Preliminary I: Rock Physics Templates for Shale Reservoirs

Abstract

The low porosity and permeability shale are nowadays known as self-resourcing reservoirs due to its ability to produce as well as reserve hydrocarbon within the pore spaces. Shale reservoirs potential should be well-defined by understanding their unique and complex characteristics. Quantitative interpretation of shale reservoirs should be done properly, including such steps from rock physics modeling, fluid substitutions, and predicting elastic properties to obtain the best image of shale systems and perhaps to lower drilling risks in the future. In this study, we built rock-physics templates (RPT) to estimate seismic response by defining the relationship between total organic carbon (TOC) and effective elastic properties of shale reservoirs. Shale source rocks are mainly composed of clay and non-clay (e.g. quartz). The pore space contains fully water determined by the in-situ conditions. RPT is carried out by incorporating the amount of organic matter into shale pore space. Pore space stiffness analysis is performed to estimate pore geometry by their aspect ratios in order to find the best fit of elastic properties of rock. A solid background of shale from several different minerals is estimated by using effective medium theory. Organic matter will be placed in the solid-filled volumes and the remaining volumes are fluid-filled. Properties of porous rocks for solid pore infill are estimated from a generalization of Brown-Korringa and Gassmann equation. Effective elastic properties of bulk rock frame filled with a fluid are obtained from Gassmann equations. Results show that increasing the TOC volumes generally reduces both P-wave and S-wave velocities, acoustic impedance, and density. On the contrary, the Vp/Vs ratio increased as the impact of immature organic matter which will be more affecting shale rigidity than its compressibility. , Tiara Larasati Priniarti2, Sonny Winardhi2, Handoyo1