Hydraulic FracturingHydraulic Fracturing

Xiaofeng Liu, Assistant Professor

Department of Civil and Environmental Engineering

University of Texas at San Antonio

http://engineering.utsa.edu/CE/Liufac.html

Email: xiaofeng.liu@utsa.edu

What is hydraulic fracturing?

• Also called “fracking”

• A process of initiating, and subsequently

propagating a fracture in a rock layer, by

injecting the pressurized fluidinjecting the pressurized fluid

• The fracturing is done from a wellbore drilled

into reservoir rock formations, in order to

increase the extraction and ultimate recovery

rates of oil and natural gas

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ww.propublica.org 3

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What is shale

• Shale is a fine-grained sedimentary rock composed of mud and tiny fragments of other minerals

• Shales are typically deposited in very slow moving water and are often found in lakes and lagoonalwater and are often found in lakes and lagoonaldeposits, in river deltas, on floodplains and offshore from beach sands.

• Shale is characterized by breaks along thin laminae or parallel layering

• Usually has low permeability

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Limestone on shale.

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Source: wikipedia 8

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Source: US DOE10

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A well head at a fracking operation near Carrizo Springs, TX

Source: SA Express News 13

Chesapeake Energy hydraulic fracturing operation over the Eagle Ford shale

formation near Carrizo Springs

Source: San Antonio Express News14

An employee of Cheapeake Energy pours a chemical mixture called

cross linked gel that is mixed with sand and used in the hydraulic

fracturing process

Source: SA Express News15

How does hydraulic fracturing work?

• Three steps:

– Pump the fracturing fluid into the wellbore at a rate sufficient to increase the pressure downhole to a value in excess of the fracture gradient of the formation rock.

– The pressure causes the formation to crack, allowing the – The pressure causes the formation to crack, allowing the fracturing fluid to enter and extend the crack farther into the formation.

– To keep this fracture open after the injection stops, a solid proppant, commonly a sieved round sand, is added to the fracture fluid. The propped hydraulic fracture then becomes a high permeability conduit through which the formation fluids can flow to the well.

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• Injected fluid: water, gels, foams, and

compressed gases, including nitrogen, carbon

dioxide and air

• Proppant: sand, resin-coated sand, and man-

made ceramics

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How much water needed?

• A multi-stage fracturing of a single horizontal shale gas well can use several million gallons of water– Compare with: 70 gallons per capita per day in US

– San Antonio has a population of 1.5 million, consumes – San Antonio has a population of 1.5 million, consumes 38,325 million gallon per year

– According to DOE by All Consulting, Marcellus shale production consumes 20,150 million gallon per year

• Most water used in hydraulic fracturing comes from surface water sources such as lakes, rivers and municipal supplies.

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How is the water handled? With care?

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21Source: http://www.mahometaquiferconsortium.org

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http://www.mahometaquiferconsortium.org

Hydraulic FracturingHydraulic Fracturing

Xiaofeng Liu, Assistant Professor

Department of Civil and Environmental Engineering

University of Texas at San Antonio

http://engineering.utsa.edu/CE/Liufac.html

Email: xiaofeng.liu@utsa.edu