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Research Papers: Energy Conversion/Systems

Exergy, Energy, and Gas Flow Analysis of Hydrofractured Shale Gas Extraction

[+] Author and Article Information
Noam Lior

Fellow ASME
Department of Mechanical Engineering
and Applied Mechanics,
University of Pennsylvania,
220 South 33rd Street,
Philadelphia, PA 19104-6315
e-mail: lior@seas.upenn.edu

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received November 3, 2015; final manuscript received November 10, 2015; published online February 1, 2016. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 138(6), 061601 (Feb 01, 2016) (14 pages) Paper No: JERT-15-1425; doi: 10.1115/1.4032240 History: Received November 03, 2015; Revised November 10, 2015

The objectives of this study are to (a) evaluate the exergy and energy demand for constructing a hydrofractured shale gas well and determine its typical exergy and energy returns on investment (ExROI and EROI), and (b) compute the gas flow and intrinsic exergy analysis in the shale gas matrix and created fractures. An exergy system analysis of construction of a typical U.S. shale gas well, which includes the processes and materials exergies (embodied exergy) for drilling, casing and cementing, and hydrofracturing (“fracking”), was conducted. A gas flow and intrinsic exergy numerical simulation and analysis in a gas-containing hydrofractured shale reservoir with its formed fractures was then performed, resulting in the time- and two-dimensional (2D) space-dependent pressure, velocity, and exergy loss fields in the matrix and fractures. The key results of the system analysis show that the total exergy consumption for constructing the typical hydrofractured shale gas well is 35.8 TJ, 49% of which is used for all the drilling needed for the well and casings and further 48% are used for the hydrofracturing. The embodied exergy of all construction materials is about 9.8% of the total exergy consumption. The ExROI for the typical range of shale gas wells in the U.S. was found to be 7.3–87.8. The embodied energy of manufactured materials is significantly larger than their exergy, so the total energy consumption is about 8% higher than the exergy consumption. The intrinsic exergy analysis showed, as expected, very slow (order of 10−9 m/s) gas flow velocities through the matrix, and consequently very small flow exergy losses. It clearly points to the desirability of exploring fracking methods that increase the number and length of effective fractures, and they increase well productivity with a relatively small flow exergy penalty.

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References

Figures

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Fig. 1

Typical hydrofracturing for shale gas and the associated water cycle, from Ref. [6]

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Fig. 2

Typical casing (using three casings) and cementing between the casings, dimensions specific to sources on Marcellus Shale [12,13]

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Fig. 3

Hydrofracturing exergy use shares in making a gas well

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Fig. 4

Exergy use shares in overall making of a hydrofractured gas well

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Fig. 5

Model diagram. The gas moves down the pressure gradient (left to right and up) from the undisturbed low-porosity reservoir matrix to the formed fractures, which then transport it to the horizontal well. Lines of symmetry are shown dashed and arrows show the direction of gas flows.

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Fig. 6

Distributions in the matrix after 1 day of: (a) gas pressure (the scale is in MPa), (b) gas velocity (the scale is in 10−10 m/s), and (c) exergy loss (the scale is in kJ/kg)

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Fig. 7

Distributions in the matrix after 3 days of: (a) gas pressure (the scale is in MPa), (b) gas velocity (the scale is in 10−10 m/s), and (c) exergy loss (the scale is in kJ/kg)

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Fig. 8

Distributions in the matrix after 5 days of: (a) gas pressure (the scale is in MPa), (b) gas velocity (the scale is in 10−10 m/s), and (c) exergy loss (the scale is in kJ/kg)

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Fig. 9

Distributions in the matrix after 15 days of: (a) gas pressure (the scale is in MPa), (b) gas velocity (the scale is in 10−10 m/s), and (c) exergy loss (the scale is in kJ/kg)

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Fig. 10

Distributions in the hydraulic fracture of: (a) gas pressure (the scale is in MPa), (b) gas velocity (the scale is in m/s), and (c) exergy loss (the scale is in kJ/kg)

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