Simultaneous analysis of multiple components in well fluids

Abstract

The current application discloses methods and systems to analyze on-site and in real-time or quasi real-time the composition of the well fluid before or during use or disposition. The method is based on capillary electrophoresis (CE) and does not require the addition of tracers into the well fluid or additive. Based on the significance of each additive on the well fluid properties, it can be decided to determine the concentration of all additives or only one or a limited number of the additives present in the fluid, and the concentrations can be adjusted as needed to reach the desired target concentration(s).

Claims

1. A method, comprising: obtaining a sample of a well fluid before or during injection of the well fluid into a wellbore; injecting the sample without a tracer into a capillary tube; inserting the capillary tube into a capillary electrophoresis system; and determining a concentration of an ingredient in the sample of the well fluid with the capillary electrophoresis system.

2. The method of claim 1, further comprising: comparing the concentration against a target concentration of the ingredient.

3. The method of claim 1, further comprising: adjusting the well fluid before or during injection of the well fluid into the wellbore based on the concentration of the ingredient in the sample of the well fluid.

4. The method of claim 1, further comprising: determining respective concentrations of a plurality of additional ingredients in the sample of the well fluid with the capillary electrophoresis system, wherein the concentration of the ingredient and the respective concentrations of the plurality of additional ingredients are determined in a single test.

5. The method of claim 1, wherein the well fluid is a drilling fluid, a cement slurry, a fracking fluid, a fracking fluid breaker, an enhanced oil recovery fluid, a spacer fluid, a settable composition, a completion fluid, an acidification fluid, a sand control fluid, a produced water, an injected water, a formation water, a river water, a sea water, a brine, or a mix-fluid for same.

6. The method of claim 5, wherein the well fluid is a mix-fluid for a cement slurry.

7. The method of claim 6, further comprising: mixing the ingredient with a carrier fluid to form the mix-fluid for the cement slurry; adding the cement powder after obtaining the sample of the mix-fluid for the cement slurry to form the cement slurry; and injecting the cement slurry into the wellbore.

8. The method of claim 6, wherein the ingredient is one or more of a retarder, a fluid-loss-control additive, and a dispersant.

9. The method of claim 1, wherein the ingredient is one or more of a retarder, a fluid-loss-control additive, a dispersant, a thixotropic additive, a lime, a salt, an additive for controlling lost circulation, an accelerator, a surfactant, a mixing aid, a foaming agent, an anti-foaming agent, an anti-settling agent, an anti-gelling agent, a gas migration control additive, and a clay stabilizer.

10. The method of claim 9, wherein the ingredient is one or more of a retarder, a fluid-loss-control additive, and a dispersant.

11. The method of claim 1, wherein the determining is performed at a location where the well fluid is prepared, used, or collected.

12. The method of claim 11, wherein the determining is performed at a well site.

13. The method of claim 1, wherein the determining is performed at a location different from where the well fluid is prepared, used, or collected.

14. The method of claim 1, wherein the capillary tube is an anionic capillary tube, a cationic capillary tube, a coated capillary tube, a coated anionic capillary tube, or a coated cationic capillary tube.

15. The method of claim 1, wherein the well fluid is mixed on the fly.

16. The method of claim 1, wherein the well fluid is batch mixed.

17. The method of claim 1, comprising obtaining the sample and a plurality of additional samples at regular intervals during or after mixing to form the well fluid.

18. The method of claim 1, further comprising: mixing the ingredient with a carrier fluid on a rig at a well site to form the well fluid; carrying out the obtaining, the injecting, the inserting, and the determining on the rig at well site; and injecting the well fluid from the rig at the well site into the wellbore.

19. The method of claim 2, further comprising: adjusting the well fluid before or during injection of the well fluid into the wellbore such that the concentration corresponds to the target concentration.

20. The method of claim 19, wherein adjusting the well fluid comprises controlling a pump to add more of the ingredient to the well fluid before or during injection of the well fluid into the wellbore.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1A. Categorization of capillary electrophoresis techniques.

