Mapping, Modeling and Evolution of Salt Structure Geometries: Implications for Improved Sub-Salt Exploration*

By

Markus Mohr¹, Peter A. Kukla¹, Janos L. Urai¹, and Georg Bresser²

Search and Discovery Article #40214 (2006)

Posted September 30, 2006

*Oral presentation at AAPG Annual Convention, Houston, Texas, April 9-12, 2006.

Click to view presentation in PDF format.

¹RWTH Aachen University, Aachen, Germany ( [email protected]  )

²Formerly Gaz de France Production Exploration Germany GmbH, Germany; now Wintershall AG.

Abstract 

The improved understanding of the structural, sedimentary and salt-tectonic evolution of salt structures and knowledge of the position and amount of subsurface salt has significant effects on seismic modelling and depth conversion. The use of this information advances the prediction of potential Upper Permian gas reservoirs in the intracontinental sub-salt sequences in northern Germany.  

High-quality seismic data enable us to present an integrated genetic interpretation of salt-structure geometries and their associated sedimentary patterns. We combine 2D and 3D seismic interpretation of pre-stack depth-migrated data with 2D and 3D kinematic and geometrical retro-deformation in order to restore and illustrate salt tectonic processes through time, unravel their tectonic trigger mechanism and reveal the respective sedimentary response.  

This study identifies several salt wedges formed by lateral extrusions during periods of diapir emergence and reduced sediment accumulation. High-resolution seismic mapping and well-log analysis of the sedimentary stacking patterns show that the effects of syn-sedimentary salt movement with respect to accommodation development and salt flow are consistent with the regional structural and stratigraphic framework. Additionally, bedded primary evaporites (halite) in near-diapir strata of peripheral sinks show extreme thicknesses of salt-sediment interbeds. We suggest that saline brine was supplied to a formerly arid landscape through diapir dissolution by groundwater. Diapiric growth and the developing relief of the peripheral sink controlled preservation and salt accumulation of the bedded salt units. These near-diapir sequences form potential hydrocarbon traps and thus represent an alternate exploration target in most salt-rich hydrocarbon provinces.

Selected Figures 

	Location map of study area.
	W-E cross section (from 3D data) across a diapir with complex geometry (salt jags).
	Lateral extrusions from an emerged diapir. Left: paleogeologic map. Right: Depth-slice map (50 m below base Cretaceous).
	W-E seismic profile across a diapir showing lateral extrusions (three preserved salt glaciers at or near faulted west contact (lower right inset).
	Late Triassic salt-bearing rim synclines. Left: Interpreted seismic profiles, with major primary salt deposits arrowed. Right: Gamma-ray/caliper logs of wells on profiles that encountered primary salt deposits.