Impact of a Vertical Temperature Gradient on H2S Gradient in Sour, Near-Critical Reservoir Fluids

Abstract

Abstract An equation of state model is presented, developed for an H2S-rich field, where the fluid type changes smoothly from gas to oil through a zone with a critical fluid and not through a classical gas-oil contact with a discontinuity in fluid properties. For use in connection with compositional reservoir simulation studies, a depth gradient model has been developed that provides a good representation of the compositional variation with depth, including the depth where the fluid type changes from gas to oil. The depth gradient model considers the influence of both gravity and the vertical temperature gradient on the distribution of the individual components in the fluid column. A depth gradient model that only considers gravity and ignores the temperature gradient will simulate an increasing H2S concentration with depth, while the fluid samples show that the H2S concentration decreases with increasing depth. When the effect of the temperature gradient is included, a good match is obtained of the development of fluid composition, saturation point and GOR with depth.