A New Eco-friendly High-effective Scale Inhibitor For Brine

With the change of underground geological conditions and the temperature and pressure in the mining process, the component of brine would appear different crystallizing and scaling phenomenon. The scale reduces the pipeline effective volume and increases the pipe resistance, which not only leads to the decline of production but also restricts the exploitation and sustainable utilization of brine. In view of this phenomenon, it’s very necessary to add scale inhibitors to inhibit scale, so as to raise the production of brine, reduce the energy consumption and increase the sustainable utilization of the brine. Considering the impact on the environment, so we should choose the readily biodegradable monomer without phosphorus and nitrogen to develop the scale inhibitor. This paper depended on National High-tech Research and Development Projects (863):the key technology of efficient exploiting deep brine in the Yellow River delta. After referred the related literature at home and abroad, a new eco-friendly scale inhibitor was developed for brine on the basis of analyzing salting scale mechanism. Besides these, not only the salt resistance and high-temperature resistance were studied, the advancement、environmental friendliness、economy and antiscaling mechanism of new inhibitor were also analyzed. The main research contents were as follows:(1) Using the analytical methods such as ICP-AES、ion-selective electrode、 temperature and pressure simulation to measure the concentration distribution of main components in the process of brine and the saturated solubility of different temperature and pressure. The results showed that:① The concentration of unsaturated brine main components don’t change with the mention depth; ② The concentration of saturated brine main components had significant change with the mention depth. Ca2+ separated out first and then Ba2+ and Sr2+ which accompanied by the precipitation of NaCl. The concentration of Sr2+ had the biggest change from 1500m to 500m.③The rate of saturated brine main components concentration change at normal pressures had the same rule with the rate of the saturated solubility with different mention depth change. The concentration of Ca2+ had the biggest change from 120℃ to 80℃. The concentration of Ba2+ had the biggest change from 80℃ to 60℃. The concentration of Sr2+ had the biggest change from 60℃ to 20℃. ④The saturated solubility of main components increased with the pressure at 60℃ but the rate of change was basically same. Therefore, the temperature change was the main affecting factor of precipitation sequence.(2) The formation process of salt deposit can be expressed as:brine�'scale elements saturated�'scale elements supersaturated�'crystal nucleus formed�'NaCl coprecipitation�'crystal grew up�'salt deposit. The main components of salt deposit were NaCl、CaSO4、BaSO4、SrSO4. In the mining process, the scaling phenomenon of unsaturated brine was lighter and the scaling phenomenon of saturated brine was serious. When the temperature reduced from 120℃ to 80℃, the main components of salt deposit was CaSO4. When the temperature reduced from 80℃ to 60℃,the main components of salt deposit was BaSO4. When the temperature reduced from 60℃ to 20℃, the main components of salt deposit was SrSO4.(3) Combined with the analysis of salt scaling factors and research of formation process, the salting scaling mechanism was elaborated in detail:With the change of the temperature and pressure, the anion and cation interacted to form ion pairs when the concentration of scale ions was higher than the equilibrium concentration. The ion pairs met the wall or other impurities could come into being the crystal nucleus and then the scale ions would spread to the wall and next crystallized、grew up, eventually formed scale on the pipe wall. NaCl crystal would also separate out due to the adsorption and coprecipitation. There existed mutual promotion between scaling and salting. The formation of salt deposit also affected by pipeline surface state、velocity、 microbial species and quantity, etc.(4) Through the study of PESA、PASP、sodium lignin sulfonate、sodium dodecyl sulfate、AEO-9 and TX-10 scale inhibition effect, the PESA and sodium lignin sulfonate were selected as the main component of new scale inhibitor. When the PESA comprised about 60% and the dosage of new inhibitor was 35mg/L, the scale inhibition rate of Na+, Ca2+, Ba2+ and Sr2+ respectively reached 99.43%, 99.45%,99.24% and 90.85%. The weighted scale inhibition rate reached 99.15%. Through the SEM comparison of brine composition、CaSO4、BaSO4、SrSO4 and NaCl before and after adding scale inhibitors, it was concluded that the new scale inhibitors for brine composition of crystal lattice distortion, chelation and charge dispersion effect was much stronger. The chelation and charge dispersion effect of CaSO4 was stronger. The lattice distortion and of chelation of BaSO4 and SrSO4 were stronger. The charge dispersion effect of NaCl was stronger.(5) Compared to the scale inhibitors suitable for mining at home and abroad, the new inhibitor had many advantages such as environmental friendly, no nitrogen and phosphorous、favorable inhibit effect and multi-function. After adding new scale inhibitor, the total costs could save 69.72% compared to the wells without scale inhibitor. The application results of new scale inhibitor in four companies showed that the new scale inhibitor had excellent scale inhibition and corrosion function and the scale inhibition rate could reach more than 90%.