# Considerations for

Fate and Transport Evaluation Of Potential Release Scenarios during Hydraulic Fracturing Operations

EPA Hydraulic Fracturing Technical Workshop on Fate and Transport
March 28- 29, 2011

# Set up a Site Conceptual ModelTo Production Zone (thousands of feet)



### Not to Scale Drilling

& Operations

Conductor Casing Surface Casing

Groundwater Groundwater Protected through Well Design and Testing Groundwater Protected through Primary and Secondary Containment Distance to Water Supplies Considered

Water Well Surface Water Shot Hole Properly Abandoned

Intermediate Casing Production Casing, Production Tubing, and Associated Protections Closed Mud System



# Consider likelihood of EventDepth to Useable Groundwater (10s to 100s feet) Depth to Limited Use Groundwater (10s to 1,000s feet)

Depth to Non Useable Groundwater (10s to 10,000s feet)

Depth to Gas Producing Formations (1,000s to 10,000s of feet) Useable Groundwater

Limited - Use Groundwater (Quality & or Quantity)

Non - Useable Groundwater (Quality & or Quantity)

Non - Useable Groundwater (Quality & Quantity) Depth to Non Useable Groundwater (10s to 10,000s feet) Non - Useable Groundwater (Quality & or Quantity) - 0 feet

- 100 feet

- 1,000 feet

- 10,000 feet 50,000 gal leak displacement (equivalent to a sphere of about 18.5 ft radius)

50,000 gal leak displacement 

# Potential Total Volumes from HF are Limited And Starting Concentrations are Low.

# Consider Potential Chemicals of Concern

for Hydraulic Fracturing Additives (Low starting concentrations) Salts, organics, metals, Produced water (actually not part of HF process) Salts, organics, metals,

# Methods for Examining Potential Produced

Water Impacts are Available

## Geochemical methods use common water chemistry parameters to identify mixing of saline and potable water. Parameters of interest may include: Na, K, Ca, Mg, Cl , SO4, Co3, HCO3, TDS, Br, I, etc. , and take advantage of potentially great differences between the makeup of saline and potable water. For example, a large database of produced water (fractionation water base) and well waters from an area show their distinct character when comparing various parameters. (Note: These plots show data from hundreds of samples from throughout a large area. Focusing on specific locations, depths, etc. may likely show more separation of the produced water and well water.)

By evaluating the differences between waters, appropriate parameters or combinations may be selected for evaluation of potential mixing.  Average ≈ 5,400 mg/L

Average ≈ 20 mg/L

 Average ≈ 9,700 mg/L  Average ≈ 5,300 mg/L

Average ≈ 400 mg/L Average ≈ 140 mg/L

## Produced Water Well Water



# Piper plots of major ions is another way of showing distinct chemical types of water. Produced waters (used to makeup fractionation water) have a fairly tight geochemical fingerprint, while well waters are generally different than produced water and variable in composition. Note that these diagrams represent water type, not concentrations.Cations Anions Na + K

Mg Ca SO4 HCO3 + CO3 Cl
100% PW Anions Na + K

Mg Ca SO4 HCO3 + CO3

Cl
100% WW

Cations

Anions Na + K

Mg Ca SO4 HCO3 + CO3

Cl
1% PW inWW

Cations

Anions Na + K

Mg Ca SO4 HCO3 + CO3

Cl
5% PW inWW

Cations Cations

Anions Na + K

Mg Ca SO4 HCO3 + CO3 Cl
20% PW in WW 

## Stiff Diagrams of major ions indicated the general chemistry of waters and mixtures. These may be used to indicate water type visually and relative concentrations.

Water Well (WW) Produced Water (PW)

# BIODEGRADATION HALF LIFE IN SOIL

Half Life Increases with Molecular Weight and Complexity

Half Lives for BTEX compounds are on the order of one month

# METALS

Solid (Soil) Phase Aqueous (Water) Phase Petroleum (Oil) Phase EL ML Pb Pb Pb Pb PbSO 4
Pb Pb

X X X X X X X Mineral Lead Occluded (Trapped) Lead Soil Surface

OH O - Soil Organic Matter ( Humics )

Dissolved EL or ML (Ethyl or Methyl Lead)

Inorganic Lead Species Exchanged Lead Precipitated Lead Soluble Lead Adsorbed Lead

Organically

Complexed Lead Organic Lead Pb PbSO 4 PbS PbCl 2 PB(CO 3 )(Cl) 2 PbCO 3 PbO Pb 5 (AsO 4) 3 Cl Pb 2 OCO 3 PbSO 4O Pb 2 O 2SO 4 Pb 4O 3SO 4 Pb 3 (AsO 4) 2 

## Minerals Pb +2 PbCl 2(aq) PbCl 3 - PbCl 4- 2 Pb(CO 3 ) 2 - 2 Pb(OH) + Pb 4 (OH) 4+4 Pb 6 (OH) 8+4 PbCl + PbHCO 3 + PbCO 3(aq) Pb(OH) 2(aq) Pb(OH) 3 - Pb 2 OH +3 PbSO 4(aq) Pb(HS) 2(aq) Pb(HS) 3 - Pb 3 (OH) 4+2 Pb(OH) - 2 Pb(SO4) - 2 Pb +2 

## Soluble Pb(OH) 2 PbSO 4 PbCO 3 PbS 

## Precipitates 

# Species and Interactions



# Previous Work indicate that Metals from O&G Materials are Immobile if Released to Soil.

## MINTEQA2, HSC3

Pb PbCl2 PbO PbO2 Pb2O3 Pb3O4 Pb(OH)2

Pb(+2a) PbCl2(a) Pb3(OH)4(+2a) Pb4(OH)4(+4a) Pb6(OH)8(+4a) 

## • Useful for forward modeling (Tier 2). • Data limited for reverse modeling. • May be linked to transport model. • May incorporate sorption. • Use to establish system boundaries. 

# PbCl 2 

# H 2 

# O 

# METALS

## Natural parameters are preferable to frac fluid additives for evaluating potential salt water influences because of variety of additives, variety of analytical procedures, natural presence of some constituents, and detection limit constraints. 

## For example, an www.energyindepth.org reference summarizes a typical frac fluid ( http://www.energyindepth.org/frac
-fluid.pdf). From that data, estimate possible levels of some components at a 0.5% produced water mixture with well water:mg/L at 0.5% mg/L Detection Limit Component PW in WW for component Detectable citric acid 0.2 1 No ethylene glycol 2.2 10 No n,n -dimethyl formamide 0.1 0.1 Maybe gluteraldehyde 0.05 1 No isopropanol 4.3 0.01 Yes petroleum distillate 4.4 0.001 (xylene ) Yes (at 0.2% Xyl ) Note that in this case two of the chemicals are potentially detectable at a level equivalent to standard inorganic parameters. Of these isopropanol is a natural component and may degrade prior to sampling and analysis or be present in background, while petroleum components are already commonly analyzed. Such evaluation must be done for each component considered.

# Domenico Equation

## Domenico Equation Applied to Salt Transport

18.5 ft – Approx. soil volume of 50,000 gal release.

## Tools are available for evaluating the fate and transport of selected

reasonable release scenarios in hydraulic fracturing operations. These methodologies consider controls in the hydraulic fracturing process as reflected in existing regulations and best management practices before selecting scenarios. This process will allow focusing on realistic release scenarios, chemicals, pathways, and receptors. 

## Background chemicals, both anthropogenic and natural, must be considered in any analysis. Tools must be used that are appropriate for uncertainty in available data and analytical techniques. Consider previous work that showed oil field waste to be high volume and low toxicity, i.e. produced water, drilling mud.