Wireline logging is a critical technique in the oil and gas industry for obtaining information about subsurface formations. Different types of wireline logs provide data on various properties of the formations. Here are some common types of wireline logs:
Lithology Logs
Lithology logs provide information about the composition and characteristics of the rock formations encountered during drilling. These logs can include data from mud logging (cuttings analysis) as well as wireline tools that measure properties like gamma ray emissions and resistivity, which can help identify different lithologies. Common wireline tools used to obtain lithology logs include:
- Gamma Ray Logs: Gamma ray logs measure the natural gamma radiation emitted by the formations. Different rock types have varying levels of gamma ray emissions, allowing geologists to differentiate between lithologies. For example, shale typically emits higher gamma ray counts than sandstone or limestone.
- Sonic Logs: Sonic logs measure the travel time of sound waves through the formations. Since different lithologies have distinct sonic velocities due to variations in rock density and elasticity, sonic logs can help identify lithology changes. For instance, shale typically exhibits slower sonic velocities compared to sandstone or limestone.
- Density Logs: Density logs measure the bulk density of the formations. Different lithologies have different densities, so density logs can aid in lithology identification. For example, denser formations like limestone or dolomite will register higher bulk densities compared to less dense rocks like shale or sandstone.
- Neutron Logs: Neutron logs measure the hydrogen content of the formations. Lithology identification can be aided by understanding the hydrogen content of rocks, which varies based on composition. For example, hydrogen-rich formations like clay-rich shales will exhibit higher neutron porosity counts compared to water or hydrocarbon-bearing sands.
- Caliper Logs: Caliper logs measure the diameter of the wellbore. Lithology changes can sometimes be inferred from changes in borehole diameter due to variations in rock hardness.
- Formation Micro-Imager (FMI) Logs: FMI logs provide images of the borehole wall, allowing geologists to visually identify lithology variations, bedding planes, fractures, and other features. These images can help in identifying lithology changes and understanding the geological structure of the formation.
Porosity Logs
Porosity logs measure the amount of pore space within the rock formations. This information is crucial for assessing the potential storage capacity of fluids (such as oil and gas) within the reservoir rocks. Common wireline tools used in obtain porosity logs include:
- Neutron Porosity Logs: Neutron porosity logs measure the hydrogen content of the formations by bombarding them with neutrons and detecting the resulting radiation. Since hydrogen is abundant in fluids like water and hydrocarbons but scarce in most minerals, neutron porosity logs can estimate the formation’s total porosity. Hydrogen-rich formations exhibit higher neutron counts, indicating higher porosity.
- Density Porosity Logs: Density porosity logs measure the bulk density of the formations using a gamma-ray source and detector. By comparing the measured density to the density of pure rock, density porosity logs estimate the formation’s porosity. This method is particularly useful in formations with low hydrogen content, such as carbonates, where neutron porosity logs may be less accurate.
- Sonic Porosity Logs: Sonic porosity logs utilize the travel time of sound waves through the formations to estimate porosity. Sound waves travel faster through solid rock than through fluid-filled pore spaces. By comparing the transit times of sound waves in the formation with the velocities in solid rock and pore fluid, sonic porosity logs can infer porosity.
- Dielectric or Capacitance Logs: Dielectric or capacitance logs measure the dielectric properties of the formation, which are related to the formation’s porosity. These logs are particularly useful in formations with high water salinity, where other porosity logs may be less accurate.
- Nuclear Magnetic Resonance (NMR) Logs: NMR logs use the principles of nuclear magnetic resonance to directly measure the amount of fluid in the formation’s pores. By measuring the relaxation times of hydrogen atoms in the formation, NMR logs can provide detailed information about pore size distribution and fluid type, which is valuable for reservoir characterization.
Resistivity Logs
Resistivity logs measure the electrical resistivity of the formations. This property can help identify the presence of hydrocarbons (which have low resistivity compared to water-filled formations) and evaluate the reservoir’s potential productivity. Different types of resistivity logs include:
- Deep Resistivity Logs: These logs measure the resistivity of formations several feet away from the borehole, providing information about the bulk resistivity of the subsurface.
- Laterologs: Laterologs measure the formation resistivity at different depths from the borehole, helping to characterize the formation’s electrical properties.
- Induction Logs: Induction logs induce an electromagnetic field into the formation and measure the resistivity based on the induced currents, providing information about formation properties.
Gulfwell provides logging pressure control equipment for monitoring and regulating pressure conditions during various downhole operations, including formation evaluation, well testing, and production logging. This equipment includes blowout preventers (BOPs), choke manifolds, hydraulic control systems, pressure control valves, pressure gauges and sensors etc. To know more about Wireline Logging products and services provided by Gulfwell please email us at sales@gulfwell.ae