Karsts, Cracks and Compartmentalization in the Fusselman and Montoya Reservoirs of the Dollarhide Field, Andrews County, Texas

BALL, BRIAN C., Pure Resources, A Unocal Company, Midland, Texas

Core and image logs have helped explain compartmentalization within the Fusselman and Montoya reservoirs in the Dollarhide field. The use of behind pipe hydrocarbon logs helped identify wells in which potential barriers existed and trapped bypassed hydrocarbons. Both were used to find new reserves in an old field.

In the fall of 2000, Pure Resources cored and ran image logs in the DHU 25-2 S to obtain a better understanding of the actual interval geometries within the Fusselman and Montoya reservoirs. There was 333 feet of core taken and 281 feet recovered. The entire Fusselman and Montoya formations were logged with image logs. They revealed tectonic fractures to exist within sections of the reservoir but they were not dominant throughout. The stratigraphic component was much more complex than originally thought. There were definite vertical barriers within the Fusselman and Montoya reservoirs. These barriers were the result of complex stratigraphic changes during deposition. There barriers formed effective internal traps for hydrocarbons.

A workover program and infill drilling program was implemented to recover these bypassed reserves. Twenty two wells were re-entered over the past 3 years and re-logged with behind pipe hydrocarbon logs. Four infill wells on 20 acre spacing have been drilled to date.

Several future recompletions and infill wells are planned at this time. To date this program has added 2.9 MMBOE of reserves to the field. This project is an example of how applying a new model to an old field can recover additional reserves.