Hydraulic Fracturing Chemicals: Structural Classification, Detections in Flowback Water and Analytical Challenges Dissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Eberhard Karls Universität Tübingen zur Erlangung des Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) vorgelegt von Kathrin Gabriele Hölzer, geb. Schreglmann aus Weiden i.d. Opf. Tübingen 2016 Tag der mündlichen Qualifikation: 20.07.2016 Dekan: Prof. Dr. Wolfgang Rosenstiel 1. Berichterstatter: PD Dr. Martin Elsner 2. Berichterstatter: Prof. Dr. Christian Zwiener Für Irene und Hermann, in Liebe. Ihr werdet in meiner Erinnerung stets lebendig sein. Table of Contents Hydraulic Fracturing Chemicals: Structural Classification, Detections in Flowback Water and Analytical Challenges .......................................................1 TABLE OF CONTENTS ..........................................................................................................1 SUMMARY ............................................................................................................................5 ZUSAMMENFASSUNG ...........................................................................................................7 1 GENERAL INTRODUCTION ............................................................................................ 9 1.1 Background...........................................................................................................10 1.1.1 Hydraulic Fracturing and Unconventional Gas: Potentials and Environmental Concerns ..............................................................................10 1.1.2 Principle of the Hydraulic Fracturing Process and Chemical Additive Requirements ................................................................................................11 1.2 State-of-the-Art and Knowledge Gaps ...............................................................13 1.2.1 Systematic Overview over Chemicals used in Hydraulic Fracturing ...........13 1.2.2 High-Resolved Insight into Complex Samples ............................................14 1.2.3 Evidence to Trace Compound Origin and Fate ............................................15 1.3 Analytical Challenges ..........................................................................................16 1.4 Instrumentation ....................................................................................................17 1.4.1 Two-Dimensional Gas-Chromatography (GC×GC) ....................................17 1.4.2 Compound-specific isotope analysis (CSIA) via Isotope ratio mass spectrometry (GC-IRMS) .............................................................................18 1.5 Aims & Objectives ...............................................................................................20 2 QUANTITATIVE SURVEY AND STRUCTURAL CLASSIFICATION OF HYDRAULIC FRACTURING CHEMICALS REPORTED IN UNCONVENTIONAL GAS PRODUCTION ... 21 2.1 Introduction ..........................................................................................................22 2.2 Methodology .........................................................................................................27 2.3 Results and Discussion .........................................................................................29 TABLE OF CONTENTS 2 2.3.1 Types of Hydraulic Fracturing Fluids and Required Properties................... 29 1. Polymers and Crosslinkers ........................................................................... 31 2. Hydrocarbons, Alcohols ................................................................................ 36 3. Inorganic Compounds ................................................................................... 42 4. Amines and Quaternary Ammonium / Phosphonium Salts ........................... 46 5. Organic Acids, Esters and Amides ................................................................ 51 6. Electrophilic Compounds .............................................................................. 57 2.3.2 Typical Chemicals of an ―Average‖ HF Operation ...................................... 62 2.4 Environmental Significance ................................................................................ 64 2.4.1 Impacts on human and ecosystem health ..................................................... 65 2.4.2 Consequences for monitoring schemes / chemical analysis ......................... 66 2.4.3 Potential for additional chemicals of relevance ........................................... 67 3 INDICATIONS OF TRANSFORMATION PRODUCTS FROM HYDRAULIC FRACTURING ADDITIVES IN SHALE GAS WASTEWATER ................................................................. 71 3.1 Introduction .......................................................................................................... 72 3.2 Experimental Methods ........................................................................................ 75 3.2.1 Overarching approach .................................................................................. 75 3.2.2 Sample collection and storage ...................................................................... 76 3.2.3 Analytical methods ....................................................................................... 78 3.2.4 Confidence assignments ............................................................................... 78 3.3 Results & Discussion ............................................................................................ 80 3.3.1 Detected substance classes and disclosure rates........................................... 80 3.3.2 Sample heterogeneity and emerging similarities: Insights from GC×GC .... 83 3.3.3 Structural classification and quantitative overview of detected compounds 90 3.3.4 Proposed Reaction Mechanisms Leading to Transformation Products ........ 93 A. Hydrolysis Reactions of Putative Delayed Acids: Intended Transformations ................................................................................................ 93 TABLE OF CONTENTS 3 B. Halogenation Reactions: Unintended Transformations ...............................95 C. Transformation Reactions of Disclosed Additives: Products of Known Additives ............................................................................................................96 3.3.5 Compounds outside the Confidence Assignment .........................................97 3.3.6 Implications for Monitoring and the Environment .......................................98 4 CARBON AND NITROGEN ISOTOPE ANALYSIS OF ATRAZINE AND DESETHYLATRAZINE AT SUB-µG/L CONCENTRATIONS IN GROUNDWATER . 101 4.1 Introduction ........................................................................................................102 4.2 Materials and Methods ......................................................................................105 4.2.1 Chemicals ...................................................................................................105 4.2.2 Solid Phase Extraction ................................................................................105 4.2.3 Environmental Samples ..............................................................................106 4.2.4 Isotope Analysis by GC-IRMS ...................................................................106 4.2.5 Method quantification limits for isotope ratio measurements ....................108 4.2.6 Correction of Isotope Values ......................................................................108 4.2.7 Preparative HPLC Cleanup Step ................................................................108 4.3 Results and Discussion .......................................................................................109 4.3.1 SPE recovery and absence of isotope fractionation ...................................109 4.3.2 Limits of precise isotope analysis for atrazine and desethylatrazine .........110 4.3.3 Cold-on-column injection versus large-volume-injection: Improved peak width and sensitivity ...................................................................................113 4.3.4 Elimination of matrix interferences by preparative HPLC-cleanup ...........114 4.3.5 Measurements of natural groundwater samples .........................................115 4.3.6 Comparison of atrazine and desethylatrazine isotope ratios ......................116 4.4 Conclusion and Outlook ....................................................................................118 5 CONCLUSIONS AND OUTLOOK ................................................................................. 119 REFERENCES ....................................................................................................................123 TABLE OF CONTENTS 4 ABBREVIATIONS .............................................................................................................. 143 DANKE ............................................................................................................................. 147 CURRICULUM VITAE ....................................................................................................... 148 PUBLICATIONS ................................................................................................................. 149 SUPPORTING INFORMATION ........................................................................................... 150 A.1.1 Supporting Information of Chapter 2 ......................................................... 150 A.1.2 Supporting Information of Chapter 3 ........................................................