In oil exploitation, increasingly severe and complex formation conditions, such as high temperature and high salinity, put forward strict requirements for water-soluble polymers. Because of its good water solubility, thickening, sand carrying capacity and shear dilution, the inverse lotion polymer is widely used as lotion variable viscosity fracturing fluid, slippery hydraulic fracturing fluid, etc.

The inverse lotion polymer can be rapidly water-soluble, avoiding the preparation of traditional guar gum and solid polyacrylamide thickener system in the early stage, and is suitable for the construction mode of large liquid volume and large displacement on site, which is conducive to reducing the construction cost.

The production of inverse lotion polymer is relatively the most difficult. The main reasons are that there are many reaction components, many reaction conditions, great difficulty in temperature control, and small window for condition adjustment. The following focuses on the components of inverse lotion polymerization.

1、 Monomer

1. Allyl monomers

For inverse lotion polymerization, commonly used monomers are water-soluble vinyl monomers, such as acrylamide, acrylic acid, methacrylic acid, vinyl pyrrolidone, acryloyloxyethyl trimethylammonium chloride, 2-acrylamide 2-methylpropane sulfonic acid, etc.

2. Monomer selection condition

The monomer can be solubilized in the lotion system, but can not be completely dissolved in the emulsifier aqueous solution;

It can polymerize at the action temperature of solubilization and dissolution;

It has no activation with water or emulsifier, such as no hydrolysis.

2、 Emulsifier

1. Emulsifier action

Reduce the surface tension of water;

Reduce the interfacial tension between oil and water;

Emulsification;

Solubilization;

Foaming;

2. Emulsifier type

Anionic type; Anionic emulsifiers mainly include alkyl carboxylates, sulfates, sulphonates and phosphates. Their emulsification effect is generally related to the number of carbon atoms in the alkyl group. The lower the number of carbon atoms in the alkyl group, the better the water solubility. They cannot form micelles in water, and the weaker the emulsification ability; The more the number of carbon atoms, the worse the water solubility, and it is difficult to disperse in water, and the same emulsification ability is also very weak; Generally, emulsifiers with 12~18 carbon atoms in alkyl have good emulsifying ability. Anionic emulsifiers are generally used at pH>7.

Cationic type; Commonly used cationic emulsifiers are mainly salts of organic amine compounds, such as fatty ammonium salts, organic quaternary ammonium salts, etc. This kind of emulsifier needs to be used at pH<7. However, amine compounds generally have polymerization inhibition, are prone to side reactions, and have insufficient emulsifying capacity, so they are rarely used in lotion polymers.

Amphoteric type; The molecular structure of zwitterionic emulsifier contains polar groups, as well as anionic and cationic groups, such as amino acids and amide sulfates, which are suitable for any pH value. Commonly used non-ionic emulsifiers include carboxylic acid, sulfate, phosphate and sulfonic acid.

Non-ionic type; The most widely used. Commonly used non-ionic emulsifiers include esters, ethers, amines, amides, etc. Common esters mainly include polyoxyethylene carboxylates, polyol carboxylates (Span series) and polyoxyethylene polyol carboxylates (Twain series). Due to its non-ionic property, it is insensitive to the change of pH value, relatively stable, and resistant to acid, alkali, salt and electrolyte. It is also suitable for water-in-oil and oil-in-water systems. However, a single non-ionic emulsifier has insufficient emulsification capacity, and is generally not used alone, usually more than two kinds of composite emulsifiers. However, when reverse micro lotion polymerization is carried out, the hydrophilicity and lipophilicity of a single non-ionic emulsifier change with temperature, and the temperature zone for forming micro lotion is generally narrow, which brings difficulties to micro lotion polymerization. Ionic emulsifiers are not easily affected by temperature, so the combination of a small amount of ionic emulsifiers that adjust the hydrophile lipophilic balance value (HLB value) and non-ionic emulsifiers as the main components can increase the temperature range of the micro lotion area and narrow the three-phase area, which can not only improve the solubilization ability, but also increase the stability of the micro lotion.