Introduction to basic knowledge of fracturing flowback fluid treatment

Most of China's oil and gas fields have reached the middle and late stage of exploitation, and hydraulic fracturing can improve the exploitation efficiency of oil and gas fields. However, a large amount of frac flowback fluid is produced during production. The mixed waste liquid is composed of fracturing fluid and pollutants in the formation, and has three characteristics of high COD, high suspended matter and high salinity.

At present, there are generally three ways to dispose fracturing flowback fluid: deep well reinjection, reuse and efflux. Most of the frac flowback fluids cannot be used directly and need to be reused or discharged after being treated to meet the standards. The treatment of frac flowback fluid can be divided into three stages: pre-treatment, advanced treatment and desalting. Among them, pretreatment is to preliminarily remove the suspended matter in the flowback liquid, reduce the viscosity and hardness of the liquid, etc., in order to facilitate the subsequent in-depth treatment. Advanced treatment is the key to the flowback fluid treatment process, which can remove organic matter and ammonia nitrogen in the flowback fluid. The desalting stage is mainly to remove inorganic salt ions from the water.

China is in the key stage to achieve carbon peak and carbon neutrality, and the reasonable treatment of fracturing flowback fluid can alleviate the huge pressure of carbon emission reduction faced by the petroleum field.

Composition of frac flowback fluid

The composition of pollutants in frac flowback fluid can be divided into two types: the pollutants in the formation and the chemical components in the frac fluid. Contaminants in the formation include naturally occurring radioactive substances (uranium, thorium, radium, radon, strontium and potassium), inorganic substances and metallic elements (aluminum, arsenic, barium, bromine, cadmium, chloride, chromium, iron, manganese, mercury, nickel, sodium, vanadium and zinc), gases (CH4 and CO2), hydrocarbons (polycyclic aromatic hydrocarbons (PAHs), phenols, long-chain fatty acids, alkyl benzene and aliphatic hydrocarbons), etc . Such substances vary greatly due to the different locations and geological conditions of oil and gas fields. The chemical components in the fracturing fluid mainly refer to various chemical agents required to improve the fracturing efficiency in the hydraulic fracturing process, mainly including proppants, drag reduction agents, glue breakers, fungicides and so on. These substances are more difficult to degrade in nature and are the main targets of treatment.

Untreated frac flowback fluid contains a lot of organic matter that is difficult to degrade and is generally acidic or alkaline, which may corrode or block pipelines during reuse, and may cause water pollution when discharged. The radioactive elements and metals are easy to pollute the soil and reduce soil fertility.

Treatment technology of fracturing flowback fluid

The physical techniques commonly used to deal with frac flowback fluid include filtration, adsorption, softening, air flotation, flocculation and so on. These technologies are often applied in the pre-treatment stage, and then need to be combined with advanced treatment processes.

Chemical method is the most commonly used method in fracturing flowback fluid treatment. Various chemical agents are added to remove contaminants in flowback fluid.

The resource utilization and recycling technology of fracturing flowback fluid is an integrated innovation of physical, chemical and biological treatment methods, which can effectively remove harmful substances and optimize the recycling of water resources. The application and improvement of this technology will not only improve the environmental friendliness of hydraulic fracturing operations, but also lay a solid foundation for the ecological security and long-term development of the oil and gas industry.

With the continuous exploitation of oil and gas fields, fracturing technology as a key technology to improve oil and gas production rate will be more widely used, and efficient and energy-saving treatment of fracturing flowback fluid will contribute to the smooth realization of China's dual-carbon goal.