The Role of Forward Seismic Modeling: Outcrop Analogs of Deep-Water Architectures

Jamie K. Pringle¹ and David A. Stanbrook^2
1School of Physical Sciences & Geography, Keele University, Keele, United Kingdom
²Nautilus UK Ltd, Hermitage, United Kingdom

Geometrical and architectural information from appropriately selected outcrop outcrops can be extremely valuable in building geologic models. Geologists must find a way to assess and distil key data from outcrop for comparison to seismic, petrophysical and other sub-surface tools. However, even high-resolution seismic can differ considerably from outcrop resolution - i.e. outcrop observations tend to be at a finer resolution than seismic. So how does the geologist bridge the gap between outcrop scale observations and seismic?

An answer to this question is the use of Forward Seismic Modeling (also known as synthetic seismic). This approach involves the collation of outcrop data in the form of large-scale photomontages which are then interpreted by a geologist which are tested by ground-truth and sedimentary logs which also provide high-resolution, 1D data. Other hand-held petrophysical tools (e.g. a gamma-ray spectrometer) may also be utilized. The detailed architectural interpretation is then fed into specialist software that convolves the model, using user-input seismic impedance contrast and dominant wavelet frequency. Impedance contrast can be calculated using published velocity and density values for different lithological types and allows the geologist to vary the rock-values to simulate the petroleum reservoir they are interested in. The geologist can also vary the frequency to simulate the depth and/or quality of seismic available to them.

Presented here are two examples of key architectural geometry models from outcrops of deep-water systems; 1) Ainsa II Channel, Campodarbe Group, N Spain; 2) Chalufy Onlap, Grès d’Annot, SE France. Varying velocities and rock-types are used in these examples to show geometries with dominant frequencies and rock values typical for Gulf of Mexico and North Sea reservoirs.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery