Anisotropic Rock Model-Guided Post-Stack Attribute Analysis With Pore Type and Production Data for a Carbonate Gas Reservoir

Abstract

The Moxi area in the Sichuan Basin is dominated by carbonate gas reservoirs, where gas productivity is most strongly influenced by their pore types. Fractured caves are the most favorable pore structure type for reservoir productivity, followed by cave and vuggy pore structures, and interparticle pore structures are the least productive. The spatial discrimination of these three pore types is important for cost-effective development. However, the pore type identification remains difficult owing to poor-quality azimuthal seismic data. A practical approach is to understand the seismic signatures of the different pore types and the related productivities from the post-stack data. In this work, seismic forward modeling is conducted using a constructed theoretical model of Hudson's anisotropic representation, and the pre-stack and post-stack anisotropy signatures are analyzed for different pore types. The rock model is further calibrated using log data, and forward modeling is performed based on the calibrated logs. We propose a new attribute of these signatures: namely, the ratio of the absolute peak and the absolute trough immediately below the peak, which is applied to the three-dimensional seismic data in the Moxi area. In contrast with other conventional attributes, this ratio effectively correlates with pore type, which allows the pore types in wells to be differentiated. This attribute also reasonably correlates with open flow gas rate of the well. The results demonstrate that this attribute from the post-stack data is a promising indicator of pore type and gas productivity and can also be readily mapped spatially for the selection of new drilling locations.