Hydraulic fracturing is one of the most important technologies for enhancing hydrocarbon production from subsurface reservoirs. The technique involves injecting fluid at high pressure into a formation to create fractures in the rock, effectively increasing the surface area of the wellbore such that hydrocarbons can be produced at higher, more economic rates from low permeability strata.
The idea of stimulating wells by creating fractures in the formation dates back more than a hundred years. Early methods in the late 1800s used explosives like nitroglycerin to break rock and enhance flow paths. However, the first intentional hydraulic fracturing treatment was carried out in 1947 in the Hugoton gas field in Kansas. The procedure was soon commercialized in 1949 and gradually became a common well-stimulation technique. Over the following decades, improvements in pumping technology, fracturing fluids, and proppants greatly increased the effectiveness of hydraulic fracturing.
Hydraulic fracturing has become an essential tool in modern petroleum engineering because many hydrocarbon reservoirs have very low permeability. The threshold below which fracturing is typically considered for conventional wells is less than 10 millidarcies (millidarcies=md=10-3 Darcies) for oil reservoirs and less than 1 millidarcy for natural gas. In unconventionals (largely shale formations), where multiple hydraulic fractures are essential for economic rates, the reservoir permeability is orders of magnitudes lower than in conventional reservoirs, in the tens of nanodarcies (nanodarcy=10-9 Darcy) (see Figure 1). In such formations, natural pore networks can have conduit sizes (pore throats) on the order of the size of an oil molecule (diameters of 1 to 10 nanometers), impeding hydrocarbon flow rates to below economical feasibility (see Figure 2). By creating high surface area and high conductivity artificial fractures that better connect the wellbore to the furthest reaches of the reservoir, hydraulic fracturing can boost well productivity by orders of magnitude.
Today, hydraulic fracturing is commonly used in both conventional and unconventional reservoirs. In shale formations, tight sandstones, and coalbed methane reservoirs, hydraulic fracturing is often essential for production. Without stimulation, these rocks may contain significant quantities of hydrocarbons but remain uneconomic to produce due to their extremely low permeability.
In summary, hydraulic fracturing addresses the fundamental challenge of limited fluid flow in low-permeability formations. By creating conductive pathways through the rock, this method enables the economic recovery of hydrocarbons that would otherwise remain trapped underground.
