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Rock physics modeling for quantitative seismic characterization of tight-gas sandstones in Neuquén Basin, Argentina
Silva, Átilas Meneses da
Silva, Átilas Meneses da
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2020
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Abstract
The basin-centered gas accumulation (BCGA) of Lajas and Punta Rosada formations is composed of a stack of low porosity (4% - 10%) sandstones, highly pressurized and pervasively saturated with gas, reaching up to a thickness of 1,000 meters. The low porosity of the reservoirs causes very low seismic sensitivity to the fluid variation, and traditional analyses used in conventional reservoirs may not give the correct assessments for this type of rock. Therefore, I apply multiple approaches to distinguish the effects of fluid, lithology, and porosity on the seismic response. A Monte Carlo simulation is used to assess the amplitude variation with angle (AVA), identify the most likely AVA class, and analyze the dispersion of the gas-bearing reservoirs within the AVA space. In addition, a hybrid rock physics modeling, which considers the pore shape as input, is used to predict the seismic properties of the reservoir rocks. The proposed workflow combines laboratory measurements with Kuster-Toksöz (KT), Differential Effective Medium (DEM), and Gassmann theories. Using the rock physics model and corresponding templates, I formulate rock physics attributes that are highly correlated with water saturation, porosity, and clay content. Finally, the rock physics templates and attributes are used with the elastic seismic inversion to enhance understanding of the anatomy of this gas field and to determine which factors drive gas migration and accumulation in this complex petroleum system. I found that the most important gas zones in the Punta Rosada Formation are located around the natural fractured regions. For the deeper Lajas Formation, however, the gas is spread throughout a wider area, as this formation lies directly above the Los Molles source rock, facilitating the vertical and lateral gas migration.
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