AAPG Bulletin, V. 83 (1999), No. 2 (February 1999), P. 193-210.

Pennsylvanian Carbonate Buildups, Paradox Basin: Increasing Reserves in Heterogeneous, Shallow-Shelf Reservoirs

Scott L. Montgomery,¹ Thomas C. Chidsey, Jr.,² David E. Eby,³ Douglas M. Lorenz,⁴ and W. E. Culham⁵

©Copyright 1999.  The American Association of Petroleum Geologists.  All Rights Reserved
 

¹Petroleum Consultant, 1511 18th Avenue East, Seattle, Washington 98112; e-mail: [email protected]
²Utah Geological Survey, Salt Lake City, Utah 84114.
³Eby Petrography & Consulting, Inc., 1780 E. Geddes Circle South, Littleton, Colorado 80122-1431.
⁴Texaco, E&P Technology Department, Houston, Texas 77042.
⁵Rega Inc., 5847 San Felipe, Suite 2030, Houston, Texas 77057.
 

The research summarized in this report was funded under the Class II Oil Field Demonstration Program of the U.S. Department of Energy National Petroleum Technology Office, Tulsa, Oklahoma, contract No. DE-FC22-95BC14988, awarded to the Utah Geological Survey as prime contractor. Additional funding and support was provided by Harken Southwest Corp., Irving, Texas, and the Utah Office of Energy and Resource Planning. 
 

ABSTRACT

Productive carbonate buildups of Pennsylvanian age in the southern Paradox basin, Utah, contain up to 200 million bbl remaining oil potentially recoverable by enhanced recovery methods. These buildups comprise over 100 satellite fields to the giant Greater Aneth field, where secondary recovery operations 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 Desert Creek carbonate mounds commonly produce at very high initial rates (>1000 bbl/day) and then suffer precipitous declines. An important new study focused on the detailed characterization of five separate reservoirs has resulted in significant information relevant to their future redevelopment. Completed assessment of Anasazi field suggests that phylloid algal mounds, the major productive buildup type in this area, consist of ten separate lithotypes and can be described in terms of a two-level reservoir system with an underlying high-permeability mound-core interval overlain by a lower permeability but volumetrically larger supramound (mound capping) interval. Reservoir simulations and related performance predictions indicate that CO₂ flooding of these reservoirs should have considerable success in recovering remaining oil reserves.