Study On CaCO₃ /SiO₂ Mixed Scale Fouling Behavior In Gathering Pipelines

The scaling problem at the oil field site is becoming increasingly prominent.Scaling will reduce the cross-sectional area of the pipeline and increase the friction along the pipeline.In severe cases,the pipeline will also be perforated by the corrosion of the scale and even blocked by the scale.And the sudden increase in internal pressure caused the pipeline to burst,which caused a series of safety accidents and affected the normal operation and production of the oil field.Oilfield surface gathering and transportation systems have many types of scale formation and complex components,which are often more difficult to remove than single component scale.In addition to the common carbonate scale,the silica scale in the oilfield mining process is also very rich,especially with the development and application of ternary compound flooding technology,the mixed scale of calcium carbonate scale and silica scale has become the most common scaling products.This paper uses CaCl₂,NaHCO₃ and NaSiO₃ as raw materials to simulate the scaling process of Ca CO₃/Si O₂ mixed scale through laboratory experiments.The scaling behavior of calcium carbonate in silicon-containing systems under different time,silica concentration and temperature conditions and the synergistic effect of Mg²⁺and Si O₂ on calcium carbonate in the presence of Mg²⁺are studied.And the calcium carbonate and its mixed scale are characterized from a microscopic perspective with the help of some modern analytical testing techniques（XRD,EDS and SEM）.The fouling characteristics of calcium carbonate in a silicon-containing system are studied,and the change of the macroscopic deposition of the scale with different conditions is obtained.Microscopic analysis shows that spherical vaterite as a metastable mesophase in a single calcium carbonate system gradually transforms into rhombic calcite with time.Low concentration of Si O₂ can stabilize vaterite,while high concentration of Si O₂ will promote the formation of calcite phase.The effect of increasing temperature is increasing.At the same time,the morphology of mixed scale under low concentration of Si O₂ is mainly crystalline calcium carbonate.As the concentration increases,it can be clearly seen that flocculent silica scale randomly accumulates around the crystalline calcium carbonate,forming a mixed scale with a"shell-shaped coating"structure.And the differences in macroscopic scaling characteristics are explained from a microscopic perspective.The calcium carbonate scaling characteristics in the system containing silicon and magnesium are studied,and it is found that the synergy between Mg²⁺and Si O₂ is not outstanding.When the two coexist,the effect of Si O₂ on calcium carbonate plays a major role,which is shown to promote the formation of diamond calcite.Although both of them inhibit the scaling of calcium carbonate to a certain extent,the mode of action and its effect on the crystal form and morphology of calcium carbonate are completely different.