The Interplay between Microbial Reservoir Souring and Barite Precipitation During Waterflooding Oil and Gas Reservoirs

Abstract

Summary Seawater flooding is a common strategy of improved oil recovery, during which seawater, containing sulfate (SO42-), is injected into oil reservoirs to maintain reservoir pressure and sweep out oil. The presence of sulfate in an oil reservoir may trigger two harmful mechanisms, namely microbial reservoir souring and sulfate scales deposition. Microbial reservoir souring is a process in which sulfate reducing bacteria (SRB) consume sulfate and produce hydrogen sulfide (H2S). Scale formation, occurs if, for instance, seawater, containing sulfate, mix with a Ba2+-rich formation brine to form barite (BaSO4) scale. Due to the possible competition of these processes on consuming sulfate ions, an inclusive simulation of these processes is desired. This study utilizes a model that is capable of simulating reservoir souring and mitigation strategies along with scale formation inside the reservoir. The model simulates multi-phase flow using a commercial reservoir simulator, the chemical species transport, and the chemical reactions. It is shown that higher reservoir souring reduces the total barite formed in the reservoir. Conversely, barite formation has minimal effect on reservoir souring unless the injected sulfate concentration is low. Furthermore, if more barite is formed deep in the reservoir, less barite is formed around the production well.