4D modeling of salt sediment interaction during diapir evolution

Jean-Paul Callot¹, Daniel Rondon¹, Christophe Rigollet², and Jean Letouzey^1
1IFP, Rueil Malmaison, France
²Gaz de France, Saint Denis la Plaine Cedex, France

We performed sand/silicon models imaged with X-ray tomography and reconstructed by 3D geomodelling for the study of (1) the interaction between host rock and the salt diapir during the diapir growth, and (2) the evolution of intra salt brittle rocks during the diapir ascent. X-ray tomography is a non-destructive imaging technique which allows us to follow the 4D evolution of the analogue model. Salt is modelled with Newtonian silicone putty and the internal rock layer, as well as the sedimentary host rock, by a granular Mohr-Coulomb material, generally coryndon. The analogue models are then compared to natural example which evolution is obtained through 3D restoration of the structures.

(1) A 4D evolutionary scenario for a salt diapir development was originally proposed by Trusheim (1960) and discussed later on by Vendeville (1999) among others (Ge et al, 1997; Zirngast et al, 1996). This scenario is reproduced through analogue models to test the relative importance of (1) extensional tectonics, (2) sediment progradations, and (3) source layer depletion and rim-syncline touchdown, in the evolution of a diapir. The comparison of our results with the restored natural analogue shows that the main parameter remains the rim-syncline touchdown and the unloading of the diapir due to erosion, which account for a drop in strength necessary to allow for the flank rotation and down building of the diapir. Extensional stresses and sediment progradations will also amplify the halokinesis.

(2) Salt diapirs from the Middle East or in Southern Permian Basin petroleum province show exotic blocks at outcrop and in salt mines, known as 'stringers' in subsurface data, usually composed of anhydrite, dolomite, marls or carbonates. These stringers, which constitute major structures inside the salt diapir, can reach a few km in size and originate from pre-existing brittle rock layers embedded in the salt layer. Stringers of the Ara carbonate within the Precambrian salt in Oman produce oil, but constitute a major exploration risk due to large technical difficulties of structural and seismic imagery, complexity in deciphering their evolution steps, and possible unexpected overpressures. 4D analogue modelling of cylindrical and salt-like diapirs is performed to reproduce the evolution of internal sand layer during diapir growth. The growth and geometry of the salt structure is entirely controlled and only driven by the overburden deposition. After a certain amount of ascent, the diapir is killed by the rapid deposition of a thick sand layer on top, and time is given to the floating stringers to fall inside the diapir. The 3D internal geometry is reconstructed for different steps to show the progressive rise, tearing apart, and fall of the stringers pieces. Complex geometry are observed and compare well to natural examples picked on seismic imagery. It appears that stringers observed in the German salt basin may originate from cap rock pieces detaching from the diapir roof and drowning in the salt.

These studies emphasize the importance of a constant forth and back re-evaluation between the model and the natural example 3D evolution, and show the interest of obtaining a 3D restoration of the natural examples studied.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands