Origin, signature, and interaction of coal bed methane produced water natural organic matter with inorganic solutes Katharine Dahm Colorado School of Mines Fourth IWA Specialty Conference Natural Organic Matter: From Source to Tap and Beyond July 27-29, 2011 Costa Mesa, California USA
Presentation Outline Introduction to Coalbed Methane Produced Water Gas Production Environment Characteristics Water Production Analytical Technique: 3-D Fluorescence Spectroscopy Produced Water Fingerprint Origin and Source Comparisons Coal Microcosm Experiments Influence of Salts, Metals and ph on the coal derived NOM signature Results Comparison of NOM Sources Unique Produced Water Signature Microcosm Interferences and Interactions Discussion Peak locations, intensities and shifts Inorganic solute interactions
Introduction to Coalbed Methane Produced Water Conventional vs. Unconventional Oil and Gas Resources Conventional Oil and Gas Increasing water over time Unconventional Coalbed Methane (CBM) High initial water production CBM Produced Water Large volumes removed to reduce hydrostatic pressure allowing gas to desorb Time dependent rates can average 30 bbls/day/well 1,260 gal/day/well Saline water ranging from < 500 50,000 mg/l total dissolved solids Mainly NaCl and NaHCO 3 salt types RPSEA Field Sampling: Coalbed Methane Wellhead Raton Basin 04/24/09
Introduction to the CBM Environment Coal Formation Heat, pressure, time Continental to brackish to marine Highly organic depositional environment Bituminous and subbituminous coals can be composed of 35 to 85% carbon Methane Generation Pathways Thermogenic methane formation Deeper formation, higher ranked coals Biogenic methane formation Shallower formation, interactions with recharge zones Coal has high surface area, large gas capacity Coalpoint Coal Seam Kaitangata, New Zealand
Motivations to Fingerprinting CBM NOM Produced Water Source Tributary/Non-tributary Well Water Quantity/Duration Biogenic Methanogenesis Bioavailable Organic Nutrients Reservoir Stimulation Water Treatment/Beneficial Use Implications Organic fouling in treatment Indicator of water composition
NOM Fingerprinting Techniques Focus on 3-D Fluorescence Spectroscopy Fingerprinting technique Organic matter fractions Developed for surface waters and impaired surface water systems Application of anlaysis in CBM environment Additional complementing analyses Total/Dissolved Organic Carbon (TOC/DOC) Ultraviolet Adsorption (UVA) ph, conductivity Ion chromatography/inductively coupled plasma (IC/ICP) Emission-Excitation Matrix (EEM) Spectra Protein-like Humic-like Fulvic-like EEM: Municipal Wastewater DOC = 35.5 mg/l
Source Water Comparison System Sources: Groundwater system Brackish Groundwater Formation Water Deep Aged Ocean Water Coal-Derived Extracts Dissolved from Coal CBM Well Production Additive Fracturing Polymer Naturally Occurring Discrete Organics BTEX Compounds Potential NOM Sources in the CBM System
CBM Produced Water Fingerprint EEM: San Juan Basin DOC = 2.91 mg/l EEM: Raton Basin DOC = 1.74 mg/l EEM: Municipal Wastewater DOC = 35.5 mg/l EEM: Atlantic Rim Basin DOC = 1.20 mg/l EEM: Powder River Basin DOC = 3.65 mg/l
CBM Signature Matching EEM: Deep Sea Water DOC = 0.45 mg/l EEM: San Juan Basin DOC = 2.91 mg/l EEM: Raton Basin DOC = 1.74 mg/l EEM: Fracturing Polymer DOC = 5.5 mg/l EEM: Atlantic Rim Basin DOC = 1.20 mg/l EEM: Powder River Basin DOC = 3.65 mg/l EEM: Municipal Wastewater DOC = 35.5 mg/l
CBM Signature Matching EEM: San Juan Basin DOC = 2.91 mg/l EEM: Raton Basin DOC = 1.74 mg/l EEM: Coal-Water Equilibrium DOC = 1.10 mg/l EEM: Atlantic Rim Basin DOC = 1.20 mg/l EEM: Powder River Basin DOC = 3.65 mg/l EEM: Brackish Groundwater DOC = 0.75 mg/l
Dissolved Coal Microcosms DI Water Initial Comparisons Reaching Equilibrium Coal:Water Ratio Salinity Salt Type Salt Concentration ph Varying ph < 2 to 10 Inorganic Solutes Common metals in CBM produced water Average metal concentrations of 111 CBM produced water samples EEM: Dissolved Coal Increasing salt concentration: Top to Bottom EEM: Dissolved Coal ph = 7.14 EEM: Dissolved Coal ph < 2.0
Dissolved Coal Microcosms DI Water Initial Comparisons Reaching Equilibrium Coal:Water Ratio Coal + Ca Salinity Salt Type Coal + Al Coal + Ba Salt Concentration ph Coal + Mg Varying ph < 2 to 10 Inorganic Solutes Coal + Cu Coal + Fe Common metals in CBM produced water Coal + Sr Average metal concentrations of 111 CBM produced water samples Coal + Mn Coal + Ni Coal + Zn
