1、 Item No. 24225 NACE International Publication 31105 This Technical Committee Report has been prepared By NACE International Task Group 072* on Oil and Gas Production: Inhibitors, Dynamic Scale Evaluation Devices and Procedures Dynamic Scale Inhibitor Evaluation Apparatus and Procedures in Oil and G
2、as Production May 2005, NACE International This NACE International technical committee report represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasin
3、g, or using products, processes, or procedures not included in this report. Nothing contained in this NACE report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as
4、indemnifying or protecting anyone against liability for infringement of Letters Patent. This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relating to the subject. Unpre
5、dictable circumstances may negate the usefulness of this report in specific instances. NACE assumes no responsibility for the interpretation or use of this report by other parties. Users of this NACE report are responsible for reviewing appropriate health, safety, environmental, and regulatory docum
6、ents and for determining their applicability in relation to this report prior to its use. This NACE report may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within t
7、his report. Users of this NACE report are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to th
8、e use of this report. CAUTIONARY NOTICE: The user is cautioned to obtain the latest edition of this report. NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10 years old. Purchasers of
9、 NACE reports may receive current information on all NACE International publications by contacting the NACE FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281/228-6200). Foreword Mineral scales, hereinafter referred to as scales, are adherent forms of inorga
10、nic solids that deposit on production equipment surfaces. Oilfield brines containing, among other constituents, excess concentrations of calcium and barium, form solid carbonate and sulfate salts when thermodynamic and kinetic conditions are favorable. When scales deposit on process equipment, produ
11、ction decreases and operators are compelled to remedy the problem, increasing production costs. Therefore, effective scale inhibition is a common preventive practice when oil and gas wells are designed and operated. Using threshold scale inhibitor chemicals to prevent scale formation is a common ind
12、ustry practice. These chemicals are effective at substoichiometric concentrations (typically in the ppm region), making them a cost-effective treatment option. Determining the minimum concentration typically used to inhibit scale formation is the focus of this report. Specifically, this report revie
13、ws the open literature for information about the dynamic scale inhibitor evaluation apparatus known as the tube-blocking apparatus. The purpose of this technical committee report is to present a resource for oil and gas professionals in using dynamic flow-through test apparatus, and procedures typic
14、ally used for evaluating chemical scale inhibitors. A discussion of the test apparatus is included and operational problems are addressed. A bibliographic reference of papers relevant to this type of testing is included. This technical committee report was prepared by NACE International Task Group (
15、TG) 072, Oil and Gas Production: Inhibitors, Dynamic Scale Evaluation Devices and Procedures. This TG is administered by Specific Technology Group (STG) 31 on Oil and Gas ProductionCorrosion and Scale Inhibition. It is also sponsored by STG 60 on Corrosion Mechanisms. This technical committee report
16、 is issued by NACE International under the auspices of STG 31. _ * Chairman Joseph W. Kirk, BJ Chemical Services, Tomball, Texas. NACE International 2 Dynamic Scale Inhibitor Test ApparatusA. General Overview of the Tube-Blocking Apparatus and Its Use Dynamic scale inhibitor test apparatus are used
17、to evaluate the efficiency of scale inhibitor chemicals in preventing formation and deposition of mineral scales such as calcium carbonate, calcium sulfate, and barium sulfate. One such test apparatus is the tube-blocking apparatus. A tube-blocking apparatus consists of the following: bottles to hol
18、d the various brine solutions, pumps (usually one for each brine solution), stainless steel (SS) or polymer capillary tubing, a heat source, pressure detectors, and data-recording equipment. The apparatus is usually fitted with electronic circuitry that automatically shuts down the pumps when the pr
19、essure differential across the capillary tube coil exceeds a preset level indicative of plugging. A backpressure regulator is sometimes used to maintain pressure in the capillary tube coil. A schematic of one such tube-blocking apparatus is illustrated in Figure 1. The tube-blocking apparatus normal
