saltwater disposal well and legacy well probabilistic risk ...€¦ · risk analysis for swd and...
TRANSCRIPT
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Saltwater Disposal Well and Legacy Well Probabilistic Risk Analysis
Ronald T. Green, Ph.D., P.G., Nick Martin, P.G., P.H., and Beth Fratesi, Ph.D. Earth Science Section
Southwest Research Institute®
Texas Alliance of Groundwater Districts Summit
San Antonio, Texas August 26, 2019
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Evaluate risks from salt water disposal (SWD) and legacy wells:
Texas has a rich history: of oil and gas exploration and development
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Evaluate risks from salt water disposal (SWD) and legacy wells:
Texas has a rich history: of oil and gas exploration and development Upside: 100+ years of sustained energy & economic development
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Evaluate risks from salt water disposal (SWD) and legacy wells:
Texas has a rich history: of oil and gas exploration and development Upside: 100+ years of sustained energy & economic development Downside: 100+ years of the environmental legacy of oil and gas exploration and development
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What’s Can That Legacy Look Like?
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What’s Can That Legacy Look Like?
2011 breakout at well plugged in 1949
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What’s Can That Legacy Look Like?
Failed shut-in well with flowing
salt water
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What’s Can That Legacy Look Like?
Water flooding into corroded well field
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What’s Can That Legacy Look Like?
Abandoned well No plug
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What’s Can That Legacy Look Like?
SWD facility with minimal protections
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What’s That Legacy Look Like?
Oil well blow out at ground surface
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What’s Can That Legacy Look Like?
Oil well blow out at ground surface
Catastrophic Tank Battery Failure
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What’s Can That Legacy Look Like?
Oil well blow out at ground surface
Virtually unlimited examples of risks to water resources from oil and gas activities
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These Examples All Have Surface Expressions
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These Examples All Have Surface Expressions
As bad as surface releases of contaminants may be…
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These Examples All Have Surface Expressions
…undetected releases into aquifers could be far, far worse…
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These Examples All Have Surface Expressions
…because these unseen releases could continue for long periods of time
before detection
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What can a GCD do to assess the risk of legacy oil and gas operations to its
water resources?
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Definition of Risk
A probability (or threat) of damage, injury, liability, loss, or any other negative occurrence that is caused by
external or internal vulnerabilities, and that may be avoided through preemptive action
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Definition of Risk
Risk = (Probability) * ($)
…that may be avoided through preemptive action
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Greatest Challenges When Calculating Risks of a SWD or Legacy Well:
Failures are rare
Data are sparse
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How are these challenges met?
1. Understand the science of failure mechanisms
2. Compile as much data as possible
3. Use expert judgement to fill gaps
4. Use rigorous analysis to assess risk
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Risk Analysis
Rigorous analysis of Class I Hazardous Waste Injection Wells conducted by Rish (2005)
1. Determined Class I wells do not pose a serious risk
2. Noteworthy: safety criteria for Class I wells far exceed safety criteria for Class II
(i.e., SWD) wells.
3. Risk analysis for Class II wells is needed
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Risk Analysis
Rigorous analysis of Class I Hazardous Waste Injection Wells conducted by Rish (2005)
1. Determined Class I wells do not pose a serious risk
2. Noteworthy: safety criteria for Class I wells far exceed safety criteria for Class II
(i.e., SWD) wells.
3. Risk analysis for Class II wells is needed
800 Class I wells and 150,000 Class II wells in the U.S.
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Risk Analysis for SWD and Legacy Wells
