Using Crosswell Seismic Tomography to Provide Better Reservoir Resolution in the Wolfcamp Formation in Lea County, New Mexico

Cynthia L. Welch, Robert L. Martin, and Greg D. Hinterlong
ChevronTexaco, Midland, Texas

In the Vacuum Field located in Lea County, New Mexico, the Wolfcamp Formation consists of alternating and intermingled layers of limestone, dolomite, and shale. Located on the southeastern edge of the Northwest Shelf, the Wolfcamp was deposited in a shallow shelf environment while experiencing considerable fluctuations in sea level. The Wolfcamp appears to be laterally discontinuous based on log and 3D seismic data, however individual reservoir-quality compartments are difficult to resolve with these methods. Depositional models of carbonates in shelf environments indicate that units of potential pay may not be laterally continuous, however they may be traceable if better resolution can be obtained regarding the depositional character of these units. In addition, identifying shale units would greatly aid in determining the best path for future horizontal wells in the Wolfcamp.

Crosswell Seismic Tomography was used to provide better reservoir resolution, which would lead to determining reservoir continuity, compartmentalization, and characterization. After data collection, processing, and interpretation, a horizontal well was drilled based on these results. The horizontal well targeted reservoir-quality intervals that had not been identified in either log or 3D seismic analysis. The horizontal well resulted in tests up to 121 BOPD, which was an increase of 91 BOPD from original vertical well results. In addition to providing horizontal drilling locations in the Wolfcamp, the crosswell seismic data has provided information essential to reservoir characterization and our understanding of Wolfcamp deposition in this area. Based on the crosswell seismic data, the Wolfcamp Formation does appear to be discontinuous with several isolated reservoir-quality compartments present. Many of these reservoir-quality compartments were not originally distinguished by either log or 3D seismic data. In addition, this high resolution data has allowed us to compare the crosswell seismic results with outcrop studies performed by the BEG near Van Horn, TX. Clinoforms have been identified in the crosswell seismic data that appear highly similar to those seen in outcrop near Van Horn, TX. Future application of this data exists in the merging of crosswell seismic, 3D seismic, log data, and core data into one three dimensional model that will provide us with a more complete understanding of the Wolfcamp Formation in the Vacuum Field.