1950s fracturing fluid used to fracture the first increase since the great evolution occurred. Early fracturing fluid as the dispersion medium is a gas, having a certain viscosity of the fluid is added, the earliest of which is oil-based fracturing fluid;

Later, with the increase in depth and well temperature increases, the viscosity of the fracturing fluid and temperature requirements increase, began to use natural plant gum fracturing fluid, fracturing fluid cellulose, synthetic polymer fracturing fluid, namely the traditional water-based fracturing fluid;

1980s, due to foam fracturing fluid formation damage is small and widely used;

To the 1990s, Eni-Agip fluid experts and Schlumberger engineers recommended a viscoelastic fluid fracturing operations, which it developed viscoelastic surfactant (VES), which is characterized by the fracturing process on their own structure viscosity carry proppant, do not need to add a crosslinking agent, breaker and various other chemical additives, less formation damage.

1999 Zhang and Gupta proposed clean fracturing fluid and foam fracturing liquid to form the cleaning foam fracturing fluid, combines the advantages of clean fracturing fluid and foam fracturing fluid, with a sand-carrying capacity, low fluid loss, the pressure split high efficiency, flowback ability, formation damage small advantage. Fracturing fluid from the 1950s to the current clean fracturing fluid, cleaning foam fracturing fluid, the application of water-based fracturing fluid system is still based.

1 oil-based fracturing fluid

1.1 oil-based fracturing fluid type

Oil-based fracturing fluid is oil as a solvent or dispersion medium with various additives formulated fracturing fluid. At present oil-based fracturing fluid used at home and abroad are mainly the following types: oil-soluble active agent as a thickening agent, mainly salts of fatty acids; oil-soluble polymeric substance as a thickening agent, there are polyisobutylene, butadiene, polyisoprene, alkenyl A- hydrogen polymers, polyalkyl styrenes, hydrogenated polycyclopentadiene, polyacrylic acid.

1.2 oil-based fracturing fluid sand-carrying mechanism

Gasoline nonpolar substances, without active functional groups, chemically inert, it is difficult to form a crosslinked structure, a gel former used is a low molecular weight surfactant per se does not increase the viscosity, but may be formed in oil micelles, gel-forming agents when the beginning of the crosslinking agent diffuses into the droplets, which contain acidic phosphate ester is dissolved in the droplets and neutralized, causing the aluminum ion concentration is reduced, the aluminum ion concentration increases, under appropriate conditions, the formation of aluminum ions eight for the heart with price. First glue contained in a phosphate bridge formed by the mesh structure of the product with Price and aluminum ion, and glue into the beginning of the formation of long-chain alkyl phosphate molecules to make a substantial increase in the viscosity of the oil .

Oil-based fracturing fluid, and formation and fluid compatibility is good, basically no water block, water sensitivity, but its high cost, modified as effective as water-based fracturing fluid, and a large amount of fluid loss, friction as well. For low pressure, high water sensitive formation.

2 water-based fracturing fluid

Water-based fracturing fluid is water as a solvent or dispersion medium, to which is added a thickening agent, additives prepared from. With high viscosity, high sand carrying capacity, low friction, and low fluid loss.

Water-based fracturing fluid generally named after the type of thickening agent named. At present water-based fracturing fluid used at home and abroad are mainly the following types: natural plant glue based fracturing fluid, fracturing fluid cellulose, synthetic polymer fracturing fluids were natural plant gum, cellulose, synthetic polymers as a thickening agent.

2.1 natural plant glue-based fracturing fluid

Natural plant gum fracturing fluid comprising guar gum and its derivatives hydroxypropyl guar gum, carboxymethyl hydroxypropyl guar gum; gum Tian Qing and its derivatives, such as glucose mannan gum. Since the polymer chains of natural plant gum containing multiple hydroxyl groups, strong adsorption capacity, easy to form a spray film, high viscosity; but it tends to produce a lot of broken plastic residues, high insoluble content, formation damage is large and broken difficulties milk.

2.2 cellulose water-based fracturing fluid

Cellulose fracturing fluid comprising carboxymethylcellulose (CMC) gel fracturing fluid, hydroxyethylcellulose, hydroxypropylcellulose and carboxymethylcellulose fracturing fluid - carboxyethyl cellulose (CMHEC). Cellulose is a nonionic polysaccharides, hydrogen bonding carboxyl many macromolecular chain between the cellulose fracturing fluid thickening ability, carrying sand, good fluid loss, less residue, but its high friction and temperature stability is poor, it is generally not available for high temperature intervals Sham Tseng.

2.3 synthetic polymer water-based fracturing fluid

Synthetic polymer fracturing fluid, the polymer used include polyacrylamide (PAM), partially hydrolyzed polyacrylamide (HPAM), acrylamide - acrylamide copolymer, methylene group polyacrylamide. Unlike the first two fracturing fluid water-based, water-based fracturing fluid thickener are synthetic polymers. Thus, the properties of the polymer can be adjusted by controlling the synthesis conditions of ways to meet the fracturing fluid performance. Its obvious advantages, can meet the higher requirements fracturing fluid temperature and viscosity after gel breaking residue rarely, formation damage is small. But the larger environmental pollution.

3 foam fracturing fluid

3.1 foam fracturing fluid composition

Foam fracturing fluid is a gas, liquid, surfactants and other chemical additives. It is Hunban in conventional plant gum fracturing fluid based on high concentrations of liquid N2 or CO2 and other components within the vapor phase, liquid-external low damage fracturing fluid.

