(1) Schlumberger RS/DCS, Houston, TX
ABSTRACT: Detection of Shallow Hazard Formations Using High-Resolution Seismic Data and Inversion Based on Rock Physics
Detection of hazardous zones, associated with high-pressured fluids in unconsolidated
sands and shales, prior to drilling, is essential for environmental as well as health and
safety. Drilling for deepwater targets is associated with high cost and risk, while
margins of commercial operations are small. Therefore, it is imperative to control cost
through accurate well planning and reliable anticipation of geohazards.
This paper deals with a novel seismic approach that uses the full bandwidth and the entire offset range of the conventional 3D seismic data to detect the presence of hazardous zones. Both in shallow and deeper zones, P- and S-velocities are determined using seismic full waveform prestack inversion. Shallow water flow (SWF) layers in the deepwater are identified through the associated high ratios of P- to S-velocities. A new, rock model-based approach especially suited for deepwater pore pressure imaging was applied to predict the presence of both shallow and deeper over-pressured zones.
This paper covesr the essential elements of the workflow – a “five-step process” for hazard identification that integrates a special data processing flow with prestack and full waveform inversion of 3D seismic data with geology and rock models appropriate for shallow water flow, gas hydrates and deeper geohazards. Real data examples from deepwater elucidate the approach.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.