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Reservoir characterization, depositional system, & diagenesis of the Atokan Grant Sand, Fort Worth Basin, Texas


The Atokan Grant Sands are a tight gas sand play that would add new reserves to the Fort Worth Basin. The Fort Worth Basin is located in north-central Texas just west of Dallas, Texas. Within the basin, the study area consists of Denton, Wise, Tarrant, and Parker Counties in Texas. The basin is bounded to the north by the Red River Arch, to the west by the Bend Arch, to the south by the Llano uplift, to the east by the Ouachita structural front, and to the northeast by the Muenster Arch. The Grant Sands are approximately 1,500 feet stratigraphically above their source, the Barnett Shale, and were discovered and mapped from early Barnett vertical drilling. This play evolved from a vertical to a horizontal drilling program with Grant wells being drilled alongside Barnett wells. The sands are divided into “upper” and “lower” units with a shale unit between the two. The purpose of this study is to determine the key performance drivers of both the “upper” and “lower” Grant Sands to improve the geologic understanding for enhanced exploration potential. It is a consensus by previous investigations that the Grant is comprised of shallow marine sands from fluvial to deltaic deposition. Although the broad depositional environment is generally agreed upon, the source of sediment is an issue of disagreement in previous works. This study analyzes core data and regional subsurface mapping to determine an interpretation for the depositional environment and diagenesis of the Grant Sand interval.