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 (FT), 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.
Introduction
The characterization of shale gas formation is rapidly gaining prominence as a result of the increasingly important role of unconventional reservoirs in South China. Engineering practices such as horizontal drilling and hydraulic fracturing in shale gas formation has created a need for volumetric quantification not only of fracturing but of other geomechanical properties such as Young’s Modulus, Poisson’s Ratio, and maximum horizontal stress direction, in addition to more conventional reservoir properties such as lithology, brittleness, TOC and porosity as input for reservoir simulations