(2) FIG. 1B. Schematic of typical capillary electrophoresis system.

(3) FIG. 2A. CE analysis of cement retarders

(4) FIG. 2B. CE analysis of cement additive.

(5) FIG. 2C. CE analysis of cement dispersant. FIG. 2C also shows a zoom of the mid-section from 3-5 minutes.

(6) FIG. 3A. Calibration curve for Retarder.

(7) FIG. 3B. Calibration curve for a major and minor constituent (inset) of a multi-functional additive.

(8) FIG. 4A. Mix-fluid analysis of multiple additives. Fluids are prepared by mixing individual additives in 1:1:1 volume ratio, wherein 3 retarders injected together into the capillary, and quantitatively separated and quantitated.

(9) FIG. 4B. Mix-fluid analysis: fluids are prepared by mixing individual additives in 1:1:1 volume ratio, wherein 3 different types of additives viz., a retarder, a dispersant and a multi-functional additive injected together and separated quantitatively.

DETAILED DESCRIPTION

(10) At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the methods, devices, and systems used/disclosed herein can also comprise some components other than those cited.

(11) Also, in the summary of the disclosure and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific numbers, it is to be understood that any and all data points within the range are to be considered to have been specified.

(12) Following examples describe applications of the methods and systems of the current application to cement additives. However, people skilled in the art should understand the methods and systems of the current application can also be applied to other well fluids, reservoir fluids, large scale manufacturing fluids, remediation fluids, disposal fluids, and the like, as well as additives, contaminants and other ingredients of such fluids.

Capillary Electrophoresis

(13) Capillary electrophoresis or “CE” is a family of electrokinetic separation methods performed in submillimeter capillaries and in micro- and nano-fluidic channels. There are (at least) six types of capillary electro-separation techniques developed to date, such as but not limited to: capillary zone electrophoresis (CZE), capillary gel electrophoresis (CGE), micellar electrokinetic capillary chromatography (MEKC), capillary electrochromatography (CEC), capillary isoelectric focusing (CIEF), and capillary isotachophoresis (CITP).

(14) CE techniques can be classified into continuous and discontinuous systems as shown in FIG. 1A. A continuous system has a background electrolyte acting throughout the capillary as a buffer. This can be broken down into kinetic (constant electrolyte composition) and steady-state (varying electrolyte composition) processes. A discontinuous system keeps the sample in distinct zones separated by two different electrolytes.

(15) In CE methods, analytes migrate through electrolyte solutions under the influence of an electric field. Analytes can be separated according to ionic mobility, additionally they may be concentrated by means of gradients in conductivity and/or pH.

(16) The electrophoretic mobility is dependent upon the charge of the molecule, the viscosity, and the atom or molecule's radius. The rate at which the particle moves is directly proportional to the applied electric field—the greater the field strength, the faster the mobility. If two ions are the same size, the one with greater charge will move the fastest. For ions of the same charge, the smaller particle has less friction and overall faster migration rate. Capillary electrophoresis is used because it gives faster results and provides high resolution separation. It is also useful because there is a large range of detection methods available.

(17) The instrumentation needed to perform capillary electrophoresis is relatively simple. A basic schematic of a capillary electrophoresis system is shown in FIG. 1B. The system's main components are a sample vial, source and destination vials, a capillary, electrodes, a high-voltage power supply, a detector, and a data handling and output device. The source vial, destination vial and capillary are filled with an electrolyte such as an aqueous buffer solution. To introduce the sample, the capillary inlet is placed into a vial containing the sample. Sample is introduced into the capillary via capillary action, pressure, siphoning, or electrokinetically, and the capillary is then returned to the source vial.

(18) The migration of analytes is initiated by an electric field that is applied between the source and destination vials and is supplied to the electrodes by the high-voltage power supply. In the most common mode of CE, ions are pulled through the capillary in the same direction by electroosmotic flow or “EOF”. The analytes separate as they migrate due to their different electrophoretic mobility, and are detected near the outlet end of the capillary. The output of the detector is sent to a data output and handling device such as an integrator or computer. The data is then displayed as an electropherogram, which reports detector response as a function of time. Separated chemical compounds appear as peaks with different retention times in an electropherogram, and area under the peak is proportional to concentration.

