Updating the Fresh-Saline Water Interface Map in Eastern Kentucky

Jerrad Grider, Ethan Davis, and Marty Parris with contributions from Bart Davidson,

Junfeng Zhu, and Charles Taylor

Kentucky Geological SurveyAnnual Meeting

Lexington, KYMay 15, 2015

• Active oil play in Devonian Berea Sandstone in eastern Kentucky (Elliott, Carter, Greenup, Lawrence, and Boyd Counties)

• Play developed using horizontal drilling (approximately 50 wells completed so far) and hydraulic fracturing at relatively shallow depth (most less than 2,000 ft)

• Though volume of fluid used in hydraulic fracturing Berea reservoir is small compared to other unconventional plays, shallow depth necessitates prudence in development of resource

Motivation

• Surface casing intended to protect groundwater during oil and gas drilling

• Depth of surface casing often based on map from Hopkins (1966) of the fresh-saline water interface

Surface Casing

http://www.rigzone.com/training/insight.asp?insight_id=333&c_id=24

• Interface defined using TDS values less and greater than 1,000 ppm to define fresh and saline water, respectively

• Used data from domestic water wells

Hopkins Fresh-Saline Water Interface Map

StudyArea

Parameters Documented by Hopkins

•Total dissolved solids (ppm)

•Chloride concentration (ppm)

•Well depth below land surface (ft)

•Well depth reference to sea level (ft)

•Assumed altitude bottom of well (feet reference to sea level) equals base of fresh water

Hopkins Map in Study Area

• Based on data from 28 wells

• Significant amount of interpolation

• Considered influence of topography on base of freshwater

• Elevation ranges from 820 to 433 ft

Hopkins’ Interface Defined

• Fresh-saline water interface (red) equals:Surface elevation (black) – well depth from surface (yellow)

• Observed > True fresh saline water interface (reference to sea level)• Hopkins’ map likely underestimates depth to true fresh-saline water interface in

many, if not most, areas• Financial and technical reasons not to drill to deeper aquifer• Aquifers discontinuous especially for Pennsylvanian sandstone

Aquifer 2

Aquifer 1

Ground surface

Aquifer 3

Sea Level

Well #1

Well #2

Saline water

True fresh-saline water

Observed fresh-saline water

Reanalysis and DeepestObserved Freshwater

• Additional data including post-1966 domestic wells (dark blue) could potentially deepen “fresh-saline water interface”

• Even w/ new data, interface will likely be underestimated—hence the term “Deepest Observed Freshwater”

Ground surface

Sea LevelSaline water

True fresh-saline water

Observed fresh-saline water

Methods

• Query Kentucky Groundwater Data Repository to extract data for wells with total depth 1,000 ft or less below ground surface

• Selected wells reporting chloride values at or below 500 mg/l AND wells completed as domestic water wells

28 Hopkins Wells120 New Wells

Deepest Observed

Freshwater

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0Little Sandy River

Drainage

Confining Interval

Thickness

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Thickness of Mississippian-Pennsylvanian strata from deepest observed freshwaterto top of Berea Sandstone

Oil and Gas Observations—A Path to Less Wrongness?

• Oil and gas wells (green) routinely penetrate depths over which fresh and salt water are found

• From about mid-1970s observations on depth of fresh and salt water recorded in oil wells (green)

• But how good are the observations?

Sea LevelSaline water

True fresh-saline water

Observed fresh-saline water

Aquifer

Aquifer

Oil and Gas Observations—Varied Quality

Salinity determination during drilling

Conductivity meter (few measurements?, quantitative)

Salinity strips

Taste test (many measurements, qualitative)

Example—Lawrence Co.

• In each 5’ carter cell, compiled freshwater depths/elevations recorded in oil and gas wells in odd-numbered 1’ carter cells

• Summarized data from each north-south row of 5’ grids; i.e., 79, 80, 81, 82, 83, and 84

Map courtesy of Tom Sparks.

O&G Deepest Freshwater (edited)—Does It Pass the Taste Test?

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DO

F (f

t, s

ea

leve

l)

Elevation (ft, sea level)

Carter_78

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5 MIN. CARTER COLUMN

StdDev Avg Median Max Min

West East

1515 12

39

21

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O&G Deepest Observed Freshwater

Hopkins

GWDB

O&G

Summary• “New” data from KGS groundwater database improved

robustness of “fresh-saline water interface” (deepest observed freshwater) map by ~4X in study area

• “New” data and derivative maps likely still underestimate true fresh-saline water interface depth

• Corollary is confining interval thickness between deepest observed freshwater and top of Berea Ss. is overestimated

• Oil and gas records might provide opportunity to significantly increase accuracy of fresh-saline water interface

• Though not shown, work with B. Davidson and J. Zhu will extend revision of fresh-saline interface statewide

• Challenge merging depths in areas based on oil and gas observations versus groundwater database

Acknowledgements and References

• John Hickman, Kentucky Geological Survey

• Fresh-Saline Water Interface Map of Kentucky (1966) by H.T. Hopkins:

http://kgs.uky.edu/kgsweb/olops/pub/usgs/saline.pdf

• Kentucky Geologic Survey Groundwater Database

http://kgs.uky.edu/kgsweb/DataSearching/watersearch.asp