Thrusted and folded sediments provide an ideal geologic setting for hydrocarbon migration from source rock to reservoir. The same tilting of beds and faulting that enhance migration and form traps also compromise the ability to capture seismic reflection and refraction data from the ground surface. Simply put, steeply dipping beds divert seismic waves deeper into the earth, rather than back to receivers placed along the ground surface.
The Pelarang antiform (Figure 1) is one of many semi-parallel fold structures hosting major hydrocarbon reserves that cross the Mahakam delta of East Kalimantan, Indonesia. The structures host several minor hydrocarbon fields. The density contrast between deformed sediments of the antiform and that of the surrounding sediments are sufficient that Air-FTG® can be used to quantify the dip of the flanks of the antiform while seismic imagery fails to produce interpretable reflections.
Figure 2 shows a published seismic profile across the Pelarang antiform along with interpreted horizons.
Interpreted horizons across the flanks of the structure follow no coherent reflections (yellow shaded area) and thus serve merely as a crutch to tie surface outcrops to subsurface reflections interpreted where continuous reflection data is of higher quality.
Figure 3 shows the Air-FTG® Tzz anomaly with Contact Lineament Processing (CLP) applied along with the approximate location of the seismic profile (red line). Linear trends are enhanced by this method and reveal subtle structural trends along the crest of the antiform.
Air-FTG reveals the geometry of the entire fold structure with unprecedented precision while seismic reflection data failed.