DEPOSITIONAL ENVIRONMENT AND PETROLEUM PRODUCTION, UL-SERIES SANDS, POINTE A LA HACHE AND DIAMOND FIELDS, PLAQUEMINES PARISH, LOUISIANA

Point a la Hache and Diamond fields, Plaquemines Parish, Louisiana, produce oil and gas from the Miocene trend along the northern edge of the Gulf of Mexico basin. The fields have a combined production of 177 BCF of gas and 49 MMBBL of oil since the discovery wells were drilled in 1948 and 1958, respectively. The reservoirs in the fields are sands in the late Middle Miocene UL series, named for the inner neritic foram Uvigerina lirettensis. Thirteen of the fourteen sands in the UL series are productive in the two fields. The sands were deposited as part of prograding delta complex near the Miocene shelf edge. The deltas resembled the modern Mississippi Delat because the sediment delivery systems and sediment dispersal systems in the Miocene were similar to those that exist today. Isopach and electrofacies distribution maps of the sands resemble those of the mouth-bar deposits of the modern Balize Delta. The reservoirs produce from proximal and distal mouth-bar deposits and from axial and marginal locations. Neither reservoir potential nor reservoir quality vary with position on the mouth bar. The hydrocarbons accumulated in both fault-related structural traps and combined structural-stratigraphic traps. The sands do not thicken across the faults, so faulting post-dated deposition of the sands. No purely stratigraphic traps were identified. Untested fault closures provide additional development opportunities in the field. Seismic data will provide the best means of recognizing these traps.