GEOLOGICAL AND PETROPHYSICAL EVALUATION OF WOLFCAMP SANDSTONES PECOS AND TERRELL COUNTIES, TEXAS
The Wolfcamp Sandstones in the Val Verde Basin have recently been the target of new drilling programs, especially in Pecos and Terrell Counties Texas. This activity, coupled with continued development extensions of the more established fields, indicates that the Wolfcamp Sandstones warrant a focused and integrated formation evaluation study. Opportunities abound for increasing Wolfcamp Sandstone productivity through an improved understanding of the controls on permeability distribution, water saturation, and relative pay contribution, which will reduce risk and increase the success of their exploration and development programs.
This approach to accomplishing these goals consists of establishing a rock property database that are integrated with log and well test information in order to establish sets of pay and non-pay criteria for the various Wolfcamp Sandstone rock types. Besides improving formation evaluation, this study will provide participating companies with data and interpretations for a better understanding of geological concepts, prediction of reserves and producibility.
The project is designed to augment and coincide with operators’ Wolfcamp drilling programs by providing them with formation evaluation data on their own wells, as well as data from other operators’ wells. Participating companies supply either rotary sidewall cores or conventional core samples from two wells, along with open-hole logs for analysis and inclusion in the study. Conventional cores are sedimentologically described in detail and interpreted for depositional environments. White light (color) photographs of the conventional cores and rotary sidewall cores are provided.
Selected samples are analyzed by thin section petrography, scanning electron microscopy, and X-ray diffraction. Additional advanced rock property tests will determine porosity, specific gas permeability, Klinkenberg gas permeability, grain density, formation factor (F), cementation exponent (m), resistivity index (RI), saturation exponent (n), capillary pressure, and effective permeability to gas at immobile water saturation. Acoustic measurements of compressional and shear wave velocities will allow determination of Young’s modulus, Poisson’s ratio, and shear and bulk moduli.
Reservoir rock types and their specific petrophysical properties are correlated to log parameters and production test data. With this approach, pay and non-pay criteria are established resulting in improved formation evaluation. Additionally, rock-fluid compatibility tests are performed on selected samples to determine which drilling, completion, and or frac fluids can be safely utilized to minimize formation damage.