Method for measuring content of calcium ions in oil field water

Abstract

The invention relates to a method for measuring the content of calcium ions in oil field water. Commonly, an EDTA (Ethylene Diamine Tetraacetic Acid) titration method is adopted to measure Ca2+ and an endpoint color is difficult to judge so as to cause inaccurate numerical reading. When the content of iron ions in water is over 1mg / L, the iron ions need to be removed, but the analysis step is cockamamie. Aiming at the measurement of the content of the calcium ions in the oil field water, a calcein indicator is used as an indicator; under the condition of a pH value of over 12, EDTA standard solution is adopted to titrate a water sample so as to measure the content of the calcium ions; the calcein indicator contains calcein, phenolphthalein and potassium chloride; the mass ratio of the calcein to the phenolphthalein to the potassium chloride is 20:7:2,000; and the EDTA standard solution has molar concentration of 0.0125mol / L. The measuring method disclosed by the invention is used for measuring the content of the calcium ions in the oil field water, is simple and convenient, has high accuracy and is suitable for in situ measurement. Moreover, the defects of difficulty in distinguishing a measurement endpoint and iron ion interference are overcome.

Description

technical field [0001] The invention relates to a method for determining the content of calcium ions, in particular to a method for determining the content of calcium ions in oil field water. Background technique [0002] The ions in oilfield produced water mainly include: Ca 2+ , Mg 2+ , SO 4 2- 、HCO 3 - , CO 3 2- , Fe 3+ etc., where Ca 2+ It is the main component of Wuqi oilfield water and the main scale-forming ion in oil well scaling. Calcium can cause serious carbonate and sulfate scaling related to oilfield water. Carbonate scale is easy to decompose with acid, and sulfate scale The problem is difficult to deal with. Once the sulfate scale has settled, there are few chemicals that can dissolve it. In routine water analysis, the determination of Ca 2+ Commonly used are EDTA titration, atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP), etc. Atomic Absorption Spectroscopy: In atomic absorption spectroscopy, a s...

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Problems solved by technology

The disadvantage of this method is that both spectral and non-spectral interference can occur, and high levels of dissolved solids can also cause problems

Atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry are instrumental analysis methods. These two methods have expensive instruments, complicated sample preparation steps, and too many interference factors, so they are not suitable for on-site measurement of Ca in oilfield water. 2+

The original EDTA titration method: use calcium indicator (sodium carboxylate) as the indicator, and measure under the condition that the pH value is 12~14. When the end point is reached, the color of the solution changes from wine red to purple to pure blue. This method The disadvantage is that it is difficult to judge the color of the end point, resulting in inaccurate readings

When the iron ion content in the water is more than 1mg / L, the iron ion needs to be removed, and the analysis steps are cumbersome, and it is only suitable for the determination of the iron ion content in the water less than 1mg / L

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