Introduction to Chemical Use
What's in Hydraulic Fracturing Fluid?
The number of chemical additives used in a typical fracture treatment depends on the conditions, such as depth or location, of the specific well being fractured and the characteristics of the formation, such as thickness and type of rock. A typical fracture treatment will use very low concentrations of between 3 and 12 additive chemicals, depending on the characteristics of the water and the rock formation being fractured. Each component serves a specific, engineered purpose. For example, the predominant fluids currently being used for fracture treatments in the gas shale plays are water-based fracturing fluids mixed with friction-reducing additives (called ‘slickwater’).
The addition of friction reducers allows fracturing fluids and sand, or other solid materials called proppants, to be pumped to the target zone at a higher rate and reduced pressure than if water alone were used. In addition to friction reducers, other additives include: biocides to prevent microorganism growth and to reduce biofouling of the fractures and oxygen scavengers and other stabilizers to prevent corrosion of metal pipes. These fluids are used to create the fractures in the formation and to carry a propping agent (typically silica sand) or proppant, which is deposited in the induced fractures to keep them from closing up. The chart below demonstrates the volumetric percentages of additives that are used for a typical hydraulic fracturing treatment of a horizontal well. The make-up of fracturing fluid varies from one geologic basin or formation to another. Evaluating the relative volumes of the components of a fracturing fluid reveals the relatively small volume of additives that are present.
The additives depicted on the right side of the pie chart represent less than 0.5% of the total fluid volume. Overall, the concentration of additives in most slickwater fracturing fluids is a relatively consistent at 0.1% to 2% with water and sand making up 98% to 99.9%. As the make-up of each fracturing fluid varies to meet the specific needs of each area, there is no one-size-fits-all formula for the volumes for each additive. In classifying fracturing fluids and their additives it is important to realize that service companies that provide these additives have developed a number of compounds with similar functional properties to be used for the same purpose in different well environments. The difference between additive formulations may be as small as a change in concentration of a specific compound. Although the hydraulic fracturing industry may have a number of compounds that can be used in a hydraulic fracturing fluid, any single fracturing job would only use a few of the available additives.