# THE HYDRAULIC FRACTURING PROCESS (HF): REAL CONCERN or MISDIRECTED FOCUS CONCERNING THREATS TO DRINKING WATER SUPPLIES (DWS)

Introduction

This author’s literature review, attendance at various hydraulic fracturing (HF) symposiums, forums, conferences, an EPA spon sor ed HF workshop on Fate & Transport and discussions with oil and gas regulatory agencies and industry representatives suggest the re is a growing, if not already strong consensus among those who have performed objective analyses of the HF process, that the risk posed to potable aquifers or drinking water supplies (DWS) from the deep underground process of HF is now miniscule. Assessments of potential impacts range from “remote” (DOE 90 Day Report) to “do not present a reasonably for ese eable risk of significant adverse environmental impacts” (NYS SGEIS). Furthermore, multiple lines of evidence including theory based on the physics of fluid flow, fate and transport modeling and empirical evidence from hundred s o f thousands of frac jobs performed by industry in the last 60+ years without documented impacts to DWS, indicate that further pu blic focus on this concern is misdirected and simply unwarranted. It is often a challenge for experts to communicate complex concepts to the public to allay fears and concerns. Terms such as imbibition, irreducible water saturatio n, and capillary pressure effects and their underlying conceptual basis while critical to a technical understanding of why 70% t o 9 0% of frac fluids remain unrecovered in flow back, also make it difficult to convey to the public why these residual frac fluids are highly unlikely to subsequently appear in a DWS. Residual frac chemicals are most likely locked in rock pore s o f the target shale with no means of escape for periods possibly on a scale approaching that of geologic time. The public rar ely differentiates between direct impacts by methane gas to DWS, and their contamination with other constituents from other mechanisms or processes. Direct impacts by methane gas to DWS have occurred, and documented pathways for this type of con tamination do exist related to gas well construction, when an uncemented annulus becomes over pressured. However, in most in sta nces methane occurrence in DWS is still attributable to sources unrelated to gas development. When methane impacts from gas development do occur, they are most typically related to non

- routine overpressuring “events” durin g drilling, cementing or casing operations unrelated to the hydraulic fracturing process itself. Some well design practices can facilitate stray gas migration when site

- specific geologic conditions, as depicted here, are not fully understood. Specifically, should shallow fractured bedrock extend below surface (two

- string design) or intermediate (3

- string design) casing depths, higher risks for gas migration may be present.

This poster illustrates two pathways for stray gas migration that may occur independently of each other, or operate in conjun cti on, to facilitate gas migration to a DWS when a 3

- string casing design with open annulus becomes overpressured. From a relative threat standpoint, a change in focus from potential hydraulic fracking fluid impacts to DWS, to the real threat of stray gas migration, is long overdue. While public concerns about HF fluid impacts to DWS have brought about better regulati on and many operational improvements by industry, including frac chemistry disclosures (e.g. fracfocus.org), use of less/non

- toxic (green) chemical substitutes and greater transparency of overall operations, few significant additional environmental gains in this area are likely to occur that further reduce risk in any appreciable manner from its already low sta te. Further, opponent arguments and concerns regarding impact to DWS from the hydraulic fracturing process appear increasing ly without technical merit. In contrast to frac fluids largely sequestered in the target formation, methane gas from

non

- target gas bearing zones is abundant and concentrated, can be highly mobile and migrate as a free phase in addition to disso lved phase, has a pathway that permits several thousand feet of cross

- strata migration (open annulus above production casing cem ent) and a drive mechanism (buoyancy). Furthermore, methane from a deeper source (normal to over pressured gas bearing geologic unit) often leads to over pressuring of casing and annular intervals at shallow depths (i.e. e xce ed hydrostatic conditions). Overpressuring is undesirable and mitigation/remediation can be problematic and costly or result in continuous venting of this potent GHG over a long period (e.g. life of well). Gas build up (overpressuring) of the annulus can also create the required gradient for stray gas to penetrate fractured bedrock through the open borehole wall and mo ve upward and around surface/intermediate casing strings of good integrity to reach a DWS. Earlier overpressure events (e.g. ga s kicks) during the drilling and completion phase may also facilitate subsequent movement through shallow fractures from annular overpressuring by establishing a continuous gas phase in the fracture system.