1. Leverage analysis by Rish (2005)
2. Need to expand events to include surface features not considered by Rish (2005).
3. Event probabilities assigned to Class I wells may not be appropriate for Class II (SWD) wells
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Characterize how Class II Well System
functions
Work Flow to Evaluate Environmental Risk
Assign probabilities to initiating event
occurrences
Identify critical elements of a
Class II Well
Identify all sequences of events that result
in waste isolation loss
Calculate probability and risk for each
loss sequence
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Characterize how Class II Well System
functions
Work Flow to Evaluate Environmental Risk
Assign probabilities to initiating event
occurrences
Identify critical elements of a
Class II Well
Identify all sequences of events that result
in waste isolation loss
Calculate probability and risk for each
loss sequence
As an example: look at critical elements and assigned probabilities for Class I wells
by Rish (2005)
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Start with injection well risk assessment
Rish (2005)
provides schematic of a typical hazardous waste
injection well
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Description Probability Lower bound Median Upper bound
Automatic alarm fails Uniform 5.E-05 3.E-04 5.E-04
Annulus pressure drops below injection pressure From fault tree 9.E-14 7.E-12 8.E-11
Loss of injection zone capacity results in over-pressurization Uniform 1.E-05 1.E-04 1.E-03
Annulus check valve fails to open Triangular 1.E-04 3.E-04 1.E-03
Transmissive breach occurs through lower confining zone From fault tree 6.E-04 3.E-03 1.E-02
Transmissive breach occurs through upper confining zone From fault tree 6.E-04 3.E-03 1.E-02
Annulus pressure control system fails, resulting in under-pressurization Uniform 1.E-06 1.E-05 1.E-04
Injection pressure control system fails, resulting in over-pressurization Uniform 1.E-06 1.E-05 1.E-04
Failure to identify abandoned well in AOR Uniform 1.E-03 5.E-03 1.E-02
Presence of unidentified transmissive discontinuity Uniform 1.E-04 1.E-03 1.E-02
Extraction of injection zone groundwater Uniform 1.E-05 1.E-04 1.E-03
Testing fails to detect injection fluid migration outside long string casing Uniform 5.E-04 3.E-03 5.E-03
Waste injected chemically incompatible with geology or previously injected waste Uniform 1.E-05 5.E-05 1.E-04
Sudden/major failure and breach of injection tube Poisson 3.E-07 6.E-07 8.E-07
Injection tube leak Poisson 3.E-05 6.E-05 8.E-05
Injected fluid is sufficiently buoyant to penetrate lower confining zone breach Single value 1.E+00 1.E+00 1.E+00
Long string casing leak located between surface Uniform 1.E-02 3.E-02 5.E-02
Long string casing leak located above base of surface casing Uniform 1.E-02 5.E-02 1.E-01
Long string casing leak is located below confining zone(s) Uniform 9.E-01 9.E-01 1.E+00
Sudden/major failure and breach of long string casing Poisson 2.E-07 3.E-07 5.E-07
Long string casing cement microannulus allows fluid movement along casing Poisson 2.E-06 6.E-06 1.E-05
Long string casing leak Poisson 2.E-05 3.E-05 5.E-05
Waste migrates between surface casing and upper confining zone Uniform 1.E-04 1.E-03 1.E-02
Failure to recognize groundwater extraction located within injection waste zone Uniform 1.E-03 5.E-03 1.E-02
Operator fails to recognize changes in confining zone capacity Uniform 5.E-05 3.E-05 5.E-04
Operator fails to detect/respond to unacceptable pressure differential Uniform 5.E-05 3.E-05 5.E-04
Operator error induces transmissive fracture through lower confining zone Uniform 5.E-05 3.E-04 5.E-04
Operator error causes injection pressure above annulus pressure Uniform 5E−05 3E−04 5E−04
Injection waste has migrated outside of Area of Review to unconfined zone Uniform 1E−05 5E−05 1E−04
Sudden/major failure and breach of packer Poisson 2E−07 4E−07 6E−07
Packer leak Poisson 2E−05 4E−05 6E−05
Confining zone has unexpected transmissive permeability Uniform 1E−05 1E−04 1E−03
Identified abandoned well plug fails Poisson 2E−04 8E−04 2E−03
Annulus pump fails Triangular 5E−05 5E−04 5E−03
Groundwater monitoring fails to detect waste release outside injection zone Single value 5E−01 5E−01 5E−01
Seismic event induces a transmissive fault or fracture Uniform 1E−05 5E−05 1E−04
Surface casing leak Poisson 2E−06 3E−06 5E−06
Unidentified abandoned well transmissive from inj zone to lower confining zone Single value 1E−01 1E−01 1E−01
Unidentified abandoned well transmissive through upper confining zone to USDW Single value 1E−01 1E−01 1E−01
