ABSTRACT

The thermal histories of sediments above and adjacent to two salt diapirs in the Scotian Basin, on the Nova Scotian continental margin, are estimated from numerical models. The purpose of the study was to determine whether the paleotemperatures of strata near salt structures were significantly different from those of contemporaneous strata unaffected by the presence of salt; if they were, the thermal maturity and potential for hydrocarbon generation of the two regimes will also be different. The results show that the thermal conductivity contrast between salt (high conductivity) and the adjacent sediments (low conductivity) allows salt diapirs to funnel heat upward into the overlying sediments. The contrast, however, does not raise the temperatures in these sediments enough to cause a significant increase in the levels of thermal maturity. The thermal effects of upward motion of hot salt are shown to be unlikely to cause a significant increase in maturity. The migration of hot fluid up the sides and across the top of a diapir appears to be the most likely cause of significant increase in the level of thermal maturity within the sediments above the salt. It is therefore concluded that the mere physical presence of salt diapirs in the Scotian Basin does not directly cause an enhancement in the thermal maturity of adjacent sediments. Fluid migration around salt diapirs, however, may be an important factor under certain circumstances, and deserves further investigation.

DIAPIRISM SALIN ET MATURITE THERMIQUE: SCOTIAN BASIN

RESUME

L'histoire thermique des sediments qui bordent et couvrent deux diapirs salins dans la Scotian Basin de la marge continentale de la Nouvelle Ecosse est estimee a travers l'utilisation de modeles numeriques. Le but de cette etude est de determiner s'il existe une difference notable entre les paleotemperatures des couches sedimentaires pres des structures salines et de celles qui sont contemporaines, inaffectees par ces structures. Les resultats montrent que le contraste en conductivite thermique entre le sel (haute conductivite) et les sediments avoisinants (basse conductivite) permet aux diapirs salins d'acheminer la chaleur verticalement vers les sediments sus-jacents. Ce contraste n'est cependant pas suffisament grand pour accroitre de facon significative les niveaux de maturite thermique. Il apparait peu probable que l'effet thermique d'une masse montante de sel a haute temperature affecte ces niveaux de maturite. La migration de fluides chauds vers le haut le long des marges et au-dessus de la crete des diapirs salins est la plus probable cause d'un accroissement significatif des niveaux de maturite des sediments adjacents. La migration de fluides autour des diapirs salins peut etre cependant un facteur important sous certaines conditions, et merite d'etre examinee en plus de profondeur.

Traduit par A. Zolnai