New field discoveries using 3-D seismic in mature, deeper Paleozoic trends beneath Permian Hugoton gas field, Southwest Kansas

Gas production at rates of one to 3.5 MMCFD is being developed from Pennsylvanian Morrow fluvial sandstones in southwest Kansas in a paleovalley formed by downwarping and fluvial incision in earliest Morrow time. Three-D seismic data have helped to locate successful wells in the valley in proximity to older dry holes which encountered porous, non-productive fluvial sandstones. Although the 20-foot-thick fluvial sandstones are too thin to be resolved seismically, the overall valley can be delineated with 3-D isopach mapping. Drilling success has been 100 percent in penetrating the valley and 50 percent in finding productive sandstones. A second key element to success is the 3-D structural picture obtained within the valley. Some difficulties in 3-D structural mapping do occur because the closest reflective horizon to basal Morrow sandstones is the Meramecian Ste. Genvevieve limestone, and intervening Chester-age rocks vary in thickness from 10 to 70 feet depending on depth of basal-valley incision. Additional complications arise from encountering sandstones at various stratigraphic positions within the valley associated with different episodes of valley incision. Two dry holes have revealed a deep, young, incised valley with a thick fill of shaley estuarine sediments. Recognition that this trough of estuarine fill is a significantmore » component of the trap for gas in older stratigraphically higher, fluvial sandstones has led to increased success.« less