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AAPG Southwest Section Annual Convention

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Sequence Stratigraphic Interpretations in Support of Drilling and Resource Characterizatoin: A Spraberry Example

Abstract

The Leonardian-age Spraberry Formation of the Midland basin, west Texas, is a historically-significant oil producing interval, having produced more than a billion barrels oil since its discovery in 1943. The tight oil-bearing siltstones within the Spraberry have been the primary target since 1950, and present-day horizontal drilling and completions activity targets both tight siltstones and interbedded organic rich mudstones. This current activity is ongoing and commensurate with the underlying Wolfcamp unconventional field development. The historical and ongoing Spraberry development has generated borehole conditions that can potentially impact deeper drilling and infill targeting operations. Understanding the intra-formational pressure regime and lithologic controls of the formation is key in establishing target specific drilling practices. The Spraberry has been studied extensively over the decades, and a genetic stratigraphic framework has generally been established with focus primarily on defining the cyclicity of conventional slope carbonate and basinal siliclastic reservoirs. Utilizing Pioneer’s basin-wide seismic and well log-based sequence stratigraphic framework, a better understanding of the distribution of organic rich mudrock and tight siltstones within the Spraberry has led to identification of key surfaces that tie to notable geomechanical contrasts and related pore pressure variations. A transgressive- regressive, sequence-based interpretation sheds light on why certain composite sequences should be considered in refined pore pressure models. Data-grounded pressure models help to improve drilling efficiencies in the horizontal well program targeting deeper Wolfcamp intervals.