Increasing inhibition performance of simultaneous precipitation of calcium and strontium sulfate scales using a new inhibitor — Laboratory and field application

Abstract

In this work, the calcium sulfate (anhydrite) and strontium sulfate precipitation simultaneous prediction was performed at various reservoir pressures, temperatures, and mixing ratios of injection and formation water. In addition, in order to prevent the precipitation of calcium and strontium sulfate scale, the inhibition performance of five various well-known scale inhibitors was evaluated by conducting different experiments. The results showed that the possibility of calcium and strontium sulfate precipitation was directly proportional to the temperature and inversely proportional to pressure. The worst scenario for the simultaneous calcium and strontium sulfate scale formation was observed in a mixing ratio of 1:1 injection and formation water. A mixture of reagents (new inhibitors) — DPAAI (three phosphonate scale inhibitors, ammonium bifluoride, isopropyl alcohol, and water) was developed in order to enhance the prevention performance of calcium and strontium sulfate salt precipitation. DPAAI had an efficiency of 94% under static conditions, and its effectiveness was not changed by increasing the temperature up to 150 °C. The induction period of strontium sulfate crystallization in the presence of DPAAI was 70 min, which was 2.89 times longer than in a blank case. The interfacial tension of DPAAI and oil was reduced more than 10 times in the presence of an alcohol propoxy sulfate at a mass concentration of 1.5%. Furthermore, the rock permeability with the use of DPAAI was improved from 33% to 95% of the initial permeability. The squeeze lifetime of DPAAI for preventing the simultaneous calcium and strontium sulfate scale precipitation was about 85% longer than the squeeze lifetime of the investigated common phosphonate scale inhibitors.