GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 141-6
Presentation Time: 2:45 PM


ENGELDER, Terry, Department of Geosciences, The Pennsylvania State University, 334A Deike Building, University Park, PA 16802,

Within a few years (ca. 1865) after Drake first produced oil, operators recognized that paraffin deposits clogged wells and limited the natural flow of oil. The solution was fracturing rock around the borehole with nitroglycerine, a process called torpedoing. When the natural flow of oil fields of Pennsylvania started declining, (ca. 1880) water flooding seemed like a possible mechanism for reestablishing production but it was not widely accepted until state law allowed the practice in 1921. For the next three decades, a five-spot was the configuration for a water flood with an injection well surrounded by four producing wells spaced evenly at 90°. This configuration produced a circular sweep that was less efficient than a line sweep, a line of injection wells pushing oil toward a line of producing wells. Here the challenge was to establish communication between lines of wells. Hydraulic fracturing was the answer. The idea was that if fractures ran between injection wells, a perfect line sweep from the plane of the fracture was possible. Two questions faced petroleum engineers as they designed water floods in the 1950s. First, what was the dip of hydraulic fractures in the Appalachian Basin: vertical or horizontal? Horizontal fractures were not going to help water floods. Second, if hydraulic fractures proved to be vertical, what was their strike? Originally, water floods ran from an E-W N-S grid with injection and producer wells aligned E-W. If hydraulic fractures ran in a direction other than E-W, fractures from injectors could hit producer wells, thus short-circuiting the water flood by bypassing plenty of oil in place. One of great discoveries in the Appalachian Basin was that hydraulic fractures ran to the ENE and WSW. Engineers responded to this discovery by aligning injection and producing wells in the ENE-WSW orientation. This same discovery dictates the orientation of laterals within unconventional reservoirs of the Appalachian Basin today.