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Petrophysics is the study of the physical and chemical properties of rocks and their contained fluid. It emphasizes those properties relating to the pore system and its fluid distribution and flow characteristics. These properties and their relationships are used to identify and evaluate:


  • Hydrocarbon reservoirs

  • Hydrocarbon sources

  • Seals

  • Aquifers


As such, it has a major application in the oil- and gas industry. The experience of our petrophysicists ranges from re-evaluation of old/existing data (e.g., log re-editing and re-interpretation) to the evaluation of recently/newly acquired well data.


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During drilling operations, OPS OES Thailand petrophysicists are responsible to report reservoirs vs. non-reservoirs, hydrocarbon type and –saturation, pay zones and additional zones of interest (AZI’s), which are hydrocarbon-bearing zones, which did not make the cut-offs to call them pay; fluid types and contacts, saturations, and porosity and permeability calculations. After the electric logs have been run, they will load the data tapes into the Client’s database and they will be closely interacting and clearly communicating on well and field data with the multidisciplinary team of geologists, geophysicists, engineers and other petrophysicists, usually the reservoir team. The petrophysical report will be reviewed with the G&G project team.


A comprehensive petrophysical interpretation includes (see diagram):


  • Well Log Interpretation

  • Thickness (bed boundaries); reservoir vs. non-reservoir

  • Lithology (rock type; grain size, composition, texture)

  • Water Saturation Sw, the fraction of the pore space occupied by water, usually measured by the resistivity logs. Hydrocarbon saturation is given by the equation (1-Sw)

  • Saturation Height Modeling

  • Porosity ϕ {phi} The percentage of a given volume of rock that is pore space and can therefore contain fluids. This is typically calculated using data from a combination of electric logs and can be calibrated with core porosities over reservoir section in which cores were cut.

  • Permeability, the quantity of fluid (usually hydrocarbon) that can flow through a rock as a function of time and pressure, related to how interconnected the pores are. Formation testing can directly measure this down hole. Log permeability can be calibrated with core permeability.

  • Fluid Identification and Characterization; This can be quickly done by using the measurements of the resistivity, the density and the neutron logs, as illustrated under Well Log Interpretation in Geological Services.

  • Clay/Shale Volume

  • Pore Pressure

  • Net Pay computed as the thickness of rock that can deliver hydrocarbons to the well bore at a profitable rate.


Petrophysics have also been applied in scientific studies to explain e.g., very low permeability in reservoir rock. A typical example was Unocal’s study in the Rotliegendes sandstones in the Dutch North Sea, where reservoir quality was limited by the formation of illite due to the percolation of brines from the overlying Zechstein salts and evaporites. The outcome of the study indicated that too high production rates from the gas-bearing reservoir would de-stabilize the illite and plug off the permeability completely and stop the flow of gas into the borehole. Petrophysical studies like this have been carried out on a global scale.


Example of a petrophysical interpretation of an exploration well based on wire-line logs and other data, such as core data (source: GEOEXPRO Volume 11, No. 1, 2014).

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