Estimation of fracture pressure gradients in the shallow sediments of the Mediterranean Sea by using ODP Leg 160 and Leg 161 data

Abstract

Pore pressure gradient and fracture gradient are two of the most important parameters while making well drilling design. Hence, in this study, these gradients were estimated for the Mediterranean Sea shallow sediments where gas hydrate might exist by using ODP Leg 160 and ODP Leg 161 data (mainly density logs). The density logs obtained during these drilling programs were used to estimate fracture pressure gradients. In this study, pore pressure gradient intervals in the Eastern Mediterranean Sea and the Western Mediterranean Sea were estimated as 0.433–0.484 psi/ft and 0.459–0.460 psi/ft, respectively. It was found that geothermal gradients of the holes drilled in the Western Mediterranean Sea sediments are quite high (up to 128 °C/km) but the maximum geothermal gradient observed in the Eastern Mediterranean Sea is 12.85 °C/km. The estimated fracture pressure gradient ranges in the Eastern Mediterranean Sea and the Western Mediterranean Sea shallow sediments are 0.604–0.659 psi/ft and 0.675 psi/ft-0.766 psi/ft. For the first time, the fracture gradients in the shallow sediments (where gas hydrate might exist) of the Mediterranean Sea were predicted in this study. These fracture gradients are suggested for the drilling and well completion designs of gas hydrate wells in the conditions of the Mediterranean Sea.