A novel rock physics model of organic-rich shale considering maturation influence

Abstract

Geochemical parameters, e.g. maturity, and total organic carbon (TOC) content, play a crucial role in the prediction of sweet spots and the exploration of oil and gas in organic-rich shales. Thermal maturity significantly affects the conversion of solid organic matter (OM) into hydrocarbons and the evolution of microstructures, thereby altering the overall elastic properties of shales. To clarify how the maturity affects shale property, we propose a novel Rock Physics Model (RPM) of organic-rich shale, in which we consider the continuous process of thermal maturity.#xD;Firstly, we present how to estimate maturity level, TOC content, and organic porosity using logging data. Secondly, different from only considering the discrete-stage maturity, we establish a novel RPM, in which a continuous kerogen maturation process serves as a key control condition. Furthermore, we propose how to calibrate the volumetric proportion of each porosity type as a function of maturation. Finally, we apply the RPM to investigate how sweet spot parameters (thermal maturity, TOC content, and brittle mineral content), overpressure and diagenesis affect the overall elastic properties and anisotropy of shale. Results demonstrate that using the proposed RPM we may predict acoustic velocity of shale formations reliably, and kerogen evolution has a noticeable impact on the elastic properties of shale rocks, particularly during the wet gas window stage of mid-to-high maturation. We conclude that thermal maturity emerges as a crucial sweet spot parameter in the case of exploration of oil and gas in organic-rich shales.