Patent Description:
Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) is the main active component in biocide products commonly used in the oil and gas industry for microbial control in water systems. The THPS-based biocides are generally considered environment-friendly since they are readily degradable.

THPS is traditionally detected and quantified using iodometric titration methods or various commercial test kits. For example, the Solvay TOLCIDE Biocides Test kit and LOVIBOND THPS kit are commonly used commercial test kits. However, these test kits have a limited detection range for THPS (e.g., <NUM> - <NUM> ppm).

Additionally, in a large water pipeline network or other large water systems, it is difficult with currently available methods and test kits to collect water samples for biocide residual measurements at downstream locations after a batch treatment of the biocide product is provided at an upstream location. This is due to the difficulties in estimating the biocide travel time in a large pipeline network because of the complexity of pipeline networks (e.g., diameters, branches, etc.) and daily operation changes and fluctuations (e.g., flow rate).

As such, there is a need for effective field measurement methods for biocides, and in particular, THPS-based biocides, in oil and gas facilities. The present application addresses these and other challenges related to measuring THPS in water, and specifically in water networks of oil and gas facilities.

<CIT> describes methods and systems for colorimetrically analyzing a liquid medium by analyzing chemical test strip images.

By way of overview and introduction, the present application discloses methods for detecting and quantifying tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in a water sample. In one or more embodiments of the method, a water sample comprising THPS (or suspected of comprising THPS) is mixed with a KMnO<NUM> solution to form a mixture. An intensity of KMnO<NUM> absorption in the mixture at a wavelength of <NUM> is then measured. Once the intensity of KMnO<NUM> absorption at <NUM> in the mixture has been measured, the measured intensity of KMnO<NUM> absorption is normalized by subtracting a background intensity at a wavelength of <NUM>. The normalized intensity of KMnO<NUM> absorption measurement is then used to determine the presence and/or concentration of THPS in the water sample by comparing the normalized intensity of KMnO4 absorption with KMnO<NUM> absorption intensity values of calibration samples comprising KMnO<NUM> and known THPS concentrations.

These and other aspects of the present methods are described in further detail below with reference to the accompany drawing figures, in which one or more illustrated embodiments and/or arrangements of the methods are shown. The methods of the present application are not limited in any way to the illustrated embodiments and/or arrangements. It should be understood that the methods as shown in the accompanying figures are merely exemplary of the methods of the present application, which can be embodied in various forms as appreciated by one skilled in the art. Therefore, it is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting the present methods, but rather are provided as a representative embodiment and/or arrangement for teaching one skilled in the art one or more ways to implement the present methods.

Further, it should be understood that, as used in the present application, the term "approximately" when used in conjunction with a number refers to any number within <NUM>% of the referenced number, including the referenced number.

Referring now to <FIG>, a flow diagram displaying steps for a method <NUM> for detecting and quantifying THPS in a water sample is provided in accordance with one or more embodiments. The method <NUM> begins at step S105 where a water sample is collected. The water sample comprises or is suspected of comprising THPS or a THPS-containing biocide. The water sample can be a freshwater sample or a saltwater sample, such as Arabian Gulf Seawater (AGS). AGS has a salinity around <NUM>,<NUM>/L, which is much higher than the average salinity in the world's oceans (approximately <NUM>,<NUM>/L).

In one or more embodiments, the water sample can be collected from an existing body of water, or from a water treatment facility or water distribution network known to comprise THPS or THPS-based biocides. Thus, in embodiments in which the water is collected from a water treatment facility, for example, the water can be collected from a conduit of the water treatment facility.

