Paul Dowling Jr., Shell Oil Co.
Carbonate environmental concepts have been applied to a typical Permian dolomite reservoir. The Monahans Clearfork field, Ward and Winkler Counties. Texas, was selected because the initial development was completed and the secondary recovery project was installed prior to the development of the carbonate environmental concept as an operational tool. The problem in the Monahans Clearfork Secondary Recovery Project is twofold. First, oil response to water injection has been less than originally anticipated. Second, as a result of early evaluation techniques, some productive zones were either cased off or not penetrated. The Clearfork reservoir was divided into five zones. The environmental dolomite types within each of the five zones ranged from supratidal to marine both vertically and laterally. Several marine dolomite types were found to be productive white the intertidal and supratidal were nonproductive in most cases. When leached. However, the supratidal becomes an effective but limited reservoir. Net pay isopachs for each zone were constructed and serve to define field limits, pay quality, and continuity. The isopachs indicate the anticipated waterflood performance of each zone, the distribution oj suspected thief zones, and wells and/or areas with additional hydrocarbon potential. A drilling and recompletion program currently underway should complete the evaluation of the Monahans Clearfork reservoir. If" success continues, the program should result in a significant improvement in supplemental recovery performance as well as an increase in field reserves.