🎙 Geologic Techniques for Improved Formation Characterization to Better
Understand Oil & Water Production in the Clear Fork Formation, Central Basin
Platform, Texas
Art Saller and Frank Messa
Many Clear Fork reservoirs in the Permian Basin have been producing oil for more than
70 years. After primary production, waterflooding and infill drilling, recovery efficiency is
still commonly less than 20% of the original oil in place (OOIP). Drilling and frac’ed
horizontal wells are being used to recover more oil. Clear Fork reservoirs are
notoriously heterogeneous because of vertical and lateral variations in depositional
facies and diagenesis. Depositional facies have porosity, permeability and capillary
characteristics that we have related to open-hole log characteristics for mapping
throughout the field. Open-hole logs are critical to the quantitative mapping of the
distribution of oil. This is complicated by variations in original formation waters. In our
field, original Clear Fork waters vary from 17 to 130 ppt. As a result, geographic
variations in resistivity are used in log analysis.
Thin sections of cuttings are used to characterize the porosity, facies and stratigraphy of
horizontal wells. This has provided valuable information in understanding the distribution
of porosity, permeability and production from those wells. As with most horizontal frac’ed
wells, substantial water is produced. The horizontal wells are in fields that have had
substantial water injection. Water geochemistry (ions and stable oxygen isotopes) has
been used to differentiate injected water from original formation water. Ultimate goal of
all of this work is to better understand oil and water flow in the reservoir and improve oil
recovery.