# Conclusions

Relative to HF fluids used in fracing target gas shales, stray gas from non

- targeted (noncommercial) gas bearing zones found abo ve targeted gas is far more abundant, concentrated and mobile with much greater upward migration potential from the deep subsurface due to the buoyancy drive mecha nis m within an open borehole annulus. A several thousand foot potential cross

- strata migration pathway exists to DWS via the open borehole (open annular space between top of pr oduction casing cement and cemented surface or intermediate casing string/shoe) under most current well designs accepted by states and the BLM. Should an overpressured a nnu lus develop from these gas sources and an open fractured/jointed condition characterize shallow bedrock that extends below surface or intermediate casing depths, this gas migration pathway to DWS is potentially complete. With the advent of unconventional shale resource plays, their expansive coverage, increased well densities and intermingling wit h rural domestic wells, greater risk over the long
term exists from non

- routine annular overpressuring events or when wells are not vented. Mitigation of annular space methane gas build up through venting is less of an option than in the past due to concerns for GHG emissions as this methane source is poorly quantified. The complexity of the stray gas migration issue suggests further research into its component parts is warranted for a better understanding of best management practices. These include 1) Quantification of the nature of the problem or approximate amount of stray gas currently vented by the gas industry, possibly through a random/probabilistic sampling design 2) Source Identification & Isolation

– methods of source (strata) identification (borehole logging options), zonal isolation, conditions fostering or limiting flow/bleed

- off to well bore/annulus 3) Annular Environment

– effects of fluids present (water, mud, brine, gas), gas transport phase (free phase gas vs. dissolved), slough/cave (borehole bridging effects) and the ir effect on gas flow from the source to the borehole and outward to country rock from overpressuring 4) Overpressure Conditions

– gas phase and entry pressure requirements for rock matrix vs. fracture (pore & aperture minimums), wetting phase of matrix/fracture faces, residual effects from non

- routine overpressure “events” that would facilitate gas connectedness in fractures and subsequent stray gas migration 5) Monitoring

– casing annular pressures correlation with annular fluid levels, freshwater zone heterogeneity (stratification) and appropriat e freshwater intervals or aquifer horizons for early detection of methane migration to DWS. There are many trade

- offs in selecting management strategies and well designs to minimize stray gas. Further analysis of the components is warranted to better assess cost

- benefit relationships and to ensure that GHG emissio ns and potential impacts to DWS are minimized. References

Bureau of Land Management, 1988. Onshore Order #2, 43 CFR 3160 Federal Register/Vol. 53, No. 223

Colorado Oil and Gas Conservation Commission, 2011. East Mamm Creek Project Drilling and Cementing Study, performed by Cresc ent Consulting, LLC, Reed Energy Consulting, LLC, and Roge, LLC (COGCC website, http://cogcc.state.co.us/.)

Engelder, T. , 2011. The Distribution of Natural Fractures above a Gas Shale: Questions about Whether Deep Fracture Fluid Le aks into Groundwater Outside the Realm of Faulty Borehole Construction , EPA Hydraulic Fracturing Workshop on Well Design and Co ns truction (Extended Abstract)

Harrison, S. S., 1985. Contamination of Aquifers by Overpressuring the Annulus of Oil and Gas Wells Groundwater, Vol. 23, N o. 3, 1985

Komex International LTD, 2002. Evaluation of Potential Groundwater Contamination Due to Surface Casing Vent Flow/Gas Migrati on, Prepared for CAPP Surface Casing Vent Flow Subcommittee

New York State Department of Environmental Conservation, 2011. Revised Draft Supplemental Generic Environmental Impact Stat eme nt on the Oil, Gas and Solution Mining Regulatory Program, prepared by NYSDEC with Assistance from Alpha Environmental Inc., Ec ology and Environment Engineering P.C., ICF

International, URS Corp, NTC Consultants and Sammons/Dutton LLC.

Osborn, S. G., Vengosh, A., Warner, N. R. and Jackson , R. B., 2011, Methane Contamination of Drinking Water Accompanying Ga s

- w ell Drilling and Hydraulic Fracturing, Proceedings of the National Academy of Science, 108 (20) 8172

– 8176

Pennsylvania Department of Environmental Protection, 2011. Office of Oil and Gas Management (http://www.dep.state.pa.us/dep/ dep utate/minres/oilgas/oilgas.htm)

Thyne, G. 2008. Review of Phase II Hydrogeologic Study, Prepared for Garfield County Colorado.

