Determination method of calcium ion content in oilfield water

Abstract

The invention relates to a method for measuring calcium ion content in oil field water. The EDTA titration method is commonly used to measure Ca2+, and it is difficult to judge the color of the end point, resulting in inaccurate readings. When the iron ion in the water is more than 1 mg / L, the iron ion needs to be removed, and the analysis steps are cumbersome. The present invention is aimed at the determination of calcium ion content in oil field water, uses calcein indicator as indicator, and under the condition of pH value above 12, titrates water sample with EDTA standard solution, measures calcium ion content; Calcein indicator contains calcium The mass ratio of chlorophyll, phenolphthalein and potassium chloride is 20:7:2000; the molar concentration of EDTA standard solution is 0.0125mol / L. The measuring method of the invention measures the calcium ion content in the oil field water, the method is simple, the accuracy is high, it is suitable for on-site determination, and it overcomes the disadvantages of difficulty in distinguishing the determination end point and the interference of iron ions.

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 oilfield 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 sa...

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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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