Laboratory investigation of using a ternary polymer of itaconic acid-sodium polystyrene sulfonate-acrylamide as an inhibitor for calcium carbonate scaling in formation water

Water flooding is one of the methods of enhanced oil recovery in which formation water is injected into the oil reservoir. Calcium carbonate deposition is one of the challenges in the field of water flooding and oil production. It leads to a reduction in oil production due to deposition on reservoir rocks and the path of oil movement.

The use of chemical additives, especially hydrophilic polymers, has been widely studied to prevent calcium carbonate deposition. In this study, a ternary hydrophilic polymer was used to investigate the inhibitory effect on calcium carbonate scale in the formation water of an Iranian oil reservoir. The optimal concentration of this polymer, considering its inhibitory performance coefficient in formation water, was determined to be 800 milligrams per liter based on the calcium ion concentration. This optimal concentration was then used for subsequent experiments. Temperature studies on the inhibitory performance of this polymer showed that at reservoir temperature (75 degrees Celsius), 800 milligrams/lit of this ternary polymer demonstrated good performance. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were used to study the physical mechanisms involved in preventing calcium carbonate deposition.

SEM results showed that calcium carbonate crystals, in the form of stable calcite with a regular uniform structure before the presence of the inhibitor, became heterogeneous and smaller in size after adding the polymer, disrupting their structure. On the other hand, XRD analysis indicated that adding this ternary polymer could significantly inhibit the growth of calcium carbonate crystals and prevent the transformation of vaterite into calcite. Additionally, aragonite crystals are dispersed in the water and washed away by the water flow.