EEM Spectra Peak Shift: Salinity Fulvic like peak: 240 excitation, 440 emission does not match dissolved coal peak Calculated maximum peaks and all maximum peak intensities are at an excitation of 270 nm NaCl Emission Shift: 18 nm lower in higher salinity samples NaHCO 3 Emission Shift: 8 nm spread, no specific trend in salinity
Salinity Influences on Peak Intensity Maximum peak location shifts with salinity (NaCl more pronounced than NaHCO 3 ) Graph Legend: dark to light NaCl and NaHCO 3 500 mg/l 1,000 mg/l 2,500 mg/l 5,000 mg/l 10,000 mg/l 25,000 mg/l Maximum peak intensity also corresponds to salinity NaCl concentrations range from 500 mg/l (dark) to 25,000 mg/l (light) NaHCO 3 concentrations range from 500 mg/l (dark) to 25,000 mg/l (light)
Acidification of Dissolved Coal Signature EEM: Dissolved Coal ph = 7.14 EEM: Dissolved Coal ph = 4.26 EEM: Dissolved Coal ph = 3.22 EEM: Dissolved Coal ph = 2.00 EEM: Dissolved Coal ph = 1.50
Metal Interactions with the EEM Spectra Classification of EEM Spectra Interactions with Metals - Negligible Effects - Limited effects of average sampled produced water metal concentrations - Spectra Suppression - Reduced or eliminated spectra with measurable DOC concentration - EEM spectra eliminated in samples with copper and iron - Spectra Manipulation - Manipulation of dissolved coal peak occurred in the presence of calcium and zinc Coal + Al Coal + Ba Coal + Mn Coal + Mg Coal + Ni Coal + Sr Coal + Cu Coal + Fe Coal + Ca Coal + Zn
Metal Manipulation of the EEM Spectra Dissolved Coal and Calcium All other experiments used a Metal- Chloride salt form Calcium hydroxide used Higher in-situ microcosm ph ~ 10 Resulted in the extraction of a different signature Similar to systems with biogenic methanogenesis Potential connection to discrete organic matter present in the system Dissolved Coal and Zinc Predominately protein-like peak deviates from most dissolved coal samples Potential interaction with certain coal organic groups Coal + Ca Coal + Zn
Resulting CBM Produced Water NOM Source Comparison EEM: San Juan Basin DOC = 2.91 mg/l EEM: Raton Basin DOC = 1.74 mg/l EEM: Coal-Water Equilibrium DOC = 1.10 mg/l EEM: Atlantic Rim Basin DOC = 1.20 mg/l EEM: Powder River Basin DOC = 3.65 mg/l EEM: Coal Brackish Water Groundwater Equilibrium DOC ph = 0.75 = 10.2 mg/l
Discussion of Results CBM produced water NOM character has the potential to provide information on: Produced Water Source: Tributary/Non-tributary, Well Water Quantity, and Source Duration Peak location (Maximum Emission-TDS relationship) may indicate proximity to recharge location More likely linked to inorganic composition Potential indicators may exist in discrete organic matter Biogenic Methanogenesis: Bioavailable Organic Nutrients, Reservoir Stimulation Potential High ph extraction of different NOM spectra Peaks may link to discrete NOM Linking fingerprint fractions to biogenic methanogenesis could imply likelihood of reservoir stimulation potential
Discussion of Results Water Treatment/Beneficial Use Implications: Organic fouling in treatment, indicator of water composition Metal interactions with organic matter Potential fouling of membranes (ongoing experimentation) NOM characterization for indicating specific water composition Peak location and intensity may indicate relative salinity Absence of spectra with measurable DOC concentration may indicate copper or iron concentrations Forms of Porous Membrane Fouling by Coal-type Organic Matter
Ongoing/Future Work Influence of ph on EEM Spectra Acidifying produced water samples Metal Concentrations Varying metal concentrations Calcium effects with CaCl 2 Biological microcosm analysis Discrete organic compound signatures EEM spectra analyses NOM fractions Calculation of peak volumes Percent similarity Pretreatment with UF membranes NOM interaction with metals NOM fouling potential in pretreatment membranes
An Integrated Framework for Treatment and Management of Produced Water Contact Katharine Dahm, Colorado School of Mines kdahm@mines.edu SPONSORED BY: Acknowledgements PhD Advisors Jörg Drewes and Junko Munakata-Marr Lab Assistant Colette Van Straaten Funding: Research Partnership to Secure Energy for America National Water Research Institute Fellowship