Seismic amplitude and coherency response of channel sand, offshore Louisiana, Gulf of Mexico

Abstract

Geological drilling hazards are a major concern in the ics. drilling and development of offshore reservoirs. Some of these hazards may display high amplitudes on seismic profiles and some may be associated with stratigraphic features. Seismic amplitude anomalies associated with channel sand deposits may indicate potential accumulations of hydrocarbons in reservoirs. However, shallow hydrocarbon accumulations are rarely of production size. More often, they are potential geological drilling hazards that could inhibit the development of petroleum resources from deeper hydrocarbon-bearing layers. Traditionally, existing and potential geologic hazards are identified by interpretation of high-resolution site survey data, acquired specifically for drilling hazard delineation. This paper describes a new technique for drilling hazard identification using a conventional 3D seismic amplitude dataset. An event coherence calculation program is applied to a 3D seismic dataset to derive seismic attributes sufficient to highlight structural and stratigraphic discontinuities in the area. A resultant 3D difference cube is used to establish fault framework and to detect spatial distribution of channel deposits in the area and their geometries. Superposition of the difference cube on seismic amplitude data allows simultaneous display of structural and stratigraphic discontinuities and reflectivity information. Therefore, it is used for the delineation of channels, which show anomalous amplitudes, identification of their dimensions and spatial locations, and implication of gas-charged sand distribution within the detected channel. The paper gives a detailed description of a workflow, which was found sufficient for delineation of likely gas-charged sand channels, and discusses the ways to adjust the proposed workbox to specific objectives.