At step S110, the collected water sample is mixed with a potassium permanganate (KMnO<NUM>) solution to form a mixture. In one or more embodiments, equal amounts of the water sample and the KMnO<NUM> solution are mixed together. In one or more embodiments, the KMnO<NUM> solution is a <NUM> to <NUM> millimolar (mM) KMnO<NUM> solution. In at least one embodiment, the KMnO<NUM> solution is a <NUM>-<NUM> millimolar (mM) KMnO<NUM> solution. The KMnO<NUM> solution can have a pH of approximately <NUM> in accordance with one or more embodiments. In at least one embodiment, the KMnO<NUM> solution comprises water that has been deionized to a high degree and purified using resin filters, such as a water purified using the MILLI-Q® Water Purification System ("MILLI-Q water"). In at least one preferred embodiment, the KMnO<NUM> solution is a <NUM> KMnO<NUM> in MILLI-Q water (pH <NUM>).

The collected water sample and the KMnO<NUM> solution are mixed for a period sufficient to enable a reaction between the KMnO<NUM> solution and the THPS in the water sample. In accordance with one or more embodiments, in the reaction, the inventors determined that the mole ratio of the reaction between THPS and permanganate is approximately <NUM>:<NUM>, meaning that <NUM> moles of THPS is able to decolorize <NUM> mole of KMnO<NUM>. In at least one embodiment, the water sample is mixed with the KMnO<NUM> solution for at least <NUM> minutes. In one or more embodiments, the water sample is mixed with the KMnO<NUM> solution for approximately <NUM> to <NUM> minutes. In one or more preferred embodiments, the water sample is mixed with the KMnO<NUM> solution for approximately <NUM> minutes.

At step S115, the KMnO<NUM> absorption in the water-KMnO<NUM> mixture is measured at a wavelength of <NUM>. As mentioned above, when the water sample and KMnO<NUM> solution are mixed, THPS present in the water sample reacts with the KMnO<NUM> solution. Thus, as determined by the inventors, when THPS is present in the water sample, the resulting measured absorption at <NUM> of the KMnO<NUM> solution following reaction with the THPS is correlated with THPS concentration in the water sample. Thus, by measuring the absorption change of the KMnO<NUM> solution after the reaction with THPS, the THPS concentration in the water sample (or the THPS concentration in the biocide product in the water sample) can be determined.

In one or more embodiments of the present methods, the THPS concentration in the water sample can be accurately determined for water samples comprising THPS in a range of approximately <NUM>-<NUM> ppm. In other words, in one or more embodiments, the present methods have a dynamic range of approximately <NUM>-<NUM> ppm for THPS. This dynamic range applies to freshwater samples and saltwater samples. This concentration range covers the normal biocide treatment concentration and residual concentration encountered in water treatment facilities and distribution networks in the oil and gas industry.

At step S120, the measured absorption of KMnO<NUM> at the wavelength of <NUM> is normalized by subtracting the background intensity at the wavelength of <NUM>. More specifically, the measured absorption of KMnO<NUM> at the wavelength of <NUM> represents the KMnO<NUM> color change after the reaction with THPS. At step S120, the absorption of KMnO<NUM> in the mixture at the wavelength of <NUM> is measured, which corresponds to the background absorption (background intensity) of the solution. The measured absorption of KMnO<NUM> at the wavelength of <NUM> is then normalized by subtracting the measured absorption of KMnO<NUM> at <NUM> (the background intensity). Normalization by subtracting the <NUM> background absorption improves the lower detection limit of THPS in the present methods.

At S125 the presence and concentration of THPS in the water sample is determined. The presence and concentration of THPS in the water sample is determined by comparing the normalized absorption measurement of KMnO<NUM> at the wavelength of <NUM> with intensity values of calibration samples comprising KMnO<NUM> and known THPS concentrations.

To begin step S125, a correlation equation (or calibration curve) is established between the THPS concentration in a given water sample and the measured normalized absorption (intensity) of KMnO<NUM>. As determined by the inventors, a change in absorption (intensity) due to the reaction of the THPS and of KMnO<NUM> is correlated with the concentration of THPS in the water sample. As such, based on this correlation, a calibration curve is established between the THPS concentration in given samples and normalized absorption of the KMnO<NUM>. As with the absorption measurements at step S120, the absorption of KMnO<NUM> in the samples for the calibration curve are normalized by subtracting the <NUM> background absorption. Using the established calibration curve, the concentration of THPS in the water sample is determined by matching the normalized measured absorption of the KMnO<NUM> at the wavelength of <NUM> with its normalized absorption (intensity) value on the curve and the corresponding THPS concentration value on the curve.

