Reexamining the Fresh-Saline Water Interface in the Area of the Devonian Berea Oil Play, Northeastern Kentucky

Abstract

Since 2011, approximately 50 horizontal wells associated with the Devonian Berea Sandstone oil play were drilled and completed in eastern Kentucky. In some areas, drilling and hydraulic fracturing occur within 1,500 feet of the surface. The amount of fluid (thousands of barrels) and sand (10,000 to more than 100,000 pounds) used to treat each well are small compared to other North American unconventional plays (e.g. Marcellus). Nevertheless, the shallow depths of oil exploitation underscore the importance of an effective casing program to protect groundwater quality. The “Fresh-Saline Water Interface Map of Kentucky” by H.T. Hopkins (published by the Kentucky Geological Survey in 1966) is an important guidance document used by operators and the Kentucky Division of Oil and Gas to make decisions about surface casing depth. Hopkins defined water with less than 1,000 ppm total dissolved solids as fresh water. The fresh-saline interface was then defined using the total depth of domestic wells having fresh water. Most domestic water wells, however, do not penetrate the deepest freshwater aquifers in the subsurface. Consequently, the Hopkins map likely underestimates the depth of the fresh-saline water interface in most areas. A corollary to this underestimate is that the thickness of the confining interval between the oil reservoir and fresh water is overestimated.

To make a more robust and accurate interpretation of the fresh-saline water interface, the Hopkins map is being updated using new groundwater data and observations of fresh and salt water in oil and gas wells. Early results have increased the number of data points by a factor of four or more. Moreover, the depth to the fresh-saline water interface has potentially increased by hundreds of feet in some areas. We recognize, however, that the updated analysis and map remain an estimate limited by data quality and the geologic complexity of aquifers. Nevertheless, an updated fresh-saline water interface map will provide a more accurate framework for deciding casing depth and analyzing groundwater quality in the context of energy resource development.

AAPG Datapages/Search and Discovery Article #90218 © 2015 Eastern Section Meeting, Indianapolis, Indiana, September 20-22, 2015