The true resistivity (R<sub>t</sub>) of a formation is its resistivity when not contaminated by [[drilling fluid]]s. It may contain formation water only (water saturation [S<sub>w</sub>] = 100%) or formation water and hydrocarbons (S<sub>w</sub> < 100%). Using a valid R<sub>t</sub> is fundamental when analyzing well logs for the presence of hydrocarbons. For a discussion of resistivity concepts see Asquith, 1982.
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The true resistivity (R<sub>t</sub>) of a formation is its resistivity when not contaminated by [[drilling fluid]]s. It may contain formation water only ([[water saturation]] [S<sub>w</sub>] = 100%) or formation water and hydrocarbons (S<sub>w</sub> < 100%). Using a valid R<sub>t</sub> is fundamental when analyzing well logs for the presence of hydrocarbons. For a discussion of resistivity concepts see Asquith, 1982.