Smart Computing- Book ISBN- 978-81-953658-1-4

Authors:- Saurav Sengupta, Ankush Kumar Mali

Abstract :-The separation of resistivity and porosity logs in organic rich intervals measured in term of logarithmic resistivity cycle called ΔlogR. This parameter is generally used to calculate total organic carbon content (TOC), with reference to the base lines established in a water bearing non-source rock of a given lithology. Application of the overlay method in organic rich Eagle Ford shale is prone to error due to non-availability of reference water base lines in similar lithology.

As increase in porosity in term of resistivity means an increase in volume of conducting water, resulting in a decrease in resistivity. These changes are proportional, so that if the porosity and resistivity are correctly modeled, the amount of increased porosity result in deflection of similar magnitude of both the resistivity and porosity curves. It means modeled resistivity of water filled resistivity curve generated with porosity, serves as base lined curves for both resistivity and porosity curves. Separation between resistivity and modeled water filled resistivity curves represent the so-called properly scaled resistivity and porosity curves defined by usually ΔlogR technique. The ΔlogR is calculated directly as logarithm of resistivity index dynamically generated through Archie’s relation, and is very robust for TOC calculation. It also eliminates the requirement of establishment of water base lines of resistivity and porosity logs in conventional techniques.

Comparison of estimates for total porosity, total water saturation and TOC obtained using new organic shale evaluation method are corroborating with the respective values derived from core laboratory measurement.

Entire procedure is illustrated with examples of Eagle Ford shale gas formation where sufficient large number of measurement on core samples are available for the calibration of log derived values of porosity, bulk volume of gas/ water and TOC. The technique in organic shale evaluation is very robust and can be extended for the evaluation of other fields in the world.

Keywords: - Total Organic Carbon (TOC), Organic Matter (OM), Hydrocarbon, Formation, Well Logging