Wilcox Reservoir Study


Recent drilling activity in the Wilcox Formation has demonstrated that this prolific horizon continues to offer new exploitation opportunity. Opportunity comes with inherent risks in a formation where “pay” is not obvious on well logs and prediction of potential productivity from logs with limited core analysis data leaves the engineer or geologist with uncertainty. The objective of this project is to generate a large database of laboratory measured rock properties, critical to expensive pipe setting decisions, on a systematically selected group of samples which might be expected to be encountered in Wilcox drilling activity throughout the South Texas region. The samples tested will serve as a collection of analogs with supplied petrographic and petrophysical data for use as comparators with similar rock samples or cuttings that have no measured data. Log response associated with each analog rock type will be provided. The database can then serve as a tool to assess production potential in a time frame required for completion decisions.

The project scope requires rotary sidewall samples or plug samples obtained from conventional core from multiple wells in the region, along with associated log data (both standard logging suites and NMR tools) to comprise the inputs into the study. Rotary sidewall cores provide the operator with the freedom to extract representative samples from the wellbore after logging has been completed. A comprehensive series of tests designed to extract the maximum amount of information from the cores is designed to specifically address the following:

  • Fluid saturations
  • Porosity and Klinkenberg permeability as a function of net overburden stress
  • Pore geometry variability through hydraulic unit analysis
  • Mineralogic variability through thin section and X-ray diffraction
  • Location and morphology of clay minerals through scanning electron microscopy
  • Water salinity estimation for Rw from core water extraction (where appropriate)
  • NMR T2 variability and calibration with pore geometry
  • Formation resistivity factor and resistivity index for cementation and saturation exponents, “m” and “n”
  • Permeability to gas at initial water saturation
  • Capillary pressure characteristics as a function of pore geometry
  • Creation of an NMR log based permeability model