Reservoir analysis and depositional systems of the Upper Cretaceous Woodbine Group in the Mexia Fault Trend of the East Texas Basin : Mexia Oil Field

The Mexia oil field, discovered in 1920, has produced 110 million barrels of oil from Upper Cretaceous sandstone reservoirs of the Woodbine Group in Limestone County, Texas. The producing Woodbine Group is primarily composed of siliciclastic sandstones, siltstones and mudstones that have been divided by flooding surfaces into nine depositional cycles. Most of these depositional cycles are fluvial-dominated deltaic in origin, with others of wave-modified deltaic origin. The depositional cycles are important in defining reservoir heterogeneities in the Mexia Fault Trend oil fields. The Woodbine sandstones are highly effective water-drive reservoirs. However, historical field development methods, such as high-volume flow rates, were ineffective at maximizing the fields’ recovery. This study is the first to recognize and map individual Woodbine depositional cycles in the Mexia Fault Trend to explore how to maximize future oil recovery efforts. This study also researched the historical development of the Mexia field cooperatively with new digital production data sources. Combining historical production data with new mapping of the depositional cycles and their net sandstones reservoir units uncovered significant bypassed oil resources. Undrilled infill locations were identified, then analog production for each reservoir unit was scaled to a field-wide redevelopment drilling program. In the Mexia field, this study indicates an estimated 51 million barrels of oil remains to be produced. This analog study can be utilized to assess other Mexia Fault Trend fields. The fault line fields contain approximately 559 million barrels of original oil in place. A similar study on each individual oil field could lead to the recovery of over 66 million additional barrels of oil.Geological Science