Interactions of common scale inhibitors and formation mineral (calcium carbonate): Sorption and transportability investigations under equilibrium and dynamic conditions

Abstract

Formation and deposition of mineral scales pose a serious threat to the safety and integrity of oilfield operations. Scale inhibitor chemicals have been widely employed to control scale threat and enhance production efficiency. The inhibitor-formation mineral interaction together with inhibitor transport behavior play significant roles in the design and optimization of oilfield inhibitor treatment. However, limited studies have been reported to investigate the principles dictating the inhibitor-mineral interaction under both equilibrium and dynamic conditions. Moreover, there are few studies focusing on the inhibitor transport at a lower inhibitor concentration. In this study, a systematic evaluation of the physicochemical nature of inhibitor-formation mineral interactions was conducted with a focus on lower inhibitor concentrations (below 50 mg L−1) by adopting two common oilfield inhibitors of diethylenetriamine pentamethylene phosphoric acid (DTPMP) and phosphino-polycarboxylic acid (PPCA). The formation mineral employed in this study is calcium carbonate (calcite). Both equilibrium and the kinetics aspects of inhibitor sorption behavior have been studied experimentally via static batch and dynamic column apparatus. It was found that the adsorption capacity of calcite for DTPMP is higher than that of PPCA. Laboratory fixed-bed column transport experiments were carried out at different physicochemical conditions of initial inhibitor concentration, ionic strength, temperature, flow rate and calcite particle size. Results indicate that an increase in both DTPMP and PPCA concentration can expedite inhibitor transport and a high initial DTPMP concentration could significantly affect the retention of DTPMP in the calcite porous medium. Ionic strength can result in a higher transportability in calcite medium for both inhibitors. Change in temperature has no significant impact on inhibitor transport. The flow rate has a considerable influence on the dispersion coefficient due to elevated mechanical dispersion at a higher flow rate for DTPMP. The calcite particle size can also impact inhibitor adsorption due to the change in surface area. Furthermore, adsorption of PPCA can subject the calcite surfaces more hydrophilic than DTPMP, which can affect the mobility of inhibitor in calcite medium. Atomic force microscopy characterization results confirmed that the wettability of calcite was increased through adsorption of DTPMP and PPCA inhibitor. This study provides deep insights into the sorptive behavior and transportability of DTPMP and PPCA inhibitors in calcite porous medium.