Saltwater Disposal Well and Legacy Well Probabilistic Risk ...€¦ · Risk Analysis for SWD and...

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

Evaluate risks from salt water disposal (SWD) and legacy wells:

Texas has a rich history: of oil and gas exploration and development


Texas has a rich history: of oil and gas exploration and development Upside: 100+ years of sustained energy & economic development


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

What’s Can That Legacy Look Like?


2011 breakout at well plugged in 1949


Failed shut-in well with flowing

salt water


Water flooding into corroded well field


Abandoned well No plug


SWD facility with minimal protections

What’s That Legacy Look Like?

Oil well blow out at ground surface



Catastrophic Tank Battery Failure



Virtually unlimited examples of risks to water resources from oil and gas activities

These Examples All Have Surface Expressions


As bad as surface releases of contaminants may be…


…undetected releases into aquifers could be far, far worse…


…because these unseen releases could continue for long periods of time

before detection

What can a GCD do to assess the risk of legacy oil and gas operations to its

water resources?

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

Definition of Risk

Risk = (Probability) * ($)

…that may be avoided through preemptive action

Greatest Challenges When Calculating Risks of a SWD or Legacy Well:

Failures are rare

Data are sparse

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

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

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.

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

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

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)

Start with injection well risk assessment

Rish (2005)

provides schematic of a typical hazardous waste

injection well

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)

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

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

A Major Challenge

Calculate the probabilities of failure that are not overly optimistic (i.e., too low) or unrealistically

pessimistic (i.e., too conservative).

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

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?

What are the factors that

lead to a SWD or legacy well failing?

(Presented at the 2015 TAGD Summit)

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

?

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?

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

Although this is closer to geologic reality,

… this is what is considered by the Railroad Commission


Olmos Formation

Navarro 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


Olmos Formation

Navarro 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

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

State of Secondary Containment?

Primary Containment

Freshwater aquifer

Confining layer

Injection horizon

Secondary Containment

Legacy Secondary Containment

Catastrophic Tank Battery Failure

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.

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”.

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


6E-07

7E-12

3E-02

5E-02

9E-01

3E-06

6E-06

3E-03

6E-06

3E-05


Event assigned Probability of

occurrence


6E-07

7E-12

3E-02

5E-02

9E-01

3E-06

6E-06

3E-03

6E-06

3E-05


These sequences of events result in a

release to the environment

Event trees need to be created to account for all possible failure pathways

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).

Probability distribution for total loss of waste isolation risks in a Class I hazardous waste injection well (Rish, 2005)

Class II SWD Well Risk ≠ Class I Hazardous Well Risk

Risks from Class II SWD releases are not the same everywhere…

Eagle Ford Shale

Permian Basin

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

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.

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.

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.

Contact Information

Ronald T. Green, Ph.D., P.G.

Institute Scientist

1.210.522.5305 (office)

1.210.316.9242 (cell)

[email protected]

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)

[email protected]

Beth Fratesi, Ph.D.

Research Scientist

1.210.522.2920 (office)

[email protected]

Saltwater Disposal Well and Legacy Well Probabilistic Risk ...€¦ · Risk Analysis for SWD and...

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