Gold Mine or Money Pit- Worsham-Waha Devonian Play Reeves & Pecos Counties, Texas
David J. Entzminger, David Sivils, Xu Long, and Huaibo Lui
Since early in 2000 the Worsham-Waha area of Reeves and Pecos Counties, Texas has seen a real boom drilling horizontal wells for the elusive Devonian gas reservoir. Worsham-Bayer and Waha Fields had great Ellenburger production with nearly 400 bcfg produced, but only 30 bcfg had been produced from the Devonian. The Worsham-Bayer Field is an east-west, large faulted anticline with two domes. The east dome had four wells where all the commercial Devonian production was found. With the horizontal boom of the Montoya in Waha and Block 16 fields, operators started to utilize the similar techniques for the Devonian. A couple early wells showed promise- The Trees Estate came in at ~ 7mmcfgpd with an EUR of 5 bcfg. Since that time a total of 22 wells have been drilled with a wide range of results from uneconomic wells (Colt #1) to wells that IPF- over 15 mmcfgpd (Horry-Pitts 49#1). The down-dip Lloyd Estate #1 well suggests a gas column of over 3000’ on a structural feature about 10 miles long and 7 miles wide. Volumetrics suggest a tremendous amount of gas-in-place. However, with drilling costs of $4-7 million per well, the well reserves need to be significant to substantiate this expense. It is not a play for those with a weak stomach or small pocketbook. The main players have been Tom Brown, PURE Resources, Finley, and Oxy Permian.
Tom Brown Inc. recognized that a better predictive reservoir model was needed to continue developing this play because of the high costs and dramatic variability in well results. In late 2003 a reservoir study was implemented to examine key-Devonian well samples in an effort to relate them to logs and production. At the same time we initiated fracture studies with EP Tech and GMI to review the fracture contribution to the reservoir and do some geo-modeling. We examined the seismic attributes in an effort to match with rock quality or fracture networks.
Image logs in both the vertical and some of the horizontal wells confirmed fractures were present in the field. The erratic production throughout the field also suggested a fracture component affected the reservoir deliverability. Seismic attributes seem to have promise identifying fracture zones. Fractures can be a two-edge sword, either enhancing gas deliverability or bringing in too much water. Most wells had been drilled longitudinal along maximum horizontal stress. The Wahlenmaier #1 was drilled in 2004 to transverse the fracture system attempting to cross the major fracture system in hopes to enhance production. The well did intersect the seismic predicted fracture system but the higher water production 200-300 bwpd has hampered the gas production of 2000-4000 mcfgpd. Drilling has essentially ceased in the area with operators licking there wounds. The two, recent prolific wells (Horry-Pitt 49#1 and Monsanto-McKellar #1) may one day entice the next generation of oil & gas finders to extract the remaining gas in this large structure.