<FIG> show example graphs showing the absorption of KMnO<NUM> absorption at <NUM> as a function of THPS concentrations in samples of Arabian Gulf Seawater (AGS) and Milli-Q water in accordance with one or more embodiments. AGS is widely used in the Middle East region for reservoir injection for pressure maintenance of oil reservoirs. The AGS is transported through complex pipeline network for reservoir injection, and the microbial activities in the AGS are controlled by biocide treatment (e.g., THPS).

In the examples of <FIG>, samples comprising <NUM> to <NUM> ppm of THPS were prepared in AGS and Milli-Q water. Equal volumes (<NUM>) of the THPS-containing sample (both AGS and Milli-Q water) and <NUM> KMnO<NUM> (pH <NUM>) were mixed and allowed to react for <NUM> minutes. Then, the intensity of the permanganate (KMnO<NUM>) absorption at <NUM> was measured and normalized by subtracting the background intensity at <NUM>. <FIG> shows the KMnO<NUM> absorption at <NUM> as a function of THPS concentrations (<NUM>-<NUM> ppm), and <FIG> shows a zoomed in version of the <NUM>-<NUM> ppm region of the graph of <FIG>.

As shown in the graphs of <FIG>, a linear relationship between the concentrations of THPS and absorption of KMnO<NUM> is established. Specifically, in accordance with one or more embodiments, the absorption of KMnO<NUM> showed a linear relationship with THPS at the range of THPS concentrations between approximately <NUM> and <NUM> ppm, with a dynamic range of approximately <NUM>-<NUM> ppm. In one more embodiments, the dynamic range can be expanded to approximately <NUM>-<NUM> ppm of THPS by increasing the concentration of the KMnO<NUM> solution. For example, at a concentration of <NUM> for KMnO<NUM> at <NUM>, the dynamic range is approximately <NUM>-<NUM> ppm. However, at a concentration of <NUM> for KMnO<NUM> at <NUM>, the dynamic range increases to approximately <NUM>-<NUM> ppm. The results shown in <FIG> also indicate that the function of THPS concentration with <NUM> KMnO<NUM> absorption at <NUM> is comparable in Milli-Q water samples and AGS samples, and that THPS can be detected at levels as low as <NUM> ppm, and as high as <NUM> ppm, in accordance with one or more embodiments. In at least one embodiment, the dynamic range for detection of THPS in the water samples at a concentration of <NUM> for KMnO<NUM> at <NUM> is approximately <NUM>-<NUM> ppm. The above dynamic ranges are applicable to freshwater and saltwater samples.

Thus, in one or more embodiments, the limit of detection is approximately <NUM> ppm. In one or more embodiments, the dynamic detection range for THPS concentration in the sample is approximately <NUM>-<NUM> ppm. Further, in at least one embodiment, by increasing KMnO4 concentration from <NUM> to <NUM>, the dynamic range of the THPS in AGS can be expanded to approximately <NUM>-<NUM> ppm.

Returning to <FIG>, after the concentration of THPS in the water sample is determined, the method ends at step S130. In at least one embodiment, the steps of the present method (steps S105 - S130) are completed using a sensor. <FIG> display various aspects of an exemplary THPS sensor <NUM> for the present methods in accordance with one or more embodiments. With reference to <FIG>, the sensor <NUM> comprises a sample reservoir <NUM> for the water sample comprising THPS and a reservoir <NUM> for the KMnO<NUM> solution. The THPS sensor <NUM> also includes a first conduit <NUM> for transferring the water sample comprising THPS and the KMnO<NUM> solution from their respective reservoirs to a mixing coil <NUM>. In the mixing coil <NUM>, the water sample comprising THPS and the KMnO<NUM> solution are mixed (step S110). Following mixing, the mixture is transferred via a second conduit <NUM> to a flow cell <NUM>. In one or more embodiments, the flow cell <NUM> is a Z-flow cell.

