Selection and Evaluation of Oilfield Scale Inhibitors
Scale inhibitors are a general term for a class of chemicals. The addition of scale prevents and prevents the formation of scale.
The scale inhibition effect is achieved by maintaining the scale-forming cations (tungsten, iron, ruthenium) in a “solution” by various mechanisms. This article mainly explains how to choose oilfield scale inhibitors and the evaluation of oilfield scale inhibitors.
The scale inhibitors used in oilfield water treatment include inorganic polyphosphate, organophosphorus corrosion inhibitor, polycarboxylic acid scale inhibitor, and natural scale inhibitor. The most used scale inhibitors are organophosphorus corrosion inhibitors and polycarboxylic acid scale inhibitors and their complex complexes.
Organophosphorus corrosion inhibitors generally have two major categories, one is organic phosphonic acid and the other is organic phosphonate.
Organophosphorus corrosion inhibitors are compared to inorganic polyphosphates. The invention has the advantages of good chemical stability, difficulty in hydrolysis and degradation, high-temperature resistance, small dosage, and corrosion inhibition and scale inhibition effects.
At the same time, the Organophosphorus corrosion inhibitors have excellent coupling ability for many metal ions such as calcium, magnesium, copper, and zinc. Even the inorganic salts of these metals have a good activation.
In addition, when they are combined with other water treatment chemicals, they can exhibit the desired “synergistic effect”. Therefore, organic polyphosphoric acid scale inhibitors are widely used in oilfield water treatment.
The polycarboxylic acid type scale inhibitors have good scale inhibition performance and they have a limiting effect. A low dose can achieve a satisfactory result. In addition, they are very toxic and biodegradable, with little or no pollution problems. Therefore, they are also used as effective scale inhibition means in oilfield water treatment.
When choosing a scale inhibitor, the following factors should be considered.
(1) The chemical composition of scale. Certain compounds are more effective at treating particular scales.
(2) The severity of scaling. the effect of many scale inhibitors is affected by the degree of supersaturation.
Many compounds have good effects when only a small amount of scale is produced per unit volume of water. In the case of high fouling rates, laboratory evaluation experiments can guide the selection of effective oilfield scale inhibitors.
(3) Temperature. The scale inhibitor usually lowers its effect as the temperature increases. Each scale inhibitor has an upper-temperature limit beyond which it loses its effectiveness.
(4) Compatibility with other chemical agents. Whether the scale inhibitor reacts with other chemicals added to the system. Whether the reaction interferes with each other. This is important for the selection of scale inhibitors.
The selection and evaluation of oilfield scale inhibitors are generally carried out in the laboratory.
Although the determination of the minimum concentration required for the application of an oil field is difficult. However, relative evaluation of different types of scale inhibitors in the laboratory is generally more effective than on site.
The scale inhibition rate, thermal stability and corrosion inhibition of the scale inhibitor are the main indicators of the reaction performance. Temperature, time of action, dosing amount, and hardness of water are the main factors affecting the index.
The above screening content is only an experiment of scale inhibition effect.
In addition, the price, the source of the loan, whether it is convenient to transport, whether it is convenient to use, toxicity, shelf life, and other factors can be comprehensively compared to determine the selected oilfield scale inhibitor.