TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFormic acid is present in some corrosion inhibitors and is used as an intensifier in the acid treatment of oil and gas wells. This organic acid is important for the protection of low-carbon steels from acid corrosion at high temperatures and pressure. In this paper, the fate of formic acid used during acid treatments at temperatures up to 250ºF in deep gas wells is investigated in detail. To the best of the authors' knowledge, this is the first study of this type.The following conclusions were made from this work:• Most of the commercial organic additives for corrosion inhibitors contain formic acid while one inhibitor intensifier contains both formic and acetic acids. • Formic acid concentration in flow back samples from high temperature gas wells was higher than 85% of the injected value in most of the treatments. • In concentrated HCl at 250ºF, the amount of formic acid present in corrosion inhibitors and intensifiers decreased with time. After 8 hours corrosion inhibitors and intensifiers contained approximately 60% of the initial formic acid concentration. Acetic acid concentration did not significantly change with time in these tests. This work shows the fate of formic acid during acidizing of high temperature wells. Formic acid concentration in acid treatment flowback samples was near the injected value, showing that it remains available to act as a corrosion inhibitor intensifier. However, since it degrades with time, long shut-in times should be avoided. High formic acid concentrations in flow back samples may promote corrosion since the corrosion inhibitor concentration in these samples is significantly reduced.

Formic and acetic acids, with and without HCl, have been used extensively over the last 40 years as stimulation fluids and as acid additives. A measurement method for these organic acids was not previously available for highly contaminated acid stimulation samples that contain high acid concentrations, dissolved oil, suspended solids, and several different acid additives. Citric and acetic acids are also used in acid treatments as iron control agents at temperatures less than 200 and 150°F, respectively. An analytical method using capillary electrophoresis was developed to simultaneously measure the concentrations of formic and acetic acids in stimulation fluids. The developed method was used to evaluate flowback samples from pickle treatments and stimulation treatments of several high-temperature wells.The following conclusions are made: • A method for the simultaneous measurement of formic and acetic acids was developed, evaluated, and implemented for acid stimulation samples.• Citric acid concentration can be determined in certain cases, which are identified in the paper.• Results of formic and acetic acid concentrations in sandstone and carbonate corefloods were evaluated.• Flowback samples from pickle treatments and acid fracture treatments were evaluated. Results from treatments of super chrome-13 and low-carbon steel tubing with 15 wt% HCl/ 9 wt% formic acid show that a small decrease in formic acid relative to chloride concentration occurred over time with carbon steel. No significant decrease of formic acid relative to chloride concentration was observed in the flowback of a well with a super chrome-13 completion.

An analytical method was implemented to simultaneously measure the concentrations of acetic, citric and formic acids in stimulation fluids. This method was not previously available for acid stimulation treatments. Capillary electrophoresis is used for rapid and accurate measurement of these organic acids in concentrated hydrochloric acid and in highly contaminated spent acidizing fluids. Commonly used titration methods are not effective at low organic acid concentrations or when more than one organic acid is present. Acetic, citric and formic acids have been used extensively in Saudi Aramco fields over the last few years as stimulation fluids and as acid additives. Citric and acetic acids are frequently used in acid treatments as iron control agents. The following conclusions are made:A method for the simultaneous measurement of acetic acid, citric acid and formic acid was developed and evaluated.The method is linear in the range of 2 to 200 mg/l of organic acid in diluted samples. Field samples will normally be diluted by a factor of 200 to provide a range of 0.02 to 2.0 wt% of organic acid.The method can be used at concentrations from 200 to 1667 mg/l, but has a nonlinear response in this region.Sample requirement is less than 5 ml in most cases.Reproducibility of the method was excellent. Relative standard deviation of organic acid standards was less than 1% at 200 mg/l, less than 3% at 20 mg/l and less than 10% at 2 mg/l.The detection limits of the method are 0.25 mg/l for acetate, 0.4 mg/l for formate, and 1 mg/l for citrate, based on a signal to noise ratio of 3 to 1.For acetate and formate measurement, no interference occurred with chloride up to 1000 mg/l, calcium up to 565 mg/l, iron (II) or iron (III) up to 500 mg/l, or sulfate up to 859 mg/l.For citrate measurement, no interference occurred with chloride up to 1000 mg/l, calcium up to 350 mg/l, or sulfate up to 859 mg/l. Iron (II) and iron (III) caused interference at concentrations of 10 mg/l. The method was used to simultaneously measure organic acid concentrations in coreflood samples and in field samples from acid stimulation treatments. Introduction Organic acids have been used extensively in Saudi Aramco fields over the last few years. For example, a mixture of acetic acid (5 wt%) and hydrochloric acid (5 wt%) was successfully used to stimulate water supply and injections wells in a sandstone field in Central Arabia.1,2 In addition, citric and acetic acids are frequently used with hydrochloric acid as iron control agents.3 Citric, acetic and formic acids are used in field treatments at concentrations up to 10 wt%.4 Formic acid is used as a corrosion inhibitor intensifier.5 To effectively evaluate stimulation treatments using organic acids, it is critical to measure their concentrations in the injected fluids and in the well flowback samples. Analysis of these samples can be difficult because they can contain high concentrations of chemical additives, dissolved solids, suspended solids and oil.

fax 01-972-952-9435. AbstractWell acidizing treatments are conducted to enhance rock permeability, remove or bypass formation damage. During field applications, corrosion inhibitors are extensively used, among many other additives, to protect well tubulars against acid attack. The inhibitors are complex mixtures containing: quaternary salts, acetylenic alcohols, surfactants, solvents and impurities. Therefore, several analytical techniques and instruments are needed to characterize these compounds.Capillary electrophoresis (CE) is a rapid and reliable analytical separation technique. It has significantly improved over the last two decades to include a wide range of analytical applications, such as: food, pharmaceutical and biomedical industries. Coupling CE to universal detectors, such as Mass Spectrometry (MS) can boost the analytical ability of this instrument in qualitative and quantitative applications.In a previous work (SPE 58801) the authors adopted a CE technique to monitor the level of key oxygenated compounds in acid additives that are also used in deep, hot and sour gas wells. In the present work, the use of capillary electrophoresis-mass spectrometry (CE-MS), chromatographic and spectrometric techniques, to identify key nitrogen compounds in acid corrosion inhibitors was investigated. The inhibitors were selected from several commercial products that are commonly used in the field.Capillary electrophoresis was also applied for quantitative measurement of the inhibitor's level in well fluids, based on the response of its key nitrogen compounds. A linear relationship was obtained for the inhibitors of interest. The cation selected was a quinoline-based quaternary salt. This cation was detected down to inhibitor's level of 0.023 wt% with an analytical precision of less than 10%.The CE technique was used to determine the level of the corrosion inhibitors during acid fracturing treatments of deep gas wells.

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