Polymer-Based Scale Inhibitors for Seawater Injection Operations in High-Salinity Formation Water Reservoirs

Abstract

AbstractWater flooding using seawater is a major oil filed operation implemented in different carbonate and sandstone reservoirs to maintain reservoir pressure and enhance oil recovery. However, due to the high sulfate content in the injected seawater, significant calcium, barium and strontium sulfate scale deposition can occur and cause severe formation damage. Typically, scale inhibitors are applied in the field to prevent the formation of calcium sulfate scale where they act either as chelating agents to form a soluble complex, as threshold inhibitors, which block the development of the supercritical nuclei or as retarders of the growth of the calcium sulfate crystals. The objective of this study is to evaluate the effectiveness of different types of scale inhibitors to prevent the formation of calcium sulfate scale during the injection of seawater into high-salinity bearing carbonate reservoirs.Jar testing and SoftPitzerTM software were used to investigate the calcium sulfate precipitation due to the mixing of high calcium-content (37,000 mg/L) formation water and high sulfate-content (4,000 mg/L) seawater. This investigation was conducted on different mixtures of formation water and seawater at reservoir temperature of 155°F. Different types of scale inhibitors were tested to prevent the scaling of calcium sulfate in mixtures of seawater and formation water. The compatibility of these scale inhibitors with calcium ions present in formation water and also their effectiveness in preventing CaSO4 scaling were investigated using bottle testing. In addition, coreflood experiments were conducted to determine the adsorption behavior of these inhibitors in carbonate rocks.Results showed that the application of two scale inhibitors (Acrylic homopolymer-based) can successfully mitigate calcium sulfate scale formation in seawater/formation water mixtures up to 155°F. Each one of these two scale inhibitors has its own effective minimum inhibition concentration (MIC). In addition to these results, the paper provides insights into the adsorption behavior of these inhibitors in carbonate rocks and how this affects their performance.