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Fracturing
Operations
The majority of the nation’s new natural gas wells do not
produce gas at sufficient rates to make the well economical. Hydraulic
fracturing is a technique used to allow natural gas and crude oil to
move more freely from the rock pores where it is trapped to a producing
well so it can be brought to the surface at higher rates. Hydraulic
fracturing technology was developed in the late 1940s and has been
continuously improved upon since that time.
In a hydraulic fracturing job, “fracturing fluids” or “pumping fluids”
consisting primarily of water and sand are injected under high pressure
into the reservoir. Most of the fracturing fluid (99% of the
liquid phase) is water. Some fracturing fluid also contains a “gelling
agent” to make the fluid more viscous to carry the sand (or “proppant”)
and accommodate the high-pressure. The proppants are used to hold
the fractures, made by the injection of the fluids, open and create new
pathways for the oil or gas to flow from the rock to the well bore.
Fracturing fluids may also contain very limited amounts of other
materials depending on the nature of the formation being fractured. The
fluid is pumped into a well bore at high pressures to create fractures
in the producing formation. Most of the fracturing liquids are recovered
as the oil and gas are produced and do not remain in the ground.
Hydraulic fracturing is considered a stimulation
treatment routinely performed on oil and gas wells in low-permeability
(having fewer connecting tunnels between the pores containing the oil
and gas) reservoirs. Specially engineered fluids are pumped at
high pressure and rate into the reservoir interval to be treated,
causing a vertical fracture to open. The wings of the fracture extend
away from the wellbore in opposing directions according to the natural
stresses within the formation. Proppant, such as grains of sand of a
particular size, is mixed with the treatment fluid to keep the fracture
open when the treatment is complete.
(Source:
Hydraulic Fracturing Process, Chesapeake Energy)
(Source:
What is
Shale Gas and Why is it So Important?, EIA)
A fluid injected into a well as part of a stimulation
operation. Fracturing fluids for shale reservoirs usually contain
water, proppant, and a small amount of nonaqueous fluids designed to
reduce friction pressure while pumping the fluid into the wellbore.
These fluids typically include gels, friction reducers,
crosslinkers, breakers and surfactants similar to household
cosmetics and cleaning products. The additives are selected for
their capability to improve the results of the stimulation operation
and the productivity of the well.
Proppants are particles mixed with fracturing fluid to hold
fractures open after a hydraulic fracturing treatment. In addition to
naturally occurring sand grains, man-made or specially engineered
proppants, such as resin-coated sand or high-strength ceramic materials
like sintered bauxite, may also be used. Proppant materials are
carefully sorted for size and sphericity to provide an efficient conduit
for production of fluid from the reservoir to the wellbore
In April 2011, a report was issued by congressional Democrats that
accused oil and gas companies of injecting "hundreds of millions of
gallons of hazardous or carcinogenic chemicals into wells in more than
13 states" during 2005 to 2009.
The chemicals were injected as fracturing fluids in the hydraulic
fracturing operation. Hydrofracturing has attracted increased
scrutiny from lawmakers and environmentalists because of concerns that
the chemicals used can contaminate underground water aquifers. The
report has also cited companies for "injecting fluids containing
chemicals that they themselves cannot identify."
The report said that more 650 of the products used in fracturing fluids
contained chemicals that are known or possible human carcinogens.
Companies injected large amounts of hazardous chemicals including 11.4
million gallons of fluids containing at least on of the toxic BTEX
chemicals, benzene, toluene, ethylbenzene, and xylene.
Another report said that
the spent hydrocracking fluids are being processed in treatment plants
not designed to fully treat the waste before it is discharged into
rivers. At one plant in Pennsylvania, the EPA found levels of benzene
roughly 28 times higher than the federal drinking level in treated
wastewater discharged into the Allegheny River.
(Source: "Oil, gas
drillers injected chemicals, report says," The Dallas Morning News,
April 17, 2011, p. 9A)
Hydraulic
Fracturing - Wikipedia
Unlocking
Tightly Trapped Gas at Shell - Very good video on horizontal
drilling, perforating, and fracking
Hydraulic Fracturing Facts - Chesapeake Energy
Hydraulic
Fracturing 101 - Earthworks
Hydraulic Fracturing - API
Copyright
2000 |
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