(19) The simplest way to identify a CE peak is to compare its migration time with that of a known compound. Thus, in the methods disclosure herein, this can be done onsite with appropriate control samples, and/or migration times and standard curves can be determined in advance and compiled for specific uses.

(20) As with other separation techniques, however, the migration time alone may not be always reliable for confirming peak identity and purity. Thus, final confirmation may require additional information. One method of confirmation entails comparing the ratio of absorbance's at different wavelengths in the unknown with that ratio in the suspected compound using spectrophotometric detection. Another method is to compare the ratio of currents obtained from two different electrical potentials using amperometric detection. Other methods are available and can be used as desired or appropriate, such as coupling with mass spectrometers similar to the LC-MS type of coupling.

(21) Exemplary equipment is available from many commercial suppliers, particularly in the biomedical industry. For example, Protein Simple (Toronto, CA), Bio-Rad (Hercules Calif.), Life Technologies (Grand Island, N.Y.), Beckman Coulter (Indianapolis Ind.) all provide commercial capillary electrophoresis instruments. Further, portable systems are in development by many groups, and EH Systems (Simpsonville S.C.) already offers robust portable CE systems. The CEP-5000 and CEP-5100 systems, for example, boast small size, light weight, and low power consumption when used together with their miniaturized detectors. Thus, these are ideal portable CE systems for field use.

(22) CE analyses are usually very fast, use very little sample and reagents, and cost much less than chromatography or conventional electrophoresis. Although modern CE is still in its teenage years, it has demonstrated tremendous potential for a wide range of applications, from small molecules that include inorganic ions, organic acids, drugs, and vitamins to larger molecules, such as proteins, nucleic acids, and even living cells. Based on the tremendous success of this technique in the biomedical sciences, we sought to determine herein if CE would also be suitable for rig-side and other large scale industrial uses and if it would be generally applicable to some of the harsher chemicals used in manufacturing or oil & gas reservoirs during drilling, primary production, secondary recovery and the like.

(23) The capillary column is a key element of the CE separation. Fused silica is by far the most frequently used material, although columns have been made of Teflon and borosilicate glass. The widespread use of fused silica is due to its intrinsic properties, which include transparency over a wide range of the electromagnetic spectrum and a high thermal conductance. Fused silica is also easy to manufacture into capillaries with diameters of a few micrometers. Many reports describe the covalent attachment of silanes with neutral or hydrophilic substituents to the inner wall of the capillary in order to reduce electroosmotic flow and prevent adsorption of the analyte; coatings also tend to stabilize the pH. Microfluidic chip channels are also used in some applications, as are chiral capillaries, isomer separation capillaries, etc.

(24) A wide variety of coatings are available to influence the performance of the capillary tubing. Examples of coatings range from poly-acrylamides (PAAM), poly-ethylene-glycol (PEG), poly-imides, poly-dimethyl-acrylamide, poly-vinyl-alcohol (PVA), poly-vinyl-pyrrolidone (PVP), poly-ethylene-oxide (PEO), and the like.

Cement Slurry Mix-Water

(25) Although retarder concentration in cement slurries is critical, there is currently no satisfactory method for checking that the concentration of retarder is correct. WO2011064632 teaches one such method, but requires the use of a tracer mixed with the additive, such that tracer levels can be detected as a proxy for additive levels. However, the tracer can impact the chemistry of the ingredients and further, one must still have added the correct amount of tracer to the additive, and this introduces another point of variability from batch-to-batch of additive.

(26) We sought therefore, to determine if CE was suitable for confirming the concentration of ingredients, such as retarder, dispersants, anti-foamers, and fluid loss additives in a cement slurry. Table 1 shows various additional oilwell cement additives that can be tested with the methods therein.

