Modeling versus The 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 of spill

Chemical analysis/identity/kind of spilled fluid

Area and vertical extent of spill

Distance to nearest surface water, water wells, groundwater

Unclear, but may include this information

Spill volume is required for brine spills, but unclear for other spills

Required
© 2011 Halliburton. All Rights Reserved. Figure from the COGCC website, Weekly & Monthly Oil & Gas Statistics 11 11
© 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

Only if collected during the course of business

Only if requested by the state

Only if 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 

Figure from Fisher, K. 2010. 18
© 2011 Halliburton. All Rights Reserved. 19

Induced Fracture Data 

Figure from Fisher, K. 2010. 19
© 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 

at http://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.