Fracturing fluids are categorized based on their composition and physical properties, primarily including oil-based, water-based, emulsified, and foam-based systems. The selection of an appropriate fracturing fluid depends on various factors such as geological characteristics, reservoir temperature, and operational cost considerations.
(1) Oil-Based Fracturing Fluids
Oil-based fracturing fluids represent the earliest type of fracturing systems used in the industry. The first fracturing operation in the United States, conducted in 1947 at the Hugoton Field in Kansas, utilized a gasoline-based oil fracturing fluid. These fluids typically use kerosene, diesel, or light crude oil as the base fluid. One type of system uses non-water-soluble high-molecular-weight polymers as thickeners, which do not form gels but rely on high-viscosity polymer solutions to carry proppants. Another type employs oil-soluble macromolecular acidic substances as thickeners, combined with polyvalent metal ions as crosslinkers, along with pH adjusters, co-crosslinkers, and breakers to form oil-based gels for fracturing operations.
Oil-based fracturing fluids are commonly used in low-permeability, water-sensitive reservoirs where conventional water-based fluids may be ineffective. Water-based fluids in such reservoirs often result in low flowback rates, clay swelling, and in severe cases, formation damage or fracture closure. Oil-based fluids demonstrate good compatibility with these formations, minimizing clay expansion, reducing fluid loss, lowering friction pressure, and facilitating easier flowback. They also offer environmental benefits in specific contexts. However, due to relatively higher costs and lower economic efficiency compared to alternatives, their use is typically limited to reservoirs with specific geological requirements.
(2) Water-Based Fracturing Fluids
The use of water-based fracturing fluids dates back to the 1940s, with early applications in Kansas, Colorado, and Texas. By the 1960s, water-based fracturing fluids had become the most widely used fracturing systems globally. These fluids use water as the base fluid, with water-soluble macromolecules such as plant gums or synthetic polymers serving as thickeners, and borate salts or polyvalent metal ions functioning as crosslinkers. Additional components include breakers, oxygen scavengers, and proppants.
Research and development of water-based fracturing fluids primarily focus on thickeners and crosslinkers. By designing the molecular structure of thickeners, it is possible to achieve enhanced thickening efficiency, shear resistance, and high-temperature stability. Selecting appropriate crosslinking metal ions and modifying them enables delayed crosslinking properties, meeting various operational requirements.
In recent years, increasing attention to environmental protection has driven the development of clean fracturing fluids. Viscoelastic surfactant (VES)-based water fracturing fluids utilize molecules with hydrophilic and hydrophobic groups as thickeners. The hydrophobic groups aggregate in the aqueous phase to form micelles, increasing fluid viscosity for proppant transport and pressure transmission. VES fluids contain no high-molecular-weight polymers or crosslinkers, resulting in easy flowback and minimal residue, making them an environmentally friendly option. Water-based fracturing fluids offer advantages such as low cost, wide availability of raw materials, ease of preparation, and suitability for on-site mixing. Their versatility and broad applicability have enabled them to capture approximately 70% of the fracturing fluid market.
(3) Emulsified Fracturing Fluids
Emulsified fracturing fluids are prepared by adding thickeners to either the aqueous or oil phase, followed by combining the two phases with surfactants to form stable emulsions. Depending on the emulsion structure, they can be classified as oil-in-water or water-in-oil types. Since emulsified fluids contain both aqueous and oil phases, they combine the advantages of both fluid types: low friction pressure, shear resistance, strong proppant-carrying capacity, and low residue.
For example, researchers have developed an emulsion system using distilled water and biodiesel, incorporating nano-silica as a proppant. Experimental results indicate that during emulsion migration, droplet coalescence leads to emulsion breakdown, releasing nano-silica particles that adsorb onto fractures. This mechanism helps stabilize shale formations, support fractures, and prevent clay swelling.
Emulsified fracturing fluids can be tailored to specific reservoir conditions by adjusting the system composition. However, due to the complexity of emulsion preparation, these fluids involve relatively higher costs. Additionally, their stability is generally lower compared to single-phase systems, which may limit their application in high-temperature reservoirs.
(4) Foam-Based Fracturing Fluids
Foam-based fracturing fluids are prepared by dispersing gases such as nitrogen or carbon dioxide as bubbles in water, acids, methanol/water mixtures, or hydrocarbon liquids. Typically, these fluids consist of 70-80% dry gas (N₂ or CO₂) and a liquid phase (aqueous polymer solution), forming a two-phase mixture. Surfactants are often added to maintain foam stability. The bubbles within the fluid impart high viscosity and excellent proppant transport capacity.
Foam-based fracturing fluids offer multiple advantages, including reduced formation damage, superior flowback efficiency, minimal fluid loss, high fluid efficiency, and suitable viscosity characteristics. They are considered environmentally friendly fracturing fluids.
Researchers have developed a foam gel fracturing fluid using CO₂ and acrylamide-based thickeners, optimizing the formulation through experiments. This foam fracturing fluid demonstrated core damage rates below 19% and maintained viscosity above 50 mPa·s after shearing at 170 s⁻¹ and 90 s⁻¹ for 90 minutes. Additionally, sensitivity analysis of the rheological behavior of CO₂ foam gel fracturing fluids revealed that influencing factors, in descending order of impact, are foam quality, temperature, shear rate, and pressure. These findings provide theoretical support for CO₂ foam fracturing technology.
The excellent breakability and high flowback efficiency of foam-based fracturing fluids represent their primary advantages. However, the inherent instability of bubbles may limit their application prospects in high-temperature reservoirs.
Post time: Mar-18-2026