3D rock physics template analysis and "sweet spot" prediction of Longmaxi-Wufeng organic-rich shale

For the purpose of identifying the "sweet spots" of rich shale gas in the Longmaxi-Wufeng target Formations of Dingshan area of Sichuan Basin, this work investigates the key indexes of shale, such as content of total organic carbon (TOC), brittleness, porosity, microfractures, etc. We analyze on the rock characteristics and perform rock physics analysis, and the results show that the sweet spot areas exhibit high TOC, high porosity, low density and high brittleness (high quartz content). Furthermore, λρ (product of the first Lamé constant and density) ranges in 18~30 GPa•g•cm-3, Poisson's ratio υ ranges in 0.18~0.22, and shear modulus μ ranges in 13~18 GPa for those reservoirs. According to the rock physics properties of reservoir, by considering the impact of porosity, crack aspect ratio and mineral components on the sensitive elastic parameters of high-quality shales, EIAS (equivalent inclusion-average stress) model is adopted to establish 3D rock physical templates for shales, and the reservoir porosity, crack aspect ratio and quartz content are predicted. Based on the log data, the constructed 3D rock physics templates are calibrated, and the calibrated templates are applied to the work area. For the 2D seismic test lines (crossing the three wells) and a 3D seismic dataset, porosity, crack aspect ratio, and quartz content are quantitatively estimated. Compared to the actual data analysis, it is concluded that the range of the predicted porosity for high-quality shale reservoirs are in good agreement with the log data. The gas production data for the target layer of the three Wells are consistent with predictions. The characteristics of high porosity, low crack aspect ratio, and high quartz content of rocks of target formation effectively indicate the spatial distribution of high-quality shale reservoirs.