Influence of salt structures on reservoir rocks in Block L2, Dutch continental shelf

Abstract

In the subsurface of the Netherlands continental shelf, thick layers of Zechstein salt have developed into salt domes and ridges that occasionally pierce through the overlying formations. To measure the influence of the salt on the laterally adjacent Mesozoic sandstone reservoir rocks, a 'cementation model' was developed. The target area, Block L2, was chosen for the presence of salt domes, reservoir rocks and five representative wells. All available well information (wire-line log, test and core data) has been used to detect the presence of salt in the Lower Triassic and Upper Jurassic reservoir intervals. This was done mainly by combining gamma ray, sonic, resistivity and density data from the well logs into a computer model. The cementation model produces displays on which the presence of halite cement is clearly indicated. Only one well, L2-2, located within a few hundred metres of a salt dome, showed salt plugging. In the main reservoir rock, the Volpriehausen Sandstone (Lower Triassic), four other wells, located at more than 1.5 km from a salt dome or ridge, did not show signs of halite cementation in this reservoir. Therefore, the influence of salt domes on the surrounding reservoir rocks is believed to be restricted to less than 1.5 km at 1-2 km depth. The salt plugging of the Detfurth Sandstone (Lower Triassic) can be attributed to early seepage from the evaporitic Rot Formation. Because the Detfurth Sandstone in the L2-2 well is not salt-cemented, seepage of Rot brines into the Volpriehausen Sandstone reservoirs can be excluded.