Hydraulic Fracturing Xiaofeng Liu, Assistant Professor Department of Civil and Environmental Engineering University of Texas at San Antonio

What is hydraulic fracturing? Also called “fracking” A process of initiating, and subsequently propagating a fracture in a rock layer, by injecting 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 2

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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 lagoonal deposits, 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 5

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Limestone on shale. 7

Source: wikipedia 8

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Source: US DOE 10

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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 News 14

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 News 15

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 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. 16

Injected fluid: water, gels, foams, and compressed gases, including nitrogen, carbon dioxide and air Proppant: sand, resin-coated sand, and man- made ceramics 17

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 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. 18

How is the water handled? With care? 19

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Hydraulic Fracturing Xiaofeng Liu, Assistant Professor Department of Civil and Environmental Engineering University of Texas at San Antonio