A multimineral Rock Physics Template built from the Perfectly Disordered Method for shale lithology interpretation

摘要

In this work, we propose a simple micromechanical model called the Perfectly Disordered Method (PDM) to compute the effective elastic properties of a number of inhomogeneous shale rocks grouped according to their geological ages. This micromechanical model assumes no knowledge about the internal microstructure of these geological materials. Instead, elastic responses are solely computed from the mechanical properties of their comprising individual n minerals. Later, based on the presence of their main composing minerals, the obtained rock's elastic responses are overlapped on lambda-rho vs mu-rho lambda rho - mu rho ternary diagrams (also built by using the PDM) which vertices are either defined by a combination of quartz-feldspar-clay respectively or quartzcalcite-clay. The resulting overlaps generate multimineral Rock Physics Template's (RPTs) that are then used to assist in the lithological characterization of these sedimentary rocks. Identified lithologies include feldspathic siliceous shales as well as siliceous and calcareous shales. These results are comparable to those obtained by the implementation of a micromechanical model called the Self-Consistent Method (SCM) which in contrast requires information about the matrix's rock and their embedded inclusions. Further, the maximum percent errors found between the PDM and the SCM for lambda rho and mu rho up in the ternary diagrams are 3.18% and 6.56% respectively while for shales points the maximum errors for lambda rho and mu rho up are 5.17% and 10.09% respectively. These errors are negligible for practical applications. However, the main advantage of the PDM is that this model is easier to implement than SCM since PDM uses explicit equations to calculate effective properties unlike SCM that uses non-linear equations that must be solved by using iterative methods.