Study On Anti - Fouling Of Screw Pump Rotor In ASP Flooding

The deposition of inorganic precipitates formed in the chemical reactions between alkali contained in ASP flooding system and formation fluid on oil extraction equipment surfaces, as well as the hard dirt produced in interactions between inorganic precipitates and organics or bacteria in ASP liquid at high temperatures in the down hole are important factors of affecting the normal operation of screw pump and increasing oil production costs. Existing studies of oilfield fouling in ASP flooding system, most of them confined to analysis the formation and deposition of the metal surface dirt from the point of view solubility of the solutes in a solution change with temperature, pressure, etc. For the bonding mechanism of dirt and metal surfaces, and the effects of different surface treatments on scaling of screw pump rotor are lack of in-depth research.In this paper, coatings with different surface structures were prepared on screw pump rotor with plasma spraying, electroless plating and electroplating. The surface properties of different coatings were characterized by contact angle measurements, surface microstructure observed, and micro-hardness testing, and calculating the surface energy with two liquids method of Owens. And to test the anti-fouling properties of different coatings’surface by simulation experiment of ASP flooding and field test. And use SEM, EDS, XRD to analyze the components of different surface dirt. Based on this, from the role of solid surface properties in the process of dirt formation, analyzed the formation mechanism of hard dirt on oilfield equipment surfaces in ASP flooding and its influence factors, and then discussed the mechanism of coating anti-fouling technology. Obtain the following conclusions:(1) The main ingredient of the surface dirt on drilling and production equipments in ASP flooding environment is calcium scale, and also contains barium, silicon dirt, etc. The formation of hard dirt on the surface of drilling and production equipments is divided into four processes, different macro and micro fine structures of scale surfaces affects each process of the dirt particles depositing on the surface of devices, especially which plays an important role in two-stage of the deposition and absorption of dirt.(2) The results of the wetting angle measurement show that the contact angle on the surface of ceramic coatings prepared by plasma sprayed was larger than that on the surface of metals in distilled water. The contact angle on the surface of nano-doped (15%) AT13coating reached96.5°, which shows that the surface of coating has hydrophobic property and water-based solution is more difficult to wet the surface of ceramic coating. Relative to the surface of ceramic coating, metal surface has larger polarity force; the interfacial tension of polar solution is smaller; and that is more conducive to deposition and absorption of dirt.(3) The surface of ceramic coatings prepared by plasma sprayed has microstructure, and the surface microstructure of different ceramic coatings has significant differences. Especially nano-doped coating surface exist nano-micron secondary microstructure increasing greatly hydrophobic property of the surface. The micro-hardness of various coating surfaces is higher than the45#steel substrate, which is beneficial to further improve the wear resistance of the rotor surface.(4) After fouling test, the XRD analysis results of surface dirt on plasma-sprayed ceramic coating, Ni-Fe-P coating and electroplated coating show that surface does not affect the crystalline of dirt, however, different fine structure of different surfaces affect the degree of crystallization of dirt crystals and the binding force between the crystal grains of dirt and surface. The dirt on nano-doped (15%) AT13coating surface is loose and porous and easily peeled off; this coating has the best anti-fouling performance; and the dirt on nano-doped coating surface has poor crystallization.(5) The nano-doped (15%) AT13coating would increase the wear resistance and anti-fouling property of rotor surface. It could enhance greatly the work efficiency and service life of screw pump, and has important meaning to promote the application of screw pump and ASP flooding system in oil field.