APPLICATION OF ROCK PHYSICS TEMPLATES TO SHALE GAS PLAYS IN SOUTH CHINA

The mineralogical composition and mineralogy classification in shale reservoirs is attractive topic for an understanding of sedimentary setting, spacial distribution and rock mechanical properties, namely brittleness in the views of geologist to screen prospective blocks and zones. It turns out that ternary-diagram approach of shale composition is much handy to observe petrologic variations and similarity of the fine-grained rocks and also brittleness index method described by the fraction of brittle minerals (quartz, pyrite, carbonates, etc.) to ductile components (clay, kerogen, etc.) become an indirect measure integrated with other parameters to identify regional potential fairway, even the target interval in hydrocarbon basins. However the information on diagenetic alteration can be more easily concealed in the conventional ternary-diagram. Factors such as porosity, pore-pressure, thermal maturity, authigenic quartz in shales/mudstones and even deformation conditions exert a remarkable mechanical variation on rock properties (elastic moduli).

A modified model that was originally proposed by Nicolás-López and Valdiviezo-Mijangos (2014, 2016) based on the synthesis of pure mineral and bulk densities via self-consistent equations is then applied to show these response variation on rock physical templates when the above factors are taken into account to predict rock physical and mechanical properties of shale intervals, especially Wufeng-Longmaxi reservoirs with over-high maturity from Upper Ordovician-Lower Silurian in the Sichuan Basin, South China and the others.

The paper concluded that simple mineralogy-based brittleness prediction has disadvantage caused by multiple causes. Primary controls inferred from the shift of mainly parameters for shale reservoirs is clearly shown in the rock physics templates and give a clear understanding of the intricacies of formation evaluation.