According to the differences in chemical composition, mechanism of action, and application scenarios, iron ion stabilizers used in oil fields can be divided into four categories. Each type of product has its own emphasis on performance, cost, and applicable conditions, providing diversified choices for the development of different types of oil and gas reservoirs.

（1） Chelated iron ion stabilizer

1. Amino polycarboxylates

This is the most classic chelating stabilizer, with representative products including EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), HEDTA (hydroxyethyl ethylenediaminetriacetic acid), etc. This type of product has the characteristics of strong chelating ability, high stability constant, and wide applicable pH range (pH 2-12). It can effectively stabilize Fe ² ⁺, Fe ³ ⁺, and other metal ions (such as Ca ² ⁺, Mg ² ⁺), and is suitable for high temperature (≤ 120 ℃), high mineralization formations, and acidification operations.

For example, an industrial grade EDTA iron ion stabilizer with a concentration of 50% can stabilize Fe ³ ⁺ concentrations up to 5000mg/L when added to hydrochloric acid acidizing fluids at a concentration of 1% -3%, and has good compatibility with other chemical agents such as acidizing fluids and fracturing fluids. But the disadvantage is that the cost is high and the biodegradability is poor, which limits its application in areas with strict environmental requirements.

2. Organic acids

Represented by citric acid, tartaric acid, malic acid, etc., these stabilizers form chelates with iron ions through carboxyl groups, which have the advantages of low cost, environmental friendliness, and good biodegradability. They are suitable for medium and low temperature (≤ 90 ℃), low mineralization formations, and environmentally sensitive areas. For example, the stability constant of iron citrate chelate is 10 Ω⁵ 2. It can stably exist in an environment with a pH of 3-8 and has minimal damage to the formation. It is commonly used for acidification of shallow oil reservoirs and water well injection operations. However, the stability of organic acid chelating agents is relatively weak, and their effectiveness is limited under high temperature or high iron ion concentration conditions. Therefore, it is necessary to increase the addition amount appropriately.

（2） Reduction chelation complex iron ion stabilizer

In order to balance stability, cost, and applicability, the mainstream products on the market are currently complex systems of reducing and chelating types, which work together through two mechanisms to enhance the comprehensive performance of stabilizers. Representative products include HJZ-801, RX-502, TS-100, etc. The following provides a detailed introduction using typical products as examples:

1. HJZ-801 type iron ion stabilizer

Technical specifications: The appearance is a light yellow transparent liquid, with a density (20 ℃) of 1.10-1.15g/cm ³, a pH value (1% aqueous solution) of 2.0-4.0, a high temperature resistance of ≤ 150 ℃, a mineralization resistance of ≤ 20 × 10 ⁴ mg/L, and a stability ability to Fe ³ ⁺ of ≥ 3000mg/L (1% added amount).

Core components: hydroxylamine reducing agent+amino polycarboxylate chelating agent+cosolvent, which inhibits the oxidation of Fe ² ⁺ through reduction, stabilizes the generated Fe ³ ⁺ through chelation, and synergistically enhances stability.

Applicable scenarios: Mainly used for hydrochloric acid acidification and soil acidification operations in oil-water wells, especially suitable for medium and deep high-temperature and high salt oil reservoirs, which can effectively prevent iron ion precipitation in residual acid after acidification from blocking the formation.

Usage: Directly add to the acidizing fluid, with an amount of 1% -3% of the acidizing fluid mass, adjusted according to the iron ion concentration and formation temperature; After mixing with the acidizing solution evenly, inject it into the formation and let it sit for 2-4 hours before flowing back.

Packaging and Storage: Packaged in 200L plastic drums, stored in a cool and ventilated place, away from direct sunlight, with a shelf life of 12 months.

2. RX-502 type iron ion stabilizer

Technical specifications: Appearance is brownish red liquid, density (20 ℃) 1.08-1.12g/cm ³, pH value (1% aqueous solution) 3.0-5.0, high temperature resistance ≤ 180 ℃, mineralization resistance ≤ 30 × 10 ⁴ mg/L, stability to Fe ³ ⁺ ≥ 5000mg/L (1% addition amount).

Core components: Sodium thiosulfate+EDTA derivatives+dispersant, with triple functions of reduction, chelation, and dispersion, suitable for high-temperature and high-pressure deep oil reservoirs and shale gas acidizing and fracturing operations.

Outstanding features: Excellent temperature resistance, able to maintain stable performance even under 180 ℃ conditions; Good compatibility with fracturing fluids, corrosion inhibitors, demulsifiers, etc., without producing secondary precipitation.

（3） Dispersion chelation complex iron ion stabilizer

This type of product is mainly targeted at old oil fields with severe iron pollution and a large amount of iron precipitation. Through dispersion, the precipitate particles are kept suspended, and chelation stabilizes free iron ions, achieving a dual effect of "clearing blockage+preventing blockage". Representative products include PA-600 type (polyacrylic acid+citric acid complex), SD-900 type (sulfonate surfactant+DTPA complex), etc.

Taking PA-600 as an example, its dispersant component can disperse the generated iron hydroxide precipitate particles to below 1 μ m, avoiding bridge blockage of pore throats; The chelating agent component stabilizes free iron ions and prevents the formation of new precipitates. This product is suitable for plug removal operations and wastewater treatment in low-permeability old oil fields. The addition amount is 2% -5% of the treatment fluid quality, which can increase the reservoir permeability recovery rate by 20% -40%.

（4） Green and environmentally friendly iron ion stabilizer

With increasingly strict environmental regulations, green iron ion stabilizers made from bio based materials have become a research and development hotspot. This type of product is composed of natural organic acids (such as gluconic acid and lactic acid) and biopolymers (such as chitosan derivatives) as its core components. It has the characteristics of high biodegradation rate (≥ 90%), low toxicity (LD ₅₀>5000mg/kg), and environmental friendliness. It is suitable for the development of oil and gas fields in ecologically sensitive areas (such as along rivers and farmland).

For example, a certain bio based iron ion stabilizer is mainly composed of gluconic acid lactone and hydroxypropyl chitosan. Under the conditions of pH 4-10 and temperature ≤ 120 ℃, the stability ability of Fe ³ ⁺ reaches 2000mg/L, and the biodegradation rate is over 95%. It has been successfully applied in oil fields in the Yellow River Basin Ecological Reserve in China, which not only solves the problem of iron ion pollution but also avoids damage to the surrounding environment.