Chemistry Applied to Fracture Stimulation of Petroleum Wells

摘要

Hydraulic fracturing is a stimulation procedure that is applied to petroleum wells that will not otherwise produce at commercial rates. Hydraulic fracturing employs fluids that are pumped with very low tubular frictional pressure, yet have sufficient viscous properties to generate fracture geometry in subterranean rock and transport solid propping agents to hold the fracture open. Fluids for commercial fracturing applications contain polymers, crosslinking agents, surfactants, clay-protective agents, and viscosity breakers. All of these must be balanced to result in the physical properties required at elevated temperatures and pressures without damaging the proppant pack or rock formation. Complex chemistry is carefully controlled on a large scale and in a hostile environment for the fracturing process to be successful. Most fracturing fluids are mixed in aqueous media. One of the polymers used in fracturing is water-soluble polysaccharides derived from natural guar. Crosslinking agents include borate, titanium, and zirconium complex ions. Formation compatibility is enhanced by clay-protective materials, such as potassium chloride and organic salts, with surfactants to lower interfacial tension. Fluids heat up as they travel down the wellbore and into a subterranean fracture. Timing of the crosslink initiation is vital to balance fluid friction in the wellbore and yet obtain proper penetration into the fracture and transport of propping agents. Finally, the viscosity developed by the crosslinked gel is broken with chemical agents to allow the injected liquid to be produced back to the surface. This paper discusses the development of fracturing fluids and shows how the kinetic reaction of polymers, crosslinking agents, and other chemical components work together to produce the favorable result of stimulating petroleum wells to produce at higher rates. With the focus of today's oil production moving from the western hemisphere to the eastern hemisphere, new research facilities have been established to apply technology-specific adaptations to the demands of eastern hemisphere reservoirs. These adaptations will improve the efficiency of oil and gas production for the future.