# Modeling versusThe Real World Of Hydraulic Fracturing Denise A. Tuck, P.E. Global Manager, Chemical Compliance 03/29/2011© 2011 Halliburton. All Rights Reserved. 2 

# Objectives

 Overview of potential migration pathways

 Identify and discuss key fate and transport (F&T) modeling parameters

 Review available data for key F&T parameters



#  Identify data gaps and discuss implications for EPA study© 2011 Halliburton. All Rights Reserved. 3 

# Potential HF Related Migration Pathways
 Surface releases of HF and flowback fluids  Migration to groundwater  Migration to surface water

 Subsurface migration of HF additives (upward migration) to drinking water aquifers  Migration from the target zone© 2011 Halliburton. All Rights Reserved. 4 

# Sensitive F&T Model Parameters

 Key model “source” characterization information for surface release simulations  Spill volume  Spill area  Chemical constituents/concentrations in spilled fluid


#  Source characterization considerations for migration from bedrock (upward migration)  Fraction of trapped HF fluid/ flowback (e.g., 9 to 35% in 

# Marcellus shale, 68 to 82% in CBM)  Geochemistry of brine and HF additives in target formation© 2011 Halliburton. All Rights Reserved. 5 

# Sensitive F&T Model Parameters

 Surface Releases: Key parameters that typically control transport downgradient from source area  Hydraulic conductivity of soils and aquifers  Direction and magnitude of hydraulic gradient relative to 

# drinking water well locations  Biodegradation of organic chemicals  Adsorption


#  Upward Migration: Factors that control potential vertical migration of subsurface fluids  Direction and magnitude of natural head gradient  Bedrock stratigraphy and hydraulic properties  Distance between HF induced fractures and drinking water 

# units  Strength of attenuation processes© 2011 Halliburton. All Rights Reserved. 6 

# Sensitive F&T Model Parameters (cont)

 Key sensitive F&T parameters can be grouped into four general categories:  Source chemical characterization 

#  Surface release  Upward migration  Hydrogeological and attenuation processes


#  Available data, gaps, and modeling challenges for each of these categories are discussed as follows

6© 2011 Halliburton. All Rights Reserved. 7 

# Source Chemical Characterization

 HF additives  Halliburton and other service companies have provided EPA-requested data  EPA should be able to use this information to assess F&T characteristics of HF fluids 

#  Flowback characterization  Data for Marcellus shale is being continually generated (e.g., Hayes, 2009; NYSDEC, 2009; The Palmerton Group, 2011), other formations are also being analyzed 

#  EPA should identify key marker HF-related compounds for F&T evaluation  HF additives vary by job and formation  Appropriate to identify group of marker compounds

7© 2011 Halliburton. All Rights Reserved. 8 

# Flowback Quality Variability Sample #1 #2 #3 #4 #5 #6 #7 #8 #9 Formation Woodford Shale Woodford

Shale Woodford

Shale Marcellus

Shale Marcellus

Shale Marcellus

Shale Marcellus

Shale Bakken

Shale Bakken

Shale Specific gravity 1.026 1.036 1.019 1.012 1.070 1.100 1.170 1.105 1.066 pH 7.92 7.51 7.91 6.61 6.72 6.68 6.05 7.11 7.04 Resistivity (ohms-cm) 20.42 14.87 36.46 54.93 8.363 6.342 4.776 5.585 8.057 Temperature ( ̊C) 23 23 23 23 23 23 23 23 23 Ionic Strength 0.59 0.881 0.319 0.199 1.919 2.794 4.96 2.874 1.754 Hydroxide (mpL) 0 0 0 0 0 0 0 0 0 Carbonate (mpL) 0 0 0 0 0 0 0 0 0 Bicarbonate (mpL) 1,010 717 1190 259 183 183 76 366 366 Chloride (mpL) 19,400 29,400 10,000 6,290 59,700 87,700 153,000 96,400 58,300 Sulfate (mpL) 34 0 88 67 0 0 0 670 749 Calcium (mpL) 630 1,058 294 476 7,283 10,210 20,100 4,131 2,573 Magnesium (mpL) 199 265 145 49.6 599 840 1,690 544 344.0 Barium (mpL) 49.4 94.8 6.42 6.24 278 213 657 1.06 5.1 Strontium (mpL) 107 179 44.7 74.3 2,087 2,353 5,049 178 112 Total Iron (mpL) 4.73 25.7 8.03 14 27.4 2.89 67.6 26.4 33.8 Aluminum (mpL) 0.17 0.21 0.91 0.38 0.18 0 0.1 0.17 0.78 Silica (mpL) 33.8 – 40.7 – – – – – – Baron (mpL) 28.2 27.1 26.7 8.82 45.1 73.1 80.4 94.5 65.7 Potassium (mpL) 192 273 78.7 85.8 977 1,559 2,273 2,232 1,439 Sodium (mpL) 10,960 16,450 5,985 3,261 26,780 39,990 61,400 54,690 32,600 TDS (mpL) 33,300 49,300 18,200 10,800 98,600 144,000 252,000 160,000 97,700 TSS (mpL) 57 246 50 30 10 12 32 120 13,762 TOC (mpL) 89 64 133 180 218 70 143 266 235© 2011 Halliburton. All Rights Reserved. 9 

# Surface Releases

 Understanding “actual” spill characteristics critical for evaluating release significance and F&T modeling  E.g., spill volume, area, location


#  Spill databases maintained by various states (e.g., PA, CO, WV)  Data are difficult to extract (by public) to perform meaningful statistical analysis  If EPA has access, would be useful to characterize the size and frequency of spills associated with HF stimulations

