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Updated USGS Resource Assessment of the Spraberry Formation, Midland Basin, Texas


The Leonardian (Lower Permian) Spraberry Formation within the Midland Basin of western Texas has been a significant oil producer since the early 1950s. The Spraberry Trend is ranked as the second largest U.S. oil field based on estimated proved reserves by the U.S. Energy Information Administration (EIA). The Spraberry Formation consists of interbedded, deep-marine sandstones, siltstones, and organic-rich shales, in addition to detrital limestones sourced from the basin margins. The first vertical Spraberry well was drilled in the late 1940s, and despite initial low recovery rates, over 48,900 vertical Spraberry wells have been drilled within the Midland Basin to date. Many of these wells have commingled production with the underlying Wolfcamp shale and are considered part of the Wolfberry play. The Spraberry Formation was previously assessed by the U.S. Geological Survey (USGS) in 2007 for undiscovered, technically recoverable petroleum resources based on two assessment units (AUs): (1) Spraberry Conventional Sandstones AU, and (2) Spraberry Continuous Oil AU. The assessment of each AU was based on vertical well drilling development and resulted in an estimated combined mean total resource of 530 million barrels of oil. More recently, operators within the Midland Basin have been focusing on horizontal development of the organic-rich shale intervals of the lower and middle Spraberry. In addition, some operators are targeting the silt-rich Jo-Mill interval, which occurs within the upper section of the lower part of the Spraberry. Within the past year, horizontal drilling has begun to eclipse vertical development of the Spraberry Formation based on wells drilled per year. As of mid-2016, more than 2,600 horizontal wells have been drilled into the Spraberry, with many of these wells targeting the organic-rich shale of the lower part of the Spraberry. An updated USGS assessment of the Spraberry Formation will focus on the recent transition to horizontal drilling and assess undiscovered, technically recoverable continuous oil resources of the lower and middle intervals of the Spraberry Formation.