Hydraulic fracturing or fracking in geotechnics is the exploitation of the pressure of a fluid, typically water, to create and then propagate a fracture in a layer of rock in the subsoil. Fracking is carried out after drilling into a rock formation that contains hydrocarbons (oil or natural gas).
The goal is to increase permeability. With the improvement of the permeability the production of the oil or gas contained in the subsoil is improved and its recovery rate is increased.
Hydraulic rock fractures can be both natural and human-created; they are created and enlarged by the pressure of the fluid contained in the fracture. The most common natural hydraulic fractures are dikes and strand layers, in addition to ice cracks in areas with cold climates.
Man-made fractures are deeply induced at precise levels of rock within the oil and gas fields. They are spread by pumping fluid under pressure, and then kept open by introducing sand, gravel, ceramic microspheres as permeable filler material.
In this way, the fractures created cannot be closed when the water pressure fails.
The hydraulic fracturing technique is used to increase or restore the extraction speed of fluids such as oil, gas, and water, including unconventional deposits such as coal or bituminous rocks.
Fracking allows the extraction of hydrocarbons from permeable rocks (for example, compact limestone, thus cemented sandstone and clay), from which it would otherwise flow in quantities such as to allow extraction at an economically viable rate. The use of fraking makes it cheaper to obtain fossil energy by making it cheaper to obtain fossil fuel.
For example, fracturing allows the extraction of natural gas from bituminous rocks, an extremely impermeable material.
Induced fractures increase the permeability of the rock around the well, increasing the extraction flow rate.
Although the main industrial use of hydraulic fracturing is to stimulate the extraction of fossil fuels, oil and natural gas, it is also used:
- in the construction of water wells.
- to prepare rocks for mining drilling
- make processes to reduce losses (generally hydrocarbon leaks)
- dispose of leaks by injecting them into suitable rock formations
- as a method of measuring the stresses in the earth's crust.
Hydraulic fracturing methodology
A hydraulic fracture is created by pumping the fracturing fluid into the wellbore, with enough pressure to overcome the fracture gradient of the rock. This causes one or more cracks into which the fluid enters, causing further expansion.
To keep the crack open after the interruption of the pumping fluid, a solid material is added. This material is called a support agent. This material is normally composed of selected granules of quartz sand or ceramic microspheres.
This added material in fractures caused by fracking prevents closure completely to pressure loss, preserving a highly permeable passageway for the fossil fuel fluid to be extracted.
Drilling a hole produces rock chips and debris that can slip into cracks and pores in the borehole wall, partially sealing the pit and reducing permeability - hydraulic fracturing can restore adequate extraction flow from the Deposit.
For this reason, it is a standard measure adopted in all wells drilled in poorly permeable rocks, and approximately 90% of all natural gas wells in the United States use hydraulic fracturing to produce gas at a competitive price.
The fluid injected into the fracking wells can be water, gel, foam, or compressed gas, such as nitrogen, carbon dioxide, or plain air. Various types of solid maintenance material are also used: usually sand, but also resin coated sand or ceramic spherules.
To detect the size and orientation of the fractures caused, microseismic monitoring is carried out during the fracture pumping, the installation of geophone arrays in adjacent wells. By mapping microsisms due to growing fractures, we can deduce the approximate geometry of the fractures. Other important information about the stresses induced in the rocks is obtained by placing inclinometric matrices.
Standard fracturing equipment used in oil fields includes a dynamic mixer, one or more high pressure, high flow pumps (usually triple or quintuple pumps) and a seismic monitoring unit.
Other necessary materials are tanks, high pressure pipes, additive units and manometers to control the pressure, flow and density of the fluid during injection. The values of pressure and flow of the fluid vary greatly in the various phases: the injection begins with low pressure and flow is also 265 liters per minute.
In the stress phase, the pressure increases to 100 MPa and the flow gradually decreases.
Advantages and disadvantages of fracking
One of the great advantages of this technique is that it allows the exploitation of gas reserves that were previously considered unreachable. These sites provide great benefits to countries, local communities and industry. In addition, different countries help achieve greater energy independence with successive geostrategic benefits.
fight against climate change
Initially, this technique received support from different sectors, including environmental groups. This was due to the fact that burning gas emits less CO 2 than burning coal or oil. However, subsequent research questioned the advantages of this technique in the fight against climate change. On the one hand, proprietary natural gas (CH 4 ) is a powerful greenhouse gas, and its direct filtration into the atmosphere during the extraction process is very dangerous.
On the other hand, the race for the exploitation of these sites may, according to the experts' comments, stagnate in the development of truly clean renewable energy sources such as photovoltaic solar energy, wind energy, geothermal energy or energy. hydraulics.
Impact on groundwater
One of the problems derived from fracking is the possible contamination of the wells and aquifers that provide drinking water to the population. The industry argues that the cement barriers introduced in the perforations prevent the possible passage of harmful substances to the groundwater layers where drinking water can be found.
However, several investigations by Duke University and the EPA (United States Environmental Protection Agency) have shown the presence of methane, chemical solvents and other substances, in water samples taken near the perforations.
Impact on surface waters
During the fracking process, a considerable part of the mix of water, chemicals, and sand that is injected into the borehole returns to the surface. In addition, in this process, water transports substances that were trapped in the depth to the surface.
This waste is highly polluting and can cause environmental disasters in the event of leaks to rivers and surface water deposits.
The classic example of this possible contamination occurred in the Dunkard Creek River in September 2009. An invasion of microscopic algae killed much of the river's indigenous life. Subsequently, it was learned that several companies had illegally discharged water from various drilling centers.
One of the proposed alternatives was to treat these waters in traditional treatment plants. However, several experts emphasized that these plants would not be prepared to purify these waters completely, especially with regard to the cleaning of radioactive (radio) substances.
History of fracking
The technique of improving the productivity of an oil well through fracking dates back to the 1860s, when in Pennsylvania, with the use of nitroglycerin, the production of some wells drilled in solid rocks was improved.
Fracturing technology, by applying pressure to the rock using hydraulic fluid, to stimulate the supply of oil from less productive fields was produced in the United States in 1947 by the Stanolind Oil and Gas Corporation in the field in Hugoton Kansas.
The first company to patent a hydraulic fracturing technique was the company's Haliburton Well Cementing Oil in 1949. This practice, given the increased production it caused, quickly spread for the first time in the entire US oil industry. USA and then in the whole world.
Environmental risks derived from fracking
Hydraulic fracturing is being monitored internationally due to concerns about the risks of chemical contamination of groundwater and air. In some countries, the use of this technique has been suspended or even prohibited.
In March 2014, the journal Endocrinology published an article on mining activities in Colorado, titled "Activities of estrogen and androgen receptor for hydraulic fracturing chemicals and surfaces and groundwater in a region of high drilling density" ... Researchers analyzed the waters of Garfield County, Colorado, where shale gas shafts are highly present.
The sampling showed that even the presence of "moderate levels" of chemicals in the fluids used for fracking had the potential to interfere with normal hormonal function. One of the study's collaborators, Christopher Kassotis, argues that high levels of impaired hormone function are linked to infertility, cancer, and birth damage.
Seismic risks derived from hydraulic fracture
Hydraulic micro-fracturing of the sediment techniques can, in some cases, generate highly localized induced microseismicity. The intensity of these micro-earthquakes is generally quite limited, but there may be local problems of soil stability when the sediments are superficial.