Presentation Identifier (Title or Location), Month 00, 2008 

## Design and Rationale for a Field

Experiment using Tracers in Hydraulic Fracture Fluid Daniel J. Soeder, NETL Morgantown, WV USEPA Technical Workshop, March 10 - 11, 2011 Well Construction and Operations2 

### Marcellus Shale in Hanson Quarry, NY Oatka Creek Member Cherry Valley LS Union Springs Member3 

# Appalachian Basin Stratigraphy4 

# Hydraulic Fracturing • Hydraulic fracturing is used to create high - permeability pathways into a formation. • Hydraulic fractures are made by filling the well with fluid and then increasing the pressure until the rock strength is exceeded. • Fluid and proppant are pumped out into the fractures; the proppant stays behind and keeps the fractures open after pressure is released.5 

# Potential for Aquifer Contamination
• Does the frac fluid get into shallow, freshwater aquifers (USDW) when under pressure creating the fractures? • Unlikely because of:

– Low hydraulic conductivity

– Flow gradients wro ng direction



### – Depth of target formation

– Long groundwater travel times • What if there are flow conduits to the surface like faults or abandoned wells? • No definitive evidence of direct water contamination from deep hydraulic fracturing has been documented, but a tracer test would help provide rigorous data.6 

# Formation Water Chemistry • Fluid recovered from the well after the frac is called flowback.

– Mix of frac water and formation water – how much of each?

– Starts fresh, then turns very salty with high TDS and odd chemistry

– Only about 1/4 - 1/3 of the injected fluid is recovered as flowback 

### • What happens to the frac fluid that remains downhole?

– Pools in the bottom of fractures?

– Evaporates and is transported out with the gas?

– All of the above?

– None of the above? 

### • Source of the TDS, and links between brine chemistry and bulk rock geochemistry of shale are not well understood. • Relationship of Marcellus water chemistry to other waters in the basin (i.e. Oriskany) is not well understood either.7 

# What is a Tracer? • Tracers are elements, compounds, or isotopes that can be used 

### to delineate groundwater flow paths and estimate time-of-travel (USGS). • Environmental tracers: anthropogenic compounds that entered into the hydrologic cycle at a known time and concentration

– CFCs, sulfur hexafluoride (SF 6

### ) from atmosphere

– Tritium/helium - 3, chlorine - 36, other radionuclides from above ground weapons testing in the 1950’s (spikes) • Introduced tracers: dyes, chemicals, or isotopes added for a test

– Conservative tracers travel with the plume; non - conservative tracers may diffuse or disperse out ahead of it.

– An ideal tracer is easily detectable, obvious, moves with the water flow, does not chemically react with passing substrates, and does not alter the properties of the water.8 

# Proposed Hydraulic Fracture Tracer Test • Collect baseline data on site groundwater, structure and geology. • Drill parallel laterals at site and prepare for frac. • Add a conservative tracer in the frac fluid mix; place instruments on -site • Hydraulically fracture the wells in the normal manner. • Monitor frac physics and sample groundwater for tracer. • Drill a vertical well to the Oriskany some time after frac. • Sample formation water all the way down to and including the Oriskany Sandstone. • Run lab analyses of groundwater and formation water to determine fate of frac fluid from detection of tracer. • Government control of design, sampling, analysis and data, with other selected participants (industry, university, etc.) following same QA. • Security is required to protect sample sites and data integrity (more QA). • Status: site and alternate sites identified, driller agreeable but service company not approached, interagency collaborators identified (USGS, EPA) • Sites: NETL- Morgantown, locations near Waynesburg, PA, possible central WV locations.910 DOE NETL Site, Morgantown, WV11 

# EGSP WV-6 Well and Core (MERC#1)1213 

# Site Issues • NETL: Management has not confirmed support; not sure 

## how facilities/safety people will react, may be difficulties with pipeline capacity to take gas. • NETL: One landowner has control of land, site is secured with fence and guards, oriented properly, old Marcellus well for stratigraphic control.
• Waynesburg: Multiple landowners, may be denied 

## access, unsecured sites near interstate highway, schedule moving rapidly. • Waynesburg: more timely, leases and permits in place and gas lines in area, existing water wells, multiple landowners might be a good thing for options.14 

# Cost (Guess)timates
• Drill the vertical wells to kickoff, drill the laterals, case, perf, zipper frac , complete: ~$4 million; industry cooperator will cover these costs in return for the gas. • Install groundwater monitoring wells and surface or downhole geophysical instrumentation: $300K • Construct a vertical well from surface to Oriskany Sandstone, including ~100 ft of Marcellus core: $800K • Interagency funds for selecting tracer, monitoring frac, collecting samples: $250K • EPA, USGS laboratory analysis of water samples: $300K • Analysis of other data (geophysics, soil gas, etc.): $250K • Assessing results and writing/publishing report: $100K • Total estimated government cost for one field experiment: $2 mill15 

# DOE Marcellus Tracer Test Goals Assess environmental impacts to aquifers. Address scientific issues related to hydrology and geochemistry Outcomes Rigorous study with well - documented data, solid QA pedigree, no question about data integrity. Applications Provide public information to help regulators, and create a more informed environmental debate. Benefits Improve understanding of hydraulic fracture injection and downhole movement. Document formation water chemistry and links to Marcellus brine.