There are many different types of fracturing chemicals you may see on a frac location. These include gelling agents, buffers, biocides, crosslinkers, breakers, surfactants, and friction reducers. All of these fracturing chemicals have different properties and functions.
The primary gelling agent used in fracturing fluids is guar. Derivatives of guar such as hydroxypropyl guar (HPG) and carboxymethyl hydroxypropyl guar (CMHPG) are also used as gelling agents. Non guar-based gelling agents are hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), and xanthan. All of these gelling agents are water soluble polymers that increase the viscosity of water. Increasing viscosity of water lowers friction pressure, increases proppant transport, lowers fluid loss, and increases frac width. Water containing hydrated gelling agent is called a linear gel or base gel. Typical linear gel viscosity is 10 to 30 cP. Gelling agents are typically used as dry powders or hydrocarbon based slurries.
Buffers are used to adjust the fracturing fluid pH for optimum performance. Fracturing fluid properties such as gelling agent hydration rate, crosslink time, and break time are all dependent on proper fluid pH. Common buffers include acetic acid, sulfamic acid, sodium acetate, sodium bicarbonate, potassium carbonate, and sodium hydroxide.
Biocides are added to fracturing fluids to prevent viscosity loss caused by bacterial degradation of the gelling agent polymer. Bacteria not only break gel polymers, but some can cause sweet oil and gas production to become sour. Once introduced into the reservoir, some anaerobic bacteria can reduce sulfate ions to hydrogen sulfide (H2S), an extremely dangerous gas.
Crosslinkers are used to increase linear gel viscosity. Higher fluid viscosity increases proppant transport, lowers fluid loss, and increases frac width. Crosslinked fluid viscosity range is 100-1000 cP. Typical crosslinkers are boron (B), zirconium (Zr), titanium (Ti), and aluminum (Al). Crosslinkers can provide a fast or delayed crosslink time. Delayed crosslinkers result in lower friction pressure compared to fast crosslinkers.
Breakers are used to lower the fracturing fluid’s viscosity before the fluid flows back. Unbroken fracturing fluid left in the fracture can reduce proppant pack permeability, resulting in less fluid flowback and less hydrocarbon production.
Typical breakers are either enzymes or oxidizers. Enzymes work better at lower BHST compared to oxidizers. Breakers can be delayed by encapsulation.
Surfactants have many functions in a fracturing fluid. They can prevent emulsions as non emulsifiers, stabilize nitrogen and CO2 foam fluids as foamers, and increase load water recovery as flowback enhancers. Surfactants are typically anionic, cationic, or nonionic. Anionic surfactants are not compatible with cationic surfactants. Nonionic surfactants are compatible with both anionic and cationic surfactants.
Friction reducers are added to water to lower friction pressure during pumping. Friction reducers are long chain, high molecular weight polymers that are water soluble. Water in turbulent flow has high friction pressure. Friction reducers lower friction pressure by increasing laminar flow and decreasing turbulent flow in the water as it is pumped down the wellbore. Friction reducers are typically anionic or cationic, salt sensitive, temperature sensitive, and shear sensitive.
Fracturing fluids contain many chemicals with different functions. Make sure you know the specific function of each chemical in the fracturing fluid recipe. Also make sure that all the chemicals in the fracturing fluid are compatible with each other. Incompatible chemicals will not perform as expected and could form insoluble precipitants that may reduce proppant pack permeability.
Momentive’s resin coated proppants are fully compatible with most, if not all, commonly used fracturing fluids, both water and oil-based systems.