Study on the scale inhibition performance of organic chelating agent aided by surfactants on CaCO₃ at high salinity condition

The salt blockage layer formed in the wellbore during the development of high salinity oil and gas fields has a serious impact on the safety of oil and gas production of the oil and gas fields. CaCO3 is the main component of scale in high salinity oil and gas fields. Herein, focusing on CaCO3 as an example, the precipitation and scaling process as well as the change of crystalline form of CaCO3 under different temperature and salinity conditions were studied. The effects of two addition methods of organic chelating agent on the solubilization and dislodgement of CaCO3 under high salinity conditions were also explored. The optimal concentration of organic chelating agent is determined to be 1 % and 5 % for solubilization and dislodgement, respectively. It was found that the solubilization is achieved by inhibiting the stable and difficult to treat calcite crystal phase to generate more irregular and more dispersed aragonite CaCO3. Organic chelating agent contains a large number of carboxyl groups in its molecules, which can be adsorbed onto the surface of CaCO3 crystals through electrostatic adsorption. By chelating Ca2+ in stable and difficult to treat calcite CaCO3, the further ordered growth of the crystals is prevented, causing lattice distortion or large crystal rupture, thereby achieving dislodgement. This study will provide theoretical and technical support for the solubilization and dislodgement of salt blockage layer in wellbore at high salinity conditions.