Salt insertions in sedimentary sequences: impacts on temperature and thermal maturation with depth

Abstract

Due to the contrast in thermal conductivity between salt and typical sedimentary formations the presence of salt in various shapes in the sub‐surface can have a significant impact on the sub‐surface temperature distribution and thermal maturation of source rocks.Using a thermal indicator tomography 1‐D modelling system, which deals with salt insertion, the thermal and excess maturity anomalies caused solely by the presence of a salt layer are investigated. Two cases, salt ‘plug’ and ‘lens’, illuminate the different patterns of vitrinite reflectance variation with depth that would be recorded by borehole sampling. Salt can be inserted either as a primary depositional layer or by secondary intrusion at depth.The effects of salt are more dominant on the subsalt layers because: 1 salt insertion changes the burial paths of subsalt sediments. Thus the compaction‐driven fluid flow of subsalt sediments, and also basement subsidence, are altered;2 iso‐temperature lines are modified by the presence of the salt and the variation depends on the thickness of the salt layer.The model was also designed to estimate the time of salt insertion and the variation of salt thickness in an inverse sense using present day data on temperature with depth and measured thermal indicators. An investigation is given of the degree to which inverse procedures resolve parameters associated with salt insertion. The sensitivity of those parameters is also discussed.