1. What is Diverting Agent?

Diverting Agent is a chemical used in oil and gas field acidizing operations. Its core function is to temporarily plug high permeability layers or cracks so that the acid can be diverted to low permeability layers. This diverting mechanism can significantly improve the uniformity of acid distribution in the formation, thereby more effectively transforming the reservoir and increasing the production of oil and gas wells. Diverting acid plays a vital role in the acidizing process, especially when dealing with heterogeneous reservoirs. It can effectively solve the problem of acid preferentially flowing to high permeability layers in traditional acidizing.

2. Characteristics of Diverting Acid

High-efficiency diverting ability: Diverting acid can significantly change the flow path of the acid, making the acid more evenly distributed in the formation, thereby improving the acidizing effect. This diverting ability is achieved through changes in the rheology of the acid. For example, during the acid-rock reaction process, the viscosity of the diverting acid will increase with the consumption of the acid, thereby plugging the high permeability layer.

Reduce formation damage: Diverting acid can reduce secondary damage to the formation by acid and improve the permeability of the reservoir. By distributing the acid more evenly, diverting acid can avoid formation damage caused by excessive local acid concentration and reduce excessive consumption of acid in high permeability layers.

Strong adaptability: Diverting acid is suitable for a variety of geological conditions and reservoir types, including carbonate and sandstone reservoirs. Different diverting acid systems can be optimized according to the characteristics of the reservoir to meet different acidizing needs.

Environmentally friendly: Some diverting acids have good biodegradability and have little impact on the environment. For example, some surfactant-based diverting acids can degrade quickly after the reaction and will not cause long-term pollution to the formation.

High temperature resistance: Some new diverting acids can maintain stable performance under high temperature conditions. For example, some viscoelastic surfactant (VES) diverting acids can still maintain high viscosity under high temperature conditions of 120°C, thereby achieving effective diversion.

Intelligent response: Some diverting acids can automatically adjust viscosity according to the progress of the acid-rock reaction to achieve intelligent diversion. This intelligent response mechanism enables the diverting acid to dynamically adjust its performance during the acidizing process to adapt to different acidizing stages.

3. Classification of diverting acids

(I) Zwitterionic surfactants

A zwitterionic surfactant is an amphoteric surfactant that can form a micellar structure with viscoelasticity in acid solution. Its molecular structure usually contains a hydrophilic group and a hydrophobic group, and can self-assemble to form micelles in acid solution. As the acid-rock reaction proceeds, the micelle structure gradually strengthens and the viscosity increases significantly. This viscoelastic surfactant diverting acid has good temperature and shear resistance and is suitable for medium and low temperature reservoirs.

Molecular formula example: Taking a common zwitterionic surfactant as an example, its molecular formula may be:

C_nH_2n+1N+(CH₃)₂RCOO⁻

Where n represents the carbon chain length and R represents the hydrophobic group.

(II) Tallow aminoamine oxide

Amine oxide is a cationic surfactant with good surface activity and wettability. Its molecular structure usually contains an amine group and an oxidizing group, which can form a stable micelle structure in acid solution, thereby increasing the viscosity of the acid solution and achieving diversion. Amine oxide diversion acid shows good diversion performance during the acidification process and can effectively improve the permeability of low permeability layers.

Molecular formula example:

R₁R₂NO

Wherein, R₁ and R₂ are usually long-chain alkyl groups.

(III) Ethoxylated Ammonium Quat

Ethoxylated Ammonium Quat is a quaternary ammonium surfactant synthesized by ethoxylation reaction. Its molecular structure usually contains a quaternary ammonium group and multiple ethoxy chains, which can form stable micelles in acid solution, increase the viscosity of the acid solution and achieve diversion. Ethoxylated quaternary ammonium salt diversion acid has good water solubility and corrosion inhibition performance, and is suitable for a variety of reservoir conditions.

Molecular formula example:

C_nH_2n+1N⁺(CH₂CH₂O)_mRCl⁻

Wherein, n represents the carbon chain length and m represents the number of ethoxy groups.

4. Application of diverting acid

Diverting acid is widely used in acidizing operations in oil and gas fields, mainly in the following aspects:

Improving acidizing effect: By blocking the high permeability layer and guiding the acid into the low permeability layer, a more uniform acidizing effect can be achieved, thereby increasing the production of oil and gas wells. For example, in carbonate reservoirs, diverting acid can significantly increase the permeability of low permeability layers, increasing the production of oil and gas wells by several times.

Reducing formation damage: Diverting acid can reduce the secondary damage of acid to the formation and improve the permeability of the reservoir. By distributing the acid more evenly, diverting acid can avoid formation damage caused by excessive local acid concentration.

Application in high temperature environment: Some new diverting acids can maintain stable performance under high temperature conditions. For example, some viscoelastic surfactant (VES) diverting acids can still maintain a high viscosity under high temperature conditions of 120°C, thereby achieving effective diverting.

Intelligent diverting and gel breaking: Some diverting acids can automatically adjust the viscosity according to the progress of the acid-rock reaction, achieving intelligent diverting and intelligent gel breaking. This intelligent response mechanism enables the diverting acid to dynamically adjust its performance during the acidizing process to adapt to different acidizing stages.

Environmental protection and economy: diverting acid has good biodegradability and has little impact on the environment. At the same time, diverting acid can improve acidizing efficiency and reduce the cost of acidizing operations.

In short, diverting acid, as an efficient acidizing additive, plays an important role in the development of oil and gas fields. Its diverse classification, excellent performance and broad application prospects make it an indispensable tool in oil and gas field acidizing operations.

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