(27) TABLE-US-00003 TABLE 1 Non-limiting examples of oilwell cement additives. Type of Additive Use Chemical Composition Benefit Type of Cement Accelerators Reducing WOC Calcium chloride Accelerated All API classes time Sodium chloride setting Pozzolans Setting surface Gypsum High early Diacel systems pipe Sodium silicate strength Setting cement Dispersants plugs Seawater Combating lost circulation Retarders Increasing Lignosulfonates Increased API Classes D, thickening time Organic acids pumping time E, G, and H for placement CMHEC Better flow Pozzolans Reducing slurry Modified lignosulfonates properties Diacel systems viscosity Weight-reducing Reducing weight Bentonite/attapulgite Lighter weight All API classes additives Combating lost Gilsonite Economy Pozzolans circulation Diatomaceous earth Better fill-up Diacel systems Perlite Lower density Pozzolans Microspheres (glass spheres) Nitrogen (foam cement) Heavyweight Combating high Hematite Higher density API Classes D, additives pressure Limenite E, G, and H Increasing slurry Barite weight Sand Dispersants Additives for Bridging Gilsonite Bridged fractures All API classes controlling lost Increasing fill-up Walnut hulls Lighter fluid Pozzolans circulation Combating lost Cellophane flakes columns Diacel systems circulation Gypsum cement Squeezed Fast-setting Bentonite/diesel oil fractured zones systems Nylon fibers Treating lost Thixotropic additives circulation Filtration-control Squeeze Polymers Reduced All API classes additives cementing Dispersants dehydration Pozzolans Setting long liners CMHEC Lower volume of Diacel systems Cementing in Latex cement water-sensitive Better fill-up formations Dispersants Reducing Organic acids Thinner slurries All API classes hydraulic Polymers Decreased fluid Pozzolans horsepower Sodium chloride loss Diacel systems Densifying Lignosulfonates Better mud cement slurries removal for plugging Better placement Improving flow properties Special cements or additives Salt Primary Sodium chloride Better bonding to All API classes cementing salt, shales, sands Silica flour High-temperature Silicon dioxide Stabilized All API classes cementing strength Radioactive Tracing flow .sub.63I.sup.131, .sub.77Ir.sup.192 All API classes tracers patterns Locating leaks Pozzolan lime High-temperature Silica-lime reactions Lighter weight cementing Economy Silica lime High-temperature Silica-lime reactions Lighter weight cementing Gypsum cement Dealing with Calcium sulfate Higher strength special conditions Hemihydrate Faster setting Latex cement Dealing with Liquid or powdered latex Better bonding API Classes A, special conditions Controlled B, G, and H filtration Thixotropic Covering lost- Organic additives Fast setting All API Classes additives circulation zones Inorganic additives and/or gelation Preventing gas Less fallback migration Reduces lost circulation

(28) In step 1 of the method, the capillary was coated with anion coating and pre-conditioned with the separation buffer. In step 2, a sample of mix-fluid for use to make a cement slurry (by adding cement powder) with one or more additives was injected in to the column, followed by separation by applying voltage in step 3. The method can be performed in presence of cement as well. After the separation and detection, in step 4, the capillary was rinsed with the condition and rinse solution. Detection was by measuring UV absorbance at a suitable wavelength using a spectrometer.

(29) This is a simple representation of the method, but persons of skill in the art can add or remove steps based on the additives and well fluid they are interested in.

Protocols

(30) Several experiments were conducted with one or more additives mixed in brine, as a typical fluid used in reservoirs. However, the dilution can be done with deionized water, tap water, brine, produced water or any other desired solvent or solution as long as the components do not affect the procedure.

(31) First, we estimated or determined the viscosity of the additive fluid, and diluted if needed. For example during retarder analysis, retarder was diluted 1000 times. If the additive was solid, then we dissolved the solid sample at reasonable concentration to enable the injection of the accurate sample volume into the system. If necessary, solids can be comminuted to powders or otherwise solubilized and/or the sample can be filtered before proceeding.

