Abstract

The ARCO-operated Corrigan Cowden Unit is located on the eastern edge of the greater North Cowden Field in the Permian Basin of West Texas. Since the first well was drilled in 1938, this unit has gone through several transformations typical of most Permian Basin fields. These old fields continue to produce more oil than initially expected. How do we recognize this additional potential, and better still, how do we economically capture it?

In July of 1976 this 480-acre unit was formed and waterflooding started in December 1976. Production increased from 300 bopd at unitization to 2000 bopd in 1990, with significant increases in 1984 and 1987 resulting from the larger development packages and continual waterflood response. Development during the late 1980’s established a 20-acre line drive configuration on the westside of the unit while much of the eastside was developed on 40-acre 5-spot spacing. Production has steadily declined to below 1000 bopd.

In 1996 a reservoir characterization study was initiated to provide a stratigraphic framework in the Grayburg-San Andres reservoir. Six cores were described including two from the Corrigan Cowden Unit. Four Grayburg sequences were recognized that have helped us understand the flow units in over 400 feet of reservoir. Preliminary work has focused on the potential oil-in-place and identification of zones that might have the most immediate potential in arresting declining production. Work is ongoing to understand the permeability relationships and seismic to petrophysical relationships in these complex carbonates to help distinguish by-passed, swept, and thief or water-cycling zones.

The poor vertical-waterflood conformance has led to several strategic plugbacks, redrills, and infill wells. It appears the Grayburg #4 zone has been getting minimal waterflood support, and parts of Grayburg #3 and #2 zones are cycling water. Two replacement wells were drilled in 1992, the #102R and #333. These wells were completed in Grayburg #4 for 150 boepd and 45 bopd, respectively. Recent plugbacks to the Grayburg #4 zone in the #324, #311, and #103 significantly reduced the watercut while the oil production remained steady. In late 1997, the #318R was drilled in a 40-acre pattern where two previous wells had been produced and plugged. The #318R potentialed for 62 bopd and 1 bwpd from Grayburg #4.

The 1999 work includes four injectors and four horizontals on the east side of the unit in order to concentrate efforts in the Grayburg #4. Future plans include adding the one remaining producer on the current 20-acre patterns, four coop-leaseline producers, four coopleaseline injectors, additional horizontals, several injector modifications, and several producer workovers and/or deepenings. CO₂-flood potential is currently under review that should take this unit into the next phase of its life.

Yes, there is life after 50, 60, ....