20、ly works as follows: Separate pumps inject two incompatible brines through separate tubing to a mixing point. Prior to mixing, the brines are heated to the specified test temperature by placing them in a constant-temperature liquid bath or an oven. If conditions are favorable, solids precipitate at
21、the mixing location or at some point in the capillary tube coil downstream. An increase in pressure indicates the onset of scaling, as the precipitate adheres to the wall and constricts the capillary tubing. Following the test, the capillary tube coil is flushed of precipitate and residual chemicals
22、, and prepared for the next test. These steps are sometimes automated. FIGURE 1: Schematic representative of a tube-blocking apparatus The brines are often laboratory-prepared with one containing the scaling anions (sodium counter ions), and the other containing the scaling cations (chloride counter
23、 ions). Separately, they have insignificant scaling potential, but when mixed they produce the potential typically used for the specific test. The brines used are sometimes field samples for which the scaling potential is already known or is under investigation. The brines are normally fed from sepa
24、rate reservoirs and are sometimes preheated before introduction into a mixing chamber or prior to mixing immediately preceding the capillary tube coil. After establishing baseline conditions for inducing scaling, researchers typically treat the brine with varying levels of threshold scale inhibitors
25、. This is normally done by injecting the chemical into the mixed stream, or adding it to the anion-containing brine or to both brines.1Adequate scale inhibition is achieved when there is no increase in pressure NACE International 3 across the capillary tube coil. The minimum concentration that achie
26、ves adequate inhibition is known as the minimum scale inhibitor concentration (MSIC). Some of the test apparatus described in the literature are based on high-pressure liquid-chromatography (HPLC) components, such as constant-volume pumps, and have multiposition valves and backpressure regulators to
27、 increase functionality and versatility.2,3,4,5,6Other components of the test apparatus include pH probes, spectrophotometers,7and filters.5In-line pH meters and filters have also been incorporated for data collection.2,8Figure 2 provides an example of a more complex tube-blocking apparatus for cond
28、ucting a dynamic scale-inhibitor test. B. Capillary Tube Coil Material of Construction and Size The heart of the tube-blocking test apparatus is the capillary tube coil. In most cases capillary tube coils have been made of readily available UNS S31600 (type 316 SS). The reported lengths include 50 m
29、m, 2 m, and 15 m, and most commonly measured about 1 m.2,3,4One researcher prepared capillary tube coils from polytetrafluoroethylene (PTFE) and polyetheretherketone (PEEK) to minimize wall adsorption of chemicals and ionic species from previous tests.7The reported capillary tube cross-sections vari
30、ed from 0.05 mm to 1.7 mm inside diameter (ID), with 1.0 and 1.1 mm most commonly reported. Again, the literature indicates significant variation.4,6The general configuration has separate tubing carrying the two incompatible brine solutions to a mixing point. For example, one tube typically carries
31、the brine containing carbonate and sulfate ions, and the other carries the calcium, strontium, or barium ions. The brine supply preheat coils are normally immersed in a thermostatically controlled heating bath where the brines are heated to a predetermined value. Differential pressure (P) across the
32、 capillary tube coil is monitored following the mixing point. Scaling in the capillary tube coil creates an increase in P FIGURE 2: Schematic Diagram of a High-Temperature and High-Pressure Apparatus NACE International 4 across the coil, which is typically recorded on a P vs. time plot.1,5,6,9,10,11
33、 C. Temperature and Pressure Ranges The literature shows that the capillary tube coils were normally held at a temperature of 70 to 90C during the tests. Temperatures in this range were most likely chosen to approximate downhole temperatures. As cited in the literature, if the test apparatus is fit
34、for use at significantly higher or lower temperatures, there are few barriers to interfere with such testing. One researcher noted the benefits of having a test apparatus capable of testing brines from -18 to 150C. By having the flexibility of testing brines under selected temperature and pressure c