(32) In the case of mixed fluids, individual additives were prepared as above, and mixed in desired ratio before proceeding.

(33) Once the sample was ready, it was analyzed with the desired method. However, the capillary was first conditioned according to the method illustrated in Table 2, where conditioning and rinse solutions were 0.1 M NaOH. A commercially available anion coating was applied (anion coating provided with CElixirOA™ kit, MicroSolv, Eatontown, N.J.) for 50 sec. duration at 20 psi pressure. Depending on the chemistry of the additive, any appropriate anion or cation coating can be used for the desired duration and at desired pressure.

(34) TABLE-US-00004 TABLE 2 Exemplary method for capillary conditioning. Pressure Voltage Inlet vial Outlet vial Step (psi) (kV) Duration position position Step 1 Rinse - Conditioner 20.0 1.00 min AI1 AO1 Step 2 Rinse - Rinse Solution 20.0 1.00 min BI1 BO1 Step 3 Rinse - Anion Coating 20.0 0.50 min CI1 AO1 Step 4 Rinse - Anion 20.0 0.50 min DI1 AO1 Separation Buffer Step 5 Separation 0.0 −30.0 10.0 min EI1 EO1 Step 6 Stop Data Step 7 Rinse - Conditioner 20.0 0.50 min AI1 AO1 Step 8 Rinse - Rinse Solution 20.0  0.5 min BI1 BO1 Step 9 End

(35) The actual samples were analyzed per Table 3.

(36) TABLE-US-00005 TABLE 3 Exemplary method for anionic retarder analysis. Pressure Voltage Inlet vial Outlet vial Step (psi) (kV) Duration position position Step 1 Rinse - Anion Coating 20.0 0.50 min CI1 AO1 Step 2 Rinse - Anion 20.0 0.50 min DI1 AO1 Separation Buffer Step 3 Inject - Sample 0.5  8.0 sec FI1 AO1 Step 4 Inject - Water 0.1 10.0 min GI1 AO1 Step 5 Separation 0.0 −30.0  8.0 min EI1 EO1 Step 6 Stop Data Step 7 Rinse - Conditioner 20.0 0.50 min AI1 AO1 Step 8 Rinse - Rinse Solution 20.0  0.5 min BI1 BO1 Step 9 End

(37) Small negatively charged molecules such as ions and aliphatic organic acids are not UV absorbing and therefore require an “indirect” method of detection when using UV detectors. The CElixirOA™ pH 5.4 and pH 8.2 buffers are phosphoric acid buffers that contain a “chromophore” that will completely absorbs all the UV energy and produces a detector response that is full and “off scale”. When a non-absorbing analyte, such as an organic acid, an added ion or a surfactant, passes the detection window, the detector senses a decrease in absorption and records the negative “peak”. One benefit of this system is that all non-UV absorbing additives can be detected at the same wavelength. The system is optimized for use at 233 nm but it will also work with a UV filter at 254 nm and with a filter of 230 nm.

(38) Some anions such as nitrate, nitrate and bromide as well as aromatic acids and unsaturated aliphatic acids are UV absorbing. They separate best in very acidic conditions such as pH 2.5 and for this reason CElixirOA™ pH 2.5 is available without chromophores and operates in the same way cathodic buffer systems do with regard to detection.

(39) Due to the negative charge of the anions, they migrate toward the anode (positive). To have these anions flow in the direction toward the detection window of an integrated instrument, the polarity of the CE instrument is reversed. All other conditions remain “normal” when using these CElixirOA™ kits and no other changes are required. Vials are loaded in the same position as before.

(40) Once the sample applied to the column, and chased with a water plug to improve sensitivity, desired voltage was applied across the capillary to perform a separation step with an anion separation buffer. For example, in the cement retarder analysis −30 kV voltage for 10 mm duration with an anionic separation buffer with pH 5.4 was used. In this step, the capillary was dipped in anion separation buffer on both ends. However, based on the chemistry of the additives, one can use an anionic separation buffer with higher or lower pH ranges. Also, we can use cationic separation buffer if the additives are cationic in nature for the desired duration and desired pressure.

