Pennsylvanian carbonate buildups, paradox basin: Increasing reserves in heterogeneous, shallow-shelf reservoirs

Productive carbonate buildups of Pennsylvanian age in the southern Paradox basin, Utah, contain up to 200 million bbl remaining oil potentially recove rable by enhanced recovery methods. These buildups comprise over 100 satell ite fields to the giant Greater Aneth field, where secondary recovery opera tions thus far have been concentrated. Several types of satellite buildups exist and produce oil from the Desert Creek zone of the Paradox Formation. Many of the relevant fields have undergone early abandonment; wells in Dese rt Creek carbonate mounds commonly produce at very high initial rates (>100 0 bbl/day) and then suffer precipitous declines, An important new study foc used on the detailed characterization of five separate reservoirs has resul ted in significant information relevant to their future redevelopment. Comp leted assessment of Anasazi field suggests that phylloid algal mounds, the major productive buildup type in this area, consist of ten separate lithoty pes and can be described in terms of a two-level reservoir system with an u nderlying high-permeability mound-core interval overlain by a lower permeab ility but volumetrically larger supramound (mound capping) interval, Reserv oir simulations and related performance predictions indicate that CO2 flood ing of these reservoirs should have considerable success in recovering rema ining oil reserves.