Impacts of vertical salt welding on pore pressure, stresses, and deformation near the weld

Abstract

We use a forward finite-element model to explore pore pressure, stresses, and deformation near a vertical weld. Dipping layers of mudrocks interbedded with a mixture of basin-center and basin-wide sand layers are deposited sequentially over a salt layer. After a salt wall rises at the downdip end of the model and emerges at the basin surface, shortening is imposed on the system until the salt wall almost welds where the wall feeder is narrowest (waist). Welding causes a significant increase in horizontal stress, which results in increased pore pressure near the weld. The pore-pressure increase adversely affects hydrocarbon accumulation and drilling near the weld because it: 1) causes remigration of pore water downdip along sand beds cresting near the weld, 2) decreases the hydrocarbon-column capacity of these beds, and 3) narrows the mud-weight window for drilling wellbores near the weld. The least principal stress near the weld is almost vertical and equal to the overburden stress in mudrocks, but horizontal and significantly lower in sand beds. Welding of the salt wall causes steepening of flanking strata and shortening of the weld wall rocks. The impacts of welding begin at a waist width of 1.35 km, long before the salt wall welds.