Rock Physics Modeling for Shale Gas Formation Characterization in China

Summary Our study applied a geophysical well log analysis, rock physics diagnostics and rock physics modelling to an exploration well log data from a shale gas exploration area in the Sichuan Basin of South China. The study established an unconsolidated model (80% quartz plus 20% clay in the shale gas formation) transform between the acoustic and elastic impedance on the one hand and lithology, porosity, water saturation, clay content, quartz content, and TOC content on the other hand. Through our geophysical well log analysis, we calculated mineral volumes using best available data, total and effective porosity, water saturation, and bulk density and VS prediction where it was missing. For rock physics modeling, the shale gas formation matrix substitution (Clay, Quartz and TOC) and porosity modeling were performed in this exploration well. Crossplots are also used to analyze the elastic properties of the shale gas formation including VP velocity vs density, Acoustic Impedance (AI) vs total porosity (OT), AI vs Poisson’s Ratio (PR), and VP vs VS. The results were quality controlled by core sample laboratory analysis data. To understand seismic effect as a result of rock physics modeling, ray traced synthetic modelling has been applied. The Ray-traced synthetics have been generated for the in situ and modeled scenarios for AVA analysis. These transforms will be upscaled and applied to acoustic and elastic impedance inversion volumes to map lithology, porosity, and TOC distribution in the shale gas exploration area