U. S. Department of Energy, 2011. Shale Gas Production Subcommittee 90

– Day Report by the Secretary of Energy Advisory Board

U. S. Environmental Protection Agency, 1996. Methane Emissions from the Natural Gas Industry, v. 9; Vented and Combustion S our ce Summary, Prepared for Energy Information Administration (U. S. DOE), Prepared by National Risk Management Research Laborat ory , Research Triangle Park, NC.

Watson, R. W. 2010. Report of Cabot Oil & Gas Corporation’s Utilization of Effective Techniques for Protecting Fresh Water Z one s/Horizons During Natural Gas Drilling

– Completion and Plugging Activities, Prepared for the Pennsylvania Department of Environ mental Protection

Wojtanowicz A. K., Nishikawa, S., and Rong X., LSU 2001. Diagnosis and Remediation of Sustained Casing Pressure in Wells, U. S. DOI Report 

## NRSS Directorate
National Park Service U.S. Department of the Interior

Pete Penoyer Hydrogeologist Natural Resource Stewardship & Science Pete_Penoyer@nps.gov Acknowledgements: PA DEP Staff for their availability , consultation and review to ensure illustrations are as accurate as possible I also wish to thank the following NPS Staff for their assistance with this poster presentation Paula Cutillo , WRD Hydrogeologist

- Graphics Design & Presentation 400 foot depth 

## Below Illustrations Modified From PA DEP and Shell Oil

Closed BH Valve Shallow Fracturing & High Angle Reverse Fault Penetrated by Borehole



### Evidence that stray gas, its monitoring and its proper management is a concern in PA DEP 

## Key Questions:

1. How accurate are these subsurface representations of stray gas migration, relative

to frac fluids, and what are the reasonable pathways (shown or not shown)?

2. When an annulus becomes overpressured, can significant amounts of methane gas (enough to impact DWS) penetrate the borehole wall in the dissolved phase or only in the free gas phase (i.e. this requires sufficient overpressuring to drive the water level in the annulus below the intermediate casing seat or further downward than in the case above, so that free gas is opposite the borehole wall)?

3. If venting is the preferred management solution to prevent borehole annuli from overpressuring, what quantity of methane is being released to the atmosphere by this standard practice?

4. Given that frac fluids have not been documented to impact DWS (few pathways exist), while methane related to stray gas migration has been implicated in several cases (due to a documented drive mechanism and a pathway), where are limited resources better spent? 1 NOTES :

1. 200’ for TOC in Figure 1A applies to minimum height above top of perforations in vertical or slant wells only (PA DEP).

2. Positive bradenhead gauge pressure not to exceed 80% x hydrostatic pressure at depth of surface casing shoe per PA DEP (.80 x 0.433 psi/ft. x 500 = 173 psi in this example Figure 1B.)

3. Base of fresh/useable water (1000 mg/L, NYDEC; 3000 mg/L, some other states; 10,000 mg/L some other states, EPA and BLM (Onshore Order #2)

4. Neither figure depicts slower gas migration through cement that can sometimes occur. These

are referred to as mechanical discontinuities that create annular conductivity. They include micro

annular flow (between cement sheath and casing or borehole wall) or matrix permeability/channeling when a slug of gas enters the cement and migrates upward before the cement sets. This is most common in the GOM where shallow overpressured gas zones that lie opposite cemented casing strings can lead to sustained (annular) casing pressures (SCM). That stray gas may also require venting. 

### Figure 1A

. Figure 1B

.

3

Potential For Non

- Targeted

Gas Sand Show Intervals in Open Annular Intervals

Below Freshwater Zones and

Surface and Intermediate Casing String Intervals

Marcellus Well Logs Illustra

ting Non

- Target Shallow Gas

Zones. Conditions similar to Figure on Left w/Surface Casing set to 450 feet below FW, Inter

mediate Casing set to 1000 feet, TOC for Production Casing at

5500 feet 400 foot depth 3

3

Disclaimer: This poster is of an interpretive nature and reflects the author’s assimilation of the published work of many researchers and information from discussions with regulatory agency staff. Its purpose is to foster informed discussion of the potential impacts from stray gas migration to drinking water supplies in the context of unconventional resource plays.