Oillogging

Oillogging is the practice of recording measurements of rock and fluid properties within a borehole to identify and characterize hydrocarbon-bearing formations. It is typically performed in open boreholes with tools lowered on a wireline before casing the well. In cased wells, specialized logging tools can be deployed via production tubing or through the casing. The goal is to obtain a continuous, quantitative picture of the formation’s electrical, physical, and fluid characteristics.

Common tools measure natural gamma radiation, bulk density, neutron porosity, sonic velocity, and electrical resistivity. Caliper logs assess borehole diameter. Advanced tools include nuclear magnetic resonance (NMR) logs and formation water saturation tools. Logs are interpreted individually and in combination to determine lithology, porosity, water saturation, and hydrocarbon content. Rock physics models, such as Archie’s law, relate resistivity and porosity data to estimate hydrocarbon saturation.

Oillogging supports several objectives, including identifying zones with hydrocarbons, quantifying porosity and permeability proxies, recognizing water-bearing zones, and guiding well placement, completion design, and reserves estimation. It also aids in cement evaluation and zonal isolation in cased wells, contributing to overall reservoir management.

Limitations and challenges include borehole conditions, drill fluid invasion, washouts, and various effects of borehole geometry on measurements, which can introduce interpretation uncertainties in complex lithologies. The field has evolved with spectral and imaging tools, NMR-based assessments of movable oil, and integrated formation evaluation workflows that combine log data with core analyses and seismic information.

In practice, petroleum engineers and geologists use oillogging results to build petrophysical models of reservoirs and to support decisions in exploration and production.