Geologic Methods to Improve Oil & Water Understanding in Clear Fork, Texas

🎙 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.

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