Figure 4. Arbitrary 3-D seismic line showing the Paleozoic section in and around Reinecke field. Note the lack of structural deformation. Selected formation tops are shown. Middle Pennsylvanian (Strawn Formation/Desmoinesian Stage), upper Pennsylvanian (Canyon Formation/Missourian Stage and Cisco Formation/Virgilian Stage), and lowest Wolfcampian (Lower Permian) shallow-marine carbonates started accumulating over a relatively flat surface. Basinal shales and carbonates of Wolfcampian age overlie the irregular upper surface of the reservoir carbonate. The Sprayberry includes basinal sand, silt, and carbonate of Leonardian age. The San Andres shelf margin prograded from east to west (right to left) across the area. The top San Andres is early Guadalupian. The Yates is late Guadalupian in age and is a shelf-interior equivalent to the middle Capitan reef. See Figure 3 for location of seismic line. TWT = two-way traveltime.