Diffraction imaging: A valuable complement to reflection imaging for sand injectite interpretation in the Norwegian North Sea

Abstract

Interpretation of sand injectite reservoirs from conventional reflection seismic data is a complicated exercise. The complex geometries of injectites are challenging to detect and resolve by using conventional seismic processing due to their lateral and vertical variability in thickness and dip. Steeply dipping injection dikes tend to appear blurred or distorted on reflection images, and interpretation of their positioning and thickness carries an important level of uncertainty. Structural attributes derived from reflection images are used to support interpretation, but they suffer from a lack of spatial resolution and vertical continuity. We introduce a novel interpretation workflow that includes a diffraction image in addition to the conventional reflection image to improve the detectability and resolution of steep injection dikes and small-scale features. The diffraction image is generated in a migrated dip-angle domain where diffracted and reflected energy can be separated. A case study from a large injection complex in the Norwegian North Sea illustrates the superiority of the diffraction image over conventional structural attributes to support the interpretation and characterization of thin and steeply dipping injectites. The complementarity of the reflection and diffraction images is exploited by visualization techniques (e.g., corendering) or by combining interpretations from separate images, providing a complete picture of the injection complex geometries. Diffraction imaging proved to be a valuable tool to improve the level of detail and confidence in the interpreted injectites, both for modeling and well-planning purposes.