Analysis of produced water from three hydraulically fractured wells with different levels of recycled water
Date
2016
Authors
McCormick, Brian E., author
Carlson, Kenneth, advisor
Sharvelle, Sybil, committee member
Stednick, John, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
With the growing use of hydraulic fracturing, injecting large amounts of water into oil and natural gas reservoirs to increase the quantity of oil and natural gas extracted, large amounts of water with low water quality are being created. This water has to be disposed of and many disposal methods have environmental concerns. One method of disposal is treating the water to remove the contaminants that have environmental concerns. Treatment of produced water for reuse, which will be identified as recycled water, as a fracturing fluid is becoming an increasingly important aspect of water management surrounding the unconventional oil and gas industry since the treatment does not have to be as robust as it would for disposal into surface water. Understanding variation in water quality due to fracturing fluid and produced water age are fundamental to choosing a data driven, water management approach. For these reasons, Noble Energy partnered with CSU to analyze the water quality differences between four wells with different levels of recycled water usage in a previous study. In that study, the findings showed a higher organic content of the produced water in the early period due to the presence of emulsified oil. The higher organic content of that produced water was the reason for using recycled water at more wells to determine if the higher organic content was repeatable at a different site. For this study, one well was 100 percent fresh water, another well was one part recycled water and five parts fresh water, and the last well was one part recycled waters and seven parts fresh water. Based on the data, the inorganic constituents vary more than the organic material. Inorganic variance being greater than organic makes sense due to the fact that the organic matter comes mainly from the fracturing fluid’s gel or slickwater component (Sick 2014), despite the organic variance seen in the previous study (White 2014). The inorganic matter mainly comes from the recycled water as seen from the ANOVA testing indicating significant difference between the wells, which is not treated to fresh water levels, and the data from the three wells shows a significantly higher value for the wells fractured with recycled water. A good illustration of the difference in the produced water quality that can be tied to the fracturing water quality is the TDS that was between four and six times higher in the fracturing fluid’s base fluid due to the use of recycled water. Of the inorganic constituents measured, aluminum, silicon, zinc, ammonium and sulfate were the only ones that did not show a statistically significant difference between the fresh water well and the recycled wells as indicated by a p value of 0.05 from an ANOVA test. None of the organic constituents showed significant statistical difference between the recycled wells and fresh water well, but they did vary over time indicating that the reactions and interactions with the geological formation affected the wells at a different rate. The wells did show a statistical difference both between the wells and over time, however, not in the way that was hypothesized as the organic material did not vary based on the wells. Total organic carbon (TOC), dissolved organic carbon (DOC), oil range organics (ORO), diesel range organics (DRO) and gasoline range organics (GRO) all had values 0.367, 0.758, 0.349, 0.768 and 0.707, respectively. The organics showed more significant difference over time with TOC, GRO, and ORO with p-values of 0.005, 0.012, and 0.029, respectively. However, the inorganic data did show significant difference between wells as well as over time. The inorganic constituents boron, barium, bromide, calcium, iron, potassium, magnesium, chlorine, strontium, sodium, and bicarbonate all had p-values of less than 0.01 except for chlorine which was 0.014. Potassium was the only constituent in that list that was not significantly different over time, but silicon and ammonium, which did not differ by well, did show significant difference over time. All of the inorganic constituents were very significantly different over time with no p-value over 0.01. The impact of this on the water management strategies shows that the understanding of the produced water quality and the factors that impact that is still largely unknown. More sampling and testing for well variability based on the ratio of recycled water in the fracturing fluid will allow more data and a better data driven management approach.