5.1.3. Model 2

Due to the uncertainty in interpretation of the salt bodies on Model 2, we have made three modeling options for determination of the temperature history and maturation (shown in Figure 13). The temperature over the profile was calculated based on thermal conductivities of the sediments (as a function of porosity; given in Table 1) and the modeled palaeo heat flow.

In Reference [26], the authors have found significant anisotropy in the thermal conductivities of shales in the North Sea. This is taken into account in our study. The vertical and horizontal thermal conductivities are shown in Figure 18a.

The palaeo heat flow was calculated by two tectonic events in the area; a Permo-Triassic event and a Mid-Jurassic to Earliest Cretaceous event; see more details in Reference [22]. The effect of the salt body on temperature history for a selected point (location; Figure 13c) above the salt is shown in Figure 18b. The calculated temperature is, as expected, the highest for the maximum-salt model.

**Figure 18.** Thermal conductivity and temperature history for the three salt models shown in Figure 13. (**a**) Thermal conductivities used in the modeling. Kv=vertical conductivity, Kh=horizontal conductivity. Note that shale and claystones have different Kv and Kh. Other lithologies have uniform conductivities in both directions. (**b**) Calculated temperature history for the point above the salt close to base of well 7/9-1 (position shown in Figure 13). (**c**) Present day calculated and observed temperature in wells 7/9-1 and 7/12-11.

The present day heat flow is found by calibration to present day temperature. The calculated versus observed present day temperatures for the wells 7/9-1 and 7/12-11 are shown in Figure 18c. The calculated present day temperature difference is approximately 10 ◦C between the max-salt model and no-salt model. We have used uniform heat flow over the profile and the same matrix thermal conductivities within the various sedimentary units over the profile. Based on these assumptions, we see that the best match with the observed temperature in well 7/9-1 is given by the minimum-salt option and the no-salt option. The largest discrepancy is given by the max-salt option. A better fit for the max-salt option could be achieved with a reduced heat flow; however, a reduced heat flow would give larger discrepancies for well 7/12-11 for all three options; the three options are already at the lower possible range.

Figure 19 compares the present day temperatures on the models with no salt and maximum salt, as defined in Figure 13. In the model with salt, isotherm curves rise above the upper part of the salt columns, but dip down in the deepest part of the salt and below the salt columns. The increase in temperature can be visible at least 2400 m above the top of the large salt column at position 13 km on the modeled profile. At the base of the intra-salt basins, the temperatures are lowered by about 20 ◦C. At the top of the salt columns, the temperature increases up to 8.5 ◦C, most above the highest ones.

**Figure 19.** Calculated present-day temperature for models with salt and without salt. The temperature isotherm curves for the model with salt (stippled lines and blue temperature numbers), and the model without salt (continuous lines, black temperature numbers). In the salt model points A–D show higher temperatures than in the model without salt. Points F–H show lower temperatures in the salt model.