Injected fluid is sufficiently buoyant to penetrate upper confining zone breach Uniform 1E−05 5E−05 1E−04
Injected waste has not transformed into nonwaste Uniform 1E−02 1E−01 1E+00 Note: frequencies are per day or per demand
Event probability distributions for a Class I hazardous waste injection well (Rish, 2005)
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Description Probability Lower bound Median Upper bound
Automatic alarm fails Uniform 5.E-05 3.E-04 5.E-04
Annulus pressure drops below injection pressure From fault tree 9.E-14 7.E-12 8.E-11
Loss of injection zone capacity results in over-pressurization Uniform 1.E-05 1.E-04 1.E-03
Annulus check valve fails to open Triangular 1.E-04 3.E-04 1.E-03
Transmissive breach occurs through lower confining zone From fault tree 6.E-04 3.E-03 1.E-02
Transmissive breach occurs through upper confining zone From fault tree 6.E-04 3.E-03 1.E-02
Annulus pressure control system fails, resulting in under-pressurization Uniform 1.E-06 1.E-05 1.E-04
Injection pressure control system fails, resulting in over-pressurization Uniform 1.E-06 1.E-05 1.E-04
Failure to identify abandoned well in AOR Uniform 1.E-03 5.E-03 1.E-02
Presence of unidentified transmissive discontinuity Uniform 1.E-04 1.E-03 1.E-02
Extraction of injection zone groundwater Uniform 1.E-05 1.E-04 1.E-03
Testing fails to detect injection fluid migration outside long string casing Uniform 5.E-04 3.E-03 5.E-03
Waste injected chemically incompatible with geology or previously injected waste Uniform 1.E-05 5.E-05 1.E-04
Sudden/major failure and breach of injection tube Poisson 3.E-07 6.E-07 8.E-07
Injection tube leak Poisson 3.E-05 6.E-05 8.E-05
Injected fluid is sufficiently buoyant to penetrate lower confining zone breach Single value 1.E+00 1.E+00 1.E+00
Long string casing leak located between surface Uniform 1.E-02 3.E-02 5.E-02
Long string casing leak located above base of surface casing Uniform 1.E-02 5.E-02 1.E-01
Long string casing leak is located below confining zone(s) Uniform 9.E-01 9.E-01 1.E+00
Sudden/major failure and breach of long string casing Poisson 2.E-07 3.E-07 5.E-07
Long string casing cement microannulus allows fluid movement along casing Poisson 2.E-06 6.E-06 1.E-05
Long string casing leak Poisson 2.E-05 3.E-05 5.E-05
Waste migrates between surface casing and upper confining zone Uniform 1.E-04 1.E-03 1.E-02
Failure to recognize groundwater extraction located within injection waste zone Uniform 1.E-03 5.E-03 1.E-02
Operator fails to recognize changes in confining zone capacity Uniform 5.E-05 3.E-05 5.E-04
Operator fails to detect/respond to unacceptable pressure differential Uniform 5.E-05 3.E-05 5.E-04
Operator error induces transmissive fracture through lower confining zone Uniform 5.E-05 3.E-04 5.E-04
Operator error causes injection pressure above annulus pressure Uniform 5E−05 3E−04 5E−04
Injection waste has migrated outside of Area of Review to unconfined zone Uniform 1E−05 5E−05 1E−04
Sudden/major failure and breach of packer Poisson 2E−07 4E−07 6E−07
Packer leak Poisson 2E−05 4E−05 6E−05
Confining zone has unexpected transmissive permeability Uniform 1E−05 1E−04 1E−03
Identified abandoned well plug fails Poisson 2E−04 8E−04 2E−03
Annulus pump fails Triangular 5E−05 5E−04 5E−03
Groundwater monitoring fails to detect waste release outside injection zone Single value 5E−01 5E−01 5E−01
Seismic event induces a transmissive fault or fracture Uniform 1E−05 5E−05 1E−04
Surface casing leak Poisson 2E−06 3E−06 5E−06
Unidentified abandoned well transmissive from inj zone to lower confining zone Single value 1E−01 1E−01 1E−01
Unidentified abandoned well transmissive through upper confining zone to USDW Single value 1E−01 1E−01 1E−01
Injected fluid is sufficiently buoyant to penetrate upper confining zone breach Uniform 1E−05 5E−05 1E−04
Injected waste has not transformed into nonwaste Uniform 1E−02 1E−01 1E+00 Note: frequencies are per day or per demand
Event probability distributions for a Class I hazardous waste injection well (Rish, 2005)
This table is a list of all events that can fail in a Class I
hazardous waste well. Included are the probabilities of failure
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SWD and Legacy Wells Need to Include Additional Initiating Events Related to Surface Facilities
• Pond leaks or failures
• Piping leaks
• Tanker truck failure
• Other surface failure events
Need to assign probabilities to these events
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A Major Challenge
Calculate the probabilities of failure that are not overly optimistic (i.e., too low) or unrealistically
pessimistic (i.e., too conservative).
