Characterization of Organic Compounds in Produced Water From Unconventional Reservoirs Using Nuclear Magnetic Resonance Spectroscopy and Carbon Isotope Analysis
Nuclear magnetic resonance (NMR) spectroscopy and carbon isotope analysis can be utilized to characterize organic compounds in produced water from unconventional reservoirs. An accurate representation of the types and concentrations of organic compounds is critical, as they play an important role in evaluating biogeochemical processes such as methanogenesis, hydrocarbon degradation, water-rock interactions, and water-oil/gas interactions. Previous research showed high proportions of aromatic, cyclic, and heterocyclic organic compounds in produced water samples from unconventional reservoirs. To effectively evaluate the organic compounds in produced water, our analytical procedure includes acquiring 1H and 13C NMR spectra of bulk produced water samples and separate organic/aquatic fractions, as well as measuring the d13C values for dissolved organic carbon (d13CDOC). NMR spectroscopy provides for the identification of organic compound functional groups, establishing a baseline for higher resolution, compound specific analyses. Carbon isotope analysis of the dissolved organic carbon reflects the source of the organic carbon, maturity of the basin, and specific biogeochemical processes, including methanogenesis. For this study, samples of produced water were taken from 16 wellheads along a northwest-southeast transect across the Brookwood and Blue Creek Fields in the Black Warrior Basin, Alabama, USA. Preliminary data show variations in NMR spectra within the basin, which may be related to the hydrodynamics and/or recharge patterns within the system. Variations in NMR data could reflect changes in organic carbon sourcing, changes in the metabolic products of microbial communities, and patterns in hydrocarbon degradation. We were also able to use d13CDOC values to identify potential sources of the dissolved organic carbon and the isotopic composition of organic compounds in the system. This combination of spectroscopic and isotopic techniques will further enhance our understanding of unconventional reservoirs, allowing for a more effective characterization of resource plays and improved oil and gas recovery techniques. Additionally, this novel approach to organic compound characterization will aid in appropriate management of produced water from unconventional reservoirs.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017