Experimental investigation and numerical modeling of barium sulfate deposition in porous media

Barium sulfate scale deposition has been a severe problem when injecting seawater into reservoirs for oil recovery. The precipitation of barium sulfate can lead to reduction in permeability and production loss. Coreflood experiments were performed to investigate barium sulfate scaling in near wellbore areas by co-injecting formation brine and seawater into Berea sandstone cores. Differential pressures at multiple segments along cores were recorded to study the permeability reduction induced by barium sulfate deposition. The mass of barium sulfate deposited in the core was calculated by mass balance and used to evaluate the relationship between permeability reduction and scale deposition. SEM-EDS was used to prove the barium sulfate deposition inside cores. The cores used for co-injection in this work had a length of 1 ft and experimental durations were up to 700 pore volumes (PV). Coreflood experiments in previous studies were only conducted for several hours, and the cores used were shorter than that used in our research. Coreflood experimental results showed that, in most of the cases, the differential pressure of the entire core increased during the co-injection process. The increases of differential pressures in the upstream section of cores were the most significant, while changes in downstream differential pressures were small. This indicates that barium sulfate deposited immediately in upstream core sections after mixing of formation brine and seawater, resulting in core permeability reduction. Micro-CT was used to characterize the distribution of barium sulfate deposition inside cores, and images showed barium sulfate mainly deposited at pore throats, and therefore, had significant impact on permeability.