35、onditions, the authors noted that, “. . . it has not only been possible to evaluate scale inhibitors under realistic conditions, but the time to test new inhibitors over a range of concentrations has been reduced from days to hours.”7In some literature, the only pressure cited was that necessary to
36、force the brine through the capillary tube coil. In others, however, significantly higher pressures were chosen. This was likely done to approximate the downhole pressures experienced by the field brines or to maintain concentrations of dissolved gases during the tube-blocking tests.2,3,6,7,8,12 Tes
37、t Methodologies and ResultsA. Overview of Test Procedures The literature contains a wide range of test conditions, but the following conditions are fairly typical: The capillary tube coil is typically made of UNS S31600 (type 316 SS) or PEEK. The coil is often 1.0 to 1.1 mm ID and approximately 1 m
38、in length.6 Backpressure on the capillary tube coil is sometimes applied to prevent the loss of carbon dioxide from the brine solution or if an above-ambient test temperature is used. With appropriate pumps and SS tubing, high-temperature and high-pressure conditions are easily achieved. The tube-bl
39、ocking tests principally evaluate the very short residence time nucleation-inhibitor mechanism (typically from seconds to less than one minute).6Precipitates that do not adhere to the capillary tube wall do not contribute to a P increase across the capillary tube coil. Thus, the tube-blocking test m
40、easures the effectiveness of chemicals, which may be classified as antiscalant as opposed to antiprecipitant.1,9The brine solutions are sometimes heated prior to mixing and subsequent introduction into the capillary tube coil. The test is typically terminated when (a) a specific P increase has been
41、experienced, (b) a predefined amount of brine has been pumped, or (c) a predetermined amount of time has expired.5,9,10,11The scale inhibitor is sometimes added to one of the test brines, or injected into the mixed brine using a separate pump. If the scale inhibitor is to be injected, a diluted inhi
42、bitor solution is typically used. The concentration of the scale inhibitor in a separately injected solution is generally as high as practical, commensurate with the lowest practical injection rate.5 B. Cleaning Procedures Between Tests When a tube-blocking test is complete and another is to follow,
43、 the test apparatus is typically prepared for that subsequent test. This is generally accomplished by flushing with a cleaning solution. Aqueous solutions of ethylenediaminetetraacetic acid (EDTA) salts, dilute nitric acid, and water are the most commonly reported washing and rinsing solvents. Becau
44、se of its critical role in the test, the capillary tube coil and its cleaning are worthy of special comment. A consortium of researchers investigated methods for evaluating calcium carbonate scale inhibitors and reported their observations regarding cleaning of new and used capillary tube coils.10Ni
45、tric acid (4 wt%) and formic acid (10 wt%) were effective cleaners that did not damage the SS (UNS S30400/S31600 type 304/316) capillary tube coils. For removing sulfate deposits most researchers chose aqueous solutions of EDTA salt as the primary scale-removal agent.1,3,9,13One team cut open their
46、capillary tube coils (of unspecified diameter) for inspection following tests. Each test began with a fresh capillary tube coil that had been pretreated with 5 wt% nitric acid (and presumably rinsed with water).5C. Effect of Flow Rate There is very little information in the literature relating the f
47、low rate to the efficiency of the various scale inhibitors. The literature contains a wide range of flow rates, from a low of 0.2 mL/min, to a high of 25 mL/min.5,9,10One author used flow rates between 1 and 4 L/h (17 and 67 mL/min) in a 1.1-mm ID capillary tube coil.5Another author used a 0.76-mm I
48、D capillary tube coil with a total flow rate of 10 mL/min.9This flow rate gave Reynolds numbers of 406 at 40C and 757 at 80C. One research team reported that testing at 16.5 mL/min required scale inhibitor dosages up to five times those required with very low flow rates (0.2 mL/min).5Typically, a to
49、tal flow rate (of combined anion and cation brine solutions) is approximately 10 mL/min or 5 mL/min for each brine solution.9Flow rates discussed are all laminar flow and have Reynolds numbers of 20 to 757.5,9NACE International 5 D. Reproducibility There is little information on the exact degree of reproducibility, but one paper reports a reproducibility factor of 8 2%.3Another reported the relative standard deviation to be on the order of 14% and stated this level of test reproducibility was considered more than adequate to differentiate sc
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