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The “Risk” of Miscalculating Risk
Prior to the loss of the Challenger in 1986, NASA set the probability of a shuttle
failure at 1 in 100,000.
Only after careful analysis in 1988, Richard Feynman (Nobel in physics)
calculated a more realistic risk probability of 1 in 100.
135 shuttle flights over 30 years: 133 successes, 2 failures
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What is Risk in Terms of a SWD Well? (Salt Water Disposal)
What are the factors that lead to a SWD well failing?
What is the probability that a particular factor will fail?
If more than one factor needs to fail in order for a SWD well to fail, what are the odds that these particular
factors will simultaneously fail?
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What are the factors that
lead to a SWD or legacy well failing?
(Presented at the 2015 TAGD Summit)
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1,200
110,000
15,000
500
5,000
80,000
5,000
TDS
Need to Understand Local Geology:
Aquifers Relative to Injection Horizon
Fresh Wilcox Formation
Edwards Formation
Saline Wilcox Formation
Carrizo
Glen Rose Formation
Confining Unit
Brackish Wilcox Formation
Formation
BUQW
USDW
USDW
Water Quality Designation
< 3,000 ppm 3,000 ppm- 10,000 ppm
Water Quality Designation
3,000 ppm- 10,000 ppm
Depth of Water Wells
?
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Key Criteria when Evaluating SWD and Legacy Wells
Injection Well
injection
Date! Older technology may not be adequate
Was base of USDW and BUQW sealed off?
Were plugs placed within confining layers?
Was mud left in borehole?
Details on cement?
horizon
cement
USDW
BUQW
Weight of mud?
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Is a ¼-mile Area of Interest Adequate?
Injected fluids tend to follow existing fractures consistent with pre-existing stress field instead of an
isotropic sphere
An injection well has greater influence in the direction of maximum horizontal stress
and major faults and fractures
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Although this is closer to geologic reality,
… this is what is considered by the Railroad Commission
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Fresh Wilcox Formation
Olmos Formation
Navarro Formation
Saline Wilcox Formation
Carrizo
San Miguel Formation
Midway Formation
SWD Locations near Old/Existing Wells Is it Acceptable?
Rustler Formation
Dockum Formation
Grayburg Formation
Confining Unit
Queen Formation
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Fresh Wilcox Formation
Olmos Formation
Navarro Formation
Saline Wilcox Formation
Carrizo
San Miguel Formation
Midway Formation
SWD Locations near Old/Existing Wells Is it Acceptable?
In this case in the Eagle Ford Shale….no
Rustler Formation
Dockum Formation
Grayburg Formation
Confining Unit
Queen Formation
In this case in the Permian Basin….yes
Depends
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0
20,000
40,000
60,000
80,000
100,000
120,000
Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14
Tota
l Vo
lum
e In
ject
ed
(B
BLs
/mth
)
Date
Accurate Injection Pressure is Essential Recorded Injected Volumes versus Injection Pressure
42
0
500
1000
1500
2000
Oct-06 Feb-08 Jul-09 Nov-10 Apr-12 Aug-13 Dec-14
Pre
ssu
re (
psi
g)
Date
Discrepancy between injection volume and
injection pressure highlights the need for digital pressure gauges.
Analog gauges do not
provide accurate record of injection pressure.
Monthly Maximum Pressure
Monthly Average Pressure
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State of Secondary Containment?
