Preparation And Performances Of Corrosion And Scale Inhibitors In Oilfields

Serious corrosion and scaling problems usually lead to huge losses to the exploitation of oilfields in the process of production. The common types of corrosion include CO2 and H2S corrosions and those under the scale, and the main scales include CaCO3, CaSO4 and BaSO4 scale. In view of this, the thesis developed highly efficient scale inhibitors for CaCO3 and CaSO4 scale, and highly efficient corrosion inhibitors for both CO2 and H2S corrosion, and the scale and corrosion inhibitor with excellent performances according to the selected the inhibitors for scales and corrosions.1. The amino trimethylene phosphonic acid (ATMP), polyepoxysuccinic acid (PESA) and ethylene diamine tetramethylene phosphonic acid sodium (EDTMPS) were used as the beginning materials to prepare the scale inhibitors for CaCO3 and CaSO4 by the means of static scale inhibition method. It was found that there is an excellent synergistic effect between ATMP and PESA in any ratios for the inhibition of calcium carbonate scale, and PESA and EDTMPS presented a synergistic effect in a ratio of 5:1. However, there was no synergistic effect between ATMP and EDTMPS for the inhibition of CaCO3 scale. There is a satisfactory synergistic effect between PESA and ATMP or EDTMPS in any ratio for the inhibition of CaSO4 scale, and the inhibiting capability of mixed scale inhibitors are much better than a single scale inhibitor. There is no synergistic effect between ATMP and EDTMPS for the inhibition of CaSO4 scale. The optimized mixed scale inhibitors A2P (ATMP:PESA=2:1) and P5E (PESA:EDTMPS=5:1) were tested, and the scale inhibition mechanism of a single scale inhibitor and A2P/P5E were studied by X-ray diffraction (XRD) and scanning electronic microscope (SEM).2. Triethanolamine, EDTMPS and disodium lauroamphodiacetate were tested through the static weight-loss method and disodium lauroamphodiacetate inhibited the most outstanding performances in the inhibition of corrosion. The surface morphology of steel slabs (A3) after corrosion were observed through an 3D laser confocal microscope, and the corrosion products film formed on the steel slab surface were characterized by SEM and X-ray energy dispersive spectrum (EDS) methods. It was found that KI gave an excellent promoting effect on the corrosion inhibition of disodium lauroamphodiacetate at a ratio of 1:5 (M5K). and the anticorrosive rate was increased by 7%, the corrosion allowance decreased by 0.0105mm·a-1. Thiourea also presented a promoting effect for disodium lauroamphodiacetate at a ratio of 1:10 (M10S). The anticorrosive rate was increased by 5.8%, and the corrosion allowance decreased by 0.0114mm·a-1, which was slightly lower than that of M5K.3. The A2P was mixed with the M5K in different ratios, and the inhibition performances for CaCO3 and CaSO4 scales were tested by the static scale inhibition method, and the scale inhibition mechanisms of the corrosion and scale inhibitor were analyzed by using XRD and SEM. The anticorrosion performances of different corrosion and scale inhibitors were tested by the static weight-loss method, and the morphology of steel slab surface after corrosion were observed through 3D laser confocal microscope, and the corrosion product film formed on the steel surface were characterized by SEM and EDS. It was found that the mixture exhibited excellent performance for the inhibition of corrosion and scale when the A2P was mixed with the M5K with the ratio of 1:1. The scale inhibition rates of CaCO3 and CaSO4 were up to 90.4% and 96.4%, respectively; the corrosion allowance and anticorrosive rate were 0.0253mm·a-1 and 81.7%, respectively. These performances meet the requirements in Q/SY 126-2007 "the oilfield water treatment with the corrosion and scale inhibitor technical requirements". The scale inhibition could be attributed to chelating solubilization and lattice distortion effect, and the anticorrosion might be due to the formation of a perfect film-forming.In this thesis, we studied the synergistic effect between scale inhibitors through the static scale inhibition, and the promotion of KI and thiourea for disodium lauroamphodiacetate in the inhibition of corrosion by the static weight-loss method. Three kinds of combination of chemical agents were optimized:A2P, M5K and (A2P)(M5K). It was found that scale inhibition performances of A2P were better than the scale inhibition performance of a single component, and the anticorrosion performances of M5K were better than the disodium lauroamphodiacetate. The optimized (A2P)(M5K) exibibited perfect scale and corrosion inhibition performances.