The contaminants in fracturing flowback fluid can generally be divided into two categories: original contaminants from the formation and chemical components in the fracturing fluid. Original contaminants from the formation include naturally occurring radioactive materials (uranium, thorium, radium, radon, strontium, and potassium), inorganic substances and metallic elements (aluminum, arsenic, barium, bromine, cadmium, chlorides, chromium, iron, manganese, mercury, nickel, sodium, vanadium, and zinc), gases (methane and carbon dioxide), and hydrocarbons (polycyclic aromatic hydrocarbons, phenols, long-chain fatty acids, alkylbenzenes, and aliphatic hydrocarbons).

Due to differences in the geographical location and geological conditions of oil and gas fields, the content of these substances varies greatly. Chemical components in fracturing fluid mainly refer to the various chemical reagents added during hydraulic fracturing to improve fracturing efficiency, primarily including proppants, drag reducers, breaker agents, and bactericides. These substances are difficult to degrade in nature and are the main targets for treatment.

Untreated fracturing flowback fluid contains a large amount of non-degradable organic matter and is usually acidic or alkaline. During repeated use, it may corrode or clog pipes; upon discharge, it may cause water pollution. Radioactive elements and metals contained within may also pollute the soil, reducing soil fertility.

The skid-mounted treatment equipment for fracturing flowback fluid is fully functional, integrating dosing, reaction, sedimentation, solid-liquid separation, and sludge thickening processes. A small amount of sludge is separated and concentrated by a sludge thickener. This equipment is easy to install, simple to operate, and has low operating costs.

This treatment system utilizes a rapid flocculation sedimentation and rapid separation technology. In the flocculation stage of wastewater treatment, high-density insoluble refined iron powder is added to the flocculation tank, utilizing the gravity sedimentation of the medium and the adsorption of the carrier to accelerate floc growth. The flocs containing the medium enter the magnetic separator for separation, achieving clear liquid separation; the remaining flocs containing the medium enter the sludge tank.

II. Equipment Components

1. Batching Skid-Mounted Equipment

The batching skid-mounted equipment consists of a dosing tank, a storage tank, a high-efficiency stirring device, a metering pump, an electrical control system, a skid, a base, and piping. It is used for preparing and storing chemical reagents and setting quantitative batching amounts according to process requirements. The main structure, including the skid and base, is made of carbon steel, while the piping is made of stainless steel and UPVC.

2. High-Efficiency Reaction Skid-Mounted Equipment

The high-efficiency reaction skid-mounted equipment consists of a continuous high-efficiency mixing reactor, a primary high-efficiency flotation system, a secondary high-efficiency flotation system pump, a sludge tank, an intermediate water tank, water pumps, an electrical control system, the skid, the base, and piping. Raw water is thoroughly mixed and reacted with chemical reagents in the reactor before entering the primary high-efficiency flotation system for flotation separation. The water separated by primary flotation enters the secondary high-efficiency flotation system for treatment and then enters the intermediate water tank. The main structure, including the skid and base, is made of carbon steel, while the piping is made of stainless steel.

3. Fine Filtration Skid-Mounted Equipment

The fine filtration skid-mounted equipment consists of a primary filtration system, a fine filtration system, a backwashing system, an electrical control system, the skid, the base, piping, valves, and other components. Water in the intermediate water tank is pumped to the filtration system for filtration treatment before being discharged. The filtration system employs fully automatic filtration and backwashing. The skid, base, and other main structures are made of carbon steel, while the piping is made of stainless steel. The filter tank body is made of carbon steel, with the inner wall coated with glass flake anti-corrosion paint. Piping fittings welded to the tank body are made of stainless steel.

4. Sludge Treatment Skid-Mounted Equipment

The sludge treatment skid-mounted equipment consists of a container, filter press system, sludge conveying system, water tank, pump, piping, valves, etc. The main structural materials for the container, water tank, etc., are carbon steel, and the piping material is stainless steel.

5. Vertical Sludge Storage Tank

With a volume of 25m³, it consists of a tank body, base, level gauge, guardrail, ladder, etc. The main structural materials for the tank body, base, guardrail, ladder, etc., are carbon steel, and the piping material is stainless steel. The tank interior is reinforced with epoxy resin and fiberglass cloth for corrosion protection, and the piping fittings welded to the tank body are made of stainless steel.

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