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Water Considerations and Hydraulic Fracturing, Ron Green
1. Hydraulic Fracturing Panel
Water Considerations
Presented at
Texas Groundwater Summit
August 28-30, 2012
by
Ronald T. Green, Ph.D. , P.G.
Geosciences and Engineering Division
Southwest Research Institute®
2. Amount of Water Needed to Hydraulically
Fracture a Well
Water demand to frack a well is substantial:
5-15 acre-ft (1,500,000-5,000,000 gallons) to frack a borehole
acre- (1,500,000- gallons)
Compared with 100,000 gallons to drill a well
Disposal of Fracking Waste Water
Considerable amount of degraded water returns to surface as
flowback:
flowback: 20% in “dry” formations, 80% in “wet” formations
Quality of flowback can be poor: fracking additives plus high-salinity in
poor: high-
situ groundwater
Disposal of flowback in Texas is often by deep-well injection
deep-
Page 2
3. Water Quality of Concern in Flowback
Flowback contains fracking additives
Precipitated & entrained solids (scaling tendencies)
Ca, Mg, Ba, Sr
Ba,
Mineral scales (calcium carbonate & BaSO4)
Iron solids (iron oxide and iron sulfide)
Dispersed clay fines, colloids & silts
High dissolved solids levels (chlorides, sulfates, calcium, etc.)
Bacteria
Suspended solids, frack sand (proppant)
(proppant)
Liquid & gas hydrocarbons
Acid gases (CO2 & H2S)
Friction reducer residue
plus formation (i.e., highly saline) water
Page 3
4. Stress-
Stress-Field Induced Preferential Flow
Injected fluids tend to follow existing fractures consistent
with pre-existing stress field instead of as a isotropic sphere
pre-
An injection well has greater influence
in the direction of maximum horizontal
stress and major faults and fractures
Actual Isotropic
volume of sphere
injection
Page 4
5. Regulations Predicated on Isotropic Media
Disposal Well Permit Guidance (Texas)
… the applicant shall review … wells that penetrate the
proposed disposal zone within a 1/4 mile radius of the
proposed disposal well to determine if all abandoned
wells have been plugged in a manner that will prevent
the movement of fluids from the disposal zone into
freshwater strata.
This regulation assumes pure radial flow and does not
account for heterogeneity that could result from stress-
stress-
field induced directional flow
Page 5
6. Inadvertent Contaminant Migration
Possible Modes of Migration
1. Migration along fault or through confining layer – not likely unless vertical
separation is minimal
2. Migration via an existing borehole (i.e., abandoned open well) – possible,
particularly if an abandoned well is not identified, reasonably close to the
disposal well, and contaminant is injected into the same horizon as the
screened section of the abandoned well
Injection of
Disposal disposal fluids
well Abandoned
open wells
Usable aquifer
Confining layer
Zone of injection
Page 6
8. Abandoned Oil/Gas Wells
RRC Database is not Comprehensive
Proposed
Disposal
± Well
Well
Symbol
A! Permitted Location
D Canceled Location
R Dry Hole
!( Oil Well
Existing Water #
* Gas Well
Wells )
" Oil/Gas Well
!. Plugged Oil Well
0 0.5 1 2 3 4
#0 Plugged Gas Well
Kilometers /
" Plugged Oil/Gas Well
Page 8
10. Stress-Field Ellipse Indicating Potential
Direction of Preferential Flow
¼-mile
radius
Proposed
Disposal
± Well
Well
Symbol
A! Permitted Location
D Canceled Location
Abandoned R Dry Hole
Wells !( Oil Well
Existing Water #
* Gas Well
Wells )
" Oil/Gas Well
!. Plugged Oil Well
0 0.5 1 2 3 4
#0 Plugged Gas Well
Kilometers /
" Plugged Oil/Gas Well
Page 10
11. Actual Threat from Disposal Wells
Failure of wells used for deep-well
disposal of waste fluids and migration of
waste fluids through 1,000s of feet of rock
are not the greatest threat
Abandoned wells pose the greatest threat
in deep-well disposal of waste fluids, and
possibly hydraulic fracking
Page 11
12. How Great is the Threat from Abandoned Wells?
Oil drilling began in earnest in the early 1900s, some
1900s,
wells have been in existence for almost a century.
Records of wells, especially older wells, are often
incomplete or absent.
absent.
Well casing is estimated effective for 20 yrs, structural
yrs,
integrity of older abandoned wells may be compromised.
How many? Estimates vary from less than 10,000 to
over 110,000 (orphan and inactive) wells.
wells.
Page 12
13. Is Waste Disposal by Deep-Well Injection
Deep-
a Problem?
Disposal of degraded fluids after fracking (flowback) by
flowback)
12,610 disposal wells in Texas
RRC requires notification of all occurrences of breakout, but
breakout,
doesn’t maintain a single database
RRC on retains records on breakout for only two years
There are documented cases of breakout
In absence of a centralized database, risk is unknown, but
possible
Page 13
14. Recommendations
There are several actions the State can take to mitigate
the threat of contamination due to “breakout” from a
disposal well.
Limit or prohibit injection of liquid wastes into oil/gas (i.e.,
productive) formations, particularly formations with a history of
formations,
oil/gas development. That’s where the abandoned wells are.
Increase the ¼-mile radial distance from proposed disposal well
¼-
over which abandoned wells are searched.
Develop a single database for all occurrences of “breakout”. Risk
from breakout can only be assessed if number of occurrences and
their severity are known.
Page 14
15. Contact Information
Ronald T. Green, Ph.D., P.G.
Institute Scientist
Geosciences and Engineering Division
Southwest Research Institute
6220 Culebra
San Antonio, Texas 78238
1.210.522.5305 (office)
1.210.522.5184 (fax)
1.210.316.9242 (cell)
rgreen@swri.edu
Page 15
17. SW Segment of the Carrizo-Wilcox Aquifer
Pre-
Pre-Development Potentiometric Surface
Groundwater elevation
reconstructed with limited
data and historical
evidence of spring flow
and flowing artesian wells.
(modified from Deeds et al., 2003)
Page 17
18. 1929- Carrizo-
1929-30 Carrizo-Wilcox Aquifer
Potentiometric Surface
Pumpage was estimated
at 27,000 acre-ft/yr in
1929-30
Zone of depression is
about 150 ft lower than
pre-development
groundwater elevation
(modified from Deeds et al., 2003)
Page 18
19. 1999 Carrizo-Wilcox Aquifer
Carrizo-
Potentiometric Surface
Pumpage was estimated
at 65,000-80,000
acre-ft/yr in 1999
Zones of depression are
about 350 ft lower than
pre-development
groundwater elevation
(modified from Deeds et al., 2003)
Page 19