**7. Evolution of fracturing fluid and the chemicals**

The first hydraulic fracturing treatment was implemented in Hugoton Gas Field in Grand County, state of Kansas, during 1947. By the end of 1952, many fracturing treatments were performed with refined and crude oils. Thus oil-based fluids were the first fracturing fluid utilized for this purpose due to their benefits which are cheap and permitting greater volumes at a lower cost. But due to the safety and environmental issues, which are associated with their applications, it was encouraged that the industry move toward in developing an alternative fluid. At the beginning of 1953, for the first time, water fluid was used as a fracturing fluid; and a number of gelling agents were developed. However, water-based fluids with water-soluble polymers mixed to prepare a viscous solution are commonly used in the fracturing treatment. Since the late 1950s, more than 50% of the fracturing treatments were performed with fluids consisting of guar gums, high-molecularweight polysaccharides composed of mannose and galactose sugars, or guar derivatives [87].

In 1964, surfactant agents were added to reduce the emulsion formation when in contact with the reservoir fluid; however, potassium chloride was added to decrease the effect on clays and other water-sensitive formation components. Later, additional clay stabilizing agents were developed to enhance the potassium chloride, allowing the use of water in different geological formations. In the early 1970s, a major revolution in fracturing fluids introduced the use of metal-based crosslinking agents to improve the viscosity of gelled water-based fracturing fluids for extreme reservoir condition (i.e., high temperature). Later a critical development was made on gelling agent to achieve a preferred viscosity. Also guar-based polymers are still used in fracturing jobs at reservoir temperatures below 150°C. Other fluid improvements, foams, and the addition of alcohol have enhanced the use of water in more geological reservoir formations. Moreover, various aqueous fluids,

such as acid, gas, water, and brines, are currently used as the base fluid in approximately 96% of all fracturing treatments employing a propping agent [87].

As the hydrocarbon drilling and production have moved toward deeper reservoirs with high pressure and temperature condition, more fracturing treatments have been developed to be compatible with these conditions. Therefore, gel stabilizers and thermally stable polymers have been developed in which gel stabilizers can be utilized with around 5% methanol, but synthetic polymers have shown a sufficient viscosity at temperatures up to 230°C [88]. After that, chemical stabilizers have been developed and possibly used with or without a methanol. The improvements, which are made in cross-linkers and gelling agents, have led to systems that can permit the fluid to reach the well bottomhole in high-temperature condition before cross-linking, therefore, reducing the effects of high shear in the production tubing. Recently, nanotechnology has been introduced in the design of new, efficient hydraulic fracturing fluids [88]. For example, nanolatex silica is used to reduce the concentration of boron found in conventional cross-linkers. Recent advancement in nanotechnology is the use of small-sized silica particles [20 nm] suspended in guar gels to improve fracturing treatment [89]. Therefore, the following section will discuss the use of CO2 and N2 as fracturing fluid to enhance the hydrocarbon fluid production and to store CO2 into the geological formation to minimize the greenhouse emission. Also it will provide a brief information on hydra-jet fracturing.
