Numerical modelling of salt diapirism and the temperature field during thin-skinned extension; in search of geothermal and hydrocarbon energy sources

Abstract

The occurrence of salt diapirs is strongly associated with potential geothermal and hydrocarbon energy sources. Many numerical modelling studies of diapirism have been done in the past, though very few of these in fact use geologically realistic settings and materials. Besides, only analogue and structural studies have been done on full scale diapirism during thin-skinned extension. Numerical modelling of this problem, using a code called ELEFANT, could answer the following questions: ”which parameters affect the growth rate and shape of the diapir, and how?” and ”what is the effect of this diapirism on the temperature field and surface heat flux?” The results show that, in compliance with both analogue modelling and structural geological studies, a diapir formed during thin-skinned extension undergoes three phases: reactional piercement, active piercement and passive piercement. Extension rates directly influence the total time required for the diapir to reach the surface, as well as how long the system remains in a state of reactional diapirism, which both affect the shape of the resulting diapir. The mass diffusivity coefficient affects the growth rate of the diapir during its active stage and the total rising time, which affects the shape of the diapir. The density contrast between the salt and the sediments also influences the growth rate during active and passive piercement. Surrounding a rising diapir the temperature is heightened, although not as much as expected. It can, however, still be valuable for hydrocarbon exploration. The heat flux above the diapir is higher than away from the diapir. Besides, both an increased bottom temperature and an increased salt conductivity give higher surface heat fluxes. This makes it an important feature for geothermal energy.