(41) Serial dilutions of each additive were assayed to create a calibration curve, which was then plotted. Using the curve, an unknown amount of additive can be determined based on the slope.

Exemplary Additives

(42) The test methods developed herein were tested with different types of cement additives:

(43) TABLE-US-00006 ADDITIVE TYPE UV absorbance Retarder 1 254 Retarder 2 254 Retarder 3 254 Multifunctional additive 254 Dispersant 254 Retarder 1 254

(44) As can be seen from the data presented in FIG. 2, the individual additives consist of a range of different chemicals with different retention time and response. Depending on the analyte, individual components may have either negative or positive response without affecting the quantitative response. As part of the CE buffer design the UV chromophore can also be optimized to enhance response factors.

(45) The test method described above requires less than 10 mm, but this can be further reduced by changing the parameters of the CE, for example, increasing voltage or flow rate, varying capillary length, buffer, pH etc. Separation can be improved by changing the size and type of the capillary, and inducing gradients of voltage during the analysis.

(46) It should be noted that all the data present in FIG. 2 was obtained with the same CE-protocol. This highlights that different cement additives (single-component or multi-component additives) can be detected accurately with a single methodology. Furthermore, for each of the additives, the retention time was different. It is therefore possible to determine the concentration of each ingredient in the mix-fluid.

(47) Our experiments also showed the CE results to be quantitatively accurate. When the calibration of one constituent in a few selected additives was performed, excellent quantitative correlation was observed. FIG. 3A-B presents the calibration curves for two different proprietary additives.

(48) Moreover, the methods and systems of the current application can analyze either individual additives as well as mix-fluids with one type or more types (functionalities) of additives. FIG. 4A-B presents the different types of mix-fluid analysis, wherein FIG. 4A shows the separation of a mixture of three proprietary retarders, while FIG. 4B shows the separation of three different types of additives—dispersant, a retarder, and a multifunctional additive—in a single mix-fluid.

(49) These experiments highlight the advantages and applicability of CE for rig-side or lab analysis of different types of additives in fluids. Although examples shown here consider only cement-based additives, it is the first demonstration where a single technique is employed to analyze all the constituents of additives and mix-fluids at the rig or lab. Further, with judicious selection of capillary type, coating, buffer, pH, and running conditions, a wide variety of additives can be successfully measured this way.

(50) In addition, since the analysis can be performed on the rig, it improves the QA/QC of the fluid design. It also avoids aging of the mix-fluids, whose composition can easily vary before its analysis back in a remote laboratory. The examples also show that the method is accurate (calibration curves).

(51) Also the methods and systems of the current application can be used to retro-control the pumps injecting the additives in the mix-fluids based on resultant mix-fluid composition and field requirements. For example, the rig mix-fluid composition is compared to the designed mix-fluid composition. If the concentration of one or several additives are lower than expected, the pump can be activated automatically or manually to add the needed amount of additive. If the concentration(s) of one or several additives are higher than expected, more carrier fluid (usually water) can be added, as well as the other additives in order to meet the required composition.

(52) The preceding description has been presented with reference to some embodiments. Persons skilled in the art and technology to which this disclosure pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this application. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

(53) The references made herein merely provide information related to the present disclosure and may not constitute prior art. The following references are hereby incorporated by reference herein in their entireties for all purposes: Non-Aqueous Capillary Electrophoresis 2005-2008, Geiser, L.; Veuthey, J-L Electrophoresis, 2009 30 36-49. Improved Analysis Techniques Quantitatively Determine Critical Organic Additives Simultaneously In Cement Blends, Cob, A; SPE 86-37-48, 1986 95-100 Well Cementing, 2nd Edition, E. Nelson, D. Guillot, 2006 WO2014014587 Capillary electrophoresis for reservoir fluid analysis at wellsite and laboratory