--> Enhancing Subsurface Imaging and Reservoir Characterization in the Marcellus Through Advanced Reprocessing of Wide Azimuth 3-D Seismic

AAPG ACE 2018

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Enhancing Subsurface Imaging and Reservoir Characterization in the Marcellus Through Advanced Reprocessing of Wide Azimuth 3-D Seismic

Abstract

The Marcellus Shale holds vast volume of unconventional gas. It was the source of over 36% of shale gas production in US in 2015. However, it has been a challenging task to identify the productive sweet spots for the best capital deployment to optimize return on investment. The Marcellus shale sits in a geologically complicated region, characterized by faults, and salt cored compressional folds. Thus large lateral velocity variations are often associated with this complex assembly. This combination of complex structure and lateral velocity changes makes seismic imaging very difficult. Even the most recently acquired 3D seismic with wide azimuth and long offset has shown poorly imaged folds and faults around the Marcellus shale. The 2013 vintage 3D seismic imaging products are not able to image the folds and faults properly. Many wells drilled show that the existing 3D seismic volumes often present incorrect dips of the faults. We have frequently mistaken folds as faults, or vice versa, due to the poor imaging quality.

We have carefully examined each processing step in the seismic processing and imaging workflow, and identified a few key drivers that could potentially provide improvements for the subsurface imaging. Starting from field seismic records, we identified geometry errors. Better noise attenuation practices including land surface related multiple elimination (LSRME) were applied to improve S/N. An extensional patch was carefully tested and validated in the 5D interpolation which improves the offset coverage in the narrow direction. Furthermore, we performed orthorhombic PSTM. Orthorhombic velocity model fits the data better than the traditional VTI model for layered subsurface with a dominant set of fracture system. Significant improvement of the subsurface imaging was observed. Steeply dipping (750 and above) faults are correctly imaged which were previously elusive or absent. Formerly identified faults are now clearly imaged as folds, small or large in scale. With these imaging improvements, we are able to accurately drill through the laterals which were otherwise missed. Some large faults are amazingly imaged which pass through both the Marcellus and upper sections to the Tully, previously barely visible. The revelation of such large faults effectively helps avoid geohazard. The dramatic improvement in the subsurface imaging and amplitude friendly processing enhance the reservoir description of the Marcellus shale.