With continued reference to <FIG> and <FIG>, in one or more embodiments the sensor <NUM> further includes a <NUM>-nm light-emitting diode (LED) <NUM> and a reference <NUM>-nm LED <NUM>, which are operatively attached to the flow cell <NUM>. In at least one alternative embodiment, the two LEDs <NUM> and <NUM> can be replaced with a multicolor LED. In the flow cell <NUM>, the mixture comprising the water sample and the KMnO<NUM> solution is exposed to the light emitted by the two LEDs <NUM> and <NUM> for absorption measurement.

In accordance with one or more embodiments, <FIG> shows a preferred optical configuration for the Z-flow cell, in which the <NUM>-nm light-emitting diode (LED) <NUM> and the reference <NUM>-nm LED <NUM> are arranged perpendicularly and directed at a dichroic mirror <NUM>. In such an embodiment, the THPS sensor <NUM> optimizes the light levels that are coupled into the flow cell by introducing a reference channel (<NUM> LED). In one or more embodiments, the Z-flow cell is a typical Z-flow cell having a Z-shaped fluidic path, which allows continuous flow up through the flow cell, and minimizes bubble entrapment. When combined with spectrometers, light sources and accessories, a Z-flow cell allows rapid analysis of the samples by measuring the optical absorbance of fluids moving through the flow injection system. Different optical pathlengths and internal volumes in Z-cells are available depending on the analytical needs. As shown in <FIG>, the Z- flow cell <NUM> can include SMA connectors for attachment to optical configuration and the microcontroller, respectively. In a preferred optical configuration for the Z-flow cell shown <FIG>, the two LED lights <NUM>, <NUM> with specific wavelengths (<NUM> and <NUM>, respectively) pass through the fluid (KMnO<NUM> and sample mixture) and the absorption is measured by a spectrometer.

Referring again to <FIG>, in one or more embodiments, the flow cell <NUM> (e.g., Z-flow cell) has an absorption path length of approximately <NUM>. When the absorption of the KMnO<NUM> is collected by the flow cell <NUM>, a signal is transported via a patch cable <NUM> (e.g., <NUM> patch cable with an SMA connector) to a microcontroller <NUM> (e.g., printed circuit board [PCB] microcontroller). A micro-processor platform <NUM> (e.g., Feather, Arduino technology) can process the analogue signals and provide pulses in order to measure the absorption of the KMnO<NUM> (e.g., step S115). After the absorption of the KMnO<NUM> has been measured and the concentration of THPS in the sample has been determined, the mixture of the THPS water sample and the KMnO<NUM> is passed out of the flow cell <NUM> via a third conduit <NUM> and can be disposed of as waste.

In one or more embodiments, the THPS sensor <NUM> is an online sensor that is operatively connected to a water treatment facility or water distribution network, for example, such that real-time measurements of THPS in the water treatment facility or water distribution network can be determined. In one or more embodiments, the sensor <NUM> can also be configured to transmit measurements (wired or wireless transmissions) and data to a control center remote from the sensor <NUM>.

In at least one embodiment, the absorption measurements can be performed with instruments other than a sensor. For example, lab-based instruments can be used to measure the absorption of the KMnO<NUM> mixture. Such lab-based instruments can include, for example, spectrometers or spectrophotometers. Examples of suitable spectrophotometers are Mettler Toledo Spectrophotometer UV5 and UV7 and Konica Minolta Spectrophotometer CM-<NUM> and CM-3600A.

The above aspects and other aspects of the present methods can be further understood through the following examples.

