Rock Physics Characterization of Organic-Rich Shale Formations to Predict Organic Properties

Hydrocarbon production from organic-rich shale formations has significantly increased since the advent of sophisticated recovery techniques which allow for economical production from such formations. The primary formation properties that operators rely on to assess the economic potential of these formations are: total organic carbon (TOC), thermal maturity, hydrocarbon saturation, porosity, mineralogy and brittleness. In this thesis, I investigate rock physics models and methods for the possible estimation of these formation properties of organic-rich shale formations from and well log and seismic data.

The rock physics model applied in this research integrates Gassmann and Sun models to predict the elastic properties of organic-rich shale formations. Sun?s model utilizes a pore-structure parameter (PSP) which relates to the rigidity and pore structure of the rock. The rock physics model is separated into two stages based on the identification that organic-rich shale contains both organic and inorganic porosity. Organic porosity contains hydrocarbon while inorganic porosity contains water; organic porosity and associated hydrocarbon are created during the maturation of solid organic matter. The first stage of the model incorporates the organic matter into the structural matrix of the rock; the second stage then introduces the current total porosity into the total rock matrix. The ideal case, studied in this paper, assumes that all porosity is organic porosity; the parameters for each stage in the ideal case would be related and potentially approximate to each other, simplifying the resulting nonlinear model.

The modeled PSP is observed to correlate with rock properties, specifically the TOC, hydrocarbon saturation, thermal maturity, clay volume and acoustic impedance. Significant variation still occurs between the PSP and some rock properties, this suggests the actual case is much more complicated than the ideal situation. A strong correlation between the PSP and organic properties is seen as the amount of organic material increases suggesting that higher amounts of variation with lower organic content relates to intervals where the ideal case is not valid; the correlation is greater with respect to the shear wave, indicating the importance of the shear wave to rock physics modeling. Through the integration of Gassmann and Sun equations a rock physics model has been developed which can potentially relate organic-rock properties to acoustic properties, this correlation can greatly enhance the evaluation of organic-rich shale play development from log analysis and possibly seismic inversion.