The Trend And Methods Of Prevention Of Scale Deposition In Water Flooding Systems Of Oil Field

Water flooding is one of the most widely used methods to improve the well productivity of inland oil fields when the fields are maturing. However, this method is faced with the problem where the injected water, having been mixed with the native flood in the formation, undergoes physical and chemical changes which leads to the formation of scales that could potentially occlude the pipeline, thus effects the continual productivity of the fields. Therefore, considering such situation, it is very important to investigate the scaling rules of water drive and evaluate the various methods used to prevent scaling.This paper will be discussing the scaling rules of N80 carbon steel and 20# carbon steel in the injected water of Shengli oil field. We simulated the production site and studied the relationship between the scale thickness and time, as well as that between the thickness and the current velocity of water inlet. We have also studied the scale inhibition efficiency and failure law of HGY-9BS corrosion and scale inhibitor in the injected water,in the hope to offer some suggestion for water flooding.The result of static simulation experiment showed that with increased temperature,the extend of corrosion and the thickness of scaling of N80 carbon steel and 20# carbon steel have also increased. The simulated pipeline flow experiment provided evidences against the idea that the rate of scale thickening is related to the kind and roughness of carbon steel. Within a certain range and with constant current velocity of water inlet, the areas with relatively higher turbulent kinetic energy will have thinner and denser scales when compared to areas with low turbulent kinetic energy which tend to have thicker and foamy scales. The relationship between maximum scale thickening rate and current velocity of water inlet is: max scale thickening rate(μm/h)=1.1222×current velocity of water inlet v(m/s)+0.5417(v≤1.5m/s). When the current velocity of water inlet is larger than a critical value, the scale thickness becomes random and unpredictable due to strong erosion of the inner wall of the tube. We have also constructed a mathematical model about the scale thickness and show the functional relations with images.HGY-9BS corrosion and scale inhibitor showed a good scale inhibition efficiency in the simulated pipeline flow experiment. After 9 days, the maximum scale thickness islower than 500μm and the minimum scale thickness is under 100μm; the scale inhibition efficiency is about 50%. This corrosion and scale inhibitor also has the effect of solubilization and lattice distortion; it is adsorbed on the surface of the steel and prevents the steel from corrosion and crystal deposition on its surface. Furthermore, it distorts the crystal lattice of existing scales so that the scales can be washed away more efficiently.However, HGY-9BS will lose its efficacy within 48 h in 60℃ injected water, therefore the effective concentration of HGY-9BS should be monitored constantly and topped up regularly to maintain a steady level.