Advanced Seismic Imaging Tools for Unconventional Targets in Complex Geology?
Operators in unconventional resource plays now generally acknowledge important roles (geosteering and geohazard avoidance) for 3D seismic data. Still, seismic is hardly “existential” to most plays, unlike traditional seismically-driven plays. If an operator acquires seismic data at all, it is only after locking up a large land position and planning the drilling program. However, with available acreage at a premium, unconventional players will inevitably move into more geologically complex areas, where conventional time migration processing may fail to resolve faults or may mis-position steeply dipping beds. Our case study highlights the performance of RTM (Reverse-Time depth Migration) on a 2D line from the Colorado Front Range. The basin sediments are about 12,000 feet thick, and against the mountain front, the fractured Niobrara Shale section produces oil. Laramide compression produced a low-angle thrust fault, which uplifted and tilted the basin sediments at a 40-degree angle. The resulting lateral velocity variation causes a false time structure and laterally mis-positions events on time migrations. By closely integrating geophysics and structural geology, we constructed a geologically-feasible velocity model which produces a well-focused seismic image. We found that a TTI (tilted transverse isotropic) RTM produced the best image of the steep dips and sub-thrust features. By combining the most advanced geophysics with structural geology, we demonstrate the potential for seismic data to play a pivotal role in de-risking unconventional plays as operators move into more complex basins.
AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014