Quantitative produced water analysis using mobile¹H NMR

Abstract

Measurement of oil contamination of produced water is required in the oil and gas industry to the (ppm) level prior to discharge in order to meet typical environmental legislative requirements. Here we present the use of compact, mobile 1 H nuclear magnetic resonance (NMR) spectroscopy, in combination with solid phase extraction (SPE), to meet this metrology need. The NMR hardware employed featured a sufficiently homogeneous magnetic field, such that chemical shift differences could be used to unambiguously differentiate, and hence quantitatively detect, the required oil and solvent NMR signals. A solvent system consisting of 1% v/v chloroform in tetrachloroethylene was deployed, this provided a comparable 1 H NMR signal intensity for the oil and the solvent (chloroform) and hence an internal reference 1 H signal from the chloroform resulting in the measurement being effectively self-calibrating. The measurement process was applied to water contaminated with hexane or crude oil over the range 1-30 ppm. The results were validated against known solubility limits as well as infrared analysis and gas chromatography.

Solid-Phase Extraction Nuclear Magnetic Resonance (SPE-NMR): Prototype Design, Development, and Automation

“…The average volume ratio of produced water to oil is 7–10:1 in the US and 2–3:1 worldwide; this ratio escalates with the age of a reservoir. , Produced water is a mixture of formation water from the reservoir (which contains reservoir hydrocarbons), any injected reservoir “flooding” water, production chemicals, and condensed water from produced gas. It thus frequently contains dissolved or dispersed organic and inorganic compounds; petroleum hydrocarbons are generally considered the most environmentally concerning components. − The estimated global discharge volume of produced water is in excess of 200 million barrels per day . The large volume of produced water, together with its complex trace composition, makes its management one of the biggest environmental challenges for the oil and gas industry. , To comply with relevant legislation, the oil-in-water (OiW) content of produced water needs to be reduced to ppm levels; this requires accurate measurement at these low concentrations.…”

“…It thus frequently contains dissolved or dispersed organic and inorganic compounds; petroleum hydrocarbons are generally considered the most environmentally concerning components. − The estimated global discharge volume of produced water is in excess of 200 million barrels per day . The large volume of produced water, together with its complex trace composition, makes its management one of the biggest environmental challenges for the oil and gas industry. , To comply with relevant legislation, the oil-in-water (OiW) content of produced water needs to be reduced to ppm levels; this requires accurate measurement at these low concentrations. For example, the Environmental Protection Agency (EPA) limits the produced water’s OiW content to a monthly average of 29 ppm and a daily maximum of 42 ppm. , Hence, reliable, low cost and low maintenance OiW measurements are critical to ensure compliance with such environmental regulations.…”

“…It is also applied in the laboratory for hydrate formation and oil field emulsions characterization, for example. − Proton ( 1 H) NMR can detect all compounds with hydrogen atoms in their structure and, as a result, can theoretically measure the total hydrocarbon contamination of produced water. Furthermore, NMR techniques are readily made self-calibrating through the inclusion of reference compounds, require no optical window, and allow for quantitative separate analysis of aromatic and aliphatic hydrocarbon content. , Conventional high-field NMR spectrometers (typically employing superconducting magnets) will provide both enhanced sensitivity and compound spectral resolution for such OiW monitoring. Their complexity, size, and cost, however, effectively preclude them from any realistic field application. , Recent advancements in NMR technology have, however, produced benchtop low-field permanent magnets with increased sensitivity and magnetic field homogeneity.…”

“…Their complexity, size, and cost, however, effectively preclude them from any realistic field application. , Recent advancements in NMR technology have, however, produced benchtop low-field permanent magnets with increased sensitivity and magnetic field homogeneity. These are mobile, significantly cheaper than conventional high magnetic field systems, and generally more robust to environmental conditions, all of which make them more suitable for field applications. , A major traditional limitation of all NMR has been comparatively poor sensitivity with ppm of OiW levels being considerably below any practical detection limit; the application of solid-phase extraction (SPE) as a sample preparation technique for NMR has, however, allowed for quantitative OiW monitoring at this ppm level. , …”

Explosive Emulsion Characterisation using Nuclear Magnetic Resonance

“…Many potential options exist to determine droplet sizes in emulsions (e. g. ultrasonics [20], microscopy, laser scattering [21]); they all however struggle with the high aqueous droplet phase concentration (~90 v/v %) of practical explosive emulsions. In contrast NMR PFG is readily directly applicable to such concentrations and in recent years this measurement option is now also available via robust benchtop hardware [19,22,23] which is much more suitable to relevant industrial environments. NMR PFG techniques have been repeatedly demonstrated to provide early detection of emulsion instability (droplet size growth), significantly before it results in visually obvious phase separation [24,25].…”