A biocide product, approximated as containing <NUM>-<NUM>% THPS and <NUM>-<NUM>% surfactant, was used in this experiment. The biocide product was diluted in AGS into samples comprising approximately <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> ppm THPS. Then, each of these samples were mixed with and <NUM> KMnO<NUM> in MilliQ water (pH <NUM>) in equal volumes and allowed to react for approximately <NUM> minutes. The intensity of the KMnO<NUM> absorption at <NUM> was then measured and normalized by subtracting the background intensity at <NUM>. This process was then repeated but using a pure THPS instead of a THPS-containing biocide. The series of samples containing pure THPS (at equal concentrations as shown above for the biocide product) were then compared to the biocide-containing samples.

<FIG> shows the normalized absorption as function of the approximate THPS concentrations in AGS for the THPS biocide-containing samples. For comparison, <FIG> also shows the corresponding samples containing pure THPS. <FIG> shows a zoomed in version of the graph of <FIG>, focusing on the <NUM>-<NUM> ppm region of interest. As shown in <FIG> and <FIG>, KMnO<NUM> absorption is an effective way to measure the THPS content in AGS, with a linear range between <NUM> and <NUM> ppm, a dynamic range of approximately <NUM>-<NUM> ppm, and a limit of detection (LOD) of approximately <NUM> ppm. There is a small offset in the graphs of <FIG> and <FIG> between the pure THPS and THPS-biocide product samples, both of which were diluted in AGS. The most plausible explanation is that the actual THPS content of the biocide product may be below the <NUM>% approximation used in the preparation of THPS-biocide dilutions in the experiment.

THPS samples of <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> ppm were prepared in fresh water, and <NUM> aliquots from each sample were transferred to respective reaction vials. Then <NUM> of acidic <NUM> KMnO<NUM> was added to each reaction vial, such that the THPS and the KMnO<NUM> reacted with one another. For each sample, <NUM> were transferred to an absorption cuvette and the absorption in the range of <NUM>-<NUM> was measured. This process was then repeated but using THPS samples in salt water (sea water) instead of fresh water.

<FIG> shows an exemplary calibration curve for freshwater and saltwater samples in accordance with one or more embodiments. As shown in the graph of <FIG>, the KMnO<NUM> absorption decreases as the concentration THPS increases. Thus, a change in intensity of KMnO<NUM> absorption in the mixture is correlated with the concentration of THPS in the water sample. As such, based on this correlation, the calibration curve is established between the THPS concentration in given samples and the intensity of the KMnO<NUM> absorption.

Although much of the foregoing description has been directed to methods for methods detecting and quantifying THPS in a water sample, the methods disclosed herein can be similarly deployed and/or implemented in scenarios, situations, and settings far beyond the referenced scenarios. It should be further understood that any such implementation and/or deployment is within the scope of the methods described herein.

It is to be further understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It will be further understood that the terms ""including," "comprising," or "having," "containing," "involving," and variations thereof herein, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It should be noted that use of ordinal terms such as "first," "second," "third," etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Notably, the figures and examples above are not meant to limit the scope of the present disclosure to a single implementation, as other implementations are possible by way of interchange of some or all the described or illustrated elements. Moreover, where certain elements of the present disclosure can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present disclosure are described, and detailed descriptions of other portions of such known components are omitted so as not to obscure the disclosure. In the present specification, an implementation showing a singular component should not necessarily be limited to other implementations including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein.

Claim 1:
A method for detecting tetrakis(hydroxymethyl)phosphonium sulfate, THPS, in a water sample, characterised by that the method is comprising:
mixing a water sample with a KMnO<NUM> solution (S110) to form a mixture;
measuring an intensity of KMnO<NUM> absorption in the mixture at a wavelength of <NUM> (S115);
normalizing the measured intensity by subtracting a background intensity at a wavelength of <NUM>; (S120); and
determining a presence of THPS in the water sample (S125) by comparing the normalized intensity with intensity values of KMnO<NUM> absorption of calibration samples comprising KMnO<NUM> and known THPS concentrations.