Preparation And Performance Studies Of Calcium Alginate Microcapsules With Inhibitor

Using CO2in the oil and gas industry can improve the oil and gas recovery efficiency. However, CO2has a severe aggressiveness to the oilwell. Usually, the liquid corrosion inhibitor is injected into the oilwell to solve the CO2corrosion problem, but such injection operation has some disadvantages, such as inconvenient to operation, difficult for the inhibitor to reach the bottom of oilwell, short effective period, large consumption of inhibitor, etc. Therefore, there are significant research and application values to develop a solid corrosion inhibitor to solve oilwell downhole corrosion problems. This thesis consists of the following two parts:(1) Calcium alginate gel microcapsules (Alg-Ca2+microcapsules) loaded with oilfield-used corrosion inhibitor and heavy additive were prepared with piercing-solidifying method. The morphologies and structure of microcapsules were characterized by scanning electron microscopy (SEM). The loading amount of corrosion inhibitor was confirmed by thermo-gravimetric analysis (TGA). The effect of heavy additive’s amount on the sinking rate was also investigated. Furthermore, the releasing of corrosion inhibitor from the microcapsules was investigated by ultraviolet spectrometrys spectrophotometer (USS), and the corresponding anticorrosion performance was studied by potentiodynamic polarization. The result showed Na+of sodium alginate and Ca2+in the coagulation bath promoted ion exchange reaction, producing a crosslinked gel. Corrosion inhibitor was found in the interconnected,3-D mesh structure internal pores of the gel. Alg-Ca2+microcapsules loaded with inhibitor swelled and splintered in a CO2saturated3.5wt.%NaCl solution, releasing corrosion inhibitor. The USS results revealed that the corrosion inhibitor release performance is quite good, and raising the temperature is beneficial to the release of corrosion inhibitor. The immersion experiments showed that the Alg-Ca2+microcapsules were able to release corrosion inhibitor, providing a good protection performance for common oil field pipe material P110. The sinking rate of containers is accelerated by the introduction of heavy additive. Thus, partial inhibitor is able to sink with the microcapsules, preventing down-hole facilities from corrosion. (2) Liquid corrosion inhibitor was firstly mixed with bentonite. Particles were then made by a similar method of spray drying granulation. Finally, the particle surface was coated by Alg-Ca2+membrane. Consequently, solid inhibitor microcapsules were prepared, of which the core consists of the mixture of inhibitor and bentonite and the shell is Alg-Ca2+membrane. We studied the release performance of the solid inhibitor microcapsules. The bentonite is a weak adsorption for corrosion inhibitor, and adsorption amount is lower than20mg/g. Alg-Ca2+membrane swelled when it was immersed in water, the channel on the surface also opened accordingly, then corrosion inhibitor gone through the membrane channel and enter into the solution. Corrosion inhibitor was controlled released by changing the thickness of the membrane and the proportion of inhibitor in raw materials. Experiment showed that it took16h to absolutely release inhibitor in90℃for the microcapsules, which have a quality ratio of bentonite and inhibitor24:10, the thickness of the membrane50.0μm and the diameter of prepared microspheres6mm. The average settling velocity of the microcapsules is more than0.2m/s. Solid inhibitor microcapsules are able to release inhibitor during their sinking, which makes inhibitor settled to the oilwell bottom to effectively enhance the protection for oilwell facilities.