Overpressure Condition Versus BSR

In order to improve the hydrate knowledge, it is very important to analyze the relationship between hydrate stability and overpressure condition. The overpressure condition in the free gas zone causes the disagreement between theoretical and seismic BSR depth. We model the effect of the overpressure condition versus sea water depth, geothermal gradient and hydrate stability. We introduce the following concepts: 1) hydrostatic BSR, which is the theoretical BSR evaluated supposing hydrostatic pressure in the pore space, and 2) the overpressure BSR, which is the BSR shifted with respect to hydrostatic condition because of the overpressure in the free gas zone. We draw the following considerations: i) the difference between the hydrostatic and the overpressure BSR depths is inversely proportional to water depth; ii) the geothermal gradient is inversely proportional to the difference between the hydrostatic BSR and the overpressure BSR depths. These results of this study are very useful in many fields. First of all, they should be considered in the environmental hazard. In fact, the hydrate present below the hydrostatic BSR is probably in meta-stable condition and more sensible to boundary conditions. Moreover, the effect of overpressure is important in shallow water, where human manufactures are located.