Base of Protected Water Depth Structure Maps Using Geologic Modeling Methods

Abstract

Protected groundwater is defined as having concentrations of total dissolved solids (TDS) <10,000 mg/L. In the subsurface, protected water is identified by calculating apparent salinity using Archie or Humble equations with rock and fluid properties derived from resistivity and porosity geophysical well logs. The calculated apparent salinity is used as a proxy for TDS to determine the base of protected water. Mapping the base of protected water at the well, field, and basin scale from open-hole geophysical logs is usually limited to wells with resistivity and porosity at or near the base of protected water. The depth to the base of protected water is typically shallow relative to the hydrocarbon-bearing zones and is not always logged with resistivity and less so with porosity, limiting the amount of data necessary to identify the base of protected water. Modeling resistivity and porosity at the wells and the volume in between is achieved using geostatistical methods that honor all available data as well as adhering to underlying data trends in the form of a three-dimensional geologic model. The modeled three-dimensional properties of resistivity and porosity are used to derive variables for the Archie and Humble equations and create a three-dimensional model of apparent salinity. Two-dimensional maps of the sub-sea depth to the base of protected water are then extracted from the apparent salinity modeled properties. The properties are compared with and calibrated to available water sample regardless if the wells were logged across the zone that was sampled. This method uses all available resistivity and porosity logs reducing data bias toward well vintage. The resulting models, paired with water samples, provide a more developed understanding of the transition between protected and non-protected water.

AAPG Datapages/Search and Discovery Article #90372 © 2020 AAPG Pacific Section Convention, 2020 Vision: Producing the Future, Mandalay Beach, Oxnard, CA, April 4-8, 2020 (Cancelled)