Characterization of kerogen in shale core plugs using T2*-based magnetic resonance methods

Abstract

Kerogen assessment is essential to evaluation of shale reservoir quality. Routine analysis techniques are sample destructive and time-consuming. 1H magnetic resonance (MR) methods offer a fast, robust, and non-destructive alternative. However, kerogen MR signal detection and quantification is challenging due to its short signal lifetime and requires new MR methods. In this work, the T1-T2* relaxation correlation method was investigated for assessment of kerogen in shales. Step pyrolysis experiments were conducted coupled with MR T1-T2* relaxation correlation measurements and thermogravimetric analysis (TGA). The results show that the short relaxation lifetime signal observed in the shale samples was dominated by the kerogen species. The shale signal was resolved in the T1-T2* relaxation correlation measurement that was calibrated to report kerogen, oil, and water 1H content of the shale samples. Kerogen 1H content was then used to evaluate the hydrocarbon generation potential of kerogen. An elemental balance analysis was conducted to estimate the kerogen chemical evolution in the Van Krevelen diagram. The results proved that a simple FID measurement was adequate to resolve and quantify the kerogen signal component in shales.