Waterflooding in different reservoirs for pressure maintenance and recovering more oil is a well established practice in the oil industry. Many research studies have shown that the success of any waterflooding process is mainly dependent on both physicochemical (fluid-rock) and geochemical (fluid-fluid) interactions. These interactions have been extensively investigated during seawater injection into carbonate formations. However, the rock/seawater chemical interactions are completely different in sandstone than in carbonate formations, due to different rock mineralogy. Therefore, the main objective of this paper is to investigate both the potential physicochemical and geochemical formation damage mechanisms that might occur during injection of seawater into a central Arabia sandstone formation.
Scaling potential due to seawater-produced brine chemical interactions was investigated at an average reservoir temperature of 186°F, based on the Pitzer theory of electrolytes. In addition to the prediction data, laboratory compatibility tests were conducted to investigate the scaling potential in different seawater/produced brine mixtures at reservoir temperature. Since this sandstone formation contained different clays, such as illite and smectite, the clay swelling and fines migration tendency was explored using coreflood setup and zeta potential technique.
The saturation index (SI) of different scales, such as calcium carbonate and calcium sulfate, was found to be mainly dependent on a seawater/produced brine mixing ratio. Additionally, it was found that scaling did not occur in supersaturated mixtures of seawater, aquifer water and produced brine, which indicated that there is a critical SI for the scaling onset. The zeta potential for different formation rocks was determined for sweater, aquifer and produced brine. It was nearly zero when using only seawater. One of the major findings of this study is that the presence of sulfate ions caused clay particles to migrate even in high total dissolved solid (TDS) seawater of nearly 55,000 ppm.