Primary Containment
Freshwater aquifer
Confining layer
Injection horizon
Secondary Containment
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Legacy Secondary Containment
Catastrophic Tank Battery Failure
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Risks do not remain constant over time…
Time Casing Steel Drilling Mud Cement Well Plugging
1900
Casing susceptible to
sulfide stressed
cracking
Water-based drilling
fluids exclusively
used
No standards for
cement
Fresh-water sands
protected with mud-
laden fluid
1910
1920
1930
1940
Oil-based drilling
fluids limited to shale
and salt formations
1950
Limited hydrostatic
bearing pressure
1960
Casing more resistant
in presence of H2S
and CO2
USDW protected
with cement
1970
1980 Increased hydrostatic
bearing pressure 1990
2000
2010
Evolution in well construction, abandonment, and plugging technologies. This adds a temporal component when assigning probability of failure to legacy wells.
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Once individual probabilities of failure are specified, need to calculate the probability that
a particular sequence of events will occur resulting in the failure of the “system”.
This sequence is the “event tree”.
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Event tree for packer leak in a Class I hazardous waste injection well (Rish, 2005)
6E-07
7E-12
3E-02
5E-02
9E-01
3E-06
6E-06
3E-03
6E-06
3E-05
One Example of an Event Tree
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Event tree for packer leak in a Class I hazardous waste injection well (Rish, 2005)
6E-07
7E-12
3E-02
5E-02
9E-01
3E-06
6E-06
3E-03
6E-06
3E-05
One Example of an Event Tree
Event assigned Probability of
occurrence
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Event tree for packer leak in a Class I hazardous waste injection well (Rish, 2005)
6E-07
7E-12
3E-02
5E-02
9E-01
3E-06
6E-06
3E-03
6E-06
3E-05
One Example of an Event Tree
These sequences of events result in a
release to the environment
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Event trees need to be created to account for all possible failure pathways
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Quantitative (Probabilistic) Analysis of Event Trees
Many, many simulations are run with each simulation based on random input determined by assigned probabilities for each event tree.
The final result is a probability distribution of failure (i.e., the chances that hazardous waste will be released to the environment –> groundwater).
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Probability distribution for total loss of waste isolation risks in a Class I hazardous waste injection well (Rish, 2005)
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Class II SWD Well Risk ≠ Class I Hazardous Well Risk
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Risks from Class II SWD releases are not the same everywhere…
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Eagle Ford Shale
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Permian Basin
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What are the Real Risks associated with Permian Basin and the Eagle Ford Shale?
• Injection into the over-pressurized Olmos/San Miguel
• Presence of legacy oil fields, 1970-1990
• Presence of legacy oil fields, 1940-1980
• H2S corrosion of well materials San Andres
• Under-pressurized San Andres • Legacy of poorly constructed
surface facilities
Permian Basin
Eagle Ford Shale
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Why Spend Time and Money to Assess Risks Associated with SWD and Legacy Wells?
• No wells, including O/G production and SWD wells, are designed and constructed to last forever.
• All wells will eventually fail.
• Left un-monitored, risks to GW posed by these wells and O/G activities will increase with time.
• Risks vary with site and require characterization.
• Unless clearly characterized, best management practices cannot be refined and improved.
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How else can risk from SWD wells be avoided through preemptive action?
Engage in an active GW quality monitoring program.
How realistic is this?
Example: GCD has 4,000 mi2 and samples 100 wells to monitor water quality => 4 mi2 covered per well
Assume GW flow in sand aquifer is 0.1 mile/year
On average, 20 yrs to detect a spill, if well is located in the same aquifer unit as spill.
Actual detection could be less, likely much more.
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Is Risk Assessment of SWD and Legacy Wells Worthwhile?
Not everywhere, most meaningful in areas with:
– high O/G activity,
– challenging geologic conditions,
– legacy wells and O/G related facilities,
– a history of hydrocarbon spills and releases to surface water and groundwater.
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Contact Information
Ronald T. Green, Ph.D., P.G.
Institute Scientist
1.210.522.5305 (office)
1.210.316.9242 (cell)
Earth Science Section
Space Science and Engineering Division
Southwest Research Institute
6220 Culebra
San Antonio, Texas 78238
Nicholas Martin, P.G., P.H.
Principal Scientist
1.210.522.5140 (office)
Beth Fratesi, Ph.D.
Research Scientist
1.210.522.2920 (office)