9© 2011 Halliburton. All Rights Reserved. 10 

# Data Collected As Part of Spill Response Measures

States Reporting Requirements Measurement Type CO OH PA WV Nature of spill Volume or flow rate ofspill Chemical analysis/identity/kind of spilled fluid Area and vertical extent of spill Distance to nearest surface water, water wells, groundwater

Unclear, butmay include this information Spillvolume is required for brine spills, but unclear for other spills Required© 2011 Halliburton. All Rights Reserved. 11 11



### Figure from the COGCC website, Weekly & Monthly Oil & Gas Statistics© 2011 Halliburton. All Rights Reserved. 12 12



## Link to more detailed info© 2011 Halliburton. All Rights Reserved. 13© 2011 Halliburton. All Rights Reserved. 14 

# Upward Migration

 Data collected at the time of well installation and stimulation  Could be used to perform screening level analysis to assess migration potential to drinking water aquifers 

#  Modeling of field conditions impracticable  Not aware of any standard models that can simulate transport processes  Data requirements to develop/calibrate a model make this unrealistic 

#  Migration of “stray gas” also common issue  Understanding F&T and modeling a challenge

14© 2011 Halliburton. All Rights Reserved. 15 

# Data Currently Reported During Well Installation 

# and Stimulation States Reporting Requirements Measurement Type CO OH PA WV Depth interval of stratigraphic units Depth interval of freshwater aquifers Depth interval of brines Depth of target formation Casing/wellbore size, type, and depth Electrical, radioactive or other geophysical logging Core/drill cutting analyses/logs Formation water chemical analysis Flowback chemical analysis Type and volume of fluid used to stimulate the well a b

Onlyif collected during the course of business Onlyif requested by the state Onlyif collected during the course of business and requested by the state Required Notes: a) Colorado requires chemical analysis of the injected fluid. b) Pennsylvania requires operators to list the chemicals or additives used.© 2011 Halliburton. All Rights Reserved. 16 16 

### Link to diagram of wellbore Link to reports and permit docs

Casing and cement data© 2011 Halliburton. All Rights Reserved. 17 

### Geologic strata© 2011 Halliburton. All Rights Reserved. 18 

# Induced Fracture Data

18 

### Figure from Fisher, K. 2010.© 2011 Halliburton. All Rights Reserved. 19 

# Induced Fracture Data

19 

### Figure from Fisher, K. 2010.© 2011 Halliburton. All Rights Reserved. 20 

# Stray Gas Migration
 Migration of natural stray methane to drinking water aquifers a common issue – no correlation with fracing  Old improperly abandoned wells are typically the cause  Serve as preferential migration pathway  EPA’s 2004 study found this to be a significant mechanism in investigated case studies 

#  Understanding communication of such wells to stray gas reservoirs and drinking water aquifers is difficult  No standard tests available for measuring such communication  Case-by-case analysis needed 

#  Credible modeling of such scenarios likely not possible  Proper abandonment is the key to the solution© 2011 Halliburton. All Rights Reserved. 21 

# Hydrogeological & Attenuation Processes

 Hydrogeological and attenuation data (e.g., hydraulic gradient, conductivity) typically not collected as part of HF jobs  However, extensive data available in the literature for F&T analyses, especially for surface releases  Attenuation process expected to have a significant influence on HF additives F&T in shales  High organic carbon resulting in high retardation  Biodegradation expected to be significant due to long travel times  Nonetheless, modeling of such processes will be challenging

21© 2011 Halliburton. All Rights Reserved. 22 

# Overall Implications for EPA Study  Key data required for F&T evaluations are available  E.g., spill databases, gas well construction details  Data will provide perspective on relatively low frequency and 

# magnitude of spill incidents, distance to drinking water aquifers  Some gaps exist, but can be addressed by using literature values/ limited data collection 

#  HF fluid composition data and flowback characterization data are also available  Additive information provided by Halliburton and others  Flowback data are being continually generated 

#  EPA should utilize all data and assess human health risks associated with drinking water  EPA study draft places significant emphasis on case studies  Unclear how broad conclusions will be drawn on the basis of a few case studies  EPA should instead conduct a human health risk assessment that utilizes all available information including that from case studies© 2011 Halliburton. All Rights Reserved. 23 

# References

23 Colorado Oil and Gas Conservation Commission (COGCC). "Database and News/Media." Accessed on March 24, 2011 athttp://cogcc.state.co.us/ Fisher, K. 2010. "Data Confirm Safety of Well Fracturing." The American Oil & Gas Reporter, July. Hayes, T. [Gas Technology Institute]. 2009. "Sampling and Analysis of Water Streams Associated with the Development of Marcellus Shale Gas (Final)." Report to Marcellus Shale Coalition. 249p., December 31. New York State Dept. of Environmental Conservation (NYSDEC). 2009. "Supplemental Generic Environmental Impact Statement on the Oil, Gas and Solution Mining Regulatory Program: Well Permit Issuance for Horizontal Drilling and High-Volume Hydraulic Fracturing to Develop the Marcellus Shale and other Low-Permeability Gas Reservoirs (Draft)." Division of Mineral Resources, Bureau of Oil & Gas Regulation, 804p., September. Palmerton Group. 2008-2009. "Flowback Data." Accessed on February 17, 2011 at http://www.palmertongroup.com/services/marcellus-shale-gas/frac-flow-back-water-study.asp. US EPA. 2004. "Evaluation of impacts to underground sources of drinking water by hydraulic fracturing of coalbed methane reservoirs (Final)." Office of Water, June.