Gas foam mass fraction (ie, at a given pressure and temperature, gas volume percentage of foam volume) is generally 50% to 70%, when the foam mass is less than 52%, which is energizing system, generally used as a conventional after trailing fracturing fluid to help pressure after the fast break flowback glue; when the bubble mass greater than 52%, the smaller particles in the bubble phase, good stability, the desired (ie, the foam when separating the half-life of half liquid time) long, evenly distributed flow contact with each other during the bubble and the bubble interference, such viscosity, sand-carrying capacity enhancement; a smaller proportion of the liquid in the foam fracturing fluid, typically only 30% to 50%, fracturing the process of reducing the amount of liquid fluid loss in the formation, the formation damage is small.

3.2 foam fracturing fluid adaptability
 

Foam fracturing fluid into the formation which foam is compressed to accumulate energy, accumulated after the fracture energy of the gas rapidly expands outward displacement fracturing fluid to break the glue, the glue quickly and thoroughly broken driven back row, and the residue out of cracks in the wellbore; slip stream layer of foam fracturing fluid stream can be formed with the wall in the wellbore so as laminar flow state, its small friction, only 30% to 40% of the conventional fracturing fluid. Based on these characteristics of foam fracturing fluid, especially for sensitive strong fracturing low temperature, low pressure, water-sensitive or water locks and other oil and gas wells.

 

4 Clean fracturing fluid system

Clean fracturing fluid is formed by adding a surfactant in saline a viscoelastic surfactant (the VES) dissolves only from each other by the surfactant and saline without crosslinking additives. Including: a cationic quaternary ammonium surfactant fracturing fluid system, betaine cationic surfactant fracturing fluids a non-ionic surfactant fracturing fluids.

4.1 Clean fracturing fluid characteristics

4.1.1 viscoelastic
 

Viscoelastic surfactant can be a rod-shaped micelles in saline (dispersion medium), and with the increase in rod micelles occurs entangled with one another, forming a cross-linked polymer macromolecules similar spatial network structure (see FIG. ). That is a small molecule substances, by intertwining to form a macromolecular structure. At the macro small molecules but it may exhibit properties of macromolecules.

 

4.1.2 shear thinning
 

Sand-carrying principle VES fracturing fluid with conventional water-based, fundamentally different from oil-based fracturing fluid. Conventional fracturing fluid rely on the apparent viscosity of the fracturing fluid to carry proppant, and VES fracturing fluid upon structural viscosity of the fluid carrying proppant. With its viscosity fluid shear stop and recover, with good shear thinning (see figure below). Thus, the apparent viscosity is very small, the friction between the fluid and the formation of relatively small. US Stin-Lab by proppant sand carrying experiments show that the viscoelastic surfactant solution at the surface viscosity of less than 30mPa · s, a shear rate of 100s-1, can also be effective proppant transport to the destination layer.
4.1.3 viscosity-temperature characteristics

As the temperature increases, the viscosity of VES fracturing fluid through a maximum and then the temperature rises, viscosity decreases (see figure below). This is due to the rise in temperature accelerates the movement of the micelles in solution at low temperatures, this effect is beneficial, the rod-like micelles accelerate wound; and when the temperature is high, the temperature rises accelerate the separation of micelles. Therefore, the use of clean fracturing fluid temperature formation has certain requirements.
 

5 cleaning foam fracturing fluid

Use clean fracturing fluid has changed the traditional polymer fracturing fluid production operations, greatly reducing the conventional fracturing fluid formation damage and pollution. To further reduce the cost of clean fracturing fluid, reduce the difficulty of the promotion of clean fracturing fluid, while improving the ability of fracturing fluid flowback, 1999 Zhang and Gupta 1st proposed clean fracturing fluid and foam fracturing liquid combine to form a cleaning foam fracturing fluid. Cleaning foam fracturing fluid is based on clean fracturing fluid, adding a foaming agent, a gas, as a foam, which formed in the gas phase within the cleaning solution is a low damage fracturing fluid fracturing fluid external phase.

In Russia in 2007 WesternSibe-rianbasin field, the use of clean foam fracturing fluid with conventional water-based polymer fracturing fluid field trials. Well 4454 using 0.48% guar gum crosslinked polymer fracturing fluid Fracturing implementation. Fracturing flowback lasted 14d. After the completion of fracturing wells yield 5.5t / d. 492 wells using cleaning foam fracturing fluid flowback after the fracturing wells only 3d time. After fracturing, oil production increase to 30t / d. In China, the Qinshui basin in 2011, the application of cleaning foam fracturing fluid to fracture two wells. PH1-6 gas production wells reach 3000m3 / d ~ 4000m3 / d, PH1 gas production reaches 2000m3 / d ~ 5800m3 / d, is 1.5 times that of the Provisional well production, increase yield.

Cleaning foam fracturing fluid combines the advantages of clean fracturing fluid and foam fracturing fluid, with a sand-carrying capacity, low fluid loss, fracturing performance, strong flowback ability, formation damage and other advantages, in recent years become fracturing liquid areas of research focus.

6 Outlook

Currently, the fracturing fluid system at home and abroad are moving towards low damage, adaptable, low-cost, high temperature, environmentally friendly direction, has been formed for a variety of ground conditions fracturing fluid system. However, domestic research and application of low damage fracturing fluid system is still in its infancy. The results of each unit is only a small range of applications in the oil field. Accordingly, reference should be foreign experience, strengthen research and development of suitable reservoir characteristics of low damage fracturing fluid system, such as: cleaning foam fracturing fluid. Following research conducted on this basis.

(1) for different reservoir characteristics, research and development applicable to different conditions of low damage fracturing fluid system. Can be evaluated through laboratory experiments were screened for different conditions formula system, to expand the application prospect of low damage fracturing fluid.

(2) to strengthen the construction of ancillary equipment and technology research and design to promote low damage fracturing fluid applications in the field of large-scale promotion.

(Source: "Petrochemical Industry Application" Author: Hu and other Chinese first branch of PetroChina Changqing Oilfield Company Technical Monitoring Centre)