Pearsall Group Reservoir Evaluation

Reservoir Characterization and Production Properties

Several oil and gas companies are directing their efforts toward the exploration and exploitation of the Pearsall Group in South Texas. Initial results are very encouraging with reported initial production rates ranging from 450 to 740 BOPD with 4 to 6 MMCFGPD of associated gas. The play appears to be expanding to the northeast in South Texas and underlies the Eagle Ford Shale. This mixed shale and carbonate reservoir has proved to be challenging in terms of reservoir characterization, predicting producibility potential, estimating ultimate recovery, and optimizing fracture stimulation techniques. Many companies either do not have or are starting to acquire rock property data that are crucial for understanding this reservoir, which is very different from the overlying Eagle Ford Shale.

Therefore, in order to properly evaluate and explore this reservoir, appropriate types of rock property data need to be measured and integrated with log data, stimulation techniques, and production test information. These integrated data sets and case histories will provide operators with the critical parameters to optimize their exploitation of the Pearsall Group and reduce finding and development costs.

Project Objectives

The primary objective of this project is to provide operators with measured geological, petrophysical, geomechanical, geochemical, and production properties of the Pearsall in order to improve their formation evaluation and to optimize stimulation and production. Our work suggests that understanding the similarities and differences in these types of reservoirs on a regional basis is the key to successful exploration and exploitation. The resultant database will be an invaluable tool to operators in evaluating, comparing, and designing completion and stimulation methods for the Pearsall. Specifically, the project objectives are as follows:

  • Geologically characterize the cored section in terms of depositional facies, environment of deposition, and rock types.
  • Characterize and classify the Pearsall in terms of lithology, mineralogy, clay content, clay types, and pore structure including macro- and micro-fractures.
  • Measure the various petrophysical properties such as porosity, permeability, grain density, and saturations (i.e. water saturation, gas saturation, mobile oil saturation, hydrocarbon-filled porosity and bound water).
  • Measure and characterize the organic content of the Pearsall in terms of total organic content (TOC), Rock Eval pyrolysis, and vitrinite reflectance.
  • Measure the key geomechanical properties that are required for optimizing fracture designs and/or horizontal wells such as Young’s Modulus, Poisson’s Ratio, Bulk Modulus, fracture conductivity, horizontal stress, and proppant embedment.
  • Core-log calibration of open-hole logs for the development of petrophysical models to determine Pearsall reservoir properties.
  • Integrate the core data with well logs, fracture stimulation techniques, and production test results to aid companies in their evaluation and exploitation of Pearsall reservoirs.
  • Provide a regional assessment of the Pearsall to aid in exploration and exploitation.
  • Develop relationships from the database to aid in evaluating and comparing the various shale rock properties.
  • Develop a “Pearsall Rock Catalog” in order to aid in the evaluation of Pearsall properties from drill cuttings and logs.
  • Provide operators with a searchable database for Pearsall properties that can be used as analogs to aid in the appraisal and exploitation of “unknown or newly discovered” Pearsall reservoirs as the play expands.