High-Resolution Characterization of Reservoir Heterogeneity and Connectivity in Clastic Environments

Abstract

This study developed new concepts and interpretative methods for mapping reservoir heterogeneity and connectivity of a fault controlled Wilcox clastic reservoir in Texas, USA. The application of high-resolution seismic enhancement in this study allows for better delineation of subsurface geologic features, detailed mapping of reservoir heterogeneities and more accurate identification of depositional, structural, and stratigraphic characteristics that control reservoir connectivity and fluid flow. Seismic enhancement in this study pertains to amplitude preserving neural network implementation of the Volterra integral equation of the first kind from a plane-wave solution of poro-viscoelasticity (Sun, et al., 2003). This enhancement amounts to an advanced spiked deconvolution of post-stack seismic data that broadened the dominant seismic frequency from 16Hz for the conventional seismic to 65Hz for the enhanced seismic. Bed resolution is improved from 175ft to 45ft and fault offset resolution is improved from 80ft to 20ft. High-resolution seismic interpretation was validated through synthetic seismograms, stratigraphic surface comparisons, and most importantly using a comprehensive model-based knowledge of regional tectonics and depositional environments. Stratigraphic features that were not resolvable in conventional seismic data can now be interpreted using the enhanced seismic data. An Upper Wilcox reservoir was identified as a transgressive sheet sand overlaying a progradational deltaic seismic facies. An Upper Middle Wilcox reservoir was identified as a probable lobate gravity flow, and a Middle Wilcox reservoir was identified as a transgressive sheet sand with over and underlying progradational deltaic seismic facies. Geobody extraction from seismic inversion volumes delineates reservoir compartments and flow units. Reservoir connectivity analysis performed on the Middle Wilcox reservoir determined the probable drainage area for a producing well by comparing estimates of compartmentalized hydrocarbon volumes with production information. The methodology developed could help extract connected geobodies defined by sand, porosity, permeability, and hydrocarbon indicators, to map in detail the internal structure of produced reservoir and to locate new development prospects. Enhanced seismic may thus enable us to find bypassed hydrocarbons and to provide better methods for improving recovery in the studied and other mature fields.