was found to be roughly 25 to 300 % higher than that for wells fractured with slickwater fluids. The coagulant demand of produced water from each well was found to decrease with the age of the well. Additional laboratory characterization techniques were conducted on a subset of samples in order to better understand the makeup of organic compounds in produced water, including an analysis of the distribution of the volatile portion of solids, a TOC size analysis, and an analysis of organic subcategories. It was found that the majority of organic compounds in produced water samples are smaller than 0.2 µm, and that the relatively small portion that is larger than 1.5 µm contributes significantly to the predominantly volatile total suspended solids (TSS) load. Carbohydrates were found to be the largest contributor to the overall organic compound load in early produced waters from wells fractured with gel fluids; petroleum hydrocarbons were found to be the largest contributor from wells fractured with slickwater fluids. Chemical coagulation was found to reduce TOC concentrations by roughly 20%, independent of this difference in makeup.
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Subject
hydraulic fracturing
Wattenberg
produced water
Niobrara
flowback
fracking